Green infrastructure for sustainable urban hazard management

Urban areas are at risk from multiple hazards, including urban flooding, droughts and water shortages, sea level rise, disease spread and issues with food security. Consequently, many urban areas are adapting their approach to hazard management and are applying Green Infrastructure (GI) solutions as part of wider integrated schemes.

This session aims to provide researchers with a platform to present and discuss the application, knowledge gaps and future research directions of urban GI and how sustainable green solutions can contribute towards an integrated and sustainable urban hazard management approach. We welcome original research contributions across a series of disciplines with a hydrological, climatic, soil sciences, ecological and geomorphological focus, and encourage the submission of abstracts which demonstrate the use of GI at a wide range of scales and geographical distributions. We invite contributions focusing on (but not restricted to):

· Monitored case studies of GI, Sustainable Drainage Systems (SuDS) or Nature Based Solutions (NBS), which provide an evidence base for integration within a wider hazard management system;
· GIS and hazard mapping analyses to determine benefits, shortcomings and best management practices of urban GI implementation;
· Laboratory-, field- or GIS-based studies which examine the effectiveness or cost/benefit ratio of GI solutions in relation to their wider ecosystem potential;
· Methods for enhancing, optimising and maximising GI system potential;
· Innovative and integrated approaches or systems for issues including (but not limited to): bioretention/stormwater management; pollution control; carbon capture and storage; slope stability; urban heat exchange, and; urban food supply;
· Catchment-based approaches or city-scale studies demonstrating the opportunities of GI at multiple spatial scales;
· Rethinking urban design and sustainable and resilient recovery following crisis onset;
· Engagement and science communication of GI systems to enhance community resilience.

Co-organized by GM12/NH9
Convener: Daniel Green | Co-conveners: Jorge Isidoro, Lei LiECSECS, Louise Slater
vPICO presentations
| Mon, 26 Apr, 09:00–12:30 (CEST)

vPICO presentations: Mon, 26 Apr

Chairpersons: Daniel Green, Lei Li
Invited speaker - Faith Chan
Faith Chan

Sponge City Program’ (SCP) is the term used to describe the Chinese government’s approach to urban surface water management. The concept was conceived in 2014 in response to an increasing incidence of urban surface flooding in many Chinese cities. While ambitious and far-reaching in its aim (of reducing national flood risk, increasing water supply and improving water quality), the initiative must be implemented by individual sub-provincial or municipal-level government entities. The concept is similar to Blue-Green Cities (BGCs); sustainable drainage systems (SuDS) in the UK, it is developing with different regional climatic and hydrological characteristics, considering rapid urbanization. Indeed, the increasing use of national rather than international examples of best practice reflects a growing body of knowledge that has evolved since the start of the Sponge City initiative. The SCP so far now has run through 6 years and experience a transition on urban stormwater management and planning practices. In this paper, the implementation of the latest SCP guidelines will be presented that using the case of Ningbo and other Chinese cities to illustrate the transformation of the current SCP practices that undertaking the consideration of climate, environmental and socio-economic factors, and how the practice tackle challenges on governance, project financing, integration and assessment by the authorities and stakeholders. These valuable experiences will be vitally important influencing future urban stormwater management and planning practices in Chinese cities.

How to cite: Chan, F.: The development of Sponge City Program (SCP) – a transition of urban stormwater management and planning practice in Chinese cities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3301, https://doi.org/10.5194/egusphere-egu21-3301, 2021.

Green infrastructure for water quality and pollution control
Azrina Karima, Carlos Ocampo, Louise Barton, and Carolyn Oldham

Rapid urbanisation, climate change and scarcity of freshwater leads to conservative water consumption practices, including wastewater recycling for non-potable ‘low exposure risk’ end-use, such as sub-surface landscape and selective garden irrigation. Small-scale decentralised and cost-effective water treatment technologies like green walls require low energy, and are ideal for implementation in both residential and commercial areas. Green walls have been shown to attenuate nutrients, with the treatment efficiency mostly dependent on soil characteristics and plant types. While green wall systems have long been used for thermal comfort under temperate climates, there has been less research on its optimised performance under Mediterranean climates, where long, dry periods in summer and sometimes water-logged conditions in winter, create challenges for both plant and soil health. Our pilot-scale research project used planters (2.5 m x 0.7 m x 0.75 m) to establish detached green façades irrigated by greywater, and to test the impact on façade viability and treatment performance of planter orientation, plant species,  deciduous and non-deciduous plants and the projected total leaf area. Influent and effluent volumes from the planters were carefully monitored, and water balances were established for the planters. The water requirements of green walls in east, west and north facing orientations, and using different plant species, were quantified under different seasons. We determined that annual water requirements for the deciduous plants were almost half that of the non-deciduous plants; as expected the leaves appeared on deciduous plants as air temperatures increased and then both type of plants showed similar water requirements. The evapotranspiration as estimated by the water balances, was validated by quantifying the plant water loss (transpiration) using a portable photosynthetic unit (LI-6400XT, Licor Inc., Lincoln, NE, USA). The transpiration measured on a single leaf (in triplicate) was scaled up to the projected total leaf area of the façade, to estimate the total transpiration from the planter. The influents and effluents were also monitored for water quality, to determine how their treatment performance changed with vegetation maturity and season. The green walls showed up to 90% total nitrogen and 80% total phosphorus removal efficiencies throughout the two years study period. However, the pathogen count was greatly impacted by the irrigation water temperature and the effluents had higher pathogen counts than the influents, irrespective of facade orientation or plant species. The results of the leaf area analysis and water balance measurements, as well as their effect on water quality, will be presented to identify suitable orientation and plant species for improving the urban micro-climate that could thrive under greywater irrigation, and in particular under Mediterranean climates.

How to cite: Karima, A., Ocampo, C., Barton, L., and Oldham, C.: A green solution for decentralised water treatment: a pilot-scale study on the performance of green walls irrigated with greywater, under a Mediterranean climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13743, https://doi.org/10.5194/egusphere-egu21-13743, 2021.

Giulia Mazzarotto and Paolo Salandin

Diffuse urban pollution is a significant factor in compromising receiving water and groundwater standards required by the EU Water Framework Directive. Many studies (e.g., Ashley et al., 2005; McGrane, 2016) show that changes in the built environment and climatic forces contribute to the increase of combined sewer system overflows and of stormwater directly conveyed to nearby water bodies. These discharges are responsible for receiving water contamination, as a result of high concentrations of pathogens, BOD, suspended solids (SS), hydrocarbons, heavy metals and nutrients, thus being a significant source of water bodies’ pollution.

To mitigate/eliminate pathogens and BOD contamination sources, the combined drainage system is usually split into separated sanitary sewer and stormwater systems, although difficulties related to economic and technical feasibility may be relevant. Nevertheless, this solution does not solve completely pollution due to SS, hydrocarbons, heavy metals from urban areas runoff and nutrients from rural drainage.

Sustainable Drainage Systems (SuDS) deal with stormwater at source, helping infiltration and storage of water, increasing groundwater recharge, and reducing peak flood and volume in the drainage system. Moreover, filtration processes through porous media may reduce pollutants driven by first flush, usually controlled by stormwater tanks and sewer system spillways. However, clogging phenomenon limits drainage efficiency in the long-term, making sometimes porous media itself a source of contamination.

In the following, a PhD project focusing on the urban area of Treviso is illustrated. Treviso is crossed by the river Sile, one of the longest (95 km) European wellspring rivers, part of a protected area. The Sile river is polluted by discharges from both the existing combined sewer system and rural drainages.

While responsible agricultural practices will be promoted to mitigate the pollution originating from rural areas, a project aims to separate the combined system, developing a new pipe network for sanitary wastewater. When properly applied in the present drainage system devoted to the stormwater control only, SuDS solutions are able to mitigate pollution coming from wash-off and reduce flood peaks.

Discharge measurement stations will be realised on the Sile river upstream and downstream the Treviso town, to quantify drainage system outflows of the urban area during rainfall events and in dry conditions. Sampling for qualitative analysis will give a measure of the pollutants’ concentration.

SuDS solutions, e.g. porous pavements, infiltration trenches and vegetated swales, will be tested with laboratory equipment (6×2 m2) capable of considering the runoff and underground drainage in a fully controlled environment subjected to a prescribed rainfall intensity. By this way it will be possible to analyse the main physical processes and assess the SuDS solutions’ efficiency both in the short and long-term, using advanced mathematical models for the interpretation of results.

If the laboratory model will provide satisfactory results, a full-scale test will be developed on an experimental site in Treviso town. The installed qualitative and quantitative monitoring system will allow to determine the effectiveness of the solutions adopted.

How to cite: Mazzarotto, G. and Salandin, P.: Impact of urban areas' drainage system on the quality of water bodies and mitigation strategies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15709, https://doi.org/10.5194/egusphere-egu21-15709, 2021.

Joana Postal Pasqualini, Jucimara Andreza Rigotti, and Lucia Ribeiro Rodrigues

Constructed Floating Wetland (CFW) has shown a high capacity to transform, recycle, retain and remove different types of pollutants, especially nutrients. A CFW was developed in mesocosms at the Institute of Hydraulic Research at the Federal University of Rio Grande do Sul, Brazil, in order to evaluate the functionality of the system on treating synthetic effluent with nutrient concentrations simulating urban surface runoff. Two species of emergent macrophytes, Typha domingensis Pers. and Schoenoplectus californicus  were employed. The CFW was evaluated under changes in nutrient concentration and water level during two subsequent experiments, identified as “shock load” in order to simulate extreme rain events, accidental spills of pollutants or illegal discharges that are common in drainage systems and urban rivers worldwide. Comparative evaluations between species and the system responses were evaluated in different hydraulic retention time (HRT). The system was exposed to 24 h of HRT, with 20 cm of water level and 1.8 mg/L of TP, 4.9 mg/L of TN (mean concentration). After sampling, the tanks were filled to 40 cm, with 3.0 mg/L of TP and 13.8 mg/L of TN concentration . Samples were collected within 2 and 4 h to quantify the system's response to shock-load. After sampling, the level was reduced to 20 cm, followed by exposure for the remaining 6 days, when final samples were collected. Temperature, conductivity, dissolved oxygen and redox potential were measured in situ. Turbidity, color and pH was measured immediately after collection in the laboratory. Total phosphorus (TP), orthophosphate (PO43-), total nitrogen (TN), total organic carbon (TOC), chlorophyll-a and pheophytin were also quantified. Only orthophosphate presented significant differences between initial and final concentrations, after the first 24h (F = 6.106, df = 1, p = 0.024). The shock load demonstrated significant differences between initial and final concentrations for TN (F = 10.097, df = 1, p = 0.005), for TP (F = 9.392, df = 1, p = 0.0067) and for TOC (F = 9.817, df  = 1, p = 0.005). As to final batch, significant differences between input shock load and output values were found for TN (F = 103.45, df = 1, p < 0.001), for TP (F = 7.584, df = 1, p = 0.0067), for PO43- (F = 6.864, df = 1, p = 0.017) and for TOC (F = 73.608, df = 1, p < 0.001). After 6 days, average removal rates for TN were about 28% for S. californicus and 87% for T. domingensis, for TP such removals were 29% and 55%, respectively. T. domingensis superior root development in association with the biofilm in the rhizosphere of the plants, were responsible for the best efficiency. The results show evidence of the benefits related to the ecosystem service associated with the CFW built in mesocosms. The understanding of the performance of compensatory techniques in controlled situations represents an indispensable tool for the knowledge of the limitations and the consequent technical improvement necessary for the feasibility of implementing nature-based solutions as the CFW. 

How to cite: Postal Pasqualini, J., Andreza Rigotti, J., and Ribeiro Rodrigues, L.: Performance of a constructed floating wetland in mesocosm scale: nutrient removal under shock load and water level oscillation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9133, https://doi.org/10.5194/egusphere-egu21-9133, 2021.

Rasool Erfani, Lena Ciric, and Tohid Erfani

Sustainable urbanisation relies on green infrastructure (GI) for its successful delivery. GI includes a network of environmental features that delivers a range of services including water purification and pollution treatment (WPPT) as measures for health and disease mitigation and adaptation for recovery. Recently wide range of innovative approaches for WPPT are introduced. This study shows how plasma engineering can be considered as a cheap and efficient alternative for WPPT in context of GI. We present, in particular, Dielectric Barrier Discharge Plasma actuator features and its integration in current infrastructure. We investigate its beneficial point of use application for delivery of a promising resilient method in responding to urban public health emergency. In particular, we show how this can be advantageous for pollution control in both city- and catchment-scale studies without reliance on additive chemicals.

How to cite: Erfani, R., Ciric, L., and Erfani, T.: Green and sustainable plasma-based water pollution control, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15770, https://doi.org/10.5194/egusphere-egu21-15770, 2021.

Concepcion Pla, Javier Valdes-Abellan, Miguel Angel Pardo, Maria Jose Moya-Llamas, and David Benavente

The impervious nature of urban areas is mostly responsible for urban flooding, runoff water pollution and the interception of groundwater recharge. Green infrastructure and sustainable urban drainage systems combine natural and artificial measures to mitigate the abovementioned problems, improving stormwater management and simultaneously increasing the environmental values of urban areas. The actual rate of urban growth in many urban areas requires the enhancement and optimization of stormwater management infrastructures to integrate the territorial development with the natural processes. Regarding the quality of runoff stormwater, heavy metals are critical for their impact on human health and ecological systems, even more if we consider the cumulative effect that they produce on biota. Thus, innovative stormwater management approaches must consider new solutions to deal with heavy metal pollution problems caused by runoff. In this study, we propose the employment of Arlita® and Filtralite®, two kind of lightweight aggregates obtained from expanded clays, to remove heavy metal concentration from runoff stormwater. Laboratory experiments were developed to evaluate the removal rate of different heavy metals existent in runoff stormwater. The lightweight aggregates acted as filter materials in column experiments to quantify their removal capacity. In addition, batch tests were also developed to evaluate the exhaustive capacity of the materials. Results from the study confirmed the efficiency of the selected lightweight aggregates to reduce the heavy metals concentration by up to 90% in urban stormwater runoff.

How to cite: Pla, C., Valdes-Abellan, J., Pardo, M. A., Moya-Llamas, M. J., and Benavente, D.: Lightweight aggregates to reduce heavy metal pollution in green infrastructure for urban stormwater management, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7915, https://doi.org/10.5194/egusphere-egu21-7915, 2021.

Experimental monitoring of GI systems for stormwater management and wider ecosystem services
Daniel Green, Ross Stirling, Claire Walsh, Eleanor Starkey, Alethea Walker, Anil Yildiz, Narryn Thaman, and Richard Dawson

Green Infrastructure (GI) offers multiple and integrated benefits to urban areas, including relieving pressure on ‘grey’ infrastructure systems by locally managing surface runoff within cities to reduce the risk of urban flooding. Although the use of GI has been shown to attenuate flooding, monitored and quantifiable data determining the effectiveness of GI is imperative for supporting widespread adoption of GI within cities and to provide an evidence-base to inform the design and maintenance procedures of such systems and ultimately influence key decision makers .

The National Green Infrastructure Facility (NGIF) based in Newcastle-upon-Tyne, UK, is a purpose-built, publicly accessible, ‘living laboratory’ and demonstration site established in 2017, funded by the UK Collaboratorium for Research on Infrastructure and Cities. The NGIF explores how a wide range of green features such as trees, shrubs and soils can help reduce flooding in cities and make them more resilient and sustainable to future changes in climate and urban pressures. The facility hosts a number of novel GI features of varying scale, monitored with dense sensor networks to allow the in-situ measurement of key hydrological, climatic and biophysical variables (e.g. precipitation, temperature, soil moisture, water depth, runoff and outflow rates) which are able to provide quantified evidence of the hydrological performance of sustainable drainage systems (SuDS). Such systems generate detailed insights into how SuDS and nature-based solutions can be used to improve surface water management, optimise geo-energy for building heating/cooling and how systems can be used for urban water treatment.

GI features across the NGIF include an experimental  and fully functional swale, providing protection to the area of Newcastle-upon-Tyne in which the feature is located, 10 lysimeter bioretention cells, a series of rain-garden ‘ensembles’ and a monitored green roof system. All experimental features are subjected to prevalent environmental conditions and act as fully functional GI systems, but conditions can also be augmented and simulated to ensure that the GI features act as semi-controlled experimental systems to determine responses outside of the natural instrumented record. All environmental data is recorded at high temporal (< 5 minutes) and spatial resolution and is publicly accessible in real-time via the NGIF API.

This presentation provides an overview of the NGIF and discusses the current research activities taking place across the site. Data is presented from each of the GI systems to demonstrate and discuss their performance and responses during natural and simulated events, including extremes, and to assess their effectiveness in responding to localised changes in climate. Future research directions and collaborative opportunities are also highlighted.

How to cite: Green, D., Stirling, R., Walsh, C., Starkey, E., Walker, A., Yildiz, A., Thaman, N., and Dawson, R.: National Green Infrastructure Facility – a specialised ‘living laboratory’ to assess the value of urban green infrastructure, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12457, https://doi.org/10.5194/egusphere-egu21-12457, 2021.

Dario Pumo, Antonio Francipane, Francesco Alongi, and Leonardo Noto

Over the last decades, we have been witnessing an increasing frequency of urban floods often attributed to the interaction between intensification of rainfall extremes due to climate change and increasing urbanization. Consequently, many studies have been trying to propose different new alternatives to mitigate ground effects of ever more frequent and severe extreme rainfall events in a context of growing urbanization, such as rain gardens, green roofs, permeable parking lots, etc., which are commonly referred to as green infrastructures.

With this regard, one of the most promising mitigation solutions is represented by multilayer green roofs. These systems, coupling classical green roofs with a rainwater harvesting system, results in a high capacity in retaining rainwater, thus improving the potential effects acted by classical green roofs on pluvial floods mitigation. These systems are particularly suited for applications in semi-arid climate, where a fraction of the rainwater can be detained during the more severe rainfall events, significantly reducing the pressure on drainage systems, and released in a later moment or reused, for instance, to sustain the vegetation during driest periods.

This study describes a multilayer green roof installed at the Department of Engineering of the University of Palermo (Sicily, Italy) and its preliminary results on its capacity to reduce the pressure of rainfall events on drainage systems in a Mediterranean context. The green roof has an extension of almost 35 m2 and is made of three different areas with different soil thickness (a mixture of volcanic material) and different Mediterranean vegetation. The green roof is equipped with multiple sensors to monitor the water level in the storage layer, soil water content, air and water temperature, and rainfall. Besides, a weighted rain gauge, a disdrometer, and a meteorological station for the collection of meteorological data are available as well.

An equal size classical roof area bordering the green roof installation is also monitored. Four different thermometers are used to measure the temperatures in different points of the roofs and a system of two rain barrels and two pressure sensors allows to collect and compare the rainwater coming from the green and the original roofs. Such an installation, differently from many others, has the advantage to allow a complete characterization of the potential benefits of a multilayer green roof through a comparison of the rainwater released by the two roof configurations at a rainfall event scale.

The study provides the preliminary results arising from the analysis of the two roof configurations' response to a series of rainfall events characterized by different duration and intensity.

How to cite: Pumo, D., Francipane, A., Alongi, F., and Noto, L.: Green roof effects on the rainwater response in the Mediterranean area: first results of a Sicilian case study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13029, https://doi.org/10.5194/egusphere-egu21-13029, 2021.

Sofia Sushko, Alexey Yaroslavtsev, Nina Tsuvareva, and Riccardo Valentini

Trees play an important role in urban ecosystem functioning and providing many ecosystem services, in particular, water and energy balance regulation. Consequently, trees can be a tool to mitigate to run-off and heat island effect in urban areas. We quantified the possibility of urban trees to provide these ecosystem services in the northernmost city with a million population – St. Petersburg (59°57′ N / 30°19′ E; Russia). Two diffuse-porous tree species – Quercus robur L. (n=2) and Tilia cordata Mill. (n=4) – were chosen for the research. These tree species are the most common in the green infrastructure of the city despite they are not typical for this biome, i.e. south taiga. During two growing season (July-Oct. 2019, April-Oct. 2020), tree sap flux was measured by thermal dissipation method using TreeTalker device (Nature 4.0 Corp., Italy). Sap flux density (Js) was calculated with modified Granier’s empirical calibration equation. Energy loss through tree transpiration was estimated from sap flux per tree (Js × sap wood area) and latent heat of vaporization. For the entire observed period, average daily Js (24 h) of Q. robur trees were almost two times higher than T. cordata trees (3.46 vs. 1.91 g cm-2 h-1). Importantly, for Q. robur Js significantly decreased with increasing tree age (from 3.75 to 1.99 g cm-2 h-1 with age alteration from 145 to 350 yrs.), while for T. cordata it did not change (1.74 and 1.69 g cm-2 h-1 for 60-80 and 100-115 yrs.). Q. robur showed a significant higher daily energy loss through tree transpiration compared to T. cordata (618 and 396 W tree-1 with 100-108 diameter at breast high) for the studying period. Thus, Q. robur compared to T. cordata was more effective in providing water regulation services, especially in shallow groundwater table typical for St. Petersburg. Moreover, this tree species also has a higher capacity in mitigate to urban heat island effect.

Current research was financially supported by Russian Science Foundation, No 19-77-30012.

How to cite: Sushko, S., Yaroslavtsev, A., Tsuvareva, N., and Valentini, R.: Capacity of Quercus robur L. and Tilia cordata Mill. trees in providing urban ecosystem services in boreal climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7125, https://doi.org/10.5194/egusphere-egu21-7125, 2021.

Marjolein van Huijgevoort and Gijsbert Cirkel

The increase in population in cities has led to increased pressure on available sport facilities. As a result, natural grass fields are converted to artificial turf, because fields with artificial turf can be used more frequently. Downsides of these artificial turf fields are the increase in surface temperature and the decrease in infiltration of precipitation resulting in faster discharge. Artificial turf can reach very high surface temperatures leading to unplayable fields and health risks, but also contributing to the urban heat island effect. To counteract these high temperatures, irrigation of the fields is needed, which leads to high water demands. In this study, a system to store precipitation below the fields and to enable evaporation to cool the artificial turf was tested. The system consists of water-storing units below the field, a capillary shockpad that enables water transport to the artificial turf and a natural infill from where water can evaporate. To quantify the effects on temperature and evaporation of the system, four test sites were created with natural grass, conventional artificial turf and two versions of the cooled artificial turf (non-infill and standard). All sites were equipped to measure evaporation, surface temperature, net radiation and water levels below the fields. A separate weather station was installed to measure other meteorological variables (e.g. precipitation, air temperature, wind). During the summer of 2020 on days with a maximum air temperature around 30°C, surface temperature reached 37°C at the cooled standard artificial grass, whereas it reached 62.5°C at the conventional artificial turf. The measured surface temperature for the cooled turf was less than 2°C warmer than the surface temperature at the natural grass site (35.3°C). Evaporation from the cooled artificial turf reached maximum values around 4 mm/d during the summer and was about half of the evaporation from natural grass, whereas evaporation from conventional artificial turf was close to zero. These results show that the system is successful in lowering the surface temperature by evaporation. This reduction in surface temperature is important to maintain playable conditions, but also helps to mitigate the heat island effect. In addition, the water storage below the fields reduces peak discharges during high-intensity precipitation. By combining these functions, the cooled artifical turf fields can help cities adapt to climate change.

How to cite: van Huijgevoort, M. and Cirkel, G.: Cooling artificial turf through evaporation from a subsurface water storage unit, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-668, https://doi.org/10.5194/egusphere-egu21-668, 2021.

Vojtech Skala, Michal Dohnal, Jana Votrubova, Michal Snehota, and Petra Heckova

Artificial substrates for green infrastructure have different composition and properties compared to natural soils. The admixture of light porous minerals such as pumice or expanded clay is often used to decrease the substrate weight and to increase water storage capacity. On the other hand, it could lead to dual porosity character of substrates and may affect their retention properties.

The dual-continuum model S1D is used to asses water flow in extensive green roof test beds with artificial substrate. The model numerically solves dual set of Richards’ equations. The soil hydraulic properties are described using van Genuchten-Mualem approach. Selected model parameters were optimized using Levenberg-Marquardt algorithm.

Two green roof test beds located at the University Centre for Energy Efficient Buildings of the Czech Technical University in Prague are studied. The test beds are filled with 60 mm of extensive green roof substrate, planted with sedum cuttings, respectively 40 mm of substrate, planted with sedum carpet. The substrate is a mixture of spongilit (55 %), crushed expanded clay (30 %) and peat (15 %). The outflow from the test beds is registered by tipping bucket flowmeter and the moisture content within the soil substrate by TDR probes. The test bed with sedum carpet is also weighted. For complete hydrometeorological characterization, data from the nearby meteorological station are available.

Dual-continuum model provides higher flexibility and overall better agreement between measured and simulated variables. Further investigation of hydrological regime of such substrates and possible hysteresis of their soil water retention curve is needed.

The research was supported by the Czech Science Foundation under project number No. 20-00788S. Experimental work has been supported by the Ministry of Education, Youth and Sports within National Sustainability Programme I, project number LO1605.

How to cite: Skala, V., Dohnal, M., Votrubova, J., Snehota, M., and Heckova, P.: Dual porosity effects in hydrological performance of extensive green roofs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2534, https://doi.org/10.5194/egusphere-egu21-2534, 2021.

Xiang Feng Hong

Due to the expansion of the urban area increases the impervious area and Inhibits the influence of evapotranspiration and infiltration of the water cycle. In addition, climate change causes extreme rainfall events, increase rainfall have greatly increased surface runoff in cities, Increase the intensity and depth of rainfall. These have led to a substantial increase in surface runoff in cities.

Green roof is one of the low-impact development measures. This study will improve the above-mentioned problems through the rainfall retention characteristics of green roofs, Calculate peak flow reduction and delay of arrival time. We have built a green roof observation system which including experimental group (green roof) and control group (no green roof) to obtain various observational data of the water cycle. Then input the data into the surface hydrological model for calibration and validation to analyze the retention characteristics of green roofs. Evaluate the flood reduction effect of green roofs in Taiwan.

How to cite: Hong, X. F.: Analyze the retention characteristics of green roofs., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14173, https://doi.org/10.5194/egusphere-egu21-14173, 2021.

Daniel Green, Ross Stirling, Simon De Ville, Virginia Stovin, and Richard Dawson

Sustainable Drainage Systems (SuDS) are a widely adopted approach for managing excess urban runoff by intercepting, retaining and attenuating the flow of water through the built environment, playing a key role in reducing urban flood risk. Vegetated bioretention cells (‘rain gardens’) are one of the most simple, practical and commonly implemented SuDS options and can be easily retrofitted into urban spaces to deal with surface water from paved areas. Although current UK and international guidance provides design guidance for SuDS, no quantitative indications on their hydrological performance are currently available. This study aims to provide evidence to assess the effectiveness of such systems to support optimal implementation of vegetated bioretention cells for stormwater management. 

Four purpose built, large-scale lysimeter experiments (2.0 m x 2.0 m, each divided into two isolated 1.0 m x 2.0 m cell pairs) were designed to provide long-term monitoring data of key hydrological variables and demonstrate the capacity and effectiveness of monitored bioretention systems. The lysimeters were filled with an engineered soil profile consisting of a surface SuDS substrate (700 mm depth) to sustain vegetation growth and store/attenuate flows, and drainage layers (300 mm depth) consisting of a fine gravel transition layer to prevent the movement of fine sediments and a course gravel base layer to allow free drainage into gauged outflow units. 

Each of the lysimeter cells feature a dense sensor network, allowing spatiotemporal soil-atmosphere interactions to be observed and changes in relation to rainfall events to be quantified. Tipping bucket rain gauges situated on each of the lysimeters allow the quantification of local precipitation inflows, which are also analysed in the context of site-wide weather monitoring stations to calculate Penman-Monteith reference evapotranspiration. Outflow from the drainage layer of each lysimeter cell is measured using an outflow gauge. Additionally, a network of in-situ soil sensors were deployed throughout the substrate profile at various depths to quantify soil water movement and changes in volumetric water content, soil temperature, electrical conductivity, soil-water potential and hydrostatic water level in accordance with localised weather conditions. Quantifying inflows, storages and losses allows an understanding of the lysimeter mass balance. Further, each of the lysimeter cell pairs were planted with different planting styles (unvegetated control, reference short grass and two uniform mono-cropped shrub species) to provide differing reference evapotranspiration scenarios and to understand the influence of vegetation on bioretention cell performance.  

This paper outlines the commissioning of a large-scale lysimeter study at the National Green Infrastructure Facility and presents results from mid-2020 onwards, highlighting the hydrological performance of the bioretention cells under a range of natural storm events and climatic conditions. Lysimeter mass balance and retention efficiencies are presented for each of the vegetation scenarios. Further, differences in soil-water retention ability between the lysimeters are examined in relation to the efficiency of various planting styles and their comparative evapotranspirative behaviour. Working together with a range of stakeholders involved in UK SuDS schemes, this work is helping to inform design criteria and anticipated bioretention cell performance using a quantified evidence base.

How to cite: Green, D., Stirling, R., De Ville, S., Stovin, V., and Dawson, R.: Investigating bioretention cell performance: A large-scale lysimeter study , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10259, https://doi.org/10.5194/egusphere-egu21-10259, 2021.

Upscaling field-collected GI data
Alexander Schütt, Selina Schaaf-Titel, Joscha N. Becker, and Annette Eschenbach

Urban trees as main part of urban green infrastructure provide manifold ecosystem services and contribute to the wellbeing of humans. Unfortunately, urban trees, especially roadside trees, are severely challenged by both, political conflicts of interests in terms of city development and a variety of physically stressors. Contrary to the known benefits of urban green, its proportion in most cities is still decreasing. Furthermore, climate change exacerbates the already challenging preconditions.

For northern Germany, climate change is predicted to shift temperature- and precipitation patterns. Simultaneously the frequency of “summer days” and “hot days” are likely to increase, leading to elevated risk of soil drying during the vegetation period.

The city of Hamburg is home to almost 220.000 roadside trees. Especially trees planted nowadays are exposed to harsh roadside conditions. In the event of drought, young-trees compared to well-established trees, are not in touch with deep- or distant water reservoirs and the risk of vitality loss or death increases.

Our research aims to characterize the soil hydrological conditions in the rooting zone of roadside young-trees during the first years after plantation. Further it aims to identify spatio-temporal dynamics of soil water response during phases of extreme meteorological drought. Our findings are based on a long-term soil water monitoring across the city of Hamburg, which was started in 2016. The monitoring covers 20 trees from 7 species, planted between 2007 and 2019 with large, medium and low soil sealing. Soil water tension and soil temperature were measured hourly with sensors in the root ball, in the tree pit filled with structural soil and the surrounding soil (16 sensors per site).

Our data provides a broad characterization of soil water conditions for young-tree sites in urban areas, and show that water supply in years of moderate meteorological drought is not only extremely heterogeneous on large scales, but can also vary greatly on a small scale. The water tension in the root ball, which should provide the highest amount of water per unit, was highly variable and exceeded thresholds even in the first year after plantation and in almost every vegetation period across all sites. In years of high meteorological drought like in 2018, the soil water tensions exceeded the thresholds in almost all compartments, which leads to a risk of vitality losses and mortality.

Our data show the need for adaption of general tree site concepts for future plantations. This unique dataset will be further completed with the aim to include future sites and plantation strategies e.g. the underground connection of planting pits, to increase the diversity of site characteristics and to develop reliable modelling and recommendations.

How to cite: Schütt, A., Schaaf-Titel, S., Becker, J. N., and Eschenbach, A.: Long time risk assessment of soil water shortage in planting pits of young urban roadside trees in the city of Hamburg, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11124, https://doi.org/10.5194/egusphere-egu21-11124, 2021.

Eric Lutete Landu, Guy Ilombe Mawe, Charles Bielders, Fils Makanzu Imwangana, Olivier Dewitte, Jean Poesen, and Matthias Vanmaercke

Many cities of the D.R. Congo are strongly affected by urban mega gullies. There are currently hundreds of such gullies in Kinshasa, Kikwit and Bukavu, representing a cumulative length of >200 km. Many of these gullies (typically tens of meters wide and deep) continue to expand, causing major damage to houses and other infrastructure and often claim human casualties. To mitigate these impacts, numerous measures are being implemented. The type and scale of these measures varies widely: from large structural measures like retention ponds to local initiatives of stabilizing gully heads with waste material. Nonetheless, earlier work indicates that an estimated 50% of the existing urban gullies continue to expand, despite the implementation of such measures. As such, we currently have very limited insight into the effectiveness of these measures and the overall best strategies to prevent and mitigate urban gullies. One reason for this is that most initiatives to stabilize urban gullies happen on a rather isolated basis and are rarely evaluated afterwards.

This work aims to improve our understanding of this issue. For this, we constructed a large inventory of measures implemented to stabilize urban gullies in Kinshasa, Kikwit and Bukavu and statistically confronted these measures with observed vegetation recovery and long-term gully expansion rates (derived from high-resolution imagery over a period of >14 years). Our preliminary results (based on a dataset of > 900 urban gullies) shows that the most commonly applied measures are revegetation and reinforcement of gully heads with sandbags or household waste material (implemented in around 65% of the cases). Retention ponds in streets and infiltration pits on house parcels are also frequently implemented (around 25% of the cases). Overall, techniques relying on vegetation are used relatively more frequently in regions with clayey soil, while techniques involving digging (e.g. infiltration pits) and topographic remodeling (e.g. gully reshaping by creation of terraces) are used mainly in sandy or sandy-clay areas. Surprisingly, small-scale local initiatives, such as stabilizing gully heads with household waste, often appear to have a higher effectivity than some large-scale civil engineering initiatives. However, such small-scale initiatives can come with important additional impacts (e.g. sanitation concerns). More research is needed to confirm these findings. Furthermore, the stability of gullies seems to be strongly linked to the degree of vegetation cover near the gully head. Nonetheless, it is not always clear if vegetation is the cause or the result of this stability. Overall, this study provides one of the first large scale assessments of the effectiveness of gully control measures in urban tropical environments. With this study, we hope to contribute to a better prevention and mitigation of this problem that affects many cities of the tropical Global South.

How to cite: Lutete Landu, E., Ilombe Mawe, G., Bielders, C., Makanzu Imwangana, F., Dewitte, O., Poesen, J., and Vanmaercke, M.: Understanding the effectiveness of measures aiming to stabilize urban gullies in Congolese cities: a systematic analysis based on field surveys, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7832, https://doi.org/10.5194/egusphere-egu21-7832, 2021.

Chuan Ching Pang

In the context of rapid global urbanization, problems such as urban thermal effects often occur, which may cause the increase in building energy consumption. Green roofs have the effect to regulating the indoor temperature of buildings. This study is expected to evaluate the cooling and energy-saving benefits of green roofs and build an experimental to simulation buildings situation , the control group without green roof and the experimental group with green roof, compare the indoor temperature and heat flux changes in the control group and the experimental group, and calculate the radiant heat, latent heat, sensible heat, conduction heat in the green roof layer , And build a model to simulation energy project to discuss the energy balance of the green roof and the impact on the energy of the buildings below, and analyze the cooling and energy saving effects of the green roof.

How to cite: Pang, C. C.: Analyze the energy balance and energy-saving benefits of  green roofs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14130, https://doi.org/10.5194/egusphere-egu21-14130, 2021.

Numerical modelling of GI systems
Sijie Tang, Jiping Jiang, and Yi Zheng

Practitioners usually design the plan of Sponge City construction (SCC) by combining LID facilities (e.g., rain garden, rain barrels, green roofs, and grassed swales) according to their personal experiences or general guidelines. The layout (including selection, connection and distribution area) of LID facilities is subjective, in the risk of far from optimal combination. Previous researchers have developed some LID optimization tools, which only consider the dimension and number of LIDs in a given scenario. Therefore, it is necessary to develop a flexible and extensible design tool with the support of urban hydrological model to conduct the facilities layout optimization. This study introduced a SWMM-based multi-variable and multi-objective optimization framework called CAFID (Comprehensive Assessment and Fine Design Model of Sponge City) to meet this end. The assessment module with multi-objective couples diverse controlling end-points (e.g., total runoff, peak runoff, pollutant concentration, cost, and customized social-ecological factors) as the candidates of assessment criteria. The optimization module with multi-variable is implemented by SWMM, starting with three steps: 1) Full allocation. Based on the availability, list the candidates of LID facility for each sub-catchment; 2) Full connection. Order the potential stream direction of surface runoff from rainfall to municipal network, based on possible hierarchical structure of sub-catchments and LID facilities; 3) Full coverage. Identify all the suitable area for LID facility in sub-catchment. The optimization on the 3 variables, the selection, connection, and area, is powered by NSGA-II and TOPSIS algorithms, which make it possible that we choose a final result from the set of nondominated solutions according to special weight distribution. The effectiveness of CAFID was illustrated through a case of Sponge City in Fenghuangcheng of Shenzhen City, one of 30 national pilot sponge cities in China. As well, this new framework is expected to be widely verified and applied in Sponge City construction in China or similar concepts all over the world.

How to cite: Tang, S., Jiang, J., and Zheng, Y.: A Multi-variable & Multi-objective Optimization Framework for LID Layout in Sponge City, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14638, https://doi.org/10.5194/egusphere-egu21-14638, 2021.

Meng Xiao, Yu Li, and Jinhui Jeanne Huang

Low impact development (LID) is an important measure to control the total amount of rainwater runoff from the source and solve the problem of non-point source pollution. However, there are many kinds of LID facilities, and the selection and layout of these facilities are restricted by the local physical and geographical conditions, hydrogeological characteristics, water resources, rainfall patterns and other factors. Therefore, the selection of LID facilities and the determination of optimization scheme are the main challenges for the construction of LID rainwater system. In this study, SWMM model and genetic algorithm (GA) are used to optimize the layout of LID. The multiple objectives include runoff reduction, occupied area and lifecycle cost. The results show that the combined LID facility scheme has obvious control effect on runoff reduction in the 10-year rainfall process.

How to cite: Xiao, M., Li, Y., and Huang, J. J.: Optimization of Low Impact Development Based on SWMM and Genetic Algorithm: Case Study in Tianjin, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8154, https://doi.org/10.5194/egusphere-egu21-8154, 2021.

Omid Seyedashraf, Andrea Bottacin-Busolin, and Julien J. Harou

The design of conventional and sustainable urban drainage systems is a complex task that requires consideration of several design objectives and decision variables. Simulation-based optimization models allow exploring the decision space and identify design options that best meet the design criteria. However, existing approaches generally require simulation of the system hydraulics for each function evaluation, which leads to prohibitive computational cost when applied to large drainage networks.

In this work, a disaggregation-emulation approach is proposed which allows sequential optimization of multiple sub-catchments in an urban area without having to simulate the full system dynamics. This is achieved by using artificial neural networks (ANN) to represent the boundary condition at the interface between neighboring sub-catchments. The approach is demonstrated with an application to a many-objective optimization problem in which sustainable drainage systems are used to expand the capacity of an existing drainage network. The evaluation of the objective function using the emulation model is found to be 22 times faster than using the physically based model, resulting in a significant speed-up of the optimization process. Unlike previously proposed optimization approaches that rely on surrogate models to emulate the objective functions, the proposed approach remains physically based for the individual sub-catchments, thus reducing the chance of bias in the optimization results.

How to cite: Seyedashraf, O., Bottacin-Busolin, A., and Harou, J. J.: A Surrogate-Based Optimization Approach for Sustainable Drainage Design in Large Urban Areas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9008, https://doi.org/10.5194/egusphere-egu21-9008, 2021.

Maria Eduarda Barbosa Veiga, Luma Gabriela Fonseca Alves, and Carlos de Oliveira Galvão

The implementation of Green Infrastructure (GI) for hazard management has been studied and evaluated for reducing the risk of and increasing resilience to flood events, flooded areas and damage costs. Still, less attention has been given to the governance aspects involved in the implementation of GI. We present the GI assessment through a robustness approach, where the urban environment is referred to as a socio-ecological system. Robustness can be assumed as the “maintenance of system performance either when subjected to external, unpredictable perturbations, or when there is uncertainty about the values of internal design parameters” (Carlson and Doyle, 2002). In this sense, it is required to investigate the socio-ecological configurations of GIs as a new component introduced within the urban system in addition to their technical aspects. We use the Robustness of Coupled Infrastructure Systems Framework (Anderies et al., 2019) to analyse the dynamics of the system through the connections between its components (resource users, public infrastructure, public infrastructure providers and natural infrastructure) and to evaluate the associated robustness through their critical feedback structures links, by analysing human behaviour (relationships and perceptions), monitoring actions, conflicts, and resource appropriation limits. In this way, it is possible to assess the changes [MEV1] that influence the functioning of the system. We applied this framework to a case of a dense precarious urban settlement subject to flash floods in Brazil. We developed three scenarios considering the application of GI, and they were simulated using SWMM model: (i) the current one; (ii) the implementation of three infiltration-based GI (permeable pavements, bioretention systems, and infiltration trenches) throughout the catchment, not only in public areas but also inside the lots, aimed at reducing flooding hotspots; (iii) the implementation of low-storage rainwater harvesting systems in all households within the catchment. We used a representative heavy rainfall event capable of producing flash floods as input for simulation of all scenarios. The SWMM was parameterised for the current land use and land occupation, representing the spatial patterns that determine runoff overflow propagation, producing, for each scenario, the spatial distribution of flooding hotspots throughout the catchment. In the current state scenario, the system has exhibited poorly robust links, furthermore flooding spots have been detected along the catchment. By applying the infiltration-based GI, besides all flooding spots have been mitigated, the system has the potential to acquire robustness by enabling trust in relationships, improvement in users' perception of resources, monitoring of actions and conflict resolution. The implementation of rainwater harvesting systems could strengthen the robustness through popular participation, processes perception by the users and appropriation limits, apart from reducing 26% of the flooding spots. The robustness analysis points out that the implementation of  GI in the catchment will be effective only if it is reached a household-level engagement, resource importance and a proper environment for conflict resolution, besides the mitigation of flood events.


Anderies, J.M. et al. (2019). Reg Environ Change, https://doi.org/10.1007/s10113-019-01529-0

Carlson, J.M.; Doyle, J. (2002) PNAS, https://doi.org/10.1073/pnas.012582499

How to cite: Veiga, M. E. B., Alves, L. G. F., and Galvão, C. D. O.: A socio-ecological robustness approach for evaluation of urban Green Infrastructure effectiveness in a dense precarious settlement, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11893, https://doi.org/10.5194/egusphere-egu21-11893, 2021.

Chairpersons: Louise Slater, Jorge Isidoro
Invited speaker - Emily O'Donnell
Emily O’Donnell

As global cities rethink their approaches to urban flood risk and water management in response to climate change, accelerating urbanisation and reductions in public green space, Blue-Green Infrastructure (BGI) is gaining increasing recognition due to the advantages of multifunctional BGI solutions over traditional piped drainage and grey infrastructure. BGI, including green and blue roofs, swales, rain gardens, street trees, ponds, urban wetlands, restored watercourses, reconnected floodplains, and re-naturalised rivers, is designed to turn ‘blue’ (or ‘bluer’) during rainfall events in order to reduce urban flood risk. In addition to managing flood risk and increasing water security, BGI generates a range of socio-cultural, economic and environmental co-benefits that help city authorities tackle other urban challenges and ultimately improve the quality of life of city dwellers.

Extensive research over the last decade has focused on improving knowledge of BGI systems in several broad areas, including: hydrological and hydraulic modelling of water flow through BGI assets; biochemical assessments of sediment and water quality; public preferences; identification and evaluation of BGI co-benefits, and; BGI planning and governance. Emerging research into adaptation pathways, natural capital accounting and social practice approaches for understanding community preferences demonstrate how BGI research is moving beyond hydrodynamic modelling to explore decision making under future uncertainty and placing greater emphasis on the role of community preferences in designing BGI that is accepted and supported by those who directly benefit.

This presentation will explore these emerging research areas, particularly focusing on the need for interdisciplinary research into BGI to enable the challenges and opportunities to be fully appreciated. Current knowledge gaps that present research opportunities in BGI will also be discussed, including the need for rigorous assessment criteria to determine the success of multifunctional BGI systems; greater investigation of the social benefits of BGI and the value people place on different types of BGI; the role of implicit perceptions in designing BGI assets, and; the role of urban watercourses as multifunctional BGI corridors able to safely convey stormwater while boosting water quality, providing multiple urban pathways (active transport, wildlife movements, etc.) and increasing green space in cities.

How to cite: O’Donnell, E.: Future directions in Blue-Green Infrastructure research, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-695, https://doi.org/10.5194/egusphere-egu21-695, 2021.

Hazard mitigation and building resilience using GI systems
Francesco Busca and Roberto Revelli

In recent years, safeguarding approaches and environmental management initiatives have been adopted both by international institutions and local governments , aimed at sustainable use of natural resources and their restoration, in order to manage hazard level of climate change consequences (urban flooding, droughts and water shortages, sea level rise, issues with food security).

Cities represent the main collectors of these effects, consequently they need to implement specific adaptation plans mitigating consequences of such future events: Green Infrastructures (G.I.) fall within the most effective tools for achieving the goal. In the urban context, they also identify themselves as valid strategies for biodiversity recovery and ecological functions.

This work analyzes the role of a G.I. in an urban environment, with the aim of quantifying Ecosystem Services (E.S.) provided by vegetation: through usage of i-Tree, specific software suite for E.S. quantification, the sustainability offered by “Le Vallere” park, a 34-hectares greenspace spread between municipalities of Turin and Moncalieri (Italy), was analyzed, in collaboration with the related management institution (Ente di gestione delle Aree Protette del Po torinese). The study, carried out using two specific tools (i-Tree Eco and i-Tree Hydro), focuses on different aspects: carbon sequestration and storage, atmospheric pollutants reduction, avoided water runoff and water quality improvement are just some of the environmental benefits generated by tree population. Tools enable to carry out the analysis also from an economic point of view, evaluating monetary benefits brought by the green infrastructure both at present day and in the future,  taking into account climate change effects through projections based on the regional climatic model COSMO-CLM (RCP 4.5 and RCP 8.5 scenarios).

The work led to deepen potential held by the greenspace, helping the cooperating management institution  to plan future territorial agenda and to find innovative approaches for an integrated and sustainable hazard control.

How to cite: Busca, F. and Revelli, R.: Urban Hazard Adaptation: Efficiency of a Green Infrastructure in an Italian metropolis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15461, https://doi.org/10.5194/egusphere-egu21-15461, 2021.

Arianna Dada, Christian Urich, Michèle Pezzagno, and Giovanna Grossi

The climate change of the last half century is globally causing an increasingly in violent meteorological phenomena. Cities are experiencing the pressures of these phenomena and they are facing many challenges - economic, social, health and environmental.

Over the coming decades the population growth and the rapid urbanization will bring to a tumultuous growth of the cities that will become more and more vulnerable, especially to flood hazards.

In order to make our urban water systems more effective to these challenges new water management strategies must be developed. The complexity of this challenge calls for the integration of knowledge from different disciplines and collaborative approaches.

The concept of Water Sensitive Cities is one of the starting points for developing new techniques, strategies, policies, and tools to ensure a better liveability, sustainability, and resilience of the cities.

In this study, the DAnCE4Water model to promote the development of Water Sensitive Cities, was applied to Parma, an Italian town that faced serious water issues in the last years. Through the model the efficiency of new decentralized technologies, as green roofs and porous pavement, and their integration with the existing centralized technologies (sewerage), was estimated.

The first phase of the study concerned the analysis of the current state of the sewerage network and the relative critical issues. Flow rates and the amount of surface runoff were calculated using the SWMM modelling software.

In the second phase three hypothetical different scenarios were created by adopting different intervention strategies. The first scenario was created by using green roofs for a percentage of existing buildings in the urban area equal to 30%; the second scenario was created by adopting the porous pavement technology. For the third scenario, a possible urban development was simulated, with its consequent population, without adopting any flood risk mitigation strategy. A hydraulic study was carried out for each scenario highlighting the differences in terms of runoff formation and percentage of infiltration.

The integrated approach enables a city to test its current water management practices and policy, it helps cities to identify their short and long term goals to enhance water sensitivity, it gives a quantification of benefits and costs and it provides an estimate,  still in the design phase, of the effectiveness of possible strategies under different scenarios like climate changes, changes in the societal needs and urban changes by modelling the complex dynamics between societal system, urban environment and the urban water system.

How to cite: Dada, A., Urich, C., Pezzagno, M., and Grossi, G.: Water Sensitive Cities: integrated approach to enhance urban flood resilience in Parma (Northen Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13085, https://doi.org/10.5194/egusphere-egu21-13085, 2021.

Qifei Zhang, Zhifeng Wu, and Paolo Tarolli

With the acceleration of urbanization, the impervious surfaces of urban areas have increased dramatically, changing the natural water cycle of the city. It is of great significance for the improvement of urban living environment and the risk management of urban waterlogging to fully understand and play the positive role of UGI in alleviating urban waterlogging. This study attempts to identify the critical factors that alleviate urban waterlogging and examine the effectiveness and stability of UGI in mitigating urban waterlogging in multiple locations. We looked at two highly-urbanized Chinese cities (Guangzhou and Shenzhen) in a comparative study. The waterlogging records from 2009 to 2015 were obtained from the local water authority and the UGI was extracted from the 0.5-m resolution remote sensing images. The complex relationship between urban waterlogging and green infrastructure was quantified and compared through partial redundancy analysis and piecewise linear regression after controlling the conditions of topography, precipitation, and drainage network. The results indicated that the spatial distribution of urban waterlogging events presents a strong agglomeration effect, while the clustering pattern varies in different cities. Furthermore, after controlling the impact of elevation, rainfall, and drainage network, the area percentage and biophysical parameters of green infrastructure are the two most important factors to alleviate urban waterlogging. The influence of these two factors on urban waterlogging is consistent in different cities. This result indicates that more attention should be paid to the area size of green infrastructure and its vegetation biophysical parameters to mitigate urban waterlogging magnitude to the greatest extent. However, the area of green infrastructure must be controlled within a certain range in order to play a corresponding role in alleviating urban waterlogging. We also found that the spatial configuration of UGI also matters. Holding UGI’s composition constant, the degree of urban waterlogging can be reduced by optimizing the spatial configuration of UGI. This finding provides additional insights that the urban waterlogging can be alleviated by balancing the relative composition of UGI as well as by optimizing their spatial configuration, which is particularly important for a highly urbanized area where land resources for UGI are scarce. This study expands our understanding of the complex mechanism of UGI on urban waterlogging mitigation and provides beneficial enlightenment for the design of UGI.

How to cite: Zhang, Q., Wu, Z., and Tarolli, P.: The mitigation effect of urban green infrastructure (UGI) on urban waterlogging, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2514, https://doi.org/10.5194/egusphere-egu21-2514, 2021.

Ákos Kristóf Csete and Ágnes Gulyás

Urban water cycle suffers from ever increasing problems for what a modern city needs to prepare. The water cycle of most cities is not implemented in a sustainable way, which needs to be redesigned as a result of climate change. Through the climate change more extreme weather situations are expected to affect the life of cities. From aspect of the water cycle, this means extremely unequally distributed rainwater supply throughout the year. During drought periods, urban vegetation requires irrigation, often covered by cities with drinking water, a practice widely considered to be unsustainable. Therefore, finding appropriate methods and resources is crucial, in order to reduce the exposure of cities to the increasing climate extremes.

By collecting large amounts of rainwater and using it as irrigation water during droughts, it is possible to avoid the unnecessary waste of drinking water and to help preserve its limited supply in the future. A significant amount of precipitation flows through the surface of urban micro-catchments (e.g. roofs or other building surfaces), a significant part of which leaves the city through the sewer system without any usage.

The aim of our research is to create a rainwater harvesting potential map based on a building database in the study area of Szeged, Hungary. We used this building database to estimate the amount of rainwater that flows or evaporates on the top of buildings during a year, as well as the amount that can be considered as potentially collectable water. In addition to the GIS data, a complex meteorological database was also used.

The study was carried out in the EPA SWMM model. The building database contains nearly 20,000 building polygons, of which nearly every single polygon represents a separate catchment for this research. Based on the database, it is also possible to separate slope/pitched roof and flat roofs, which also allowed us to determine which roofs have the potential to be used as a green roofs to further facilitate efficient rainwater harvesting. Our result can be used to produce both city- and district-level (downtown, housing estate, garden house zones) summaries about the rainwater harvesting possibilities within Szeged. These results can be used to delineate areas where harvesting systems can be realistically installed. In addition to the spatial data, we can also acquire information on the seasonal distribution of the precipitation and thus the amount of collected water which can be used in drought periods.

Through our results we can get estimate the volume of rainwater that can be potentially collected from the surfaces of the building in Szeged. We believe, that our research may encourage urban planners to make into greater account the potential of rainwater storage in the local planning processes. This can greatly contribute to the decision-making processes at the local levels, and to the expansion of the knowledge related to green space-based integrated urban infrastructure management.

How to cite: Csete, Á. K. and Gulyás, Á.: Mapping of rainwater harvesting potential derived from building data-based hydrological models through the case study of Szeged, Hungary, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6431, https://doi.org/10.5194/egusphere-egu21-6431, 2021.

Christophe Rousson, Hervé Piégay, and Guillaume Fantino

The “green infrastructure” metaphor have put a new emphasis on river spatial planning as a mean to protect fluvial corridors on the long term (Kline and Cahoon, 2010) as they provide ecosystem benefits such as flood expansion zones or better functioning ecological networks. In order to provide support data for strategic planning at the regional or national scales, we have developed automated mapping tools of fluvial corridors and floodplains based on high-resolution DEM and landcover datasets. Our goal is to characterize the continuity of fluvial corridors in the longitudinal and lateral dimensions and produce indicators on their integrity.

Following the work done by Alber and Piégay (2011) and Roux et al. (2015), we produced high-resolution detrended DEM (height maps) that support the delineation of valley bottoms, can be used for 0D flood risk mapping or to identify potential wetlands. Based on the hypothesis that fluvial processes imprint the modern landscape, even in the presence of human-driven disturbance, we have also developed a novel landcover continuity analysis method. These continuity maps provide insights on the spatial scale of river processes and the amount of space, if not natural, that is still well connected to the river and is eventually available for floodplain restoration. Finally, we explored the possibility to disseminate our results through a web platform to share the database across scales for promoting participative approaches and land use planning.

At the intersection between fluvial risks mitigation, water resource preservation, and biodiversity and landscape conservation, this strategy is rooted in the concept of “freedom of space” and unifies the concepts of greenways, waterways and floodways in a common approach to making room for the river and working with natural processes, integrating the concept of natural infrastructures that has been proposed in the 1990s (Mermet, 1993). This holistic view insists on river corridors and floodplains as multifunctional spaces. It is expected that this spatial knowledge will in turn raise awareness and encourage local authorities to better protect river corridors as green infrastructures through land planning.

Further perspectives include studying how the intended recipients of our approach, such as local authorities or river practitioners, appropriate the produced maps and information, and to what extent they contribute to an effective protection of river corridors. This understanding should prove useful to integrate such data into regional observatories and communicate a more integrative view of the river.

How to cite: Rousson, C., Piégay, H., and Fantino, G.: Mapping river corridors at the network scale for integrating natural infrastructures into rural/urban spatial planning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6520, https://doi.org/10.5194/egusphere-egu21-6520, 2021.

Ping Yu Fan, Kwok Pan Chun, Ana Mijic, Mou Leong Tan, Omer Yetemen, and Jaivime Evaristo

Based on the interplays between land use and water resources, the green and blue infrastructure (GBI) is a central landscape approach for hydrological environment management. However, evidence-based principles of regional GBI planning are not well developed. The Budyko framework is widely used to explore water balance in land-use change studies. It provides a method to relate land use changes and streamflow variations based on two indices – the evaporative index (EI) and the dryness index (DI). Using the Dongjiang River Basin (DJ) as an example, we use the Geographically Weighted Principal Components Analysis (GWPCA) with adaptive kernels to classify the dominant land types based on local spatial variances. Then, we apply the Emerging Hot Spots Analysis (EHSA) to identify spatial-temporal hotspots of EI and DI for the Budyko analysis. From the EHSA, two wet years (1998 and 2016) and three dry years (2004, 2009, and 2018) are focused to investigate how land uses are related to water resources in different climatic conditions. On both catchment and hotspot scales, movements within the Budyko space are observed. These movements illustrate the associations between land use and hydrological response. These data-driven relationships can be used to explain the underlying mechanism of catchment forms (land surface property) and functions (evapotranspiration and runoff) for setting best practices for land use planning. Specifically, our results show that planners should consider to 1) reduce the area of croplands and trees, while increase the extent of grassland and water body on a catchment scale; and 2) increase rain fed croplands, broadleaved evergreen trees, and grasslands in the upstream catchment. Overall, this study highlights the scale considerations in land use planning, and land use strategies are developed based on reanalysis data and remote sensing products for catchment water resources management.

How to cite: Fan, P. Y., Chun, K. P., Mijic, A., Tan, M. L., Yetemen, O., and Evaristo, J.: Land use and cover changes related to green and blue infrastructure planning for water resources management based on a Budyko framework, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10451, https://doi.org/10.5194/egusphere-egu21-10451, 2021.

Future challenges and opportunities within GI
Thea Wingfield, Neil Macdonald, and Kimberley Peters

Nature Based Solutions (NBS) is a practice based approach developed in response to the global challenge of on-going environmental degradation and biodiversity loss. Interventions that restore or mimic hydrological processes to slow water within a catchment come under an umbrella term of NBS for flood management. Proponents of the practice link its use as beneficial in reducing flood risk but also climate change adaptation, urban hazard management, sustainable agriculture and eco-hydrology. Despite promising an integrated and sustainable future and receiving policy support, catchment scale adoption is limited. Understanding, designing and delivering NBS flood management is complex, crossing multiple disciplinary divides and practitioner communities, each with its own history, background, methods and uncertainties. Barriers and intervention points within the delivery system has received little investigation from the view of environmental professional practice. This research addressed this gap through participatory case studies of projects delivering NBS in England. We found low agreement amongst practitioners on how NBS for flood management is distinguished, resulting in differing perspectives on its identity and contested boundaries between it and other land and water interventions. Our transdisciplinary research project sought and generated a context for delivery that breaks down disciplinary boundaries and in doing so a new system and intervention point emerged. The problem that practitioners used NBS for flood management to address is a homogenised water cycle: reduced infiltration and increased surface runoff. Therefore NBS for flood management aims to reverse this by restoring catchment hydrodiversity in harnessing hydrological processes for integrated sustainable urban and catchment management. The implications for academic thinking and land and water management practice created by the novel conceptualisation of a catchment possessing an attribute of hydrodiversity is far reaching. In relation to supporting NBS for flood management mainstream adoption: the conceptualisation draws together different land use systems and a shared goal to deliver catchment hydrodiversity emerges enabling coordinated flood management at multiple spatial scales and across professional practice and disciplinary groups.

How to cite: Wingfield, T., Macdonald, N., and Peters, K.: Practitioners can’t agree on what Nature Based Solutions for flood management is: Why this matters and how to respond, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1821, https://doi.org/10.5194/egusphere-egu21-1821, 2021.

Martin Coombes and Heather Viles

Green infrastructure and other nature-based solutions (NbS) offer opportunities to incorporate green elements into cultural heritage conservation and management practice in cities and unlock their associated co-benefits. There are concerns, however, about the potential negative impacts of nature on built heritage including biodeterioration, the loss of heritage values, and practical challenges for heritage conservation and management. These issues can act as barriers to the wider uptake of GI, especially in historic cities. Here, we illustrate how built heritage can benefit from GI interventions by reducing or mitigating the deterioration of heritage materials, improving the visitor experience, enhancing values, and stimulating investment. At the same time, built heritage conservation can support the delivery, connectedness, and success of GI schemes by offering additional locations for implementation, providing inspiration for closer relationships between nature and society, and enriching the benefits of GI by adding a cultural element. Better integration of built heritage into the wider GI paradigm shows great promise for strengthening and broadening these linkages in cities.

How to cite: Coombes, M. and Viles, H.: Challenges, opportunities and prospects for linking green infrastructure and the conservation of urban built heritage, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3022, https://doi.org/10.5194/egusphere-egu21-3022, 2021.

Elena Cristiano, Roberto Deidda, and Francesco Viola

The modern society is facing new environmental and socio-economic challenges: population is growing fast, and it is projected to continue with this trend, reaching 9.8 billion of people by 2050, with 2/3 of them living in cities. Moreover, climate changes are leading to an increase of hot and dry periods and of short but intense rainfall events, forcing policy makers to rethink to the water management system. For these reasons, it is important to integrate in the urban planning, sustainable solutions that can help dealing with these new challenges. In this context, green roofs are powerful and flexible tools, that can play a fundamental role in the creation and development of smart and resilient cities. So far, green roofs have been generally investigated focusing on one single field at the time, following a so called “silo approach”. This approach, however, does not allow to highlight the interconnections and feedback between the different sectors, limiting the understanding of the potential of this tool. An integrated water-energy-food-ecosystem nexus approach is hence required to fully explore all the potential benefits of a large-scale installation of this tool. This work presents a review of green roofs’ benefits, following an integrated water-energy-food-ecosystem approach, with the aim to identify the potential positive impacts for the development of sustainable and resilient cities. Green roofs present multiple benefits for the urban environment, which are in line with the Development Goals proposed in the Sustainable Agenda 2030 (SDGs). Green roofs can, for example, mitigate pluvial floods, adapting to climate changes (SDG13: Climate Action) and contrasting the urbanization (SDG11: Sustainable Cities and Communities). The installation of these tools on the rooftops guarantee thermal insulation for the building, reducing the energy consumption for heating and cooling systems (SDG7: Affordable and Clean Energy). Thanks to the potential applicability of urban agriculture on its surface, green roofs can reduce the population food demand (SDG2: Zero Hunger), especially in poor countries, where many people have limited or no access to food. Moreover, the harvested rainwater, if properly stored and treated, can be reused for several domestic purposes, reducing the pressure on the water supply system and consequently increasing the availability of clean water (SDG6: Clean Water and Sanitation).The installation of vegetation in urban areas partially aims to restore the natural conditions, increasing the biodiversity and attracting different species of insects and small vertebrates, which are fundamental to guarantee maintenance of the ecosystem (SDG15: Life on Land). Moreover, the installation of this tool in an urban environment contributes to improve the mental and physical well-being of citizens (SDG3: Good Health and Well-being), which is particularly relevant in relation to the health crisis caused by the COVID-19 pandemic.

How to cite: Cristiano, E., Deidda, R., and Viola, F.: The importance of green roofs in an urban Water-Energy-Food-Ecosystem nexus context, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4145, https://doi.org/10.5194/egusphere-egu21-4145, 2021.

Kuan Lin Chou

In Taiwan, it is easy to encounter typhoons or heavy rain events with high rainfall intensity, and urban areas are prone to flooding and causing disasters. Rural areas are no exception. Flooding can cause crop necrosis. The reason may be attributed to the rural areas’s old drainage system or not yet complete drainage system, so the goal is to find the most suitable low-impact development facilities through model simulation, evaluate whether various low-impact developments are feasible, and how much flooding depth and savings can be reduced after installation. How much water is used for future irrigation as a decision-making benefit, and the scope of the setting is planned according to the flow sharing plan set by the government, hoping to provide effective improvement in rural areas.

How to cite: Chou, K. L.: Benefits of low-impact development in rural areas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14284, https://doi.org/10.5194/egusphere-egu21-14284, 2021.