HS5.10

Abstract

Green roofs received increased scientific attention with respect to climate adaptation in urban environments for their hydrological, biodiversity and insulative capacities. Yet, the thermal properties of roofs with an additional water layer underneath the vegetation substrate (blue-green roofs) are not well represented in scientific research. In this field study, we examined the impact of surface temperatures, indoor temperature and insulative properties of blue-green, green, and conventional gravel/bitumen roofs in the city of Amsterdam for early 20^th century buildings. Temperature sensor (IButtons) results indicate that outside surface temperatures of blue-green roofs were more stable than for conventional roofs. For instance, for three warm periods during summer (2021) surface substrate temperatures peaked much higher for gravel roofs (+8 ^oC) or bitumen roofs (+18 ^oC) than for blue-green roofs. On top of that, during a cold period in winter average water crate layer temperatures remained 3.0 ^oC higher and much more stable than substrate temperatures of blue-green roofs and conventional roofs, implicating that the blue layer functions as an extra temperature buffer. The effect of lower daily variation of surface temperatures in winter and summer is also reflected by inside air temperatures. Inside temperatures showed that locations with blue-green roofs are less sensitive to outside air temperatures, as daily temperature fluctuations (standard deviations) were 0.19 and 0.23 ^oC lower for warm and cold periods, respectively, compared to conventional roofs. This effect seems rather small but comprises a relatively large proportion of the total daily variation of 24% and 64% of warm and cold periods respectively.

How to cite: Föllmi, D., Corpel, L., Solcerova, A., and Kluck, J.: What is the thermal effect of ‘blue’ in blue-green roofs? A quantitative case study on the insulative effects of blue-green roofs in Amsterdam, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2949, https://doi.org/10.5194/egusphere-egu22-2949, 2022.

Multi-stage constructed wetlands (CWs) are widely used for water quality improvement, especially in the treatment of wastewater. Many studies focus on their treatment efficiency under steady loading, but fewer studies consider their stability and sustainability under variable conditions. This study monitors the hydrology and water quality at the multi-stage CWs in the Hong Kong Wetland Park. Five wetland units along the flow path are examined for their long-term performance and sustainability in terms of water quality under seasonal changes, storm events, and shock loadings of pollutants. Time-series statistical analysis indicates that the multistage design well achieves stable performance. Each wetland unit has certain roles and they work together to achieve good performance. The reliability analysis shows that the CW system can largely buffer the fluctuations from most disturbances. While the resiliency analysis also shows that most water quality indicators could recover in a few days after the fluctuations. The water levels recover quickly but it was difficult to return to original water levels in multi-stage CWs. Besides, a numerical model is developed, calibrated, and utilized to predict future water quality changes. This will help evaluate measures to improve the sustainability of multi-stage CWs by simulating water quality changes under different influent concentrations and rainfall conditions. This study could provide appropriate recommendations and early warnings for wetland management and improvement.

How to cite: Jiang, L. and Chui, T. F. M.: Sustainability of a multi-stage free water surface constructed wetland in terms of water quality under changing conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3745, https://doi.org/10.5194/egusphere-egu22-3745, 2022.

Sustainable drainage systems (SuDS) design and management can contribute to a healthier and greener urban development. We show how the inclusion of innovative approaches to SuDS namely the plasma engineering can lead to a more effective and less detrimental water quality treatment. The treatment method using Dielectric Barrier Discharge Plasma actuator, can be retrofitted to the current urban setting, it is cheap and provides efficient alternative for water purification and pollution treatment. We present its environmental benefits causing minimal impact to the surroundings while controlling and managing the pollution. We investigate this in both the city and catchment scale contexts.

How to cite: Erfani, R., Ciric, L., and Erfani, T.: Plasma water quality treatment for SuDS development, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3941, https://doi.org/10.5194/egusphere-egu22-3941, 2022.

Trees in urban environment face plenty of problems that hamper vital and long-standing growth, which would be essential to counteract urban heat island effect. The major issue is a tremendously reduced volume of appropriate rooting space due to impervious surface and highly condensed underground in the immediate surrounding. Sponge city substrate based on the model of Stockholm promises to provide conditions suitable for root growth even underneath sealed surfaces. This innovative type of substructure construction method consists of unconsolidated fine substrate flushed into the voids of edged stones that serve as load-bearing structure. If well-designed in a function-oriented manner, the volume of sponge city substrate is able to serve as an underground retention basin saving soil water for transpiration and enabling excess water to infiltrate further into the groundwater. To support the creation of such highly functional substrate-pore systems, knowledge about the effects of different materials and methods on the hydrological functions is needed.

In Austria several projects using sponge city for urban tree planting have been implemented in recent years in various cities and municipalities. In order to increase the understanding of the system in hydrological, soil physical and implementational terms and to enable improvements and identification of reasons for malfunction, research is performed at laboratory, lysimeter and field scale. The latest monitoring project has been built in a small street in Graz, where both sides next to the street have been excavated and rebuilt with sponge city substrate. Two different substrate types have been used and 9 trees have been newly planted. The closest monitored part consists of about 100 m³ sponge city substrate, 4 trees and various types of surface design and usage including parking space, perennial plantings and a seepage basin with topsoil passage for purification of street water. Sensors measuring matric potential, volumetric water content, electrical conductivity, soil temperature, sap flow and water inflow from roof and street deliver the basic data to calculate the full water balance within this area and set up a water balance model offering the opportunity to assess the impact and potentialities of sponge city substrate in various temporal and spatial scenarios.

Coupling data from sponge city lysimeters, laboratory experiments and other field monitoring sites an estimation of ecosystem services accomplished by this innovative construction type will be attempted. Focus will be put on retention behaviour for heavy rainfall, plant water availability as well as tree vitality, growth and transpiration.

How to cite: Zeiser, A., Murer, E., Strauss, P., Zimmermann, D., and Weninger, T.: In-situ evaluation of sponge-city-type sites for urban trees to tackle flooding and heat islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9488, https://doi.org/10.5194/egusphere-egu22-9488, 2022.

Bioretention cells, also referred to as ‘rain gardens’, are Green Infrastructure features with a functional role of managing urban flood risk and relieving pressure on traditional grey infrastructure systems. These Sustainable Drainage Systems (SuDS) rely on the use of soil and vegetation to attenuate and discharge stormwater via infiltration into the ground or via underground outlets into sewer networks whilst filtering pollutants in urban runoff and providing value to public space. Soil makes up a large proportion of these systems and plays a key role in providing the storage capacity for retaining stormwater and determining outflow discharges. This role is typically characterised using laboratory or in-field surface assessments of saturated hydraulic conductivity (K_sat), which provide an empirical assessment of SuDS performance. Guidance suggests that SuDS substrates should have a K_sat that ensures that systems are able to collect and store runoff to provide water retention without becoming waterlogged before the next rainfall event. However, in-field evaluations are rarely conducted due to cost and testing rarely identifies variation with depth through the soil profile.

This paper presents in-field K_sat testing from four-purpose built, vegetated bioretention cell lysimeters at the UKCRIC National Green Infrastructure Facility, Newcastle-upon-Tyne, UK, commissioned as part of the Engineering and Physical Sciences Research Council (EPSRC) project ‘Urban Green Design and Modelling of SuDS’ (EP/S005536/1). K_sat was measured using a Soil Moisture Equipment Corporation Guelph Constant Head Field Permeameter to obtain stratified K_sat values throughout the 750 mm deep soil profile of the lysimeters. K_sat was assessed in the context of four different vegetation treatments, including an unvegetated control lysimeter, an amenity grass covered lysimeter and two mono-cropped lysimeters planted with Iris sibirica and Deschampsia cespitosa.

Results show that K_sat values are systematically variable through the soil column and are a function of confining pressure with soil depth and wash through processes. Trends in porosity with soil depth are shown to be comparable across all lysimeter planting styles with some subtle differences associated with vegetation planting. All lysimeters feature higher K_sat values at the near-surface (ranging from 160.2 – 648.0 mm/hr at 0 – 100 mm depth), thought to be due to weathering and wash-through processes associated with near-surface soil strata being exposed to prevalent weather conditions. Where larger vegetation is present, higher K_sat values are recorded, reflecting the presence of root-derived preferential flow pathways. The depth of elevated near-surface K_sat values reflects the rooting depth and structure of the plant species studied.

The use of a single K_sat value does not adequately capture the spatially variable hydraulic properties of bioretention systems. The results presented herein also have implications for SuDS design and maintenance, suggesting that the hydraulic properties of these systems may change through time. Consequently, SuDS scheme planners and developers should conduct multiple assessments of K_sat through the soil profile to provide robust empirically-based model parameter values to ensure that systems are fit for purpose.

How to cite: Green, D., Goddard, A., and Stirling, R.: Stratified hydraulic conductivity testing of green infrastructure: A lysimeter bioretention cell study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13418, https://doi.org/10.5194/egusphere-egu22-13418, 2022.

The consequences of climate change are exacerbated by land-use changes, which affect the control of rainfall-runoff relations and the impact on flooding hazards. Effectively, urbanization is constantly contributing to the increase of impervious areas and reducing the time-to-peak. The effect of Natural Water Retention Measures (NWRMs) in the mitigation of these phenomena is known. Nevertheless, this kind of sustainable infrastructures are still poorly known by citizens and administrators, and consequently barely adopted in many parts of the European Countries. The LIFE BEWARE project aims to enhance hydraulic safety and spread good practices on rainwater management by promoting and facilitating the adoption of NWRMs in the Altovicentino, a highly rainy foothills area in Northern Vicenza Province (Veneto Region, Italy). In order to support the dissemination activities, some full-scale NWRMs have been realized in the area of intervention of the project. The hydrological functioning of these nature-based green infrastructures is continuously monitored thanks to the installation of devices measuring inlet and outlet runoff. The aim of this research is to present the realized NWRMs and the adopted monitoring system, and to analyze the data collected during the firsts two years. Results show that at this field-scale experiment all the monitored interventions were able to manage almost all the rainfall events occurred during these two years and the fraction of the rainfall runoff that reached the outflow was always less than 2%. Finally, the research provides insights in better understanding the behavior of NWRMs exposed to different weather and environmental conditions. This also adds some useful information at the design phase of such green infrastructure.

How to cite: Bettella, F., Bortolini, L., Baggio, T., and D'Agostino, V.: Hydrologic performance of Natural Water Retention Measures: outcomes from the LIFE BEWARE project test site, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8387, https://doi.org/10.5194/egusphere-egu22-8387, 2022.

Nature-based Solutions are presented as relevant features to make the cities more resilient in a context of global change. By providing ecosystem services, they are considered as particularly efficient solutions to mitigate urban heat islands and floods, while preserving biodiversity. Nevertheless, despite this consensus, it is still very difficult to quantitatively assess these services. Some methodologies and tools have therefore to be developed to better understand the thermo-hydric behavior of such infrastructure in relation with biodiversity, and to assess their performances across scales.

This presentation aims to present the work carried out to solve these issues through two current projects dedicated to NBS. On the one hand, the French ANR EVNATURB project aims to develop an operational platform to assess some of the eco-system services (ie stormwater management, cooling effect, or biodiversity conservation) provided by NBS at the district scale. On the other hand, the LIFE ARTISAN project deals with the creation of a framework to promote NBS for the implementation of the national plan for adaptation to climate change (PNACC) in France by improving scientific and technical knowledge. Both aim to develop and disseminate relevant tools for project leaders (for the design, sizing, implementation and evaluation of ecosystem performance).

The presentation of the results is particularly focused on monitored pilot sites and modelling platforms developed during these projects. In addition to these scientific investigations devoted to the thermo-hydric balance, some specific literature reviews and interviews were conducted to facilitate the choice of the more efficient species to implement, and the way to arrange NBS to optimize their performances. One of the results of this work is a dedicated database related to the a priori main ecosystem functions provided by plant species, and a list of quantitative indicators relevant for an urban project (certification, labelling, compliance with local regulations, ...) and that NBS can comply. Then this presentation concludes on remaining research gaps that have be to filled on this topic.

How to cite: Versini, P.-A., Al Sayah, M., Duffaut, C., and Schertzer, D.: How to choose the most relevant Nature-Based Solutions and to assess their performances? Insight from two projects implemented on the French territory., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9465, https://doi.org/10.5194/egusphere-egu22-9465, 2022.

In order to mitigate the expected increase in coastal flood risk it is critical to better understand how adaptation measures can reduce that risk, including Nature-based Solutions. We present the first global scale assessment of the (future) flood risk reduction and the benefits mangrove restoration. Unlike previous studies on Nature-based Solutions, we provide a quantitative assessment of mangrove restoration and nature contributions to people in terms of monetary flood risk reduction, people exposed to flooding, and poverty indicators. We find that mangrove restoration is an effective measure to contribute to future flood risk reduction and estimate that a large share of future flood risk may be reduced by implementing mangrove restoration. Our estimates indicate that nature-based solutions like mangrove restoration constitute promising complementary measures to other adaptation measures (e.g. structural measures). We further indicate that the benefits of mangrove restoration are unevenly distributed across the population in terms of poverty, and show that only looking into property damages and people exposed is not enough to understand the range of impacts of adaptation on population distributions. Even though this study can only be used as a first proxy analysis or indicative, it provides valuable insight into the feasibility of mangrove restoration at the global scale, and supports the need for sustainable adaptation and global assessmenst of Nature-based Solutions. Furthermore, implementing adaptation measures, such as mangrove restoration, in developing countries will contribute to the resilience of people in poverty, poverty alleviation and help tackle poverty traps.

How to cite: Tiggeloven, T., Mortensen, E., Worthington, T., de Moel, H., Spalding, M., and Ward, P.: Nature-based Solutions, mangrove restoration and global coastal flood risk reductions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-369, https://doi.org/10.5194/egusphere-egu22-369, 2022.

The modern society is facing multiple challenges, that are reshaping urban areas: the fast population growth, with a consequent high urbanization, combined with an increase of the average temperature and an intensification of extreme rainfall events, facilitates the pluvial flood risk in cities. Several solutions have been proposed in the literature to mitigate the runoff generation from rooftops and to contribute to a sustainable water management. In this context, multilayer blue-green roofs incorporate the high retention capacity of traditional green roofs with the storage capacity that characterizes rainwater harvesting systems. Moreover, these innovative nature-based solutions present countless benefits for the creation of smart, resilient and sustainable cities, e.g., they contrast the urban heat island, reducing the surrounding air temperature, they contribute to the building thermal insulation, limiting the energy consumption, they attract multiple species of insects and small animals, increasing the biodiversity, etc. 

The potential impacts of multilayer and traditional blue-green roofs and rainwater harvesting systems on the runoff generation reduction have been investigated mostly at local scale, analysing the impact of the installation of these tools on single buildings. However, in order to estimate and to evaluate the potential benefits and limitations for a sustainable urban development, it is fundamental to simulate the potential implications of a large-scale installation of these tools on large neighbourhoods or entire cities. For these reasons, in this work we simulate the installation of multilayer blue-green roofs on all the suitable roofs of the cities of Cagliari and Perugia (Italy). Thanks to the two multilayer blue-green roofs, installed in Cagliari and Perugia as part of the EU Climate-KIC Polderroof field lab project, it was possible to calibrate an ecohydrological model to simulate the potential retention and storage capacities of these nature based solutions. The potential discharge reduction and water storage capacity at large urban scale are discussed using as input for the model long historical time series of local rainfall and temperature.

How to cite: Cristiano, E., Annis, A., Viola, F., Deidda, R., and Nardi, F.: Large scale installation of multilayer blue-green roofs as solution for a sustainable urban water management, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1444, https://doi.org/10.5194/egusphere-egu22-1444, 2022.

In subarctic regions, a significant part of annual precipitation occurs as snow. This creates challenges since (a) the occurrence of rain on snow during melting season might increase runoff peak flow and cause flooding in urban areas and (b) snow needs to be removed from roofs and streets. Current snow management practice includes removal of snow to large deposits outside of cities. Downsides of this approach are the carbon footprint and air pollution caused by transport and the release of untreated polluted melt water to nearby water bodies. One strategy to reduce transport and increase treatment of meltwater could be to integrate snow deposits with existing green infrastructure that manages stormwater within the urban environment, i.e. multifunctional areas.

When studying the potential performance of multifunctional areas with respect to snow management it is important to consider the flood risk that comes with increased snowmelt and rain on snow. Prior studies have evaluated the combined effect of frozen soils, snowmelt and rainfall during the melting season on runoff from urban catchments, but there are no similar studies on facility scale. Hydrological models can be used to investigate these factors and the snow deposit potential, without risking flooding. It is, however, unclear to what extent current urban hydrological models are suited to this purpose. This study aims to explore how hydrological models can be used to predict snow deposition volumes in multifunctional areas and the effect on runoff.

This study used EPA SWMM because it is a commonly used urban hydrological model with a relatively advanced snow management module. The modelled facility was a grassed swale in Luleå, Northern Sweden, receiving runoff from a 60 ha catchment with commercial and light industrial land use.  The swale was separated into 6 identical parts to test different scenarios for the amount and distribution of snow deposited in the swale. The long-term performance of the swale with regard to stormwater quantity was investigated with historical rain and temperature data. Runoff from the catchment to the swales was calibrated based on observed data from late spring 2021.

Hydrological models as a support tool for snow management using green infrastructure shows promising results. Using the model, it was possible to evaluate the effect of snow volume and placement within the swale. Such information can be of great use when designing green infrastructure and snow management strategies. However, SWMM has some limitations in this regard. For example, pollutants such as sediments (gravel, sand and micro plastics) affect the properties and melting behavior of urban snow and the release of pollutants, yet these factors are not represented in SWMM. Differences in the actual melt rate will affect the total volume of snow that can be deposited in the swale, hence this topic requires further research.

How to cite: Hedlund Nilsson, E., Broekhuizen, I., Muthanna, T. M., and Viklander, M.: Evaluation of Snow Management using Green Infrastructure in Subarctic Climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9977, https://doi.org/10.5194/egusphere-egu22-9977, 2022.

The implementation of Nature-based Solutions (NbS) has become a priority in many cities. The benefits of urban demineralization or ‘greening’ initiatives are manifold and range from the mitigation of the urban heat island effect, reduction of flooding risk, to improvements in the outdoor environmental quality. The positive impact on pedestrian level well-being and comfort is also to be taken into account from not only an environmental, but also a visual perspective, given the psychological benefits induced by the attractiveness to nature, and enhanced walkability of streets and squares.

Today, the green infrastructure (GI) evaluation methods utilized in urban planning processes focus on the quantification of the total greenery ratio making use of remote sensing technologies, or often incomplete geospatial databases. The Normalized difference Vegetation Index (NDVI) deduced from aerial imagery, however, does not match the green infrastructure perception at the pedestrian level. From the geospatial databases, on the other hand, tree location and park areas can be retrieved, however these datasets only provide a partial and oversimplified description of the GI. Strategies for the implementation of range in scale and type. Aside from the diverse tree species, cities are populated by diverse grass fields, bushes, and green walls amongst others. Based on the type and distribution of each GI, the impact on the pedestrian level well-being is different. Thus, the quantification of green infrastructure requires the identification of the distinct GI and their distribution evaluated from a pedestrian perspective.  

Our research investigates a novel methodology to quantify the perception of GI from the pedestrian perspective.  We propose to combine NDVI index metrics computed from high-resolution satellite images, with green view index metrics. Making use of a 360° six-lens camera, videos have been collected for 12 different squares selected based on their varied GI ratios and located in the neighborhoods of Saint Gilles and Molenbeek in the city of Brussels. Through Light Detection and Ranging (LiDAR) scanning technologies, point clouds have also been collected for these sites. Once the remote sensing datasets, video recordings, and scans were completed, through geospatial processing and semantic classification, the distinct GI types and ratios were quantified. Our research methodology enables a comparison between remote sensing, geospatial analysis, and first-person quantification of GI computation, and addresses the need of high-res urban environmental analysis for the development of an accurate GI infrastructural evaluation.

How to cite: Meulen, M. and Llaguno-Munitxa, M.: Pedestrian Level Greenery Perception quantification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10925, https://doi.org/10.5194/egusphere-egu22-10925, 2022.

Cities are open living systems, which rely on the confluence of multiple layers of infrastructure and corresponding services. The interaction among these components is made even more complex by the demands of businesses and governments, together with constraints arising from ecological and environmental considerations. Climate change-related phenomena are putting an enormous strain on cities’ infrastructure, basic services, human livelihoods, public health and well-being. In many parts of the world concerns mount in regard to the scarcity of resources and growing risk of natural disasters (heat waves, urban flooding, droughts).  The converse also holds true, cities are major contributors to climate change through greenhouse gas emissions, notwithstanding other sources of pollution. This, together with the increase in urban growth and urbanization, results in an expansion of urban hazards - including water pollution, disease spread and issues with food security. Despite these pressing issues, we are witnessing an almost paradoxical mismatch between the needs of future cities and the practices currently used in numerous urban projects. A wholesale re-thinking of existing urban design methods at systems level (Systemic Design), is therefore not only necessary, but also provides significant opportunities to explore critical aspects of Blue-Green Infrastructure (BGI) and systematic assessment of possible future scenarios of different scales (local, urban, regional…). Nature-based solutions (NBS) are at the very core of the conception and development of BGI and provide a range of ecosystem services including alleviation of flood risk, mitigation of climatic effects, increase in biodiversity and amenity values, improvements in water quality, and further, rather more intangible benefits related to the residents’ health and wellbeing.

In this work we provide a systemic design as an innovative and integrated approach, based on ecology and ecological design, which introduces the systematic context analysis (environmental, climatic, historic…).  A GIS-based mapping of the context, produced in relation to the functional purpose, can give us synthetic prospects to better understand the potential effectiveness of BGI solutions (design options) in relation to their wider ecosystem. The systemic design approach allows an examination of possible steps to reduce actual cities vulnerability and to explore the main drivers of urban development, climate change mitigation and urban resilience. In this way, the systemic design approach also supports decisions for further planning and anticipates actions for the management of the multifaceted hazards of the entire urban system.

How to cite: Boskovic, S., Puchol-Salort, P., Krivtsov, V., and Mijic, A.: Systemic Design Approach: A Framework for a resilient urban transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8783, https://doi.org/10.5194/egusphere-egu22-8783, 2022.