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Anthropogenic intervention is exerting enormous pressure on natural ecosystems, affecting water quantity and quality, and, as a consequence, threatening socio-economic and human development as described by the UN Sustainable Development Goals. Yet, we still lack a proper understanding of how catchments respond to changing environmental conditions and disturbances. Answering these open questions requires interdisciplinary approaches in combination with novel monitoring methods and modelling efforts.
This session has two key foci: 1) hydrological processes in forested catchments in various climates, and 2) hydrological processes specifically in tropical systems.
Forests are recognized as prime regulators of the hydrological cycle and their change has effects on, for example, energy cycles and ecosystem services they provide. The traditional idea that forest hydrology emphasizes the role of forests and forest management practices on runoff generation and water quality has been broadened in the light of rapid global change. Some of the largest forested areas are located in the tropics and have suffered rapid land-use changes. These tropical systems are still markedly underrepresented in hydrological studies compared to temperate regions, especially concerning long-term observations. This session will bring together studies that will enhance our understanding and stimulate discussions on the impact of global change on forest and tropical hydrological processes at different scales.
We invite field experimentalists and modelers to submit contributions on process-oriented studies that investigate the hydrological cycle in forests and other land uses/land covers, from boreal to tropical regions, including also water quality and ecohydrological aspects.

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Convener: Luisa Hopp | Co-conveners: Alicia CorreaECSECS, Daniele Penna, Rodolfo NóbregaECSECS, Christian Birkel
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| Attendance Thu, 07 May, 16:15–18:00 (CEST)

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Chat time: Thursday, 7 May 2020, 16:15–18:00

Chairperson: Luisa Hopp, Alicia Correa, Daniele Penna and Rodolfo Nóbrega
D1 |
EGU2020-18733
| solicited
| Highlight
Josie Geris

Understanding of plant water uptake and ecohydrological interactions between plants and soil water is crucial for developing effective and sustainable water use strategies, in particular for agricultural areas. To explore these questions, isotopic analyses of plant and source water provide useful tools alongside traditional techniques. Although such studies in tropical regions are less abundant, recent meta-analyses have revealed that vegetation water generally resembles that of deeper soil water sources than in temperate and cold climate regions. However, water uptake patterns from different sources can also vary in time, especially in the tropics where seasonality in precipitation and associated water availability is strong. As the distinct wet and dry seasons are expected to become more intense, this can have important implications for ecosystems and agriculture.

This presentation will bring together results from recent isotope studies on plant-soil-water interactions in tropical climate regions across the world. In particular, it will focus on system changes at the extreme ends of hydroclimatological conditions. It will also explore the implications this might have for agriculture, e.g. in terms of the sustainability of agroforestry where competition for water between co-existing vegetation might increase during dry periods, and how additional irrigation or flooding from extreme rainfall can change runoff dynamics and recharge leading to enhanced leaching of pollutants.

How to cite: Geris, J.: Plant-soil-water interactions in the tropics: using isotopes to explore environmental change implications for agriculture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18733, https://doi.org/10.5194/egusphere-egu2020-18733, 2020

D2 |
EGU2020-1211
| Highlight
Nicola Mathura and Kegan Farrick

Climate change and unsustainable land use practices such as quarrying have the potential to negatively impact the hydrology and water resource availability in catchments. Throughout the Caribbean, hillside quarrying has become a common practice. While these activities remove large sections of the critical zone, very little work has been done on how hillside quarrying impacts storm response and catchment water storage.  The study is particularly important given the expected changes to rainfall patterns in the Caribbean under future climate change. We hypothesised that the removal of the critical zone during quarrying will increase the magnitude of streamflow response to storm events due to its close proximity to the river, while also reducing the overall storage of the watershed. This study utilized a hydrometric and geochemical approach with direct measurements of rainfall and streamflow, and bi-weekly water sample collections for geochemistry and 18O and 2H stable isotopes between the 3.6 km2 Acono (forested) and the adjacent 3.6 km2 Don Juan (quarried) watersheds, located in Trinidad and Tobago. A total of 1207 mm of rainfall occurred, with 87.3% falling from August to November (wet season) and 12.7% from December to March (dry season). The δ 18O in rainfall ranged from -7.7 to 0.3 ‰ across both seasons with an average δ18O of -3.5±1.8‰ during the wet season and 0.1±0.5‰ in the dry season. During the dry season the mean δ 18O of stream water showed a difference between the forested (-2.8±0.3‰) and quarried (-3.1±0.3‰) catchments whereas there was little differences in δ18O in the forested catchment (-3.3±0.3 ‰) and quarried catchment–(-3.2±0.27‰) in the wet season. Our stream δ18O dry season results suggests that different sources of water or anthropogenic influences such as water from settling ponds in the quarry could have impacted the δ18O of the quarried stream as we expected the forested catchment to be more stable. Sample collection at these sites is ongoing and additional parameters such as soil water isotopes and rainfall, soil and stream ion chemistry are expected to improve our understanding of the translation from rainfall to streamflow. This research will allow us to gain a better insight of the current hydrological processes within this catchment and aid in the long term adaptive planning for factors such as climate change and further land use change.

 

How to cite: Mathura, N. and Farrick, K.: Analyzing Land Use Impacts on Streamflow Response in a Tropical Watershed: A Hydrometric and Geochemical Approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1211, https://doi.org/10.5194/egusphere-egu2020-1211, 2019

D3 |
EGU2020-8303
Alexander Horton, Anja Nygren, Miguel Diaz-Perera, and Matti Kummu

Global climate change and anthropogenic activities are disrupting flood frequency-magnitude distributions along many of the world’s large rivers, posing critical threats to rising populations and infrastructure. Isolating a single discharge signal amidst the multitudes of competing anthropogenic signatures is a persistent, yet important challenge if we are to mitigate against their negative consequences. The Usumacinta River in southern Mexico provides an ideal opportunity to study an anthropogenic driver in isolation: tropical forest conversion. The Usumacinta flows unobstructed along the entirety of its course, meaning the 55-year discharge record (1959 – 2014) represents the river’s response to a changing landscape under climatic variability. This paper employs a novel approach to disentangle the anthropogenic signal from climate variability, and provides valuable insight into the impact of forest conversion on flood severity.

Here we analyse continuous daily time series of precipitation, temperature, and discharge to identify long-term trends, and compare ratios of catchment-wide precipitation totals to daily discharges in order to account for climatic variability, and identify an anthropogenic signature of tropical forest conversion at the intra-annual scale. We successfully reproduce this signal using a distributed hydrological model (VMOD), and demonstrate that the continued conversion of tropical forest to agricultural land will further exacerbate large scale flooding.

We find statistically significant increasing trends in annual minimum, mean, and maximum discharges that are not evident in either precipitation or temperature records. We also find that mean monthly discharges have increased between 7 and 75% in the past decade, in contrast to mean monthly precipitation, which has decreased during the dry-season. Model results demonstrate that forest cover loss is responsible for raising the 10-year return flood by 20%, and the total conversion of forest to agricultural land may result in an additional 23% rise. Meaning the return period for a flood on the order of the 2008 peak discharge would fall from the current estimate of 41 years to just 12 under the total forest conversion scenario.

These findings highlight the need for a holistic approach to catchment-wide land management in developing tropical regions that weights the benefits of agricultural expansion against the consequences of increased flood prevalence, and the economic and social costs that they incur.

How to cite: Horton, A., Nygren, A., Diaz-Perera, M., and Kummu, M.: Flood severity along the Usumacinta River, Mexico: identifying the anthropogenic signature of tropical forest conversion., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8303, https://doi.org/10.5194/egusphere-egu2020-8303, 2020

D4 |
EGU2020-14092
| Highlight
Jérôme Latron, Mariano Moreno de las Heras, Antonio Molina, Francesc Gallart, Teresa Cervera, Teresa Baiges, Joaquim Garcia, Gabriel Borràs, Antoni Munné, Andreu Manzano, Miquel De Cáceres, and Pilar Llorens

Although forest provides multiple ecosystem services (e.g., soil conservation, carbon sequestration, regulation of water cycle), it often cannot provide all of them simultaneously because of the trade-offs between some of them. In particular, while afforestation and reforestation have been recommended as a means of sequestering carbon in forest biomass and soils to limit climate change impacts, these practices may significantly alter streamflow and groundwater recharge, particularly in Mediterranean headwater catchments. In this context, a better understanding of forest hydrology is necessary to anticipate the undesirable trade-offs of forest management that can affect water resources.

Within the MASCC and LIFE + CLIMARK projects, which respectively aim to establish possible land cover scenarios for the next decades and to implement forest management practices to strengthen the capacity of the forest to mitigate the effects of change climate, the Vallcebre research catchments (North Eastern Spain) were selected as a reference site to assess the effect of forest (green) management on water resources (blue water) in a Mediterranean environment. These research catchments offer available medium-term (15 years) hydrological series (precipitation, discharge and water table) prior to forest management and a detailed knowledge of their hydrological response, essential for this evaluation.

In October 2018, the forest cover of a small sub-catchment (0.0248 km2) which initially represented 54% of the basin was thinned (removing between 35% and 60% of the basal area depending on the locations) to assess the effect of multifunctional forest management on streamflow. In the same way, the forest covering the contribution areas (0.0138 and 0.0139km2) of two shallow piezometers was thinned according to the same procedure to evaluate possible changes on the dynamics of the piezometric levels.

This work aims to present the general framework of the study, the type of forest management carried out as well as a first analysis (at different temporal scales) of the water table and discharge dynamics observed during the first year after the forest management.

How to cite: Latron, J., Moreno de las Heras, M., Molina, A., Gallart, F., Cervera, T., Baiges, T., Garcia, J., Borràs, G., Munné, A., Manzano, A., De Cáceres, M., and Llorens, P.: Investigating blue water response to green management in a Mediterranean headwater catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14092, https://doi.org/10.5194/egusphere-egu2020-14092, 2020

D5 |
EGU2020-19167
| Highlight
Theresa Blume, Daniel Balanzategui, Lisa Schneider, Daniel Rasche, Markus Morgner, Andreas Güntner, and Ingo Heinrich

Many forests in Central Europe experienced unprecedented drought conditions in 2018. The exceptionally long dry period, lasting from early-summer 2018 and into the winter, was followed by another dry summer with record-breaking temperatures.   Ecohydrological consequences of extended droughts for these temperate forest systems are difficult to anticipate, and investigating the resilience of forest hydrological systems requires comprehensive and systematic long-term observations.

Monitoring at the TERENO-NE temperate forest observatory in northeastern Germany includes input characterization (throughfall and stemflow), high-resolution soil moisture observations in 14 different forest stands down to a depth of 2 m below the soil surface, shallow and deep groundwater observations, sap flow, tree water deficit and high-resolution tree growth measurements since 2012. The investigated forest stands cover the three tree species pine, oak and beech in both pure and mixed stands. This is complemented by terrestrial gravimetric measurements of total water storage changes. Steep hillslope transects allow us to investigate the impact of presence or absence of groundwater availability on tree water uptake and growth.

We find that after the unprecedented drought in 2018, which already had pronounced ecohydrological effects, the rainfall amounts over the winter 2018/19 were insufficient to refill the subsurface water storages. Dry conditions altered the growth phenology of each monitored tree species, while tree-water deficit and tree growth were negatively impacted in both years, but to varying extent. Soil moisture storage and dynamics are strongly affected and the drought caused a long-term memory effect.

How to cite: Blume, T., Balanzategui, D., Schneider, L., Rasche, D., Morgner, M., Güntner, A., and Heinrich, I.: The 2018 drought and its consequences: Investigating the resilience of different tree species based on comprehensive long-term monitoring of forest hydrology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19167, https://doi.org/10.5194/egusphere-egu2020-19167, 2020

D6 |
EGU2020-21661
| Highlight
Ruonan Li, Hua Zheng, Ying Pan, and Fei Lu

Human activities have had a dramatic impact on the forest ecosystem, which has changed from initial overexploitation to the current regional restoration. Such kind of human interference with forest ecosystem aggravates the uncertainty on regional hydrology in the contest of global climate change. Here we analyze the hydrology variation over 30 years in Daqing River Basin covered by the ecological restoration project, North China. We identified the influence of climate and human disturbance (ecological restoration project) on surface runoff and soil water. In addition, combined with the future plan of ecological restoration projects in the upper reaches and Xiong’an New Central Area construction in the lower reaches, regional hydrological effects and water demand gaps in the lower reaches under different restoration scenarios were analyzed. The results showed that since 1980's, the surface and soil water in Daqing River Basin had a sudden change in 1999, and the influence of human interference after the change was significantly higher than before, among which the influence of forest area and quality was the dominant contributors. The results of the scenario analysis show that under the existing regional ecological restoration projects and climate change trends, there will be about 1/6 water resource gap in the lower reaches of the basin by 2050, of which about 35% will be caused by ecological projects. Our research results show that changes in forest area and quality brought about by basin-level ecological restoration projects will significantly increase upstream evaporation and water conservation, thereby affecting the regional hydrological cycle and aggravating the conflict between supply and demand of water resources downstream.

How to cite: Li, R., Zheng, H., Pan, Y., and Lu, F.: Hydrological effects triggered by large-scale forest restoration in catchment scale, a case study in Daqing River Basin, North China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21661, https://doi.org/10.5194/egusphere-egu2020-21661, 2020

D7 |
EGU2020-107
Kelly Hokanson, Kevin Devito, and Carl Mendoza

A widely accepted approach in both conceptual and numerical models of groundwater flow is to assume that the water table (WT) is a subdued replica of topography, where groundwater recharges at topographic highs and discharges at topographic lows. However, WTs in low-relief, water-limited environments are generally not topographically controlled, therefore traditional paradigms where forested hummocks are sources of water to both adjacent local wetland-pond systems and catchment-scale runoff do not usually hold true. Local groundwater flow systems (flow in which the recharge area is directly adjacent to its discharge area) are necessary to link forested hummocks with adjacent peatlands or ponds. However, the development of the groundwater mounds beneath topographic highs required to generate local groundwater flow systems is both spatially and temporally infrequent in low-recharge settings like the Boreal Plains. Thus, identifying the spatiotemporal controls on groundwater mounding is crucial to understanding the climatic and geological conditions required for landscape connectivity and runoff generation at larger, regional scales. This insight is becoming increasingly important as water security, ecosystem sustainability, and environmental quality become the focus of land management and reclamation efforts.

The Canadian Boreal Plains are dominated by aspen mixedwood forests, shallow lakes, and peatlands, and has a sub-humid climate that causes large interannual variability in runoff generation and hydrological connectivity at the landscape scale. Through a combination of field observations and numerical modelling, this study identifies the role of aspen forested hummocks in the generation (or loss) of groundwater and hydrologic connectivity to adjacent peatlands and lakes. WT elevations and climate data (precipitation (P) and potential evapotranspiration (PET)) collected over the last 20 years at nine fine-textured forested hummocks were examined for frequency and magnitude of groundwater mounding and/or depressions relative to their adjacent peatlands. It was evident that no simple metric (e.g., annual P, multiyear cumulative P-PET, etc.) was a good predictor for WT position. Through a combination of 1D and 2D, variably saturated numerical modelling, we identify the relative spatiotemporal controls that hummock morphometry, texture, and climate have on groundwater recharge and WT position. Multiple scales of climate forcings (seasonal, interannual; P, PET), substrate texture, hummock height, and rooting parameters all affect groundwater recharge (both positive and negative). Groundwater recharge is most dependent on timing and magnitude of snow melt; however, during periods of large interannual moisture surplus, when available subsurface storage is low, large summer and fall storms can also contribute to recharge. Otherwise, the overwhelming majority of scenarios result in hummocks storing and transpiring water and receiving inputs of groundwater from neighboring peatlands, therefore acting as a net sink of water to the larger landscape.

We show that groundwater mounds, and therfore the development of local topographic flow systems, under forested hummocks are spatiotemporally rare in sub-humid, low-relief regions, resulting in these hummocks being net sinks of water. Not only does this study emphasize the role of peatlands in the generation of landscape-scale runoff, it encourages a reconceptualiztion of the overall hydrologic function of forestlands and peatlands in catchment hydrology.

How to cite: Hokanson, K., Devito, K., and Mendoza, C.: The give and take (but mostly take) of forested boreal plains hummocks: Are they hydrologic sources or sinks?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-107, https://doi.org/10.5194/egusphere-egu2020-107, 2019

D8 |
EGU2020-155
Maria Arenas, Pedro Felipe Arboleda Obando, and Leonardo David Donado Garzón

Hydrologic models allow to simulate the water fluxes and storages inside a watershed, and so, to compute the water budget at different time and spatial scales. Even if they are important tools for water management, uncertainty can affect their results. The output data of the hydrologic model can be used to run other models, i.e, a hydrogeologic model (which needs recharge data) and hydrodynamic models (which need discharge data for some tributaries with no gauge stations). Therefore, with the scope to reduce uncertainty and to achieve a better representation in tropical basin systems, we focus on building a coupled hydrology model able to simulate data to be used inside of groundwater flow and surface water hydrodynamic models.  In order to do so, we decided to use Dynamic Topmodel, a recent development from the well – known Topmodel, as the hydrologic module, through the HRU (hydrological response units) approach to split the area in smaller units. Then, to include the routing processes, we decided to couple Dynamic Topmodel to the Variable Infiltration Capacity model 2D routing module (VIC-2D), to represent the drainage network using cells, and simulate discharge values at some non-gauged locations. The coupling was built under one single main hypothesis: all the cells inside a single HRU will produce the same recharge and runoff value. Based on this hypothesis we built the input data maps to run the routing module.

 

As our case study, we chose a 31 140 km2 basin in the Middle Magdalena Valley (MMV), a central area with important economic activities, as oil and gas (O&G) exploration and production, agriculture and livestock. Our model used cells of size 3 km with 76 HRU, but only seven parameter sets, so many of those 76 HRU shared parameter values, according to the digital elevation model (DEM), soil texture, and land used data. Our analysis is grounded on a record of 30 years of hydro-meteorological variables. The results of the coupling model described in a satisfactory way the following outcomes: (i) the fluxes among hydrosystems, (ii) channel flows, (iii) optimizing the computational performance (budget) of models in basins of tropical regions and (iv) allowing identification of trends on the discharge across the area to support the calibration of hydrodynamic models. In addition, the developed technique reduces the uncertainty of the model outcomes in areas with no data.

How to cite: Arenas, M., Arboleda Obando, P. F., and Donado Garzón, L. D.: Coupled hydrology - routing model to improve hydrogeological and hydraulic data across a tropical basin in Colombia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-155, https://doi.org/10.5194/egusphere-egu2020-155, 2019

D9 |
EGU2020-588
Adonis Gallentes, Peter Jeffrey Maloles, and Cesar Villanoy

The Philippines is a country within the Coral Triangle which is known to be the center of the most biologically diverse marine ecosystem in the world. Despite being a crucial area for marine biodiversity, discharge measurements of many rivers in the country are either sparse or non-existent. Such data are important in assessing aspects such as sedimentation which is highly related to the health of the reef community.

Here, we applied SWAT hydrological model in order to simulate the sediment yield of sub-basins and river discharge surrounding Davao Gulf, one of the country’s richest zones in terms of fish production. Monthly-averaged results of the model from 2001 to 2018 indicate that the relative maxima of sediment yield coincide with precipitation maxima, and that consecutive rainfall events which start around midyear results to higher erodibility and thus, higher peaks in sediment yield during the second half of each year until the early part of the following year. Dependence of sediment yield on slope class/angle and land use was also observed, identifying the northwestern catchments as critical sources of land surface erosion. Good agreement was obtained between simulations of river discharge and the sparse observed streamflow values during model validation (Davao River: NSE=0.61, R2=0.61, PBIAS = 2.87, r= 0.78; Hijo River: NSE=0.62, R2=0.90, PBIAS = -2.1630, r= 0.95).

Overall, this modeling study helped fill in the temporal gaps of observed streamflow data from river gauges, and provided estimates of the historical streamflow pattern of those rivers with no river gauges. Outputs of this study can also be used as science-based reference in crafting laws and ordinances for proper land use and Marine Protected Area (MPA) management plans, with emphasized consideration of the likely effects of climate change such as the latitudinal shift of typhoon tracks, increasing temperature, and more pronounced precipitation events which have already been observed in the area during the past two decades. 

How to cite: Gallentes, A., Maloles, P. J., and Villanoy, C.: Simulation of sub-basin sediment yields and river runoffs into Davao Gulf, Philippines, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-588, https://doi.org/10.5194/egusphere-egu2020-588, 2019

D10 |
EGU2020-5670
Cristina Vásquez, Mario Córdova, Galo Carrillo, and Rolando Célleri

The correct determination of reference evapotranspiration (ETo) is fundamental for countless scientific and management applications such as closing the catchment water balance, the planning of irrigation schemes, and for simulation models. Nevertheless, the records of weather variables are often not available or incomplete. This usually happens when a sensor breaks or malfunctions due to severe weather conditions, lack of maintenance or electronic failure, which leads to data loss and consequently makes it hard to estimate ETo. Frequently, that is the case in mountain regions where meteorological sensors are subject to harsh environmental conditions as in the Andes. In case of missing data, the only solution is to estimate the required variable using a given equation. Therefore, these equations need to be calibrated to specific local conditions. The aim of this study was to calibrate and validate equations to estimate Solar Radiation (Rs) on daily and monthly scales and to evaluate the impact of using these estimations for the calculation of ETo through the Penman Monteith (PM) equation in an Andean altitudinal gradient in the páramo ecosystem. The páramo occupies the upper portion of the northern Andes, where the tussock grasslands are the dominant vegetation. In addition, this ecosystem provides essential environmental services for inter-Andean cities. We used six years of observations (2013–2019) from the Quinoas Ecohydrological Observatory. This Observatory has four meteorological stations: Toreadora (3955 m a.s.l), Virgen Cajas (3626 m a.s.l), Chirimachay (3298 m a.s.l) and Balzay (2610 m a.s.l). We evaluated five models to estimate Rs based on the maximum and minimum daily air temperature. A calibration was performed for each weather station and a simultaneous calibration for the entire gradient. We used four years of data for calibration and validation of the Rs model, and two years to evaluate the impact on ETo calculations. We found that all models yielded estimations that are highly correlated with the observed data. However, no model was able to capture high Rs values, greater than 185.4 W m-2 (16 MJ m-2 d-1), found in cloud-free days. The best model to estimate Rs was the locally calibrated Chen model, which showed a mean error of 2.9 W m-2 (0.25 MJ m-2 d-1).  Estimated Rs values reduced the estimation error of PM-ETo and, thus, allows its application for further studies.

How to cite: Vásquez, C., Córdova, M., Carrillo, G., and Célleri, R.: Improving reference evapotranspiration (ETo) calculation under limited data conditions in the Tropical Andes , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5670, https://doi.org/10.5194/egusphere-egu2020-5670, 2020

D11 |
EGU2020-12884
Caroline Tramier, Pierre Genthon, Quentin Delvienne, Nicolas Sauvan, Jean-Jérôme Cassan, Etienne Ebrard, Pascal Dumas, and Yann Queffelean

In New Caledonia wildfires and invasive animal species (deers and wild pigs) constitute major agents of land surface degradation and an important threat to forests. As a result of land degradation the lagoon and the quality of drinking water are impacted by sediments transported by rivers. The study area, the Thiem watershed, is located on the northeast windward coast of New Caledonia and on micaschist basement. The landscape is constituted by a mosaic of savannahs and forests. Forests are restricted to highest remote areas or near talwegs and waterways. Savannahs are located on the crests and on the superior slopes of watersheds, near the villages. The hydrological regime of contrasted land surfaces is assessed using a 1 year record from three 100 m2 plots located in a healthy forest, in a forest degraded by invasive fauna and in a woody savannah regularly burned. Significant isolated rainy events (50-100 mm rainfall) were observed during the dry season (May-December), while the wet season presented only few isolated dry periods. Difference of monthly rainfall between the three plots were less than 10% as a general rule. However rainfall difference reach 30% at the scale of a rainy event. Moreover, 40% of rain occurs during small events with less than 50 mm cumulated rainfall, although events larger than 200 mm were observed. The healthy forest corresponds to an annual runoff coefficient of 0.04 which is commonly observed in tropical forests. The savannah corresponds to a 0.16 coefficient which is in the high range of those commonly observed in similar tropical areas. The degraded forest presents a 0.86 runoff, rising to more than 100% for many rainy events of the wet season. The maximum event-based runoff coefficient was observed in the three plots during the OMA cyclone, corresponding to 0.18, 0.71 and 2.7 at the healthy forest, savannah and degraded forest respectively. It is proposed that the extra runoff (ER) regularly observed at SCAR results from subsurface flow originating from the upstream area and focused toward the plot. A reservoir model is proposed and calibrated against available data. The model results indicate that ER accounts for 47% of the total observed runoff in this plot. Our study confirms the major role played by subsurface flow in the water regime of forested and savannah areas. It is emphasized that subsurface flow exfiltration in degraded land surfaces could enhance erosion and transport of harmful bacteria (leptospira). Moreover savannah, as a dominant high runoff surface in upper catchments of our study area, might control runoff at the scale of the watershed and might constitute a target for controlling downstream flooding and gullies erosion.

How to cite: Tramier, C., Genthon, P., Delvienne, Q., Sauvan, N., Cassan, J.-J., Ebrard, E., Dumas, P., and Queffelean, Y.: Impacts of invasive fauna and wildfires on hydrological regimes in a tropical valley of New Caledonia (SW Pacific), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12884, https://doi.org/10.5194/egusphere-egu2020-12884, 2020

D12 |
EGU2020-11971
Franciele de Bastos, José Miguel Reichert, Éderson Diniz Ebling, and Stephan Hörbinger

In the last years, the intensification of erosive processes from inappropriate land use and management have made sediment production a worldwide problem, compromising soil physical and chemical quality, and water quality and quantity. This source of pollution can be reduced by understanding hydrological processes. Catchment scale monitoring allows the identification of the effects of anthropogenic actions on these processes, enabling assertive decision-making to reduce erosion processes. Modeling tools have been widely used in environmental studies, helping to understand the processes and providing the prediction of future scenarios. However, the development and use of models capable of simulate hydrossedimentological flows in forest areas are still incipient. The goal of this study was to represent the behavior and to understand the dynamics of hydrological and sedimentological processes by monitoring and modeling with the Limburg Soil Erosion Model (LISEM) two small paired rural watersheds. The study was conducted in two paired watersheds, with land use based in eucalyptus plantation (EW, 0.83 km²) and grassland (GW, 1.10 km²), both located in the Pampa biome, in the state of Rio Grande do Sul, Brazil. The hydrosedimentometric monitoring was conducted from January to March 2019, in fluviometric monitoring sections composed of flumes and equipped with level, precipitation, and turbidity sensors to quantify flow, rainfall, and concentration of suspended sediments, respectively. Three events of similar magnitude, with total rainfall accumulation of approximately 30 mm, were simulated for the two catchments studied. The modeling was applied to the scale of individual events. The results were evaluated by surface runoff, peak flow time, and total sediment production, observed and simulated. The percentage trend (PBIAS) was used to evaluate the percentage of overestimation or underestimation of the simulated data in relation to the measured ones. To evaluate the simulated hydrograph shapes and total sediment yield, the Nash and Sutcliffe Efficiency Coefficient (NSE) was used. LISEM satisfactorily represented the runoff in rainfall events of different intensities for both basins, supported by the Nash and Sutcliffe coefficients (> 0.50) and PBIAS or ERROR (< 25% for runoff and < 55% for the production of sediments). The model was unable to represent sediment production satisfactorily (< 0.50). This may be associated with spatial variability of the soil and the characteristics of the model used, which simulates the surface flow promoted by individual rainfall events in watersheds. In the study area, the influence of forest cover associated with sandy soil with deep clay accumulation favors the subsurface erosive process. FW had lower total sediment yield and lower peak flows, which is associated with the vegetation type. With the incidence of rain in the forest compartment, part of it is compartmentalized upon reaching the forest canopy, part seeps through the trunk, reaching the litter at a lower speed, favoring infiltration and decreasing surface runoff. Our studies are in the early stages, continued monitoring is necessary to evaluate events of different magnitudes, and to identify a model capable of adequately representing the predominant subsurface runoff in forest areas.

How to cite: de Bastos, F., Reichert, J. M., Ebling, É. D., and Hörbinger, S.: Hydrosedimentological monitoring and modeling in paired watersheds in the Pampa biome, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11971, https://doi.org/10.5194/egusphere-egu2020-11971, 2020

D13 |
EGU2020-20254
Alexandra Nauditt, Hamish Hann, and Marko Kallio

Although water-rich, tropical regions are facing severe drought disasters worldwide, especially during their dry seasons. To design site appropriate adaptation measures, a profound understanding of spatially varying hydrological drought severity and frequency is of crucial importance. However, low flow behaviour can strongly vary in space and time, depending on catchment characteristics, but discharge datasets of high temporal and spatial resolution needed for its assessment are rarely available. Our objective was therefore to provide hydrological drought hazard information to detect hydrological drought anomalies in quickly responding tropical environments.

We used daily discharge time series of an unregulated rural tropical test catchment, the Muriaé in southeast Brazil, to calibrate the semi distributed hydrological model SWAT2012. For the outlets of 93 hydrological response units, we simulated discharges to obtain an adequate spatial distribution. The hydrostreamer 4.0 downscaling approach (https://github.com/mkkallio/hydrostreamer) was applied to the ISIMIP 2a global discharge data product and calibrated with discharge observations and the simulations. Downscaling to a resolution of 450 m was carried out by evaluating the relationship between a spatial unit of discharge and the overlaid river network. To assess hydrological drought hazard, we applied the daily variable Q95 threshold to the dry season flow time series for each grid cell (0.1°). Drought events were defined for periods when the discharge values fell below this dry season threshold during 5 days (and 12 days respectively). To further understand the role of catchment characteristics in low flow evolvement, we tested the sensitivity of different climate and catchment related model input variables against low flow events and simulated artificial drought risk scenarios.

Drought hazard assessment results showed the largest number of drought events in the downstream area, probably attributed to geological and tectonic fracturation and hence increased infiltration, followed by the Western upstream region – that could be linked to  smaller subcatchment sizes and lower precipitation inputs.
Only limited hydrological drought sensitivity of the system against changes in land cover type and temperature was found in the model results, while geology and soils turned out to play a larger role for low flows. The drought scenarios also indicated that low flows were more severely affected than high flows by climatic changes such as decreased precipitation.

Our findings related to the ocurrence of hydrological hazards in the region coincide with institutional records by government institutions (CEMADEM), newspaper reports and stakeholder communication about water shortage in communes and districts.  We conclude that the here presented hydrological drought assessment approach provides science based data sets, indicators and information to be used in regional and local drought management in tropical regions.

How to cite: Nauditt, A., Hann, H., and Kallio, M.: Assessing spatially distributed hydrological drought hazard in data scarce tropical catchments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20254, https://doi.org/10.5194/egusphere-egu2020-20254, 2020

D14 |
EGU2020-13019
Monica Bonilla-Rodriguez and Sebastian Gomez-Rios

The Colombian Amazon exhibits complex hydro-meteorological features, as it links the biggest tropical rainforest of the world with the Andes range and the savannahs of the Orinoco basin. Similar to other amazon areas in neighboring countries, this high-biodiversity region faces severe deforestation due the agricultural expansion, illegal logging, and mining. Numerous studies have stated the role of the Amazon over the climatic system, and the complex interactions between the rainforest, the atmospheric dynamics and the hydrological response of the rivers. Furthermore, previous studies have warned about the effects of the loss of vegetal coverage in the Amazon over hydro-meteorological patterns in northern South America.

This work aims to study the effects of deforestation over some atmospheric and hydrological features in the Colombian Amazon. Taking into account present and historical rates of deforestation, there are defined scenarios of moderate and intense forest loss. Changes in precipitation and moisture fluxes over the area are investigated using the atmospheric model WRF (Weather Research and Forecasting). High-resolution simulations are performed for a study period composed of typical rainy and dry months, considering the changes in land use of each scenario. The effects of forest loss over streamflow in some rivers of the region are assessed using the results from the atmospheric model and simulations in an aggregated hydrological model. The main finding suggests that low-level moisture flux over the Colombian Amazon and neighboring Andean foothills decrease with the reduction of the rainforest cover in both of the considered seasons. As a consequence, precipitation decreases over the area, triggering a reduction of the streamflow in the studied rivers.

How to cite: Bonilla-Rodriguez, M. and Gomez-Rios, S.: Changes in atmospheric and hydrological dynamics at the Colombian Amazon in scenarios of forest loss, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13019, https://doi.org/10.5194/egusphere-egu2020-13019, 2020

D15 |
EGU2020-15895
Claudia P Romero and Felix Frances

According to United Nations, the world population in 2050 will reach 9.7 billion and it is expected that 68% will live in urban centers. An important part of the urban population in Latin America is concentrated in megacities such as Mexico City and Sao Paulo, which currently have more than 20 million inhabitants. Buenos Aires, Rio de Janeiro, Lima and Bogotá are now megacities under development. This accelerated process of urbanization entails effects on the demand of the natural resources and the impulse of the environmental negative effects related to the contamination of soil, air and water.

The megacity of Bogotá and its metropolitan area includes more than 10 million inhabitants being the higher population density of Colombia. Being the country’s capital city, it is the core of its economic development and it is currently one of the main business centers of South America.

From an environmental perspective Bogotá basin becomes a territory with high water vulnerability. The accelerated population increase (it has doubled during the last four decades), has caused, among others, high water resources demand. The industrial concentration in this territory has also affected both surface and subsurface water quality, causing an increase in the purification costs.

The objective of this study is to analyze the influence in the water cycle of the urban growth of the city of Bogotá in the last forty years. In this period the Bogotá river basin was modeled for the years 1985, 2005 and 2014, using the TETIS distributed hydrological simulation model. Results allow to identify the alterations in the basin water balance induced by changes in land use during the period of analysis.Por favor inserte su resumen HTML aquí.

How to cite: Romero, C. P. and Frances, F.: Impact of the megacity’s growth over the hydrological cycle of the Bogotá basin (Colombia) using distributed model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15895, https://doi.org/10.5194/egusphere-egu2020-15895, 2020

D16 |
EGU2020-647
Lukas Strebel, Klaus Goergen, Bibi S. Naz, Heye Bogena, Harry Vereecken, and Harrie-Jan Hendricks Franssen

Modeling forest ecosystems is important to facilitate adaptations in forest management approaches necessary to address the challenges of climate change, particularly of interest are ecohydrological states and fluxes such as soil water content, biomass, leaf area index, and evapotranspiration.

The community land model in its current version 5 (CLM5) simulates a broad collection of important land-surface processes; from moisture and energy partitioning, through biogeophysical processes, to surface and subsurface runoff. Additionally, CLM5 contains a biogeochemistry model (CLM5-BGC) which includes prognostic computation of vegetation states and carbon and nitrogen pools. However, CLM5 predictions are affected by uncertainty related to uncertain model forcings and parameters. Here, we use data assimilation methods to improve model performance by assimilating soil water content observations into CLM5 using the parallel data assimilation framework (PDAF).

 

The coupled modeling framework was applied to the small (38.5 ha) forested catchment Wüstebach located in the Eifel National Park near the German-Belgian border. As part of the terrestrial environmental observatories (TERENO) network, the SoilNet sensors at the study site provide soil water content and soil temperature measurements since 2009.

CLM5 simulations for the period 2009-2100 were made, using local atmospheric observations for the period of 2009-2018 and an ensemble of regional climate model projections for 2019-2100. Simulations illustrate that data assimilation of soil water content improves the characterization of past model states, and that estimated model parameters and default model parameters result in different trajectories of ecohydrological states for 2019-2100. The simulations also illustrate that this site is hardly affected by increased water stress in the future.

The developed framework will be extended and applied for both ecosystem reanalysis as well as further simulations using climate projections across forested sites over Europe.

How to cite: Strebel, L., Goergen, K., Naz, B. S., Bogena, H., Vereecken, H., and Hendricks Franssen, H.-J.: Modeling of a forested study site with the Community Land Model version 5 using climate projections for the 21st century. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-647, https://doi.org/10.5194/egusphere-egu2020-647, 2019

D17 |
EGU2020-6463
Tomoki Oda, Megumi Kuroiwa, Naoya Fujime, Kazuo Isobe, Naoya Masaoka, Kazumichi Fujii, Hiroto Toda, and Nobuhito Ohte

Ammonium (NH4+) and nitrate (NO3) concentrations and production rates in forest soil vary by hillslope position due to variation in ammonia-oxidizing microorganism concentrations, soil chemistry, and surface soil moisture. These spatial distributions have a significant effect on nutrient cycles and streamwater chemistry. Soil moisture conditions significantly restrict microbial activity, influencing the spatial distribution of NO3 concentrations on forest hillslopes. However, studies linking forest hydrological processes to nitrogen cycling are limited. Therefore, we investigated the determinants of spatial variation in soil moisture and evaluated the effects of soil moisture fluctuations on spatial variation in NO3 concentration and production rate.

The study sites were the Fukuroyamasawa Experimental Watershed (FEW) and Oyasan Experimental Watershed (OEW) in Japan. The two have similar topographies, climates, and tree species. In each watershed, a 100 m transect was set up from the ridge to the base of the slope, and soil moisture sensors were installed at soil depths of 10 cm and 30 cm at both the top and bottom of the slope. We collected surface soil samples at a depth of 10 cm at the top, middle, and bottom of the slopes using 100 cm3 cores, and measured soil physical properties, particle size distribution, volcanic ash content, chemical properties (pH, NO3, NH4+, nitrification rate, and mineralization rate), and microbial content (archaeal content). Spatial and temporal changes in soil moisture on the hillslope were calculated using HYDRUS-2D to examine contributing factors of soil moisture.

At FEW, high NO3 concentrations and nitrification rates were observed only at the slope bottom and middle, and no NO3 concentrations were detected at up slope. By contrast, at OEW, high NO3 concentrations and nitrification rates were observed at all points. NH4+ concentrations were similar at all points in both watersheds. At FEW, 10 cm surface soil moisture fluctuated within 25–40% at the slope top but was within 40–50% at the slope bottom. At OEW, surface soil moisture was 30–40% at both the slope top and bottom, with no significant differences according to slope position. It was confirmed that soil moisture was significantly involved in NO3concentration and nitrification rates. Model simulations showed that the difference in soil moisture fluctuations between FEW and OEW was mainly explained by the spatial variation in soil physical properties. In particular, volcanic ash influenced soil moisture along the entire slope at OEW, resulting in high water retention, but only influenced soil moisture at the slope bottom at FEW. These findings indicate that spatial variability in soil physical properties has a significant effect on soil moisture fluctuation and leads to a spatial distribution of NO3 production.

How to cite: Oda, T., Kuroiwa, M., Fujime, N., Isobe, K., Masaoka, N., Fujii, K., Toda, H., and Ohte, N.: Spatial variation in soil physical properties and effects on soil NO3– production on forest hillslopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6463, https://doi.org/10.5194/egusphere-egu2020-6463, 2020

D18 |
EGU2020-8774
Xinyue He, Dominick Spracklen, Joseph Holden, and Zhenzhong Zeng

Mountain forests cover a small fraction of the Earth’s surface, but may exert important influence on the hydrological cycles of river basins (e.g., evapotranspiration, river flow). Many montane ecosystems are currently experiencing forest loss or gain, due to direct land-use change and due to changes in climate. Previous studies revealed most deforestation and afforestation occur in the lowlands, while how forest cover changes at different altitudes in the mountains has not been fully understood. Here we present a study that aims to better understand the distribution of mountain forest change. We use a high-resolution global map of forest change during 2000-2018 combined with elevation data to complete a global analysis of the relationship of elevation with tree cover and tree cover loss and gain. We also assess which climate variables (temperature, rainfall, wind speed) might explain observed variations in tree cover. Our analysis provides new information on how and why mountain forests are changing.

How to cite: He, X., Spracklen, D., Holden, J., and Zeng, Z.: Global analysis of mountain forest distribution and change during 2000 to 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8774, https://doi.org/10.5194/egusphere-egu2020-8774, 2020

D19 |
EGU2020-10136
Mouna Feki, Giovanni Ravazzani, Tommaso Caloiero, and Gaetano Pellicone

Forests ecosystems provide several ecosystem services among which the regulation of the hydrological cycle. These ecosystems are exposed to different forms of disturbances induced by human activities, management strategies, and climate change. The objective of INNOMED project, for the Italian case study, is to understand the response of forest to different silvicultural practices under climate change conditions. The study site is the the Bonis catchment located in the mountain area of Sila Greca (39°25’15’’N, 16°12’38’’W), in the Calabria region (southern Italy). This small catchment has a surface of 1.39 km2 and a mean elevation of 1131 m above sea level. Almost 93% of the total area is covered by forest stand, dominated by about 50-year-old Calabrian pine (Pinus laricio Poiret) forests. In order to simulate the response of the catchment to different climate and management scenarios, FEST-WB distributed hydrological model was used. Within the framework of this project, FEST-FOREST module has been implemented in order to consider vegetation dynamics interactions with the hydrological response of the watershed. Since 1986, the basin was monitored through the installation of different instruments. Rainfall was measured by three rain gauges (with a tipping bucket) together with temperature that were measured at three different meteorological stations. In May 2003, a tower for measurement of eddy fluxes was installed at an altitude of 1100 m a.s.l, on a 54 years old plantation of Laricio pine which allowed monitoring of other parameters. Runoff was measured at the outlet of the catchment using a gauging structure. These data were used for the calibration and validation of the model before being implemented for future scenarios simulations. The results of these simulations delivered the potential impacts and the vulnerability of the Bonis catchment to different scenarios. These outcomes provide for the stakeholders a scientifically based and solid information for a sustainable management of the catchment.

How to cite: Feki, M., Ravazzani, G., Caloiero, T., and Pellicone, G.: The response of Bonis Catchment in Calabria –Southern Italy to different management options under climate change scenarios., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10136, https://doi.org/10.5194/egusphere-egu2020-10136, 2020

D20 |
EGU2020-11234
Marinos Eliades, Adriana Bruggeman, Hakan Djuma, and Maciek W. Lubczynski

Quantifying rainfall interception can be a difficult task because the canopy storage has high spatial and temporal variability. The aim of this study is to examine the sensitivity of three commonly used rainfall interception models (Rutter, Gash and Liu) to the canopy storage capacity (S) and to the free throughfall coefficient (p).  The research was carried out in a semi-arid Pinus brutia forest, located in Cyprus. One meteorological station and 15 manual throughfall gauges were used to measure throughfall and to compute rainfall interception for the period between January 2008 and July 2016. Additionally, one automatic and 28 manual throughfall gauges were installed in July 2016. We ran the models for different sets of canopy parameter values and evaluated their performances with the Nash-Sutcliffe Efficiency (NSE) and the bias, for the calibration period (July 2016 - December 2019). We validated the models for the period between January 2008 and July 2016. During the calibration period, the models were tested with different temporal resolutions (hourly and daily). Total rainfall and rainfall interception during the calibration period were 1272 and 264 mm, respectively. The simplified Rutter model with the hourly interval showed a decrease of the NSE with an increase of the free throughfall coefficient. The bias of the model was near zero for a canopy storage between 2 and 2.5 mm and a free throughfall coefficient between 0.4 and 0.7. The Rutter model was less sensitive to changes in the canopy parameters than the other two models. The bias of the daily Gash and Liu models was more sensitive to the free throughfall coefficients than to the canopy storage capacity. The bias of these models was near zero for free throughfall coefficients over 0.7. The daily Gash and Liu models show high NSE values (0.93 – 0.96) for a range of different canopy parameter values (S: 0.5 – 4.0, p: 0 – 0.9). Zero bias was achieved for a canopy storage capacity of 2 mm and above and a free throughfall coefficient between 0 and 0.7. Total rainfall and rainfall interception during the validation period were 3488 and 1039 mm, respectively. The Gash model performed better than the Liu model when the optimal parameter set (highest NSE, zero bias) was used. The interception computed with the Gash model was 987 mm, while 829 mm with the Liu model. This study showed that there is a range of canopy parameter values that can be used to achieve high model performance of rainfall interception models.

How to cite: Eliades, M., Bruggeman, A., Djuma, H., and Lubczynski, M. W.: How sensitive are rainfall interception models to the canopy parameters of semi-arid forests? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11234, https://doi.org/10.5194/egusphere-egu2020-11234, 2020

D21 |
EGU2020-13328
Takahiko Yoshino and Shin'ya Katsura

Rainfall-runoff processes in a headwater catchment have been typically explained by water flow in permeable soil layers (comprised of organic soil layers and mineral soil layers produced by weathering of bedrock) overlying less permeable layers (i.e., bedrock). In a catchment where mineral soils are characterized by clayey materials (e.g., mudstone, slate, and serpentine catchment), it is possible that mineral soil layers function substantially as less permeable layers because of a low permeability of clayey materials. However, roles of clay layers in rainfall-runoff processes in such a headwater catchment are not fully understood. In this study, we conducted detailed hydrological, hydrochemical, and thermal observations in a serpentinite headwater catchment (2.12 ha) in Hokkaido, Northern Japan, where mineral soil layers consisting of thick clay layers (thickness: approximately 1.5 m) produced by weathering of the serpentinite bedrock underlies organic soil layers (thickness: approximately 0.4 m). Saturated hydraulic conductivity (Ks) and water retention curve of these two layers were also measured in a laboratory. The observation results demonstrated that groundwater was formed perennially in the organic soil layers and clay layers. The groundwater level within the organic soil layers and specific discharge of the catchment showed rapid and flashy change in response to rainfall. In contrast, the groundwater level within the clay layers showed slow and small change. Temperature of the groundwater and stream water suggested that water from the depth of the organic soil layers contributed to streamflow. The electric conductivity (EC) of the groundwater in the clay layers was very high, ranging from 321 to 380 µS cmˉ¹. On the other hand, the EC of soil water (unsaturated water stored in the organic soil layers) was relatively low, ranging from 98 to 214 µS cmˉ¹. Hydrograph separation using EC showed that contribution of water emerging from the clay layers to the total streamflow ranged from 31 to 76% in low to high flow periods. Temporal variation in the total head, measured using tensiometers installed at four depths at the ridge of the catchment, indicated that in wet periods when the groundwater level in the organic soil layers was high, water flow from the organic soil layers to the clay layers occurred, whereas, in dry periods, water flow from the clay layers into the organic soil layers occurred. The laboratory measurements showed that the organic soil layers had high Ks (10ˉ² cm sˉ¹) and low water-holding capacity, whereas the clay layers had low Ks (10ˉ⁴ cm sˉ¹) and high water-holding capacity. It can be concluded from these results that clay layers play two roles: (1) forming perched groundwater table and lateral flow on the clay layers (the role of less permeable layers) and (2) supplying water into the organic soil layers in the dry periods (the role of water supplier).

How to cite: Yoshino, T. and Katsura, S.: Roles of clay layers in rainfall-runoff processes in a serpentinite headwater catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13328, https://doi.org/10.5194/egusphere-egu2020-13328, 2020

D22 |
EGU2020-14495
Saki Omomo, Yuichi Onda, Boutefnouchet Mohamed, Chenwei Chiu, Takashi Gomi, Sean Hudson, Yupan Zhang, and Janice Hudson

 Many researchers have studied the effects of plantation thinning on forest environments, including plantation thinning-induced changes in soil water, which recharges ground water. However, most of these studies have sampled only either preferential flow or matrix flow. To properly understand soil water movement, soil water must be classified into matrix flow and preferential flow, and we must sample and analyze them separately. Therefore, our purpose is to reveal the differences in the water stable isotope rates in soil water on different vegetation distributions to consider the change of soil water.

 We used suction lysimeters adding 60kPa and zero-tension lysimeters to collect two types soil water separately. We used modular zero-tension plate lysimeters which improve the problems in conventional zero-tension plate lysimeter of both low water collection efficiency by unsaturated soil on the plate and soil disturbance by inserting the plate.

 Matrix flow tended to be isotopically heavier under open canopy than under closed canopy, and isotopically heavier in areas with no understory vegetation than in areas with understory vegetation. Preferential flow tended to be almost the same water stable isotope rate as throughfall. We could see this trend better in heavy rain events than in light rain events, and the trend suggests mixing with matrix flow in the light rain. There was little difference between water stable isotope rates of throughfall in different vegetation distributions.

 The implications of these results suggest that soil water which recharges ground water is isotopically heavy in a degraded plantation, and becomes isotopically heavier with the increase in forest floor evaporation after plantation thinning, but becomes isotopically lighter as understory vegetation grows.

How to cite: Omomo, S., Onda, Y., Mohamed, B., Chiu, C., Gomi, T., Hudson, S., Zhang, Y., and Hudson, J.: Stable isotope-based approach to validate effects of stand structure and understory on soil water in a Japanese forest plantation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14495, https://doi.org/10.5194/egusphere-egu2020-14495, 2020

D23 |
EGU2020-20932
Di Wang, Guangyao Gao, Junran Li, Chuan Yuan, Yihe Lü, and Bojie Fu

Global climate change is likely to change the timing, frequency and magnitude of precipitation events, studying the response of sap flow (SF) of plants to rainfall events is thus important for understanding the response of ecosystems to global climate change. Here, we conducted a comprehensive study on the SF, rainfall events, meteorological factors and soil water for two typical xerophytic shrub stands (Caragana korshinskii and Salix psammophila) on the Loess Plateau of China for two rainy seasons (from June-September) in 2015 and 2016. The rainfall events were classified into three rainfall categories using the K-means clustering based on the rainfall amount (RA), rainfall duration (RD) and rainfall intensity (RI) (category I: lowest mean RA, RD and RI, category II: moderate mean RA, RI and highest mean RD and category III: highest mean RA, RI and moderate mean RD). The results showed that the response of SF at both C. korshinskii and S. psammophila stands to rainfall events differed under the three categories. The occurrence of rainfall events significantly decreased daily SF of C. korshinskii in three rainfall categories, whereas the daily SF of S. psammophila is more strongly influenced by rainfall category II. Maximum decreases in daily SF between the pre-rainfall and the rainfall weather condition of the two stands both occurred in rainfall category II. Daily rainfall SF at both stands was strongly correlated with daily SR, RH and VPD, regardless of the rainfall categories. Diurnal variation of hourly SF at both stands also differed among the days with similar RA and RD in the same rainfall category. It can be inferred that SF of C. korshinskii is more susceptible to rainfall events than S. psammophila. Rainfall characteristics (RA, RD and RI) and rainfall distribution should be fully considered when assessing the response of SF of shrubs to rainfall events.

How to cite: Wang, D., Gao, G., Li, J., Yuan, C., Lü, Y., and Fu, B.: Sap flow dynamics of xerophytic shrubs differ significantly among rainfall categories in the Loess Plateau of China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20932, https://doi.org/10.5194/egusphere-egu2020-20932, 2020

D24 |
EGU2020-20974
| Highlight
Assaf Inbar, Richard Benyon, Raphaël Trouvé, Patrick Lane, Shane Haydon, and Gary Sheridan

Most of the drinking water provided to the Melbourne metropolitan area originates from catchments that are covered by tall-wet eucalyptus forests, which have an estimated mean fire return interval of 80-150 yr. When stand-replacing fires occur in these forests, they result in a significant reduction in streamflow for an extended period of time due to the recovery strategy of the dominant tree species (Eucalyptus regnans and Eucalyptus delegatensis) and the water use of the dense regrowth. Current hydrological models that express this phenomenon are based on empirical data and lack the mechanistic explanation that links changes in streamflow with forest stand dynamics after disturbance. Here, for the first time, we present a simple theoretical framework that shows that this post-fire reduction in streamflow could be explained by the self-thinning behaviour of forest regrowth, which is driven by competition for water and light during recovery after a stand-replacing fire. First, we show that the trend in streamflow following a stand-replacing fire can be replicated simply by using the generic self-thinning line (which represents the maximum carrying capacity of a forest stand for a given mean tree diameter) of the dominant tree species. We then go one step further and show that the magnitude of streamflow reduction and the time it takes for streamflow to recover to pre-fire conditions, are sensitive to both the recovery success and the environmental conditions that control the maximum vegetation carrying capacity across the catchments. By using a simple stand growth and mortality model, we link the competition for water and light and the self-thinning behaviour of the forest to evapotranspiration and streamflow trajectories. This theory provides a simple alternative approach that can be used to improve models that predict streamflow from forested catchments after stand-replacing fires.

How to cite: Inbar, A., Benyon, R., Trouvé, R., Lane, P., Haydon, S., and Sheridan, G.: Post-fire changes in streamflow explained by forest self-thinning behavior, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20974, https://doi.org/10.5194/egusphere-egu2020-20974, 2020

D25 |
EGU2020-21679
Michael Rinderer and Markus Weiler

Phosphorus (P) is one of the key limiting nutrients in forest ecosystem resulting in tight P-recycling strategies in natural forests. Hydrological fluxes in the subsurface during rainfall events can however lead to a relocation and export of P from the forest stands. We present results from six large-scale sprinkling experiments on three highly instrumented experimental hillslope in the Bavarian Forest, Black Forest, and the Swabian Alb in Germany that differ in their soil P stocks. We simulated an extreme 150 mm rainstorm with intensities between 12 and 15 mm/h. The aim of these experiments was to quantify the lateral and vertical fluxes of subsurface storm flow and phosphorus under a range of input fluxes and to identify differences in the degree of nutrient retention depending on the prevailing soil properties of the three forest sites.

We sprinkled the 200 m2, steep hillslopes with 60,000 l of isotopically (deuterium) labeled water for 11 h. Lateral subsurface flow was measured at three depths (10cm, 240cm, 300cm) at a 10 m wide trench at the bottom of the hillslope and with large zero-tension lysimeters (area of 0.6 m2) installed at four depths into the undisturbed soil profile. This setup allowed us to quantify the lateral and vertical fluxes of subsurface flow and phosphorus concentration during the experiment in 30 min temporal resolution. We found vertical subsurface flow to dominate over lateral flow by more than one order of magnitude. We could identify a P-flashing (i.e., high P concentrations) in the first 2 hours after start of subsurface flow across all soil depths. During the rest of the sprinkling the P-concentrations were lower but did not change significantly despite further increasing subsurface flow. We explored P concentrations as a function of subsurface flow and found for all observations, except those from the litter layer, to be chemostatic. We also found no change in P-concentrations with increasing new water fraction, calculated based on a two-component hydrograph separation approach using the deuterium label as tracer. However, when calculating the internal and total P-fluxes we realized that the majority of P, that was leached from the litter layer (i.e., 0.22 kg/ha at the P-poor site and 1.17 kg/ha at the P-rich site), was retained in the mineral soil. The total vertical and lateral losses from the experimental hillslope were small (i.e., 0.07 kg/ha at the P-poor site and 0.06 kg/ha at the P-rich site during each experiment).

Therefore, our results suggest that P-poor and P-rich forest ecosystems are efficiently retaining phosphors in their mineral soils. However, as phosphorus export is transport limited but not source limited an increase in the frequency of heavy rainstorms, as predicted under future climate conditions, might still lead to a relocation of phosphorus to soil depths below the depth of tree roots or even cause increased P-export from the forest stands.

How to cite: Rinderer, M. and Weiler, M.: Is phosphorus export from beech forest stands transport-limited of source-limited?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21679, https://doi.org/10.5194/egusphere-egu2020-21679, 2020

D26 |
EGU2020-22353
Vaclav Sipek, Jan Hnilica, Lukáš Vlček, Soňa Hnilicová, and Miroslav Tesař

This study focuses on the description of soil water dynamics at four sites with different land cover types, namely beech forest, conifer forest, meadow and clipped grass. The analysis was based on soil tensiometer measurements from five consecutive vegetation seasons (comprising both wet and dry years). We investigated both column average pressure heads and also their vertical distribution. The soil water balance was studied by the HYDRUS-1D model. The highest pressure heads were observed at the grassland site, followed by the meadow site. The forested sites were generally reaching lower pressure head values, which was a result of higher evapotranspiration and different soil properties. The differences between the spruce forest (Picea abies (L.)) and beech forest (Fagus sylvatica L.) were evident namely in dry periods, when the beech site was experiencing lower pressure heads. Contrarily, the spruce site was drier (with recorded lower pressure heads) in wet periods and at the beginning of each season. Compared to the conifer forest, lower pressure heads were observed in beech forest, namely at the bottom of the inspected soil column (down to 100 cm). The inspection of the soil water balance revealed different rates of evapotranspiration and drainage at all sites. The evapotranspiration was highest in the beech canopy followed by spruce and both grass covered sites. The differences between spruce and beech forest were based namely on the water consumption efficiency and differences in interception rates, vertical distribution of the roots, and soil hydraulic properties.

 

This research was supported by the Czech Science Foundation (GA CR 20-00788S), SoilWater project (EIG CONCERT-Japan), and by the institutional support of the Czech Academy of Sciences, Czech Republic (RVO: 67985874).

How to cite: Sipek, V., Hnilica, J., Vlček, L., Hnilicová, S., and Tesař, M.: Influence of beech and spruce forests on soil water dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22353, https://doi.org/10.5194/egusphere-egu2020-22353, 2020