ALBERT

Description: The skill of the land surface model HTESSEL is assessed to reproduce evaporation in response to land surface characteristics and atmospheric forcing, both being spatially variable. Evaporation estimates for the 2005 growing season are inferred from satellite observations of the Western part of Hungary and compared to model outcomes. Atmospheric forcings are obtained from a hindcast run with the Regional Climate Model RACMO2. Although HTESSEL slightly underpredicts the seasonal evaporative fraction as compared to satellite estimates, the mean, 10th and 90th percentile of this variable are of the same magnitude as the satellite observations. The initial water as stored in the soil and snow layer does not have a significant effect on the statistical properties of the evaporative fraction. However, the spatial distribution of the initial soil and snow water significantly affects the spatial distribution of the calculated evaporative fraction and the models ability to reproduce evaporation correctly in low precipitation areas in the considered region. HTESSEL performs weaker in dryer areas. In Western Hungary these areas are situated in the Danube valley, which is partly covered by irrigated cropland and which also may be affected by shallow groundwater. Incorporating (lateral) groundwater flow and irrigation, processes that are not included now, may improve HTESSELs ability to predict evaporation correctly. Evaluation of the model skills using other test areas and larger evaluation periods is needed to confirm the results. Based on earlier sensitivity analysis, the effect of a number of modifications to HTESSEL has been assessed. A more physically based reduction function for dry soils has been introduced, the soil depth is made variable and the effect of swallow groundwater included. However, the combined modification does not lead to a significantly improved performance of HTESSEL.

Description: Ecosystem accounting is an emerging field that aims to provide a consistent approach to analysing environment–economy interactions. One of the specific features of ecosystem accounting is the distinction between the capacity and the flow of ecosystem services. Ecohydrological modelling to support ecosystem accounting requires considering among others physical and mathematical representation of ecohydrological processes, spatial heterogeneity of the ecosystem, temporal resolution, and required model accuracy. This study examines how a spatially explicit ecohydrological model can be used to analyse multiple hydrological ecosystem services in line with the ecosystem accounting framework. We use the Upper Ouémé watershed in Benin as a test case to demonstrate our approach. The Soil Water and Assessment Tool (SWAT), which has been configured with a grid-based landscape discretization and further enhanced to simulate water flow across the discretized landscape units, is used to simulate the ecohydrology of the Upper Ouémé watershed. Indicators consistent with the ecosystem accounting framework are used to map and quantify the capacities and the flows of multiple hydrological ecosystem services based on the model outputs. Biophysical ecosystem accounts are subsequently set up based on the spatial estimates of hydrological ecosystem services. In addition, we conduct trend analysis statistical tests on biophysical ecosystem accounts to identify trends in changes in the capacity of the watershed ecosystems to provide service flows. We show that the integration of hydrological ecosystem services into an ecosystem accounting framework provides relevant information on ecosystems and hydrological ecosystem services at appropriate scales suitable for decision-making.

Description: The skill of the land surface model HTESSEL is assessed to reproduce evaporation in response to land surface characteristics and atmospheric forcing, both being spatially variable. Evaporation estimates for the 2005 growing season were obtained from satellite observations of the Western part of Hungary and compared to model outcomes. Atmospheric forcing was obtained from a hindcast run with the Regional Climate Model RACMO. Although HTESSEL slightly underestimated the seasonal evaporative fraction, the mean, 10th and 90th percentile of this variable were of the same magnitude as the satellite observations. The initial water as stored in the soil and snow layer did not have a significant effect on the statistical properties of the evaporative fraction. However, the spatial distribution of the initial soil and snow water affected significantly the spatial distribution of the calculated evaporative fraction and the models ability to reproduce evaporation correctly in low precipitation areas in the considered region. HTESSELs performance appears to be less in dryer areas. In Western Hungary these areas are situated in the Danube valley, which is partly covered by irrigated cropland and which also may be affected by shallow groundwater. Incorporating (lateral) groundwater flow and irrigation, processes that are not included now, may improve HTESSELs ability to predict evaporation correctly. Evaluation of the model skills using other test areas and larger evaluation periods is needed to confirm the results. Based on earlier sensitivity analysis, the effect of a number of modifications to HTESSEL was assessed. A more physically based reduction function for dry soils was introduced, the soil depth was made variable and the effect of swallow groundwater included. However, the modification did not lead to significant improved performance of HTESSEL.

Description: Ecosystem accounting is an emerging field that aims to provide a consistent approach to analysing environment-economy interactions. In spite of the progress made in mapping and quantifying hydrological ecosystem services, several key issues must be addressed if ecohydrological modelling approaches are to be aligned with ecosystem accounting. They include modelling hydrological ecosystem services with adequate spatiotemporal detail and accuracy at aggregated scales to support ecosystem accounting, distinguishing between service capacity and service flow, and linking ecohydrological processes to the supply of dependent hydrological ecosystem services. We present a spatially explicit approach, which is consistent with ecosystem accounting, for mapping and quantifying service capacity and service flow of multiple hydrological ecosystem services. A grid-based setup of a modified Soil Water and Assessment Tool (SWAT), SWAT Landscape, is first used to simulate the watershed ecohydrology. Model outputs are then post-processed to map and quantify hydrological ecosystem services and to set up biophysical ecosystem accounts. Trend analysis statistical tests are conducted on service capacity accounts to track changes in the potential to provide service flows. Ecohydrological modelling to support ecosystem accounting requires appropriate decisions regarding model process inclusion, physical and mathematical representation, spatial heterogeneity, temporal resolution, and model accuracy. We demonstrate this approach in the Upper Ouémé watershed in Benin. Our analyses show that integrating hydrological ecosystem services in an ecosystem accounting framework provides relevant information on ecosystems and hydrological ecosystem services at appropriate scales suitable for decision-making. Our analyses further identify priority areas important for maintaining hydrological ecosystem services as well as trends in hydrological ecosystem services supply over time.