Integrating human water uses in a regional scale distributed hydrological model : model evaluation

Climate change challenges the availability and allocation of water resources among different human uses, even in large river systems. Water managers are confronted with the risk of water scarcity and conflicts that can vary in time and space across catchments. Hydrological models incorporating different human water uses are being developed to improve our understanding of how such complex systems operate, to make projections of future water resources under climate change, and to test adaptation scenarios for water management. Three major human uses have been integrated into the process-oriented distributed hydrological model J2000: water abstraction for drinking water (and associated water release through wastewater treatment plants), water abstraction for irrigation, and river regulation through the management of hydroelectric reservoirs. The model has been applied to the Rhône Basin (~ 100,000 km²), covering part of Switzerland and France. The parameterisation of water uses was based on existing models (econometric model for drinking water consumption, crop water demand for irrigation, reconstructed dam influence for reservoir management) and national databases for the location of abstraction points. The model was evaluated against observed discharge from 63 gauging stations throughout the catchment, observed groundwater levels from 107 piezometers and against water abstraction volumes sourced from an independent database. The sensitivity of the model to potential irrigation adaptation scenarios was also assessed. The results show that although the model gives correct results in terms of discharge, it struggles to reproduce abstraction volumes. The parameterisation of the water use components appears to be the main problem, in particular because of the need to make simplifying assumptions for the selection of abstraction/release points. The water use model also appears to be very sensitive to the quality of the representation of natural hydrological processes, especially precipitation in mountain areas and groundwater storage. Finally, the influence of irrigation scenarios appears to be limited beyond a certain catchment size. This study shows the advantages of using several different variables for model evaluation and the interest of distributed models to analyse simulation results at appropriate spatial scales.