Impact of Land-Use Change and Climate Variability on Soil Hydrologic Processes in the Upper Oum Er Rabia River Basin, Morocco

Abstract

Given Morocco’s per capita water availability, basin hydrologic modelling can sustainably help in: planning for the anthropogenic actions and varying climate effect on scarce water resources; reviving ecologically sensitive areas; and ascertaining the river basin’s water and power supply capacity to the region and the country. Previous works within the Upper Oum Er Rabia (UOER) watershed focused on the river’s potential pollutants sources, precipitation trend and climate change scenarios analysis, impact of land use and climate change on soil fertility. There are no hydrologic studies evaluating the combined impacts of land use and climate variability within the watershed and thus affecting water allocation among competing users. This research aimed at investigating and evaluating land use change and climate variability influence on soil hydrological processes using the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS). The study area is UOER watershed (1049 km2) where unsustainable land uses have impacted the watershed’s capacity to regulate flow thus impacting water availability especially to the main dams within the basin. This work presents model development using HEC-HMS for event-based and continuous-process simulation of the UOER watershed. The use of HEC-GeoHMS facilitated the digital data processing for coupling with the model. The basin’s physical characteristics and the hydro-climatic data helped to generate a geospatial database for HECHMS model. Modelling (calibration and validation) focused on reproducing daily-observed runoff hydrographs for the 1980-2011 period using the SCS Curve Number and the Soil Moisture Accounting (SMA) loss methods. SMA was coupled with the Hargreaves evapotranspiration method. To evaluate the model performance for both calibration and validation, the Coefficient of determination (R2), Nash-Sutcliffe efficiency (NSE), Root Mean Square Error (RSR) and Percent Bias (PBIAS) criteria were exploited. The average calibration NSE values were 0.740 and 0.585 for event-based (daily) and continuous-process (annual) respectively. The R2, RSR and PBIAS values were 0.624, 0.634 and +16.7 respectively. This is rated as good performance besides the validation simulations were satisfactory for subsequent hydrologic analyses. It was concluded that the basin’s hydrologic behavior due to land use change and climate variability is significant to both positive and negative scenarios. The results give an insight into the land use implications and can guide in developing ecologically sound watershed management and development strategies.