Simulation of Land Use Changes and Impacts on the Water Balance of an Unconfined Aquifer, Case Study: Saiss Aquifer, Morocco

Abstract

Ground water is widely a used fresh water source upon which plants, animal and human life relies. However, over years this golden source has become under diverse threat of depletion and degradation more so in circumstances where aquifers are heavily allocated or where there are changes in recharge rates due to several factors. The inter-connectness between land use, hydrological events and processes is a contingent linkage where by any modifications and transformations made on land either due to rapid population growth and or increased rate of urbanization, in one way or the other has a direct response on the water balance components. Assessment of effects of land use and cover changes serves as a principle indicator for water resource base analysis and development of effective and efficient plans for sustainability management. This study presents a methodology of quantifying the impacts of land use change on water balance of unconfined aquifer Saiss located in the center of Sebou watershed, and between the cities of Meknes and Fes (Morocco), through the objectives of evaluating historical land use changes for the period (1987-2016) and simulating the water balance components of recharge, evapotranspiration and surface runoff. Using a spatially distributed water balance model (WetSpass), with primary and secondary input data of meteorological from eight weather stations, land use, soil texture and general morphology of the basin. The evolution of land use in the study period of 29 years indicated significant changes, urban, irrigated land, olive trees, orchards, increased by 131%, 86%, 101% and 99% whiles as, open water surface, arable lands decreased by 33% and 20% respectively. The WetSpass simulated results indicated that the annual long-term mean precipitation of 409 mm was spatially distributed within the basin as, evapotranspiration (205 mm), run-off (76 mm) and recharge (126 mm) under land use condition 1987 and as 274 mm, 26 mm and 107 mm respectively under land use 2016, hence an increase of 33% evapotranspiration and decrease of 65% run off, decrease of 15% recharge due to land use change. For sustainability of Saiss aquifer, water abstraction for any intended use should not exceed the safe yield from the current annual ground water recharge of 107 mm (230 Mm3) of 2016. This study recommends practical remedies of artificial recharge, use of recycled waste water in agricultural fields and adoption of modern efficient irrigation technologies.