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In arid and semi-arid countries, drought monitoring is a difficult issue to deal with, mainly due to the low density of precipitation measurement stations. The present study aims to evaluate the ability of the Tropical Rainfall Monitoring Mission (TRMM) 3B42 (v7) to monitor annual precipitation in Morocco. The accuracy of TRMM data to estimate annual rainfall was evaluated. Annual precipitations derived from 5113 daily TRMM 3B42 V7 data were compared to the corresponding in situ rainfall measurements from 23 rain gauges, between 1998 and 2012. The results showed a general, good linear relationship between TRMM and rain gauges data. When considering annual records, the Pearson correlation coefficient, R2, was equal to 0.73 and the Root Mean Square Error, RMSE, was equal to 159.8 mm/year. The correlation between rain gauge measurements and TRMM rainfall has been clearly improved when working with long-term annual average precipitation. The R2 increased to 0.79 and the RMSE decreased to 115.2 mm.

Water supply for the arid irrigated plains in Morocco depends largely on the upper mountainous basins where significant amounts of precipitation fall as snow. In the Oum Er-Rbia River Basin (OER), snow covers the highest elevations from November to April. Despite the importance of this component in the hydrological cycle, snowmelt contribution to streamflow is still poorly understood and no monitoring stations exist in this zone. Therefore, studying the spatiotemporal change of snow cover through satellite observations to investigate its influence on the hydrological response of this scarce region is thus required to better manage water resources. This chapter explores basic characteristics of snow cover area (SCA) in the upstream area of the OER River (Tillouguite sub-basin) using MODIS daily snow cover products (MOD10A1). Correspondence between streamflow, accumulated air temperature and SCA changes during the winter and spring periods was examined from 2001 to 2009 at a weekly time step. The result shows an inverse linear relation between the maximum SCA and the mean normalized stream flow values, and a significant relation between the relative streamflow and cumulated temperature, especially during spring melt season depending on the length of the melt period. These primary results could be used to develop simplified predictable models for spring discharge in ungauged watershed using remote sensing and accumulated air temperature.