Abstract
Abstract. The High Atlas, culminating at more than 4000 m, is the water tower of Morocco. While plains receive less than 400 mm of precipitation in an average year, the mountains can get twice as much, often in the form of snow between November and March. Snowmelt thus accounts for a large fraction of the river discharge in the region, particularly during spring. In parallel, future climate change projections point towards a significant decline in precipitation and enhanced warming of temperature for the area. Here, we build on previous research results on snow and climate modelling in the High Atlas to make detailed projections of snowpack and river flow response to climate change in this region. We develop end-of-century snowpack projections using a distributed energy balance snow model based on SNOW-17 and high-resolution climate simulations over Morocco with the MIT Regional Climate Model (MRCM) under a mitigation (RCP4.5) and a business-as-usual (RCP8.5) scenario. Snowpack water content is projected to decline by up to 60 % under RCP4.5 and 80 % under RCP8.5 as a consequence of strong warming and drying in the region. We also implement a panel regression framework to relate runoff ratios to regional meteorological conditions in seven small sub-catchments in the High Atlas. Relative humidity and the fraction of solid-to-total precipitation are found to explain about 30 % of the inter-annual variability in runoff ratios. Due to projected future atmospheric drying and the associated decline in snow-to-precipitation ratio, a 5 %–30 % decrease in runoff ratios and 10 %–60 % decrease in precipitation are expected to lead to severe (20 %–70 %) declines in river discharge. Our results have important implications for water resources planning and sustainability of agriculture in this already water-stressed region.
Highlights
The High Atlas is the major source of freshwater for the semi-arid plains of central Morocco
All models succeed in accurately reproducing snow cover dynamics in the region, the ERA-Interim simulation tends to have a positive bias at high elevations, above 3000 m (Fig. 5b), and all simulations have a negative bias at low elevations (Figs. 5d, e and 5a, b)
Consistent with these results, the spatial distribution of snow-to-precipitation ratio is generally well reproduced in the global climate models (GCMs)-driven experiments (Figs. 7a, d and A1), apart from negatives biases at low elevations associated with the underestimation of snow cover (Fig. 6)
Summary
The High Atlas is the major source of freshwater for the semi-arid plains of central Morocco. Much of the discharge of the Oum-Er-Rbia and Tensift, the two main rivers of central Morocco, comes from the mountainous terrain where they begin their course In this region, precipitation essentially falls at elevations above 1000 m (Boudhar et al, 2009); below that, it is scarce, and evaporation is extremely high, leading to minimal runoff. Snow is a major component of the regional water cycle (Marchane et al, 2015; Tuel et al, 2020) It accounts for a substantial fraction of annual runoff, up to 50 % in some mountain catchments (Boudhar et al, 2009), and for most of the runoff during spring, as the wet season comes to an end. Snow cover in the High Atlas is characterised by large inter-annual variability (Marchane et al, 2015; Tuel et al, 2020), mostly following that in wet-season precipitation, itself largely shaped by Published by Copernicus Publications on behalf of the European Geosciences Union
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