Future water availability in North African dams simulated by high-resolution regional climate models
Résumé
In North Africa, the countries of Morocco, Algeria and Tunisia are already experiencing water scarcity and a strong
interannual variability of precipitation. To better manage their existing water resources, several dams and reservoirs
have been built on most large river catchments. The objective of this study is to provide quantitative scenarios of
future changes in water availability for the 47 major dams and reservoirs catchments located in North Africa. An
ensemble of regional climate models (RCM) with a spatial resolution of 12km, driven by different general circulation models (GCM), from the EuroCORDEX experiment have been considered to analyze the projected changes
on temperature, precipitation and potential evapotranspiration (PET) for two scenarios (RCP4.5 and RCP8.5) and
two time horizons (2040-2065 and 2065-2090). PET is estimated from RCM outputs either with the FAO-PenmanMonteith (PM) equation, requiring air temperature, relative humidity, net radiation and wind, or with the Hargreave
Samani (HS) equation, requiring only air temperature. The water balance is analyzed by comparing the climatic
demand and supply of water, considering that for most of these catchments groundwater storage is negligible over
long time periods. Results indicated a future temperature increase for all catchments between +1.8◦
and +4.2◦, depending on the emission scenario and the time period considered. Precipitation is projected to decrease between -14% to -27%, mainly in winter and spring, with a strong East to West gradient. PET computed from PM or HS
formulas provided very similar estimates and projections, ranging between +7% to +18%. Changes in PET are
mostly driven by rising temperatures and are greatest during dry summer months than for the wet winter season.
Therefore the increased PET has a lower impact than declining precipitation on future water availability, which is
expected to decrease by -19% to -33% on average.