Modelling lake water and isotope mass balance variations under Mediterranean climate: Lake Azigza in the Moroccan Middle Atlas
Résumé
As many Mediterranean headwater catchments, the Moroccan Middle Atlas plays an important role in the highly vulnerable regional water resources. Mountain lakes are numerous in this region, and could be regarded as possible sentinels of hydro-climatic changes, using appropriate modelling tools able to simulate the lake-climate relation. We present a detailed study of Lake Azigza, based on a 4-year (2012-2016) observation period, including lake level measurements, isotope analyses of precipitation, lake and spring waters, and local meteorological data. The approach is based on a calibration of a daily time-step lake water and isotope mass balance model, fed by precipitation and evaporation rates, to estimate the ungauged components of the water balance. Results show the dominance of groundwater exchanges in the lake water balance, with significant interannual variations related to annual precipitation. At the annual time-step, groundwater inflow varies between twice and up to six times the amount of direct precipitation, while the groundwater loss reached up to five times evaporation. However, a significant decrease of groundwater loss is observed in 2016, suggesting that a threshold effect probably limits the seepage when the lake level decreases. This study underlines the importance of groundwater fluxes in the lake level variations for Lake Azigza, probably representative of many similar lakes in the Middle Atlas. The model was able to simulate the continuous lake level decrease (4 m) observed over 2012-2016 and can be further used to explore lake-climate relations at different timescales.
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