Multi-decadal analysis of water resources and agricultural change in a Mediterranean semiarid irrigated piedmont under water scarcity and human interaction.

Mediterranean piedmonts are an important hydro-agricultural systems. They constitute the junction between the mountains, where the streamflow is generated, and the surrounding plains, where the water is used. In Morocco, these traditional systems extend largely along the High Atlas Mountains. Yet, changing conditions in the Mediterranean basin as well as recurrent droughts in recent decades remain poorly understood in terms of hydrological and agricultural impacts, particularly in traditional hydro-agro-systems. The combined effects of climate variability and ineffective management of water resource dynamics may lead to increased water scarcity in these regions. The present work aims to assess the effects of climate variability and associated agricultural changes on water resources in a traditional irrigated piedmont of the Moroccan High Atlas. To that end, a trend analysis, together with change points detection, was carried out on annual and monthly precipitation, and streamflow from 1965 to 2018. Then, the standardized precipitation index (SPI) was employed to identify meteorological droughts. Also, groundwater, and spring discharge data were analyzed and discussed from 1973 to 2021. SPI outcomes revealed three major droughts, in 1981-1988, 1999-2008, and 2013-2018. Although the precipitation data showed no significant trend, except for Tahannaout station, the average annual precipitation over the piedmont area decreased by 28%. Similarly, streamflow decreased significantly by almost 40% for all stations, as did the Abainou spring's discharge. Consistent with that, groundwater level has declined dramatically over the past decades in the downstream piedmont. These decreases in water cycle components were tightly aligned with droughts. Yet, irrigation diversions were maintained in both dry and wet periods. Paradoxically, this decrease in water resources was associated with an agricultural transition from seasonal crops (cereals) to perennial crops (olive trees). This conversion is likely to amplify the water shortage, leading to groundwater resources overexploitation to satisfy the growing agricultural demand.