Hydrological response of two contrasting small Mediterranean Mountainous catchments in the Middle Atlas - Morocco

Mediterranean catchments are within the most complex environments due to the seasonality of their climate, the catchment geology and the long history of landscape modification by human activity, which strongly influenced their hydrological response. These characteristics make this region sensitive to the global change (i.e. land uses and climate changes) and therefore subject to changes that will affect the sustainability, quantity, quality and management of water resources. In addition, mountainous areas play a key role for water supply as they provide between one and two thirds of the global freshwater discharge, which can reach more than a 90% of the runoff on the catchment scale. Furthermore, Mediterranean mountains constitute the wettest areas of catchments ranging from mild to arid climates, being natural reservoirs for water uses downstream. Thus, assessing the hydrological response at different timescales is fundamental for a better comprehension of process interactions and feedbacks between different runoff drivers across timescales.

This study investigates the runoff response at multiple temporal scales in two representative small Mediterranean catchments (< 2 km²) located in the Srou River basin (Middle Atlas - Morocco) to achieve a better understanding of their hydrological response. The first catchment (Talhiant, 1.14 km²) is agricultural (98%), while in the second one (Mougeryberdan, 1.15 km²) predominates forest (73%), especially in the upstream part. Continuous monitoring of water fluxes during two natural years (2018-2019) was used to establish rainfall-runoff relationships in order to recognize the role of land uses and lithology variables during two natural years in the runoff response at annual, seasonal and event scales. At the annual and seasonal scale, rainfall amount and runoff yields were computed. At the event scale, a rainfall-runoff relationship assessment was carried out with 84 events, being analysed through a Pearson correlation matrix using different variables extracted from the hyetograph and hydrograph.

At the annual scale, the annual rainfall ranged from 807 to 328 mm yr⁻¹ at Talhiant, and from 925 to 604 mm yr⁻¹ at Mougeryberdan for the natural years 2018 and 2019, respectively. According to the rainfall values, the annual runoff coefficient was 23% and 26% at Talhiant, and 14% and 39% at Mougeryberdan during the studied years respectively. At the seasonal scale, winter was the rainiest season (486-584 mm) at both studied catchments, followed by autumn, spring and summer. Monthly evapotranspiration increased from winter (< 17 mm) to summer (19-91 mm) and spring (39-142 mm). At both catchment, monthly runoff coefficient decreased from autumn (9%-45%) and winter (33%-49%) to summer (< 8%). At the event scale, rainfall amount had positive correlation with runoff and discharge peak at both catchments (R² > 0.55). At Talhiant, antecedent rainfall positively correlated with runoff, runoff coefficient and discharge peak, whereas rainfall intensity correlated with discharge peak. At Mougeryberdan, antecedent rainfall positively correlated with discharge peak, whereas no correlation was observed between rainfall intensity and other variables.

The results of this research will improve the comprehension of hydrological processes in regions characterized by a low water resources availability and scarcity of hydrological data.