Ancestral managed aquifer recharge systems and their impacts on the flow regime of a semi-arid alpine basin (Sierra Nevada, Spain)

Study region Sierra Nevada, Spain. Study focus The local communities of the Sierra Nevada mountain range adapted to recurrent dry periods by spreading water along hillslopes with unlined channels that deviate surface runoff from headstreams during high flow periods. However, the impact of the so-called careo practice on river regimes in Sierra Nevada remains mostly unquantified. This work aimed to fill this gap by monitoring and analyzing streamflow in a major careo channel and river during three consecutive years (2021–2023) in the Mecina watershed (51 km², Las Alpujarras). New hydrological insights for the region This study reveals unexpectedly high proportions of groundwater and human influence in total basin runoff within the hard rock environment of the Sierra Nevada. The data shows consistent streamflow gains between controlled river sections despite experiencing three years of below average precipitation, most remarkably below high infiltration channel stretches. The relationship between careo recharge and river flow kept constant even during the driest of the observed years. The influence from careo recharge was most noticeable during the low flow period (summer) when it represented between 40 % and 60 % of river streamflow. In addition, about 32 % of the total recharge to the aquifer in the basin comes from water transported and infiltrated by just one of the basin's careo channels, which means that such a careo recharge channel increases the natural infiltration of meteoric water by 47 %.