Active network dynamics of temporary streams in the Mediterranean climate

Abstract:

In Mediterranean climates, intra- and inter-seasonal variability of river network dynamics is strongly influenced by hot and dry summers that facilitate the shrinking of the active drainage network potentially until its complete dry down. In these settings, surface water flow is limited during summer and early autumn to ephemeral reaches that are temporarily reactivated by single rain events, until accumulated precipitation excess in late autumn/winter succeeds to compensate the water deficit induced by high evapotranspiration rates and replenish groundwater storages that feed non-permanent springs, therefore allowing more persistent regime. The study addresses these highly non-linear activation/deactivation processes through a comprehensive analysis based on a field campaign carried out in two Mediterranean headwater catchments with an overall contributing area of 1.15 km². Therein, the active network was continuously monitored for a 15-month long period (from April 2019 to June 2020) through bi-weekly surveys aided by 5 water presence sensors installed in strategic nodes of the network. The campaign analyzed two flow recessions and the subsequent network dry down, and one flow reactivation phase induced by autumn/winter rainfall inputs. The observational dataset was used to calibrate and validate a non-linear model which allows the estimation of the temporal evolution of the total active drainage network length based on meteorological drivers and enables the prediction of the spatial distribution of active stretches using topographic and geologic information. The integrated model was able to reproduce with a good accuracy the drainage network dynamics observed in our study catchments, proving to be a useful tool for the characterization of temporary streams in Mediterranean regions. The study has important implications for river research, watershed management and policy in seasonally-dry climates.