Slackwater Sediments Record the Increase in Sub-daily Rain Flood due to Climate Change in a European Mediterranean Catchment

In this work we propose an original method to determine the magnitude of the discharge, the intensity of the precipitation and the duration of short-rain floods in small torrential basins (< 2000 km²), extending our earlier approach for long-rain floods in larger basins (Water 2016, 8, 526; Remote Sens. 2017, 9, 727). The studied areas are located in ungauged catchments with high erosion rates where torrents deposit slackwater sediments near the outlet of the basins. Such deposits and erosive morphologies allow us to analyse sub-daily extreme hydrological events by combining standard techniques in paleohydrology, the kinematic wave method and remote-sensed paleostage indicators. The formulation was correctly verified in extreme events through reliable gauge measurements and a high-resolution distributed hydrological model showing the accuracy of our calculations (10% ≤relative error ≤ 22%). In catchments of the European Mediterranean region where the frequency and magnitude of short-rain floods are increasing (e.g. the Guadalquivir Basin), the main hydrological variables can thus be quantified post-event using the proposed approach. The outputs may serve to construct a new database for this kind of events complementary to the existing daily database for long-rain floods (> 24 h). The need is evident for safety designs of civil infrastructures and flood risk mitigation strategies in the current climate change scenario.