Influence of Climate Change on the Design of Retention Basins in Northeastern Portugal

Retention basins are used to control the quantity and quality of stormwater runoff. Their design is based on Intensity-Duration-Frequency (IDF) curves and on the assumption that the rainfall distribution is stationary. The analysis of rainfall observed for recent past conditions and projected for the future suggests the existence of significant changes in the frequency and intensity of extreme rainfall events. This study aims to assess the potential impacts of climate change in the design of retention basins. The adopted multi- and interdisciplinary methodological approach comprises: Rainfall aggregation and disaggregation, distribution fitting for different climate change scenarios, durations and return periods, model bias correction, robust regression of rainfall intensity for different durations and, finally, engineering design based on IDF curves. Results obtained with IDF curves defined in the Portuguese law and estimated from the ECHAM5/MPI-OM1/COSMO-CLM regional climate model for recent past and future climate scenarios point to: (i) Increase in the volume of the retention basin, more expressive in the end of the XXI century; (ii) changes of different magnitude within the country and the same rainfall region; and (iii) increase of 20% to 23% on average, and 46% to 65% at most, for the conditions of B1 and A1B scenarios, respectively.