Climate change scenarios for IDF curves for mainland Portugal

Abstract

Rainwater drainage systems and other hydraulic infrastructure are scaled considering the intensity of precipitation and its probability of occurrence. The estimation of precipitation intensity through the analysis of the frequency of occurrence of extreme precipitation events is a key instrument for the dimensioning of hydraulic infrastructures and the associated risk of collapse. Sub- or over-estimated rainfall intensities can cause significant problems in various types of hydraulic infrastructures, including flood mitigation and support works due to flooding.The aim of this study is to determine how climate change will influence extreme rainfall and, consequently, the future sizing of hydraulic systems, including rainwater drainage and hydraulic passages. Towards this aim, the Intensity-Duration-Frequency (IDF) curves were computed (durations between 24 and 72 hours), considering the historical period between 1950 and 2001, and for future precipitation projections (ensemble of biased-corrected Regional Climate Models, RCMs). The period 2041‒2070 under the RCP8.5 (Representative Concentration Pathways) and 2071‒2100 under the RCP4.5 and RCP8.5 emission scenarios were analyzed for 25 udometric stations studied in Brandão et al. (2001 and 2004) located in mainland Portugal.Results show an increase in precipitation intensity, however, the differences between the projected IDF and those obtained with observed data (ERA5 dataset) for the 2, 5, 10, 20, 50, and 100 years return periods are not spatially uniform. The outcomes reveal North/South contrasts between the station’s IDFs, being also quite apparent in the influence of the orography.Overall, this study is the first approach to the problem of extreme rainfall in a changing climate, due to the severe consequences of sudden floods and the resilience of territories and their hydraulic infrastructures to these extreme events. Therefore, planning of new policies and the dimensioning of new and existing infrastructures in the medium and long term is thus highly relevant.Acknowledgment: This work was supported by National Funds by FCT - Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020.Keywords: Climate change, IDF curves, Hydraulic passages, Extreme precipitation, Drainage systems, Portugal.