Projecting Extreme Rainfall in Sicily: Integrating Simple Scaling and Hourly Projections into Depth-Duration-Frequency Analysis

In this present work, we propose a robust methodology for the derivation of future rainfall depth-duration-frequency curves (DDFs), utilizing hourly projections, the assumption of simple scaling of precipitation, and the application of the method of moments for parameter estimation in dimensionless precipitation height distributions. The methodology introduced herein involves the application of change factors derived from climate projections to precipitation averages across various durations (1, 3, 6, 12, and 24 hours) and to the dimensionless moments of the precipitation series. To implement this methodology, we leverage regional scale models (RCM) from the EURO-CORDEX initiative, characterized by hourly temporal resolution. The direct utilization of hourly projection data allows to bypass the necessity for temporal disaggregation techniques. Change factors are calculated through an analysis of annual maxima derived from both future and control series (1971-2000) generated via RCMs. We consider two distinct emission scenarios, namely RCP (Representative Concentration Pathways) 4.5 and 8.5, spanning three future periods: near future (2021-2050), middle future (2051-2070), and far future (2071-2100). Our methodology is applied to multiple rain gauges located across the Sicily region. The outcomes of our investigation underscore an upward trend in future DDFs, particularly pronounced in the RCP 4.5 scenario and during the far future period. This trend is attributed to an observed intensification in the variability of rainfall events. Depending on the specific geographic location, chosen emission scenario, and future time period, future Depth-Duration-Frequency (DDF) curves may correspond to return periods that more than double those observed in the control climate. The methodology, given the easy availability of the exploited data, can turn useful for updating hydrological design criteria for flood mitigation.