Combined use of relative drought indices to analyze climate change impact on meteorological and hydrological droughts in a Mediterranean basin

Abstract

Standardized drought indices have been traditionally used to identify and assess droughts because of their simplicity and flexibility to compare the departure from normal conditions across regions at different timescales. Nevertheless, the statistical foundation of these indices assumes stationarity for certain aspects of the climatic variables, which could no longer be valid under climate change. This contribution provides a framework to analyze the impact of climate change on meteorological and hydrological droughts, considering shifts in precipitation and temperature, adapted to a Mediterranean basin. For this purpose, droughts are characterized through a combination of relative standardized indices: Standardized Precipitation Index (rSPI), Standardized Precipitation Evapotranspiration Index (rSPEI) and a Standardized Flow Index (rSFI). The uncertainty and the stationarity of the distribution parameters used to compute the drought indices are assessed by bootstrapping resampling techniques and overlapping coefficients. For the application of the approach to a semiarid Mediterranean basin (Jucar River Basin), the Thornthwaite scheme was modified to improve the representation of the intra-annual variation of the potential evapotranspiration and low flow simulation in hydrological modelling was improved for a better characterization of hydrological droughts. Results for the Jucar basin show a general increase in the intensity and magnitude of both meteorological and hydrological droughts under climate change scenarios, due to the combined effects of rainfall reduction and evapotranspiration increase. Although the indicators show similar values for the historical period, under climate change scenarios the rSPI could underestimate the severity of meteorological droughts by ignoring the role of temperature.