Historical and projected drought characteristics across different hydrological regimes in Central Chile

Drought is one of the main hydroclimatic hazards worldwide, affecting water availability, ecosystems and socioeconomic activities. Since 2010, Central Chile (30–38°S) has been experiencing a drought with unprecedented duration and severity (also known as the Central Chile megadrought), producing drastic reductions in river flows, snow cover and reservoir levels. Nevertheless, there is limited understanding of how hydrological processes have been altered and whether such variations will persist during the 21st century. In this study, we characterize the magnitude, frequency, and duration of drought events under historical conditions and future climate scenarios across different hydrological regimes in Central Chile. To this end, we generate daily time series of streamflow, evapotranspiration, soil moisture and other hydrological variables in six case study basins with little human intervention for the period 1981-2100, using the Structure for Unifying Multiple Modeling Alternatives (SUMMA) framework and the mizuRoute model. Simulations are conducted at a 0.05º x 0.05º horizontal resolution, using a combination of the CR2MET gridded product and ERA5 outputs to obtain historical meteorological forcings, and statistically downscaled global climate model (GCM) outputs from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to obtain future climate time series. Finally, we characterize drought events with the Standardized Precipitation Index (SPI), Standardized Streamflow Index (SSI), and Soil Moisture Index (SMI). The calibrated hydrologic model parameters yield daily streamflow simulations with a Kling-Gupta Efficiency (KGE) greater than 0.78 and 0.61 in all basins for the calibration and evaluation periods, respectively. The drought indices estimated for the historical period enable identifying the severe events of 1998-1999 and 2010-2020 (with standardized values smaller than -1.28); however, the magnitude and duration varies depending on the event and hydrological variable analyzed. Ongoing work seeks to examine inter-basin differences in terms of drought characteristics, along with projected changes in the frequency and intensity of this type of event.