Abstract
To address the increasing need for hydroclimatic hazard assessment, a framework to map hotspots and analyze trends in heat waves, droughts, floods, and their compound occurrences was developed. The framework uses temperature, precipitation, river discharge, and derived climate indices to characterize the spatial distribution of hazard intensity, frequency, duration, co-occurrence, dependence, and their projected changes. The relevant climate indices applied are Standardized Precipitation Index (SPI), Standardized Precipitation and Evapotranspiration Index (SPEI), Standardized Streamflow Index (SSI), Heatwave Index (HWI), and Daily Flood Index (DFI). Suitable environmental indicators and corresponding thresholds for each hazard were selected based on estimated extreme event detection accuracy using receiver operating characteristics. Compound hazard dependence was assessed using Likelihood Multiplication Factor. The framework was tested for the case of Sweden, using daily data for the period 1922-2021. The results show that HWI, SPEI12, DFI are suitable indices to represent heat waves, droughts, and floods, respectively. Application of these indices shows increasing heat wave and flood occurrence in large areas of Sweden, but no significant change trend for droughts. Compound drought-heat wave and drought-flood events are found to be positively correlated in some locations, which can exacerbate their impacts. The novel framework developed here adds to existing hydroclimatic hazard research by (1) using local data and documentation to validate indicator-based hazard hotspots, (2) evaluating compound hazards at regional scale, (3) requiring just a few widely available input variables to (4) attain satisfactory accuracy levels for indicator-based hazard assessment, and (5) being generalizable to various hazard types.