Hydrological Drought Risk Assessment and Management Prioritization under Changing Climate: Part 1. Scenario-Neutral Assessment of Bivariate Drought Hazard

The results of a climate change impact assessment can differ substantially depending on the choice of climate change scenario and climate model. This study introduced a scenario-neutral approach that does not depend on specific future projections and evaluated the hydrological drought hazard of the 113 middle-sized watersheds of South Korea across a precipitation-temperature exposure space defined by systematic perturbations in precipitation and temperature. The design drought return period was estimated by copula-based bivariate frequency analysis of drought duration and severity applied to the simulated daily streamflow for 1974–2025, and watershed-specific response surfaces were constructed from 252 precipitation-temperature perturbation combinations (\(\:{R}²\)=0.568–0.932). Local sensitivity analysis around the baseline point showed that the return period increased with increasing precipitation and decreased with rising temperature, and the national median precipitation increase required to offset 1℃ of warming was 2.64%. When the 72 projections from 18 general circulation models (GCMs) under 4 Shared Socioeconomic Pathway (SSP) scenarios were mapped onto the response surfaces, the ensemble median showed an increase in the return period for all SSP-period combinations, whereas 13.5–31.3% of the individual projections showed a decrease, identifying unfavorable projections that run counter to the central tendency. These results show that the scenario-neutral response surfaces allow changes in drought hazard under diverse future projections to be compared on a consistent basis, and they provide the hazard information for the watershed-level management prioritization.