A comparative assessment of climate change impacts on drought over Korea based on multiple climate projections and multiple drought indices

Abstract

This study assesses future changes in drought characteristics in response to different emission scenarios over Korea based on multiple climate projections and multiple drought indices. To better resolve regional climate details and enhance confidence in future changes, multi-model projections are dynamically downscaled, and their systematic biases are statistically removed. Bias-corrected climate data are directly used to calculate the standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI), and they are fed into a hydrological model to generate runoff used for the calculation of the standardized runoff index (SRI). The analysis is focused on changes in the frequencies and severities of severe or extreme droughts measured by the SPI, SPEI, and SRI for the Han River and Nakdong River basins. Fine-scale ensemble projections reveal robust changes in temperatures that monotonically respond to emission forcings, whereas precipitation changes show rather inconsistent patterns across models and scenarios. Temperature and precipitation shifts lead to changes in evapotranspiration (ET) and runoff, which modulate the drought characteristics. In general, the SPEI shows the most robust pattern with significant increases in both drought frequency and severity. This result is mainly due to the excessive potential ET that is hypothetically estimated without considering water availability. While the SPI based on only precipitation exhibits behavior different from that of the SPEI, the SRI that considers actual ET produces an intermediate level of changes between the SPI and SPEI. Compared to the large uncertainty of the frequency changes that overwhelm the change signal due to inconsistency across models and indices, the severity of future drought is likely to be exacerbated with enhanced confidence.