Potential changes of future dryness over Korea from a regional climate projection

We present an analysis of future dryness over Korea based on the projected temperature and precipitation. For fine-scale climate information, the ECHAM5/MPI-OM A1B scenario simulation has been dynamically downscaled by using the RegCM3 double-nested system. A 130-year long-term climatology (1971-2100) from the mother domain (East Asia: 60km) and nested domain (South Korea: 20km) is discussed with a focus on the future dryness in response to global warming. For validation during the reference period (1971-2000), the mother domain simulation reasonably reproduces mean climatology in surface variables as well as large scale circulation. The temperature and precipitation from the nested domain capture well the temporal variations and trends compared to station observations over Korea. This success is translated to the Palmer Drought Severity Index (PDSI) which is applied to measure drought condition, indicating a good agreement with observed estimates.

In the future projection, the significant warming in the range of 2-4 ºC is found throughout the entire region and in all seasons. The change in precipitation shows a distinct seasonal variations and a complicated spatial pattern. While changes in total precipitation do not show any relevant trend, the change patterns in daily precipitation clearly show an enhancement of high intensity precipitation and a reduction of weak intensity precipitation. The increase of temperature enhances the evapotranspiration, and hence the actual water stress becomes more pronounced in the future climate. This is related to the negative trends of the PDSI. Although PDSI is overall associated with the precipitation variation, its long-term trend tends to be modulated by the temperature trend. It is confirmed that the detrended temperature has masked the tendency for the decreasing of the PDSI. The result indicates that without an increase in precipitation appropriate for atmospheric moisture demand, future dryness is a more favorable condition under global warming. Despite large details in the spatial distributions from the downscaled results, a broad agreement between the projections obtained with the ECHAM5/MPI-OM and RegCM3 is found.