Assessment of climate change impacts on drought severity using SPI and SDI over the Lower Nam Phong River Basin, Thailand

摘要

The Lower Nam Phong River Basin, which is located in Northeast Thailand, is impacted by drought, which is likely to increase in severity in the future. Since drought seriously affects human life and well-being, this assessment was focused on the impacts of climate change on drought severity in the Lower Nam Phong River Basin. Daily climate data, such as rainfall and temperatures, for 2020 to 2050 under emission scenario Representative Concentration Pathway (RCP8.5), were obtained from “HadGEM2-AO”, downscaled by the Regional Climate Model version 4 (RegCM4), and bias-corrected via the Delta Change Method. Drought conditions were then classified based on the Standardized Precipitation Index (SPI) calculated from future daily rainfall, and the Streamflow Drought Index (SDI) derived from future daily discharge at each sub-basin outlet obtained from the Soil and Water Assessment Tool (SWAT) model simulations. At the E.22B gauging station, the SWAT performance was found to be satisfactory for all evaluation criteria, i.e. R2 and NSE values were 0.86 and 0.74 for calibration (2005 – 2010), and 0.92 and 0.89 for validation (2011 – 2016), respectively. For drought risk assessment, the point-based SPI and SDI values at 3- and 6-month time scales were spatially interpolated using kriging to assess short-term drought conditions. Based on the SPI-6 during the mid-future period (2041 – 2050), the Lower Nam Phong River Basin would have the highest chance of drought with cumulative frequency of 90.7%, whereas based on SDI-6 the highest chance of drought would occur during the near-future period (2031 – 2040) with cumulative frequency of 97.5%. These findings imply that both SPI and SDI indices can be used as good alternatives for monitoring droughts in the Lower Nam Phong River Basin; however, validation is required to ensure forecast accuracy of droughts in the near- to mid-future time horizons.