Assessment of drought severity in the upper phong river basin

Abstract

            The assessment of drought severity in the upper phong river basin under future climate change impacts was based on the applications of SWAT and WEAP models. For future climate change during 2020 – 2099, the global climate models, i.e. CNRM - CM5, IPSL - CM5A – MR, and MIROC5, were used to project future climate under RCPs 4.5 and 8.5. The SWAT was calibrated and validated using R² and Nash-Sutcliffe Efficiency (NSE) by comparing simulated with observed daily inflow to Ubol Ratana Reservoir during 2012 – 2017 and 2007 – 2011, respectively. The results indicated the R² values of 0.76 and 0.70 and NSE values of 0.82 and 0.69 during calibration and validation, respectively, which give confidence on the result reliability. Considering the future climate prediction for 2020 – 2099, it was found that the maximum and minimum temperatures, and the mean annual rainfall, under RCPs 4.5 and 8.5 tend to be higher than the present, in which the mean annual rainfall under RCP 8.5 seems to be higher than RCP 4.5. Regarding the WEAP simulation results, during 2000 – 2017, it was found that Non Mueang Subdistrict Municipality and Din Dam Subdistrict are the areas with highest water demand, whereas the subdistricts of Din Dam, Nong Kae, and Nong Saeng are the areas with highest water scarcity. In addition, under both RCPs 4.5 and 8.5, the future water demand and water scarcity for agriculture tend to be decreasing, whereas for domestic, industry, and ecology, seem to be increasing. Thereafter, the assessment of drought severity was carried out based on Drought Hazard Index (DHI) which was calculated from Standardised Precipitation-Evapotranspiration Index (SPEI) and Water Scarcity Index (WSI), and the severity was categorized as normal, moderate, high, and very high. As a result, during 2000 – 2017, the years 2005, 2007, 2008, 2010, 2012, 2013, 2015, and 2016 are the periods with drought severity fluctuating between high and very high levels. The future climate change was also found to induce severe drought. As can be seen that under RCP 4.5 during 2020 – 2039 and 2040 – 2059, the area of 2,697.53 km² is expected to fall in high level, whereas 688.86 km² is anticipated in a very high level. In years 2060 – 2079 and 2080 – 2099, the area of 3,386.39 km² might fall in a very high level. Under RCP 8.5, a high level is likely to occupied 3,386.39 km² during 2020 – 2039 and 2040 – 2059, whereas a very high level is predicted throughout 3,386.39 km² during 2060 – 2079 and 2080 – 2099. In conclusion, the main findings will be the information for analyzing and predicting drought severity levels. The action measures, preparedness, and coping strategies to mitigate future drought impacts, which might affect the residents in the upper phong river basin, can be determined, and the findings can also be used as a guideline for other river basins experiencing drought.