RAINFALL AND RESERVOIRS SITUATION UNDER THE WORST DROUGHT RECORDED IN THE UPPER CHAO PHRAYA RIVER BASIN, THAILAND

Abstract

Thailand has continually faced serious drought conditions since the severe flooding of 2011. No deaths ensued from this disaster; however, agriculture and drinking water were adversely affected. This study reports on hydrological conditions in the Chao Phraya River Basin (CPRB) since 2012, following a recent drought that followed historically severe flooding. Annual rainfall during 2012–2014 was approximately equal to the average annual rainfall during that period. However, annual rainfall was 77% of the mean annual rainfall in 2015, which was the second lowest rainfall recorded in 63 years. Annual rainfall in 2012, 2014, and 2015, and inflow over this 4-year period, were all below the annual means. The annual inflow in 2014 and 2015 were 56% and 37% of the mean annual inflow, respectively. Two large reservoirs experienced severe drought conditions and the Bhumibol reservoir was experiencing a water shortage in September 30, 2016. Comparing the ratio of the mean value to rainfall and inflow since 2012, the ration of mean inflow to observed inflow was larger than rainfall each year, indicating that the upper CPRB was affected by hydrological, as opposed to climatological, drought. Finally, we propose a useful drought index for the upper CPRB based on a mean storage volume in April of 6,000 MCM in the Bhumibol and Sirikit reservoirs.