Abstract
The objective of this study is to investigate the trend of hydrologic variable changes by applying the Mann-Kendall statistical trend test to daily historical record of reservoir operations data such as inflow to dam reservoirs, release from dam reservoirs, dam storage as well as precipitation and temperature. The five large scale dam reservoirs located in the northern, central and western parts of Thailand are selected to analyze the trend of the Ping River basin Bhumibol Dam, the Nan River basin having the Sirikit Dam, the Pasak River basin having the Pasak Jolasid Dam and the Mae Klong River basin having the Srinagarind and Vajiralongkorn dams. Through the analysis, we found that the temperature and precipitation show in-creasing trends except the Ping River basin; water resources availability in terms of inflow to the Bhumibol Dam and Pasak Jolasid Dam shows decreasing trend during dry season; the inflow of all reservoirs in rainy season had increasing trends; and dam releases of the all reservoirs shows significant increasing trends in dry season. Furthermore, water storage for Bhumibol dam were found dramatically decreasing trends throughout the year while the Srinagarind dam was detected increasing trends. Also, the increasing trends of water shortage in Bhumibol and Pasak Jolasid Dam and raising trend of excess storage volume in Sirikit dam and both dams in Mae Klong River Basin were observed.
