The Impacts of Climate Change on Future Hydrometeorological Regimes in the Chao Phraya River Basin, Thailand

The major aim of this study is to investigate the impacts of climate change on hydrometeorological regimes including air temperature, rainfall, potential evapotranspiration and consequently natural runoff. Chao Phraya basin was selected as the case of study area. Rainfall variation and change of the selected irrigation projects in the Chao Phraya basin was also examined. The historic records of air temperature and rainfall were collected from 41 meteorological stations located in and nearby the basin area. Climate change was investigated by using the Generalized Circulation Model (GCM) projection of A1B balance of all source scenario. The study used output data from the United Kingdom Hadley Center’s Global Climate Model “HadCM3 (10) (13)” with approximately 180 × 180 km. spatial resolution. Downscaling into the Chao Phraya basin was accomplished using the PRECIS Regional Climate Model with approximately 25 × 25 km. resolution along with the bias correction technique with reference to the mean observed time series. It was found that in the 20-year period during 2017–2036, the average monthly maximum and minimum air temperatures in the Chao Phraya basin trend to increase throughout the normal baseline values during 1981–2010 by 0.5–2.0 degree Celsius. The monthly rainfall under climate change in the Chao Phraya basin over 20-year period during 2017–2036 which is an average of every 5 years, shows significant deviation both higher and lower from the normal baseline values during 1981–2010 in the range of 10 mm per month to 50 mm per month. The monthly average runoff in the Chao Phraya basin over the 20-year period during 2017–2036, average every 5 years across all 4 periods during 2017–2021, 2022–2026, 2027–2031, and 2032–2036 are significantly varied. The highest values during the rainy season were found in the 2027–2031 average period. While the lowest values during the rainy season were observed in the 2022–2026 period. These findings should be useful for water allocation management and appropriate use of water resources under climate change condition in the Chao Phraya basin.