Use of CMIP3 and CMIP5 Climate Models to Simulate Change Discharge in the Chao Phraya River Basin

Climate change that coincides with global warming is generating enormous damages to many countries. The 2011 large-scale floods over the Chao Phraya River Basin is the worst floods ever recorded in Thailand, and the estimated damages by World Bank at US$ 46.5 billion. Although efforts have been made to mitigate the flood damage in the Chao Phraya River Basin through several structural measures, flooding still causes much more impact as a result of deforestation, farmland expansion and urban development. In this study, the impact of climate change on the discharge in the Chao Phraya River Basin is analyzed, using nonlinear autoregressive neural network with exogenous input (NARX) model. Future climate data were extracted from phase 3 and phase 5 of Coupled Model Intercomparison Project (CMIP3 and CMIP5) under the greenhouse gas emission scenarios: B1, A2, RCP4.5, and RCP8.5. The future precipitation was downscaled using the Distribution Mapping. Using NARX, future monthly dischagre was predicted at Nakhon Sawan for the period 2010 - 2099. Depending on the emission scenario, the projected discharge for future periods are shown to increase in overall. However, there are decreasing discharge in the near future and the mid future periods under B1 emission scenario. These findings suggest that the risks of climate change in the Chao Phraya River Basin will affect on millions of people, social and environment.