Climate change is progressing and is now one of the most important global challenges for humanities. Water resources management is one of the key challenges to reduce disaster risk. In Northern Thailand, flood and drought have always occurred because of the climate change impact and non-systematic management in the conjunctive use of both sources of water. Therefore, this study aims to assess the climate change impact on surface water and groundwater of the Yom and Nan river basins, located in the upper part of Thailand. The surface water and groundwater regimes are generated by a fully coupled SWAT-MODFLOW model. The future climate scenarios are considered from the Representative Concentration Pathways (RCPs) 2.6 and 8.5, presented by the Coupled Model Intercomparison Project Phase 5 (CMIP5), in order to mainly focus on the minimum and maximum Green House Gas (GHG) emissions scenarios during the near future (2021–2045) periods. The results show that the average annual air temperature rises by approximately 0.5–0.6 °C and 0.9–1.0 °C under the minimum (RCP 2.6) and maximum (RCP 8.5) GHG emission scenarios, respectively. The annual rainfall, obtained from both scenarios, increased by the same range of 20–200 mm/year, on average. The summation of surface water (water yield) and groundwater recharge (water percolation) in the Yom river basin decreased by 443.98 and 316.77 million m³/year under the RCPs 2.6 and 8.5, respectively. While, in the Nan river basin, it is projected to increase by 355 million m³/year under RCP 2.6 but decrease by 20.79 million m³/year under RCP 8.5. These quantitative changes can directly impact water availability when evaluating the water demand for consumption, industry, and agriculture.

Floods are a regularly occurring form of natural disaster in Thailand. They commonly occur during the monsoon season. Although the Chao Phraya River basin is strategically important because it accommodates several primary sectors that form the backbone of the Thai economy, it is vulnerable to flooding. The causes of flooding in this basin are both natural and human-induced. Climate and land-use changes are believed to be factors that elevated the severity of recent flood events. In 2011, Thailand suffered the worst floods in half a century; this is ranked as among the top five costliest natural disaster events in modern history. Thailand has developed a number of structural and non-structural measures to prevent devastating flood impacts. This paper reviews the flood management and adaptation measures within the Chao Phraya River basin, serving as a stepping stone towards sustainability.