Applying Budyko framework to explore the projected hydrologic changes in southern Taiwan

This study combines future rainfall and temperature projections with the Budyko framework to analyze future water resource changes in four key watersheds in southern Taiwan under climate change scenarios. Since only temperature and rainfall data are available in the future climate change projections, the future evapotranspiration projections are estimated by this study. This study establishes Budyko equations of each watershed, using historical evapotranspiration and temperature data along with potential evapotranspiration estimates, to project future evapotranspiration based on future temperature and rainfall data. The future rainfall is expected to gradually increase, with the most significant increase under the SSP5-8.5 scenario. However, the rainfall increase varies with the geographical location (latitude) of the watershed, with higher rainfall increases in northern watersheds, such as Zengwen, Jiaxian, and Nanhua. Moreover, the projected evapotranspiration differs in watersheds in southern Taiwan indicating the uncertainty and challenge of evapotranspiration projection under climate change. The future runoff projections indicate an increasing trend with a significant increase (13.4–20.3%) by the end of the century (2081–2100), due to projected increases in rainfall and minor changes in evapotranspiration. The projected increase in runoff implies an optimistic outlook in water resources planning and management, but may pose a threat in flood disasters due to increased rainfall in the wet season.