A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Water Engineering and Management

Thesis (M. Eng.) - Asian Institute of Technology, 2024

One of the main issues with water resource management is climate change because it hurts hydrological processes and irrigation systems for agricultural productivity. Extreme weather events are occurring more frequently, and patterns of precipitation and temperature are shifting, disrupting water supply, reservoir operations, and irrigation systems, providing considerable difficulties to agricultural output. Reservoir performance and irrigation water releases and hydropower production are impacted by variations in the average amount, timing, and frequency of river flow.The study investigates how climate change influences reservoir operations to ensure water provision for irrigation at a dam. With an emphasis on how future weather conditions may impact water availability for downstream agricultural needs, this study evaluated the role of climatic variations in impacting reservoir storage for irrigation water in Pasak Jolasid Dam in Thailand. With the increasing risks posed by climate variability, particularly shifts in precipitation patterns and rising temperatures, the study aims to assess projected changes in reservoir findings indicate that climate change is likely to reduce reservoir storage during critical growing seasons due to higher evaporation rates and potential sedimentation, resulting in increased water deficits for irrigation. The primary objective is to assess how climate change affects reservoir functionality and irrigation reliability using projected future climate scenarios. Specific objectives include projecting future climate variables in the study area under selected Shared Socioeconomic Pathway (SSP) scenarios, developing a hydrologic model to forecast inflow changes, and building a reservoir model to estimate future water availability and releases for irrigation. Additionally, the study examines the reliability of reservoir operations in meeting irrigation demands under projected climate scenarios. By integrating climate projections, hydrologic modeling, and reservoir analysis, this research provides valuable insights into the potential challenges facing reservoir dependent irrigation systems and offers recommendations for adaptive inflows, evaporation losses, and storage capacity. Using multiple climate models (GCMs) and hydrological analysis, we evaluated how projected temperature increases, altered rainfall patterns, and seasonal water demand could impact reservoir reliability. Key management strategies to enhance water supply reliability under changing climatic conditions. Firstly, the multiple climate models (GCMs) were downscaled to analyze the Pasak River basin (PRB)'s future climate change scenarios and bias-corrected by the quantile mapping method with observed station data points that are utilized for future climate projections within the Pasak River basin. Secondly, simulations of the reservoir inflow were done in the rainfall-runoff model, and calibration and validation were carried out at the S34 discharge station to facilitate the watershed simulations of the Pasak River. For future scenarios, bias-corrected climate change data from ACCESS-CM2 and CanESM5 were used to simulate future reservoir inflows within the validated hydrological simulation model. Thirdly, the reservoir model was configured by setting up the watershed and reservoir network, defining the reservoir parameters, and incorporating operation 2upper and lower rule curves3 by using the reservoir simulation modeling. The inflow of the dam was used for both model calibration and validation. After all calculations were completed, the model calibration of water level and releases were conducted from 2000 to 2014. The validation was carried out for the years 2015 through 2023. For future scenarios, inflow data derived from the 2HEC-HMS3 model was used as the contribution to calculate future water levels, as well as inflows and outflows from the reservoir. Finally, the upcoming allocation of water for irrigation from the dam was examined for dependability to satisfy demand considering scenarios related to shifts in climate patterns. From the results, it is evident that water supply meets the demand consistently during January, February, and December, with maximum deficit. However, notable moderate deficits are observed in March, April, June, July, August, and November, suggesting these months experience moderate water demand. This seasonal variation highlights periods of potential water stress, highlighting the necessity of focused water management techniques during these deficit-prone months to ensure a reliable supply throughout the year. These findings emphasize the need for improved resource planning, especially for high-deficit months, to optimize water allocation and minimize the irrigation supply deficits that impact agricultural productivity.