A thesis report 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, 2016

Ecosystems and ecosystem services are one of the biggest lives supporting system on the earth. Climate change is identified as the main driver for ecosystem alteration. It is confirmed that changes in the meteorological variables are directly caused for river flow alterations. As many river basin ecosystem services are linked with river flow, significant alterations in flow regime cause for alterations in river basin ecosystem services especially food provisioning and habitat provisioning service for aquatic life. The study mainly focused on analyzing climate impact on river flow regim e and fish production (food provisioning service) in the Songkhram river basin, Thailand. Fish habitat alterations are analyzed purely based on physical flow characteristic change. Impact of flow alterations on air - breathing and non - air breathing fish are evaluated. Air {u2013} breathing fish are more tolerate to the low flow conditions than non - air - breathing fish. Future rainfall and temperature over the study area is predicted throug h GFDL - CGCM3, MRI - CGCM3 and MIROC5 climate model simulations for RCP45 and RCP85 scenarios with baseline period of 1975 - 2004. Predictions are made for near future (2016 - 2045) and far future (2031 - 2060) time scales. End of 2060s the annual average of daily maximum temperature is expected to increase by 2.1 o C and annual average of daily minimum temperature is expected to increase by 2.6 o C with respect to the baseline temperatures of 31.6 o C and 21.1 o C respectively. As per the GCM simulations over the study area total annual rainfall is expected to increase by 32.7% in the near future and 28% in far future. HEC - HMS model is used to simula te future flows for 8 scenarios. Flow alterations are found through 33 environmental flow related indices which are given in IHA tool. RVA is used to calculate the degree of alteration in the pre and post climate impact periods. Overall in near future, flow is expected to alter with 20% - 44% and in the far future time scale flow alteration is expected to be 20% - 43%. Therefore in the Songkhram river basin flow alterations are always between low and moderate classes. Empirically it is found that around 65% of IHA ind ices form a parabolic relationship with fish production with R 2 of 0.00 {u2013} 0. 20. While only 12% of indices have relatively strong (R 2 is 0.41 - 0.60) mathe matical relationships with fish production. It is found that magnitude of the flow has higher influence on the fish production compared to the other flow characteristics. Production increment of air {u2013} breathing fish is very much higher than that of non - air breathing fish. Therefore in an average due to higher availability of the habitat, 87 % of air breathing fish production and 16 % of non - air breathing fish production increment can be expected in Songkhram River basin at the end of 2060s