A dissertation submitted in partial fulfillment of the requirements for the degree of doctor of Philosophy in Climate Change and Sustainable Development

Thesis (Ph.D.) - Asian Institute of Technology, 2023

While climate change has been affecting agricultural production globally, scarce literature has quantified the impacts of climatic factors on crop failure and cropping intensity with particular attention to growth periods, specific water regimes, and spatiotemporal variations. This study aimed to analyze and quantify the effects of climatic variables at the early (Growth Phase I) and latter (Growth Phase II) paddy growth phases, crop seasons (Maha and Yala)1 , water regimes (major irrigation, minor irrigation, and rainfed) in the three climatic zones (dry zone (DZ), intermediate zone (IZ), and wet zone (WZ)) on paddy yields, Unharvest Index (UI) (representing crop failure), and Cropping Index (CI) (representing the intensity of crop cultivation in the same land area per year) in Sri Lanka. A panel dataset was constructed, covering 20 districts for the 39-year period (1981 to 2019), which was analyzed by panel regression methods. The dependent variables were paddy yield (seasonal), UI (seasonal), and CI (annual). The results revealed that temperature had significant non linear effects on yields in the DZ and IZ; rainfall significantly reduced yields in the DZ and WZ, whereas it increased yields in the IZ; and rainfall fluctuation decreased yields in the WZ. In general, 5% of the cultivated area underwent paddy crop failure with variation of up to 60%; crop failure was prominent in rainfed production, the DZ and IZ, and Maha season; higher variability in seasonal temperature increased crop failure; and higher rainfall in Growth Phase I reduced crop failure in rainfed production. CI was averaged at 141%, 108%, and 105% in major, minor, and rainfed areas, respectively; CI of irrigated areas rose with Maha rainfall, while it fell with rising temperature in Yala. The findings suggest the need for several actions: specific climate adaptation policies considering spatiotemporal variations for each water regime; specific crop insurance programs for rainfed paddy; and improvement of water storage capacity and irrigation systems. Future research should incorporate more variables, such as socioeconomic characteristics, replanted area, and occurrence of flood and drought events into the analysis.