Lack of attention to spatial and temporal cross-scale dynamics and effects could be understood as one of the lacunas in scholarship on river basin management. Within the water-climate-food-energy nexus, an integrated and inclusive approach that recognizes traditional knowledge about and experiences of climate change and water resource management can provide crucial assistance in confronting problems in megaprojects and multipurpose river basin management projects. The Mahaweli Development Program (MDP), a megaproject and multipurpose river basin management project, is demonstrating substantial failures with regards to the spatial and temporal impacts of climate change and socioeconomic demands for water allocation and distribution for paddy cultivation in the dry zone area, which was one of the driving goals of the project at the initial stage. This interdisciplinary study explores how spatial and temporal climatic changes and uncertainty in weather conditions impact paddy cultivation in dry zonal areas with competing stakeholders’ interest in the Mahaweli River Basin. In the framework of embedded design in the mixed methods research approach, qualitative data is the primary source while quantitative analyses are used as supportive data. The key findings from the research analysis are as follows: close and in-depth consideration of spatial and temporal changes in climate systems and paddy farmers’ socioeconomic demands altered by seasonal changes are important factors. These factors should be considered in the future modification of water allocation, application of distribution technologies, and decision-making with regards to water resource management in the dry zonal paddy cultivation of Sri Lanka.