This comprehensive book examines the intricate relationships between hydrology, agriculture, pollution, and climate change across multiple regions. The text begins by highlighting the crucial role of headwater catchments in regulating water flow, carbon storage, and ecosystem health. Through various case studies and research findings, it explores three main themes: hydrological changes in catchment areas, agricultural systems and water management, and pollution remediation strategies. The first section analyzes streamflow regime shifts in headwater catchments and presents projections for water availability in regions like the Indus basin, incorporating CMIP6 climate scenarios. The agricultural focus emphasizes innovative approaches such as coconut husk mulch for water conservation and examines climate extremes’ impact on crop productivity, particularly in Indian agricultural systems. A significant portion addresses water pollution challenges, particularly in agricultural and industrial contexts. The text details various remediation technologies for contaminated groundwater systems, including both ex-situ and insitu methods, with special attention to simulation-optimization models for aquifer restoration. The book also explores the complex dynamics of fertilizer leaching and heavy metal contamination in industrial corridors, presenting case studies from regions like Tamil Nadu. The final sections integrate advanced technological solutions, including precision agriculture, ERA5-Land reanalysis data, and Bayesian Model Averaging for streamflow prediction. The book concludes by addressing policy perspectives on transboundary water conflicts and water quality assessment, emphasizing the need for integrated approaches to tackle contemporary environmental challenges.