Climate-smart agriculture in South Asia: a quantitative meta-analysis of productivity, water–energy use, and greenhouse gas mitigation

South Asia faces a dual challenge of ensuring agri-food and nutritional security for rapidly growing population while addressing the climate change, resource degradation, and environmental sustainability. Climate-smart agriculture (CSA) has emerged as a promising pathway to enhance productivity, resilience, and environmental performance; however, its system-level impacts across the water–energy–food–climate nexus remain insufficiently quantified. This study present a quantitative meta-analysis of 229 peer-reviewed studies to evaluate the multidimensional impacts of CSA practices across major South Asian agr-food systems, particularly rice-wheat, and maize-based production systems. A structured meta-analytical framework was applied to estimate effect sizes, assess variability across studies, and examine interactions among productivity, resource use, and environmental outcomes. Results indicate that CSA practices significantly improve system performance, increasing crop productivity by 12-20% compared to conventional practices. At the same time, CSA adoption reduce irrigation water use (15-40%), energy consumption (20-45%), and greenhouse gas emissions (20-45%) demonstrating strong co-benefits across the environmental nexus. Precision nutrient management tools, such as GreenSeeker and Leaf Color Chart, contribute to 8-14% reduction in nitrogen use, while improving nutrient use efficiency and lowering environmental footprints. Soil health also responds positively, with increases soil organic carbon and nutrient availability, alongside improvements in soil physical properties. Despite these benefits, the magnitude of CSA impacts varies across agroecological conditions, management practices, and socio-economic contexts, highlighting the importance of site-specific adaptation and uncertainty in outcomes. The analysis further reveals critical trade-offs and synergies between productivity gains and resource conservation, emphasizing the need for integrated, system-based approaches rather than isolated interventions. Overall, this study advances current understanding by quantifying the cross-sectoral impacts of CSA within a nexus framework, providing robust evidence for its role in sustainable intensification of South Asian agriculture. Scaling CSA will require strengthened policy support, institutional alignment, and targeted investments to address adoption barriers and ensure long-term sustainability. These findings offer important implications for advancing multiple Sustainable Development Goals related to food security, climate action, and resource sustainability in the region.