Hydrological and water balance studies to evaluate options for climate resilience in smallholder irrigation systems in Sri Lanka

Smallholder agriculture shares a great portion of Sri Lanka's economy and provides a livelihood to 20% of the country's labour force. However, smallholder agricultural systems are considered highly vulnerable to climate variability and change. As such, improving their climate resilience is critical to ensuring sustainable development of the country. In the country's dry zone, agricultural systems are supported by thousands of small and large irrigation tanks in cascades, whose water supply potential keeps fluctuating widely between years and seasons due to rainfall variability which is a unique characteristic of this zone. In this study, we assessed the hydrological potential of the catchments of these tanks in a typical irrigation system and provided a framework to design an optimal strategy to enhance climate resilience of such systems for improved agricultural production, using a water balance model. The results show that climate-induced impacts on hydrology coupled with population growth and agricultural expansion increase irrigation water demands in the near future. Moreover, demand-side interventions will be more effective than supply-side adaptation in reducing the demand-supply gap. The study recommends evaluating more adaptation measures under expert guidance, uncertainty assessments of future climate and socio-economic pathways, and incorporating a cost-benefit assessment in the model.