Abstract

This study assessed the impacts of climate change on diversion water requirements for irrigation system planning and development in the Philippines. Representative sites with high potential for irrigation development were selected from each of the four climatic types in the country. Cropping calendars were developed based on evapotranspiration and rainfall patterns. The CROPWAT program was used to determine the net irrigation requirement, from which the irrigation diversion requirements were derived based on estimated irrigation efficiencies. Recently published climate projections using the representative concentration pathways were used as climate change scenarios. Results of this study showed that the CROPWAT estimates of evapotranspiration were satisfactorily calibrated and validated using the eddy covariance methods. Climate change could lead to a significant increase in diversion water requirement. The increase in diversion water requirement was projected to reach + 43% during dry years, + 32% during normal years, and + 42% during wet years. A favorable reduction in diversion water requirement due to timely occurrence of rainfall was however observed at the site with distinct wet and dry season during dry years (up to − 7%), normal years (up to − 11%), and wet years (up to − 12%). The cropping patterns varied within and across climate types. The projected estimates of diversion water requirements generated in this study could be used for irrigation system planning and development particularly for assessing water storage requirements and design irrigable areas. Results could also be used as part of planning and design criteria for dams and reservoirs and thereby contribute to climate proofing of irrigation systems. The application of methods developed in this study for estimating diversion water requirements with the incorporation of climate change may be extended to other parts of the country and in other parts of the world for a more climate-resilient water resources planning.

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