Abstract

In many agronomic settings, irrigation is the only plausible system to sustain a dependable and economically viable agriculture. That is the case of semi-arid and Mediterranean basins such as the Limar? basin in Chile. In this basin a complex reservoir and irrigation system helps sustain more than 40,000 has of cultivated land with less than 150 mm of average annual precipitation. The very existence of this infrastructure, combined with favorable solar radiation fluxes throughout the year, causes water demand for irrigated agriculture to grow steadily. Upstream from the reservoir system there are 9,000 has of irrigated land that benefits indirectly from the built infrastructure (by using all available water during hydrologically average years). However, the lack of storage capacity makes these higher lands very sensitive to the significant climate variability, characteristic of the region. On the other hand climate change scenarios for this basin project a strong decline in available streamflow and a change in seasonality towards a higher relative proportion of water in winter months relative to summer months (when water is most needed). In this work we present a method to estimate climate impacts and a vulnerability assessment for a semi-arid snowmelt dominated basin and a method to test the value of irrigation policies as an adaptation strategy. Examples of these policies are related to new infrastructure that helps reduce the impacts of climate variability and seasonality changes as well as policies designed towards expanding the amount of land under irrigation. © 2011 ASCE.