Ecologically sustainable surface water withdrawal for cropland irrigation through incorporation of climate variability

Abstract

In several regions of the world, interannual variations in precipitation and stream flows are related to ocean-atmosphere oscillation known as El Niño Southern Oscillation (ENSO) in the Pacific Ocean. El Niño events, which occur after every 2 to 10 years, are caused by high sea surface temperature and a low Southern Oscillation Index. La Niña events are caused by low sea surface temperature and a high Southern Oscillation Index. Because ENSO events can be accurately predicted in advance using a physical model of the coupled ocean-atmosphere system, it is now feasible to incorporate ENSO predictions in real-time water resources management. The objective of this study was to establish the relationship between ENSO and precipitation, ENSO and temperature, and ENSO and stream flows, and then use these relationships to develop a surface water withdrawal prescription for cropland irrigation in a southwest Alabama, United States, watershed. An additional objective was to determine the percentage of the watershed that could be irrigated through ENSO–based, ecologically sustainable surface water withdrawal. The study was conducted in the Big Creek watershed located in Mobile County, Alabama, using the Soil and Water Assessment Tool (SWAT) model for simulating stream flows and developing surface water withdrawal prescriptions. Strong relationships were found between ENSO and precipitation, ENSO and temperature, and ENSO and stream flow in this watershed. From November to July, El Niño episodes generated higher precipitation than La Niña episodes. On the contrary, in September and October, La Niña episodes resulted in higher precipitation than El Niño episodes. Results suggest that El Niño episodes produced higher stream flows during November to August than La Niña episodes. Water withdrawal followed the same trend as the stream flow did. On an average, it was found that around 20% of the watershed can be irrigated through ENSO–based, ecologically sustainable surface water withdrawal.