An innovative approach to rainwater harvesting for irrigation based on El Niño Southern Oscillation forecasts

Abstract

The southeastern United States observed a widespread expansion in area under irrigation over the past half century, primarily due to inadequate rainfall during crop growing season. In this region, El Nino Southern Oscillation (ENSO), a seasonal-to-interannual climate-variability phenomena, may result in bringing suitable precipitation in any year while generating extremes of too much or too little precipitation in others. Therefore, this climate variability phenomena results in uncertainties over the availability of stream water for withdrawals to meet irrigation needs. The overall goal of this study was to quantify the impact of ENSO on the amount of water that can be sustainably withdrawn from streams for irrigation. The specific objectives of this study were to (1) quantify the relationship between ENSO and precipitation, and ENSO and simulated streamflow; (2) develop surface water withdrawal prescription for irrigation without disturbing the ecological integrity of streamflow; (3) quantify the area of watershed that can be irrigated via surface water withdrawals from different order streams; and (4) determine pond size for the storage of withdrawn water from streams for irrigation. The study was conducted in the Swan Creek watershed located in Limestone County of north Alabama, United States. The Soil and Water Assessment Tool (SWAT) model was used to simulate streamflows and develop water withdrawal prescriptions. The La Nina phase of ENSO generated more rainfall from January to March, and the El Nino phase generated more rainfall from May to December (except October). The results of this study indicate that as a function of year, during a La Nina phase 14% to 55% more water can be sustainably withdrawn from streams in the winter months (January to March) than the El Nino phase. Furthermore, irrespective of the ENSO phase, about 42% more water could be withdrawn during the noncrop growing months than the crop growing months. Based on the water withdrawal criteria, about 16% of the watershed cropland area can be irrigated if the withdrawals are made throughout the year, 9% if stream water is withdrawn in noncrop growing season months, and 5% if stream water is withdrawn in the crop growing season. If farmers plan water withdrawal in accordance with the ENSO phase, it would not only provide them ample volume of water for irrigation during the crop growing season but would also help to maintain stream water quality and aquatic biota.