Conjunctive use of green and blue water resources in agriculture: Methodology and application for supplemental irrigation

Abstract

Supplemental irrigation (SI) ensures an efficient conjunctive use of green and blue water resources in dryland cropping by alleviating the negative impacts of precipitation shortages and drought spells on plant growth and production. The management of SI at the field level is well documented but little is known about planning at basin scale. This work uses a geographic information system-based modelling approach together with suitability criteria to identify potential areas for expanding SI at scale. A spatial water allocation algorithm is developed to model SI water allocation using data layers consisting of climate surfaces, classified land-use maps, and a digital elevation model. Areas are prioritized stepwise, according to land suitability, until the available water is fully utilized. The analysis was applied in a watershed in western Iran. The analysis revealed that, with SI, available water resources in the winter season can supplementally irrigate a new land area of about 2,900 ha, about twice the area conventionally irrigated in the dry season. However, adopting a deficit SI strategy allows irrigation of additional 3,220 ha, more than double of the current water allocation efficiency. The approach can be applied in any rainfed area with available water without major modifications, but further analysis is needed to evaluate its economics at scale.