Underground transfer of floods for irrigation (UTFI): Exploring potential at the global scale

Abstract

Underground Transfer of Floods for Irrigation (UTFI) is an approach to co-manage floods and droughts at the river basin scale. It involves targeted recharge of aquifers using seasonal excess surface water flows that potentially pose a flood risk, with the aim of mitigating downstream flooding and increasing groundwater storage. Increased groundwater storage provides the opportunity to increase agricultural production during the dry season and enhance resilience to droughts. Identifying suitable areas for UTFI is a vital first step towards successful implementation outcomes. In this study, an analysis was carried out at the global scale – with a spatial resolution of 30 arc-minutes, translating to approximately 55 km2 pixels at the equator – to map and classify areas suitable for implementation of the UTFI approach. Lessons learned from initial UTFI conceptualization in Thailand and pilot implementation of the approach in the Ganges River Basin were also taken into consideration. Datasets on flood and drought hazard frequency, mortality, economic losses, groundwater depth, aquifer type and groundwater salinity were arranged into three broad thematic groups that cover water supply, water demand and water storage. Each data layer in the three thematic groups was assigned a weight based on its relative importance in the theme, and the features within each data layer were given a reclassified value based on their likely correlation with UTFI potential. The results of the analysis highlight that, at the global scale, areas with high to very high UTFI suitability account for a population of approximately 3.8 billion people and a crop area of 622 million hectares. South Asia, East Asia, Southeast Asia and sub-Saharan Africa (SSA) are regions with the highest UTFI potential. Aggregation of UTFI suitability levels at the river basin scale reveals high suitability across some of the major river basins in Asia (Ganges, Chao Phraya, Mekong), SSA (Volta, Awash, Tana, Save, Shebelle), Latin America (Rio Balsas, Magdalena, Rio Parnaiba) and North America (Sacramento, Brazos). An economic analysis was undertaken in three selected river basins in different regions: Awash Basin in Ethiopia, Ramganga Basin (part of the Ganges River Basin) in India and Chao Phraya Basin in Thailand. These basins show high economic viability for UTFI implementation with internal rate of return values ranging from 20% to 122% for the base case scenario. Analysis of different scenarios of economic viability reveals the importance of recharge rates and crop prices in particular. The major benefits associated with UTFI implementation vary across the three basins and contrasting regional contexts. Enhanced crop production is the predominant benefit arising from UTFI implementation in the Awash and Ramganga basins, while it is flood damage mitigation in the Chao Phraya Basin. Results show that areas with high UTFI suitability emerge in diverse contexts, including the more disasterprone areas of Asia and Africa. The maps and data from this study provide an early identification of the likely potential for UTFI implementation. They also provide the basis for more detailed investigations at country and basin scales to ascertain UTFI potential with higher confidence. The broad prerequisites and steps needed to implement UTFI in practice and potential areas for further research are also highlighted in this report.