Enhancement of rainfall and runoff upstream from irrigation location in a climate model of West Africa

Abstract

This study investigates the impact of potential medium-scale irrigation (about 60,000 km 2 ) on the climate of West Africa using the MIT Regional Climate Model. We find that irrigation at this scale induces an atmospheric response similar to that of large-scale irrigation (about 400,000km 2 ) which was considered in our previous theoretical study. While the volume of water needed for large-scale irrigation is about 230-270 km 3 , the medium-scale irrigation requires about 50 km 3 , and the annual flow of the Niger river in the relevant section is about 70 km 3 . The remote response of rainfall distribution to local irrigation exhibits a significant sensitivity to the latitudinal location of irrigation. The nature of this response is such that irrigation from the Niger River around latitude 18 N induces significant increase in rainfall of order 100% in the upstream sources of the Niger River and results in significant increase in runoff of order 50%. This additional runoff can potentially be collected by the river network and delivered back toward the irrigation area. By selecting the location of irrigation carefully, the positive impacts of irrigation on rainfall distribution can be maximized. The approach of using a regional climate model to investigate the impact of location and size of irrigation schemes, explored in this study, may be the first step in incorporating land-atmosphere interactions in the design of location and size of irrigation projects. However, this theoretical approach is still in early stages of development and further research is needed before any practical application in water resources planning.

Understanding the Dominant Sources and Tracks of Moisture for Summer Rainfall in the Southwest United States

“…Bohn and Vivoni (), however, argued that the use of an outdated land cover map and misidentification of irrigated pixels in Mahalov et al () could have resulted in a substantial overestimation of the impact of agricultural irrigation in parts like Chihuahua and regions surrounding the GoC. Agricultural irrigation has also been found to impact monsoons in other parts of the world such as the Asian Monsoon (E. M. Douglas et al, ; Saeed et al, ) and the African Monsoon (Alter et al, ; Im et al, ; Im & Eltahir, ).…”

Impact of Irrigation on Regional Climate Over Eastern China

“…This study aims to investigate the impact of irrigation on regional climate based on observational data and model simulations over Eastern China. We test the hypothesis advanced in Im & Eltahir () and Im, Marcella, et al () (Figure S1 in the supporting information) that irrigation with a scale of millions of hectares, such as in NCP, would reduce temperature, increase surface humidity and surface pressure, and induce an anticyclonic circulation that forces changes in precipitation over surrounding regions. The specific objectives of this study are (1) to estimate the local climate change due to irrigation over Eastern China based on observations and (2) to investigate the nature of the physical mechanisms shaping the observed changes in precipitation that are caused by irrigation using numerical modeling experiment.…”

“…The rapid development of large‐scale irrigation can cause changes in regional climate due to land‐atmosphere interactions. Many studies demonstrate that incremental change in soil moisture through irrigation can lead to increasing local evapotranspiration and latent heat flux and to decreasing temperature and sensible heat flux, which is a first‐order effect on the local surface energy and water budget (Adegoke et al, ; Alter et al, ; Cook et al, ; Douglas et al, ; Huber et al, ; Im & Eltahir, ; Im, Marcella, et al, ; Kang & Eltahir, ; Kueppers et al, ; Mueller et al, ; Qian et al, ; Sacks et al, ). However, the effect of irrigation on precipitation is more complex because of the multiscale processes, including the role of atmospheric circulations.…”

“…In some cases, irrigation enhances precipitation as a result of a positive feedback between soil moisture and precipitation at the local scale (Adegoke et al, ; Moore & Rojstaczer, ; Pal & Eltahir, ; Segal et al, ). In other cases, evaporative cooling locally drives a precipitation decrease over irrigated areas due to lower height of the planetary boundary layer, and the anomalously high pressure (Alter et al, ; Im & Eltahir, ; Im, Marcella, et al, ). This higher pressure also causes the low‐level circulation to change and modulates the precipitation change at remote location surrounding the irrigated area (Alter et al, ; Douglas et al, ; Im & Eltahir, ; Im, Marcella, et al, ; Huber et al, ).…”

Regional Impacts of Urban Irrigation on Surface Heat Fluxes and Rainfall in Central Arizona

“…The impact of large‐scale agricultural irrigation on rainfall has been extensively investigated and debated in previous studies (e.g., DeAngelis et al, ; Fowler et al, ; Im et al, ; Im & Eltahir, ; Mahalov et al, ; Zhang et al, ). Irrigation through increased soil moisture can possibly increase rainfall mainly due to enhanced low‐level moisture availability and increased moist static energy for convection.…”