Regional Impacts of Irrigation in Mexico and the Southwestern United States on Hydrometeorological Fields in the North American Monsoon Region

Abstract

In this study, the impacts of Mexican and southwestern U.S. agricultural and urban irrigation on North American monsoon (NAM) rainfall and other hydrometeorological fields are investigated using the Weather Research and Forecasting (WRF) Model by implementing an irrigation scheme into the WRF–land surface model. Taking the 2000–12 monsoon seasons as examples, multiple WRF simulations with irrigation are conducted by designing different crops’ maximum allowable water depletions (SWm). In comparison with gridded rainfall observations in urban and rural area, the WRF simulations with/without irrigation generally capture the observations very well, but with underestimation along the western slope of the Sierra Madre Occidental (SMO) and overestimation over southern Mexico. The simulations of WRF with irrigation are slightly improved over those without irrigation, compared with rainfall and sounding observations. Sensitivity studies reveal that the impact of irrigation on rainfall varies with location and NAM rainfall variability. Irrigation increases rainfall in eastern Arizona–western New Mexico and in northwestern Mexico because of the irrigation-induced increases of convective available potential energy (CAPE) and precipitable water. Overall, irrigation decreases rainfall in western Arizona, along the western slope of the SMO, and in central Mexico because of irrigation-induced increases of convective inhibition (CIN), decreases of CAPE, and/or large-scale water vapor divergence.

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

“…The increase in rainfall from land trajectories across almost the entire region could be due to several reasons—(i) increased moisture recycling due to increasing temperatures and evaporation (Dominguez et al, , ; Gimeno et al, ), (ii) increased antecedent precipitation (Koster et al, ), and (iii) increased water on the land due to agriculture activity (Kustu et al, ). In the full NAM region (southwest United States and Mexico), Mahalov et al () found irrigation to have a positive impact on the rainfall in eastern Arizona‐western New Mexico and in northwestern Mexico. An increase in irrigation leads to increases in evapotranspiration, surface mixing ratios, and vertical vapor fluxes, thus causing an increase in precipitation.…”

“…An increase in irrigation leads to increases in evapotranspiration, surface mixing ratios, and vertical vapor fluxes, thus causing an increase in precipitation. 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, ).…”

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.…”

“…Im and Eltahir () found that irrigation over West Africa increases rainfall in the upstream portion of the Niger River basin and produces more runoff downstream. The modified atmospheric circulation associated with large‐scale irrigation can make rainfall anomalies even more complicated and unpredictable (Alter et al, ; Fowler et al, ; Mahalov et al, ). A distinct feature of urban irrigation from large‐scale agricultural irrigation is that a considerable fraction of urban vegetation irrigation is presented as isolated patches, such as private gardens and roadside trees (e.g., J. Yang et al, ).…”

HESS Opinions: A planetary boundary on freshwater use is misleading

“…Others suggest that irrigation affects local rainfall, too: irrigation-induced surface cooling could increase local atmospheric stability, and thus reduce local rainfall (Lee et al, 2009;Guimberteau et al, 2012;Tuinenburg et al, 2014). Or, irrigation could increase convective available potential energy and precipitable water, and thus increase local rainfall (Mahalov et al, 2016). Irrigation-induced changes in local precipitation are mostly tied to changes in large-scale moisture convergence, and thus to changes in precipitation elsewhere.…”