The sensitivity of southeastern United States climate to varying irrigation vigor

Abstract

Four regional climate model runs centered on the Southeast United States (SEUS) assuming a crop growing season of May through October are irrigated at 25% (IRR25), 50% (IRR50), 75% (IRR75), and 100% (IRR100) of the root zone porosity to assess the sensitivity of the SEUS climate to irrigation. A fifth run, assuming no irrigation (CTL), is used as the basis for comparison. Across all IRR runs, it is found that there is a general reduction in seasonal mean precipitation over the irrigated cells relative to CTL. This manifests as an increase in dry (0–1 mm/d) days and reduction in > 1 mm/d rainfall events. A comparative moisture budget reveals that area‐averaged precipitation over the irrigated cells displays a reduction in precipitation and runoff in IRR100 with a weaker reduction in IRR25. This is despite an increase in vertically integrated moisture convergence and local evaporation. We find that irrigation increases the lower atmospheric stability, which in turn reduces the convective rainfall over the irrigated areas. Seasonally averaged temperatures reduce over irrigated areas, with the intensity of the reduction increasing with irrigation vigor. This is largely attributed to a repartitioning of sensible heat flux into latent heat flux. There is also, however, a small increase of heat flow to deeper soil layers. Precipitation ahead of transient cold fronts is also reduced by irrigation as they pass over irrigated cells, owing to the increased stability in the lower troposphere. The intensity of this precipitation reduction becomes more intense as irrigation vigor increases. Lastly, heat waves in the SEUS are reduced in intensity over irrigated cells.

Modeled effects of irrigation on surface climate in the Heihe River Basin, Northwest China

“…Such contrasts between these competing mechanisms have also been reported for many irrigated regions, such as the Southern Great Plains of United States [ Qian et al ., ], the North China Plain [ Zhang et al ., ], and West Africa [ Marcella and Eltahir , ]. As well as, for the southeastern United States, Selman and Misra [, ] reported that suppressing effects of precipitation increase along with intensified irrigation strength.…”

Plant Growth Nullifies the Effect of Increased Water‐Use Efficiency on Streamflow Under Elevated CO2 in the Southeastern United States

“…The lower Mississippi River Valley is one of the most intensively developed irrigated agricultural regions in the United States (Massey et al, 2017). The irrigation has expanded due to frequent drought in the region (Alston et al, 2010;McNider & Christy, 2007;Schaible & Aillery, 2012;Selman & Misra, 2016).…”