Irrigation impacts on California's climate with the variable‐resolution CESM

Abstract

The variable‐resolution capability within the Community Earth System Model (VR‐CESM) is applied to understand the impact of irrigation on the regional climate of California. Irrigation is an important contributor to the regional climate of heavily irrigated regions, and within the U.S. there are few regions that are as heavily irrigated as California's Central Valley, responsible for 25% of domestic agricultural products. A flexible irrigation scheme with relatively realistic estimates of agricultural water use is employed. The impact of irrigation on mean climatology and heat extremes is investigated over the 26 year period 1980–2005 using a relatively fine grid resolution of (∼28 km). Three simulations are performed, including an unirrigated control run and two irrigation‐enabled runs, with results compared to gridded observations and weather station data sets. During the summer months (when irrigation peaks), irrigation leads to cooling of the daily maximum near‐surface temperature field (Tmax) by approximately 1.1 K. Under irrigation, latent heat flux increased by ∼61% during the daytime as a result of increased surface evaporation; specific humidity increased by about 12%; heat stress was reduced by 22% and the average soil moisture exhibited a small (∼4.4%) but statistically significant increase. Compared with observations, irrigation improved the frequency distribution of Tmax, and both length and frequency of hot spells were better represented with irrigation enabled. Consequently, we argue that high‐resolution simulations of regional climate in CESM, particularly over heavily irrigated regions, should likely enable the irrigation parameterization to better represent local temperature statistics.

Local land–atmosphere feedbacks limit irrigation demand

“…Prior research has not quantified the impact of the near-surface feedback, but they do offer insight into methods to deal with it. Recent work by Huang and Ullrich (2016) using a variable resolution atmospheric model to simulate irrigation demonstrates a possible future research direction. Variable resolution climate models allow small scale features, such as localized feedbacks over irrigated regions, to be captured.…”

“…If irrigation occurs over large areas, it can have a significant impact on regional climate. Evaporation is increased by irrigation (Leng et al 2013, Lu et al 2015 which cools and moistens the near surface air (Sacks et al 2008, Huang andUllrich 2016) reducing the maximum monthly air temperature by up to 7.5°C in California (Kueppers et al 2007). Because irrigation demand is dynamic, responding to changes in water use, atmospheric conditions, and plant growth, the irrigation induced changes in near surface climate is a feedback on irrigation demand.…”

Sensitivity of Mountain Hydroclimate Simulations in Variable‐Resolution CESM to Microphysics and Horizontal Resolution

“…With the advent of regional refinement capabilities within select climate models, such as variable‐resolution in the Community Earth System Model (VR‐CESM) (Zarzycki et al, ) and the Model for Prediction Across Scales (MPAS) (Rauscher et al, ; Skamarock et al, ), climate modelers have gained the ability to glimpse into the future of extremely‐high‐resolution global‐scale climate modeling for a fraction of the cost of equivalent resolution global climate models (Leung et al, ; Sakaguchi et al, ). Over the last five years, VR‐CESM has gone from an experimental model to a proven applied research tool for use in regional climate assessment (Gettelman et al, ; Huang et al, ; Huang & Ullrich, ; Rauscher et al, ; Rhoades et al, ; Wu et al, ; Zarzycki et al, ), modeling synoptic‐scale weather systems (Rauscher & Ringler, ) and tropical cyclones (Zarzycki, ; Zarzycki & Jablonowski, ; Zarzycki et al, ), and most recently in regional climate change assessments (Huang & Ullrich, ; Rhoades et al, ).…”

The future of wind energy in California: Future projections with the Variable-Resolution CESM

“…Seasonal synoptic-scale patterns were investigated as part of this work to better understand how shifts Previous studies [14,15] utilizing VR-CESM have demonstrated its competitiveness in studying high-resolution regional climatology when compared to other regional climate models, especially when non-local processes have significant influence on the local climatology. VR-CESM has demonstrated a much 55 better representation of climatology within regions of complex topography, due to the relatively fine regional resolution compared with conventional GCM simulations [16,17,18]. The remainder of the paper is as follows.…”