Abstract
AbstractStratocumulus clouds (SC) often exist over the eastern subtropical oceans during the summer and have significant impacts on the surface radiation budget. Both atmospheric subsidence and lower troposphere stability (LTS) have been found to play important roles in maintaining SC. Using global climate model simulations, we find that irrigation in California's Central Valley results in a decrease of land surface temperature, leading to a smaller land‐sea heat contrast, and a corresponding reduction in sea breeze, subsidence, and LTS over the near‐coastal region. The decrease in LTS directly drives a reduction in modeled SC coverage, and it would arguably do so in reality because of the well‐known link between LTS and SC coverage. Consequently, simulated absorbed surface solar radiation over this region increases by 8 W/m2 (3.7%) due to the reduction in SC cover, resulting in the warming at the Earth's surface. This study has important implications for how SC can change with regard to future climate. In contrast to the general effects of climate change on the formation of SC, our results suggest that irrigation practices in the Central Valley may drive a decrease in nearby SC coverage.
Highlights
[2] Stratocumulus clouds (SC) cover a large area of the world’s oceans, typically extending over hundreds to thousands of kilometers
We find that irrigation modifies the surface energy budget by increasing latent heat flux and decreasing the sensible heat flux and surface temperature over the irrigated area
In CAM3.5, this causes a reduction in both SC coverage and precipitation
Summary
[2] Stratocumulus clouds (SC) cover a large area of the world’s oceans, typically extending over hundreds to thousands of kilometers. Clement et al [2009] show that the changes in cloud cover over the Northeast Pacific are affected by both local vertical temperature structure (changes in lapse rate) and large-scale circulation from both observational data and model simulations. All of these studies have focused on large-scale forcing of SC; none have examined how regional climate change might affect nearby SC coverage. This excess of evapotranspiration over precipitation results from irrigation has substantial effects on local climate and the regional hydrological cycle [e.g., Bonfils and Lobell, 2007; Kueppers et al, 2008; Lobell et al, 2009; Ozdogan et al, 2006, 2010; Kustu et al, 2010, 2011; Sorooshian et al, 2011; Kueppers and Snyder, 2012] and has the potential to increase precipitation in downwind regions [DeAngelis et al, 2010; Puma and Cook, 2010; Lo and Famiglietti, 2013]
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