Regional simulations to quantify land use change and irrigation impacts on hydroclimate in the California Central Valley

Abstract

In this study, the influence of land use change and irrigation in the California Central Valley is quantified using the Pennsylvania State University/National Center for Atmospheric Research fifth generation Mesoscale Model (MM5) coupled with the Community Land Model version 3 (CLM3). The simulations were forced with modern-day and presettlement land use types at 30-km spatial resolution for the period 1 October 1995 to 30 September 1996. This study shows that land use change has significantly altered the structure of the planetary boundary layer (PBL) that affects near-surface temperature. In contrast, many land-use change studies indicate that albedo and evapotranspiration variations are the key processes influencing climate at local-to-regional scales. Our modeling results show that modern-day daily maximum near-surface air temperature (Tmax) has decreased due to agricultural expansion since presettlement. This decrease is caused by weaker sensible heat flux resulting from the lower surface roughness lengths associated with modern-day crops. The lower roughness lengths in the Central Valley also result in stronger winds that lead to a higher PBL. The higher PBL produces stronger sensible heat flux, causing nighttime warming. In addition to land use change, cropland irrigation has also affected hydroclimate processes within the California Central Valley. We generated a 10-member MM5-CLM3 ensemble simulation, where each ensemble member was forced by a fixed volumetric soil water content (SWC) between 3% and 30%, at 3% intervals, over the irrigated areas during a spring-summer growing season, 1 March to 31 August 1996. The results show that irrigation lowers the modern-day cropland surface temperature. Daytime cooling is produced by irrigation-related evaporation enhancement. This increased evaporation also dominates the nighttime surface cooling process. Surface cooling and the resulting weaker sensible heat flux further lower the near-surface air temperature. Thus, irrigation strengthens the daytime near-surface air temperature reduction that is caused by land use change, and a similar temperature change is seen for observations over irrigated cropland. Based on our modeling results, the nighttime near-surface warming induced by land use change is alleviated by low-intensity irrigation (17%<SWC<19%), but such warming completely reverses to a cooling effect under high-intensity irrigation (SWC>19%). The land use changes discussed in this study are commonly observed in many regions of the world, and the physical processes identified here can be used to better understand temperature variations over other areas with similar land cover changes.

Land cover changes and their biogeophysical effects on climate

“…LCC-related temperature reductions can be further amplified by irrigation. Over recent years, a series of observation and model based studies have been conducted over the key irrigated areas of the United States (Mahmood et al, 2004(Mahmood et al, , 2006Christy et al, 2006;Lobell et al, 2006aLobell et al, , 2006bBonfils and Lobell, 2007;Kueppers et al, 2007Kueppers et al, , 2008Lobell and Bonfils, 2008;Jin and Miller, 2011;Sorooshian et al, 2011), India (Sen Roy et al, 2007;Biggs et al, 2008), Australia (Geerts, 2002), and globally (Guimberteau et al, 2011) and have reported lowered growing season temperature in these areas. For example, an observational study by Christy et al (2006) estimated a 0.26 • C cooling trend decade −1 in the daily maximum temperature in California during the growing season while Bonfils and Lobell (2007) reported a 3.2 • C lower daily average temperature.…”

Twentieth Century Regional Climate Change During the Summer in the Central United States Attributed to Agricultural Intensification

“…For example, from 1950 to 2010, the amount of corn harvested annually in the Corn Belt increased by 400%, from 2 billion to 10 billion bushels (National Agricultural Statistics Service, ) (Figure b and Movie S1). These large‐scale land use modifications likely affected atmospheric processes, as changes in rain‐fed and irrigated cropland have previously been shown to influence climatic variables such as evapotranspiration (Adegoke et al, ; Cook et al, ; Harding & Snyder, ; Huber et al, ; Im, Marcella, et al, ; Jin & Miller, ; Lo & Famiglietti, ; Mahmood et al, ; Ozdogan et al, ; Qian et al, ; Wei et al, ), temperature (Adegoke et al, ; Alter et al, ; Barnston & Schickedanz, ; Cook et al, ; Harding & Snyder, ; Haugland & Crawford, ; Huber et al, ; Im, Marcella, et al, ; Jin & Miller, ; Kueppers et al, ; Mahmood et al, ; Mueller et al, ; Qian et al, ), humidity (Adegoke et al, ; Cook et al, ; Harding & Snyder, ; Haugland & Crawford, ; Huber et al, ; Lo & Famiglietti, ; Mahmood et al, ; Qian et al, ), and precipitation (Alter et al, ; Barnston & Schickedanz, ; Cook et al, ; DeAngelis et al, ; Harding & Snyder, ; Huber et al, ; Im, Marcella, et al, ; Lo & Famiglietti, ; Mueller et al, ; Qian et al, ; Stidd, ; Wei et al, ). Given these established linkages, one would expect that these historical increases in crop production have impacted regional climate in the central United States.…”

Evapotranspiration Trends (1979–2015) in the Central Valley of California, USA: Contrasting Tendencies During 1981–2007

“…Irrigation at such a massive spatial scale modifies the climate and hydrology of its environment (Adoegoke et al, 2003;Christy et al, 2006;Huang & Ullrich, 2016;Jin & Miller, 2011;Kanamaru & Kanamitsu, 2008;Kueppers et al, 2007Kueppers et al, , 2008Kueppers & Snyder, 2012;Lobell et al, 2009;Lobell & Bonfils, 2008;Ozdogan et al, 2010;Sacks et al, 2009;Sorooshian et al, 2011Sorooshian et al, , 2012Sorooshian et al, , 2014Szilagyi, 2018a;Yang et al, 2017). For example, Lobell and Bonfils (2008) observed a 2.5-3°C mean daily summertime air temperature difference between extensive irrigated and nonirrigated land areas in the Central Valley.…”