Abstract
AbstractIn this study, a regional climate model (RCM) is employed to investigate the effect of irrigation on hydrology over California through implementing a “realistic irrigation” scheme. Our results indicate that the RCM with a realistic irrigation scheme commonly practiced in California can capture the soil moisture and evapotranspiration (ET) variation very well in comparison with the available in situ and remote sensing data. The RCM results show significant improvement in comparison with those outputs from the default run and the commonly used runs with fixed soil moisture at field capacity. Furthermore, the model reproduces the observed decreasing trends of the reference ET (i.e., ET0) from the California Irrigation Management Information System (CIMIS). The observed decreasing trend is most likely due to the decreasing trend of downward solar radiation shown by models and CIMIS observations. This issue is fundamental in projecting future irrigation water demand. The deep soil percolation rate changes depending on the irrigation method and irrigation duration. Finally, the model results show that precipitation change due to irrigation in California is relatively small in amount and mainly occurs along the midlatitudes in the western United States.
Highlights
Anthropogenic land cover and land use changes have dramatically altered the global land surface, especially with regard to the conversion of agriculture and pastures from natural lands [Kueppers and Snyder, 2012; Ramankutty et al, 2008]
Our results indicate that the regional climate model (RCM) with a realistic irrigation scheme commonly practiced in California can capture the soil moisture and evapotranspiration (ET) variation very well in comparison with the available in situ and remote sensing data
In this third paper in the sequence, we focus on studying the effects of irrigation on land hydrological processes using RCM simulations, available observations, and off-line land surface model outputs from the North American Land Data Assimilation System (NLDAS) Phase 2
Summary
Anthropogenic land cover and land use changes have dramatically altered the global land surface, especially with regard to the conversion of agriculture and pastures from natural lands [Kueppers and Snyder, 2012; Ramankutty et al, 2008]. Kueppers and Snyder [2012] investigated the surface flux (sensible, latent heat flux) variations from diurnal to seasonal scales through fixing the soil root zone moisture at field capacity at each time step. In the second study [Sorooshian et al, 2012], the effect of irrigation on ET was examined against remote sensing observations In this third paper in the sequence, we focus on studying the effects of irrigation on land hydrological processes (e.g., surface runoff, groundwater recharge, and soil moisture) using RCM simulations, available observations, and off-line land surface model outputs from the North American Land Data Assimilation System (NLDAS) Phase 2
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