Abstract
Accurately estimating consumptive water use in the Colorado River Basin (CRB) is important for assessing and managing limited water resources in the basin. Increasing water demand from various sectors may threaten long-term sustainability of the water supply in the arid southwestern United States. We have developed a first-ever basin-wide actual evapotranspiration (ETa) map of the CRB at the Landsat scale for water use assessment at the field level. We used the operational Simplified Surface Energy Balance (SSEBop) model for estimating ETa using 328 cloud-free Landsat images acquired during 2010. Our results show that cropland had the highest ETa among all land cover classes except for water. Validation using eddy covariance measured ETa showed that the SSEBop model nicely captured the variability in annual ETa with an overall R2 of 0.78 and a mean bias error of about 10%. Comparison with water balance-based ETa showed good agreement (R2 = 0.85) at the sub-basin level. Though there was good correlation (R2 = 0.79) between Moderate Resolution Imaging Spectroradiometer (MODIS)-based ETa (1 km spatial resolution) and Landsat-based ETa (30 m spatial resolution), the spatial distribution of MODIS-based ETa was not suitable for water use assessment at the field level. In contrast, Landsat-based ETa has good potential to be used at the field level for water management. With further validation using multiple years and sites, our methodology can be applied for regular production of ETa maps of larger areas such as the conterminous United States.
Highlights
Water management is becoming more challenging, in the arid western United States because of changes in climate, land use, and demography
The operational Simplified Surface Energy Balance (SSEBop) model was used for estimating ETa within the Colorado River Basin (CRB)
Accurate information on water availability and water use is necessary for planning sustainable use of water, in an arid region like the southwestern United States
Summary
Water management is becoming more challenging, in the arid western United States because of changes in climate, land use, and demography. One climate change study has indicated that annual runoff in the Colorado River Basin (CRB) will be reduced by 14%, 18%, and 17% for the periods 2010–2039, 2040–2069, and 2070–2098, respectively [1]. The reduced availability of water in the basin could prevent water allocation requirements of the Colorado River Compact from being met [2]. Increased demand for water from various sectors has motivated water managers to demand more accurate water budgets at higher resolution so that available water resources may be better allocated. Remote sensing has great potential but remains underutilized by practicing water resource managers [3,4]. Estimating consumptive water use using remotely sensed data helps water managers in planning, distribution, and management of water resources. Agro-meteorological models based on remote sensing are the most suited for estimating crop water use at the field and regional scales [5]. Various publications have reviewed some of these models and other methods for estimating ETa using remotely sensed data [5,17–19]
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