Abstract
Crop evapotranspiration (ETc) estimates, on a regional scale, hold enormous potential in managing surface and groundwater resources. This is particularly important for the headwater state of Wyoming, which provides water to found major river basins of the US. In this study, METRIC (Mapping evapotranspiration at high resolution with internalized calibration), a satellite-based image processing model, was used to map and quantify daily, monthly, and seasonal ETc and other energy balance fluxes, i.e., net radiation (Rn), sensible heat (H), and soil heat flux (G) dynamics for different land-use classes. Monthly and seasonal ETc estimated were further used to approximate regional water consumption patterns for different land-use types for nine irrigation districts in semi-arid to arid intermountain region of Big Horn Basin (BHB), Wyoming. The validation of METRIC retrievals against Bowen ratio energy balance system (BREBS) fluxes measured over three vegetative surfaces, viz. sugar beet in 2017, dry bean in 2018, and barley in 2019, indicated high accuracy. The pooled correlation observed between estimated (pooled) and measured instantaneous fluxes had R2 values of 0.91 (RMSE = 0.08 mm h−1, NSE = 0.91), 0.81 (RMSE = 49.6 Wm−2, NSE = 0.67), 0.53 (RMSE = 27.1 Wm−2, NSE = 0.53), and 0.86 (RMSE = 59.2 Wm−2, NSE = 0.84) for ETc, Rn, G, and H, respectively. The biggest discrepancy between measured and estimated monthly ETc values was observed during times when BREBS flux tower footprint was devoid of any crops or the crops at footprint were not actively transpiring. Validation results improved when comparisons were made on monthly scales with METRIC underestimating growing season ETc in the range between 3.2% to 6.0%. Seasonal ETc by land-use type showed significant variation over the study area where crop ETc was 52% higher than natural vegetation ETc. Furthermore, it was found that, in the arid to semi-arid intermountain region of Wyoming, the contribution of irrigation to total seasonal ETc varied in the range of 73–81% in nine irrigation districts that fall within the study area. The high relative contribution of irrigation highlights the importance of identifying and quantifying ETc for improved management in irrigation system design and water allocation.
Highlights
The availability of freshwater resources for agroecosystems has been an important issue for the sustainability of agricultural production in the U.S and around the world
Situated in the Rocky Mountain region of the Western United States, the Big Horn Basin (BHB) is dominated by mountain ranges and high elevation plains and covers the highly developed irrigation-based agricultural system within nine irrigation districts which are fed by three major rivers in the regions, namely the Shoshone River, Big Horn River, and Greybull River (Figure 1)
Cubic spline interpolation performed a bit better as compared to linear interpolation, and a comparison of estimated and measured monthly ETc values for cubic spline had R2 and slope of 0.9 and Root mean square error (RMSE) of 18.3 mm with growing season ETc underestimated in the range between 3.2 to 6.02%
Summary
The availability of freshwater resources for agroecosystems has been an important issue for the sustainability of agricultural production in the U.S and around the world. As Wyoming’s agricultural, municipal, industrial, and recreational/environmental water uses increase, the state’s limited water supplies have come under increased scrutiny. This has led to the scrutiny of surface and groundwater by the state and local governments, leading to the development of new regulatory approaches and groundwater policies. Interstate compacts and decrees between upstream and downstream user states have placed some restrictions on the amount of streamflow Wyoming users can deplete Under these circumstances, the management of water resources at the field, watershed, and regional scales is critical to sustained crop production and economic vitality in the region’s agro-ecosystem
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