Operational Evapotranspiration Mapping Using Remote Sensing and Weather Datasets: A New Parameterization for the SSEB Approach

Abstract

The increasing availability of multi-scale remotely sensed data and global weather datasets is allowing the estimation of evapotranspiration (ET) at multiple scales. We present a simple but robust method that uses remotely sensed thermal data and model-assimilated weather fields to produce ET for the contiguous United States (CONUS) at monthly and seasonal time scales. The method is based on the Simplified Surface Energy Balance (SSEB) model, which is now parameterized for operational applications, renamed as SSEBop. The innovative aspect of the SSEBop is that it uses predefined boundary conditions that are unique to each pixel for the "hot" and "cold" reference conditions. The SSEBop model was used for computing ET for 12 years (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011) using the MODIS and Global Data Assimilation System (GDAS) data streams. SSEBop ET results compared reasonably well with monthly eddy covariance ET data explaining 64% of the observed variability across diverse ecosystems in the CONUS during 2005. Twelve annual ET anomalies (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011) depicted the spatial extent and severity of the commonly known drought years in the CONUS. More research is required to improve the representation of the predefined boundary conditions in complex terrain at small spatial scales. SSEBop model was found to be a promising approach to conduct water use studies in the CONUS, with a similar opportunity in other parts of the world. The approach can also be applied with other thermal sensors such as Landsat.(KEY TERMS: drought; evapotranspiration; irrigation; remote sensing; water use.)

Calibration of Spatially Distributed Hydrological Processes and Model Parameters in SWAT Using Remote Sensing Data and an Auto-Calibration Procedure: A Case Study in a Vietnamese River Basin

“…An operational version of SSEB was proposed [78,79] by assimilating air temperature to account for the topographical and latitudinal heterogeneity impact on surface temperature. The SSEBop model defines the temperature scalar using hot and cold reference values for any pixel.…”

Evapotranspiration Mapping in a Heterogeneous Landscape Using Remote Sensing and Global Weather Datasets: Application to the Mara Basin, East Africa

“…SSEBop is a simplified SEB algorithm that calculates ET as a fraction of the ET0, in which the ET fraction is determined using Ts and predefined hot and cold reference temperatures [9]. The ET is computed as:…”

“…The difference between the hot and cold reference temperatures is predefined for each location and period using a simplified climatological energy balance procedure [9]. The cold reference temperature is calculated as a fraction of the maximum daily air temperature, based on the …”

Complementary Relationship for Estimating Evapotranspiration Using the Granger-Gray Model: Improvements and Comparison with a Remote Sensing Method

“…Furthermore, Senay et al (2011b) 15 proposed a revised SSEB to handle both elevation and latitude effects on surface temperature using the difference between Land Surface Temperature (LST) and air temperature. Recently, Senay et al (2013) proposed an operational SSEB, renamed as SSEBop, that uses predefined boundary conditions for hot and cold reference pixels so that ET can be calculated as a function of LST and reference ET. The SSEBop approach has been validated comprehensively by comparing with 45 EC flux tower observations and then with both MOD16 and 60 EC flux tower observations (Velpuri et al, 20 2013).…”

“…Despite the general consensus of using SSEBop for estimating ET, a detailed study of SSEBop conducted by Senay et al (2013) showed that the use of reference ET can introduce a significant difference of up to 20 % in the magnitude of ET.…”