Basin scale estimates of evapotranspiration using GRACE and other observations

Abstract

[1] Evapotranspiration is integral to studies of the Earth system, yet it is difficult to measure on regional scales. One estimation technique is a terrestrial water budget, i.e., total precipitation minus the sum of evapotranspiration and net runoff equals the change in water storage. Gravity Recovery and Climate Experiment (GRACE) satellite gravity observations are now enabling closure of this equation by providing the terrestrial water storage change. Equations are presented here for estimating evapotranspiration using observation based information, taking into account the unique nature of GRACE observations. GRACE water storage changes are first substantiated by comparing with results from a land surface model and a combined atmospheric-terrestrial water budget approach. Evapotranspiration is then estimated for 14 time periods over the Mississippi River basin and compared with output from three modeling systems. The GRACE estimates generally lay in the middle of the models and may provide skill in evaluating modeled evapotranspiration.

Estimating groundwater storage changes in the Mississippi River basin (USA) using GRACE

“…Error sources not foreseen before launch have impacted the effective resolution, so that based on the analysis of Swenson and Wahr (2006b), the figure may be closer to 500,000 km 2 , if an optimized data filtering and smoothing technique is used. Many studies are now demonstrating the value of GRACE to hydrological research and applications (e.g., Rodell et al 2004b;Chen et al 2005b;Syed et al 2005;Velicogna et al 2005;Swenson and Wahr 2006a). This paper presents a case study of the application of GRACE to the estimation of groundwater storage variability in the Mississippi River basin, USA.…”

Estimating soil moisture storage change using quasi-terrestrial water balance method

“…Limited, inadequate or non-availability of soil moisture and groundwater observations hinder detailed quantification of terrestrial hydrological processes (Rodell et al, 2004a;Alsdorf et al, 2007;Zhang et al, 2008). In especially semi-arid regions where surface water resources are limited, water balance for the terrestrial component of the hydrologic cycle is mainly driven by changes in soil moisture and groundwater; generally quantified as (Strassberg et al, 2007;Swenson et al, 2006;Moiwo et al, 2009;Rodell et al, 2009):…”

“…Note that all the storage change terms here are treated as averages in both time and space (Yeh et al, 1998). The terrestrial component of the hydrologic cycle is likewise expressed in terms of precipitation, evapotranspiration and runoff as (Yeh et al, 1998;Rodell et al, 2004aRodell et al, , 2004bSeneviratne et al, 2004;Moiwo et al, 2011):…”

“…Unlike field surveys, satellite observations provide cost-and labor-effective means of monitoring soil moisture at sufficient spatial and temporal scales (Becker, 2006;Zhao et al, 2010). In fact, there is a huge potential for monitoring soil moisture and other land-state processes from space (Rodell et al, 2004a(Rodell et al, , 2004b. Space-borne or remote sensing (RS)-based data resolutions are often refined for higher sensor accuracies.…”

“…ETWatch is now used in the continuous monitoring of ET in the Hai River Basin (HRB) (Wu et al, 2008b). Hence the advent of RS-based data along with the related energy balance algorithms has greatly enhanced the estimation of ET and other land-surface processes for sustainable hydro-ecological management (Yeh et al, 1998;Rodell et al, 2004aRodell et al, , 2004bZhang et al, 2008).…”