GRACE-based mass conservation as a validation target for basin-scale evapotranspiration in the contiguous United States

Here, we evaluate basin-scale evapotranspiration (ET) estimates for eleven major river basins in the contiguous United States against a water balance approach with Gravity Recovery and Climate Experiment (GRACE) satellite observations. The relatively precise measurements of large-scale changes in water mass from GRACE are used to estimate the storage rate term in the terrestrial water budget and consequently provide anestimate, with propagated uncertainty, of basin-aggregated ET from mass conservation.We apply GRACE-based ET to two modeling systems (NLDAS-2, GLDAS-2.1) comprised of five land surface models and three remote sensing-based products (MOD16, PT-JPL, FLUXCOM) for 2003 to 2014. Both the land surface model-based and remote sensing based ET are persistently lower than GRACE-based ET in all eleven basins tested. W also find that interannual variability is greater for GRACE-ET than the model and remote sensing products, and this is attributed to precipitation variability.

本研究针对美国本土11个主要流域的流域尺度蒸散发（evapotranspiration, ET）估算结果，结合重力恢复与气候实验（Gravity Recovery and Climate Experiment, GRACE）卫星观测数据，采用水量平衡法开展评估。GRACE获取的大尺度水质量变化高精度观测数据，被用于估算陆地水收支中的储水速率项，进而基于质量守恒原理得到流域聚合蒸散发的估算结果，并附带误差传递得到的不确定性。本研究将基于GRACE的蒸散发数据应用于2003至2014年期间的两类建模系统（NLDAS-2、GLDAS-2.1）与三类遥感反演产品（MOD16、PT-JPL、FLUXCOM），其中两类建模系统由5个陆面模式（land surface model）构建而成。在全部11个受试流域中，基于陆面模式与基于遥感反演的蒸散发结果均持续低于基于GRACE的蒸散发结果。本研究同时发现，GRACE衍生蒸散发的年际变率大于各类建模与遥感产品，该现象可归因于降水的年际变化。