Girotto Manuela, De Lannoy Gabriëlle J M, Reichle Rolf H, Rodell Matthew, Draper Clara, Bhanja Soumendra N, Mukherjee Abhijit
Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, MD, USA.
GESTAR, Universities Space Research Association, Columbia, MD 21044, USA.
Geophys Res Lett. 2017 May 16;44(9):4107-4115. doi: 10.1002/2017GL072994. Epub 2017 Apr 24.
This study investigates some of the benefits and drawbacks of assimilating Terrestrial Water Storage (TWS) observations from the Gravity Recovery and Climate Experiment (GRACE) into a land surface model over India. GRACE observes TWS depletion associated with anthropogenic groundwater extraction in northwest India. The model, however, does not represent anthropogenic groundwater withdrawals and is not skillful in reproducing the interannual variability of groundwater. Assimilation of GRACE TWS introduces long-term trends and improves the interannual variability in groundwater. But the assimilation also introduces a negative trend in simulated evapotranspiration whereas in reality evapotranspiration is likely enhanced by irrigation, which is also unmodeled. Moreover, in situ measurements of shallow groundwater show no trend, suggesting that the trends are erroneously introduced by the assimilation into the modeled shallow groundwater, when in reality the groundwater is depleted in deeper aquifers. The results emphasize the importance of representing anthropogenic processes in land surface modeling and data assimilation systems.
本研究探讨了将重力恢复与气候实验（GRACE）的陆地水储量（TWS）观测数据同化到印度陆面模型中的一些利弊。GRACE观测到印度西北部与人为地下水开采相关的TWS消耗。然而，该模型并未体现人为地下水抽取情况，在再现地下水年际变化方面也缺乏技巧。同化GRACE TWS数据引入了长期趋势，并改善了地下水的年际变化。但这种同化也在模拟蒸散中引入了负趋势，而实际上灌溉可能会增强蒸散，这在模型中也未体现。此外，浅层地下水的实地测量未显示出趋势，这表明这些趋势是在同化过程中错误地引入到模拟的浅层地下水中的，而实际上更深层含水层中的地下水正在减少。研究结果强调了在陆面建模和数据同化系统中体现人为过程的重要性。
