Scaling methods of leakage correction in GRACE mass change estimates revisited for the complex hydro-climatic setting of the Indus Basin

[摘要] Total water storage change (TWSC) reflects the balance ofall water fluxes in a hydrological system. The Gravity Recovery and ClimateExperiment/Follow-On (GRACE/GRACE-FO) monthly gravity field models,distributed as spherical harmonic (SH) coefficients, are the only means ofobserving this state variable. The well-known correlated noise in theseobservations requires filtering, which scatters the actual mass changes fromtheir true locations. This effect is known as leakage. This study exploresthe traditional basin and grid scaling approaches, and develops a novelfrequency-dependent scaling for leakage correction of GRACE TWSC in aunique, basin-specific assessment for the Indus Basin. We harness thecharacteristics of significant heterogeneity in the Indus Basin due toclimate and human-induced changes to study the physical nature of thesescaling schemes. The most recent WaterGAP (WaterGlobal Assessment and Prognosis) hydrology model (WGHM v2.2d)with its two variants, standard (without glacier mass changes) andIntegrated (with glacier mass changes), is used to derive scaling factors.For the first time, we explicitly show the effect of inclusion or exclusionof glacier mass changes in the model on the gridded scaling factors. Theinferences were validated in a detailed simulation environment designedusing WGHM fields corrupted with GRACE-like errors using full monthly errorcovariance matrices. We find that frequency-dependent scaling outperformsboth basin and grid scaling for the Indus Basin, where mass changes ofdifferent frequencies are localized. Grid scaling can resolve trends fromglacier mass loss and groundwater loss but fails to recover the smallseasonal signals in trunk Indus. Frequency-dependent scaling can provide arobust estimate of the seasonal cycle of TWSC for practical applicationssuch as regional-scale water availability assessments. Apart from thesenovel developments and insights into the traditional scaling approach, ourstudy encourages the regional scale users to conduct specific assessmentsfor their basin of interest.

[学科分类] 妇产科学