Multi‐model and multi‐sensor estimations of evapotranspiration over the Volta Basin, West Africa

Abstract

ABSTRACT:The estimation of large-scale evapotranspiration (ET) is complex, and typically relies on the outputs of land surface models (LSMs) or remote sensing observations. However, over some regions of Africa, inconsistencies exist between different estimations of ET fluxes, which should be investigated. In this study, we evaluate and combine different ET estimates from moderate-resolution imaging spectroradiometer (MODIS), Global Land Data Assimilation System (GLDAS) and terrestrial water budget (TWB) approaches over the Volta Basin, West Africa. ET estimates from water balance equation are obtained as residuals from monthly terrestrial water-storage (TWS) changes derived from Gravity Recovery and Climate Experiment (GRACE), Tropical Rainfall Measurement Mission (TRMM)'s rainfall data, and in situ discharge from Akosombo Dam (Ghana). An averaged estimation of ET time series is derived from all the ET estimations under study, while taking into account their uncertainties. The resulting ensemble-averaged ET was then used to assess each of the individual ET estimates. Overall, out of the seven investigated ET estimates (two from the water balance approach of which one considers water storage using GRACE-derived TWS and the other ignoring it, four from GLDAS and one from MODIS), only MODIS (28.12 mm month -1 ), GLDAS-NOAH (32.74 mm month -1 ) and TWB (32.84 mm month -1 ) were found to represent the range of variability close to the computed averaged reference ET (30.25 mm month -1 ). ET estimations inferred from MODIS were also found to represent relatively lower magnitude of uncertainties, that is, 3.99 mm month -1 over the Volta Basin (cf. 7.06 and 18.85 mm month -1 for GLDAS-NOAH and TWB-based ET estimations, respectively).

Characterizing Drought and Flood Events over the Yangtze River Basin Using the HUST-Grace2016 Solution and Ancillary Data

“…responsible for the observed TWS variations [7,16,48,49], a cross-comparison was also implemented between GRACE-derived TWS, TRMM-derived precipitation and NCEP/NCAR-derived vertical velocity. As shown in Figure 11, the consistency between the non-seasonal values can also be seen during the 'universal' drought and flood events.…”

Water Availability of São Francisco River Basin Based on a Space-Borne Geodetic Sensor

“…Therefore, they were replaced by those derived from satellite laser ranging as provided by Cheng and Tapley [42]. Neglecting the degree-1 coefficients would impact the amplitudes of annual and semi-annual variations of TWS estimates [43]. A glacial isostatic adjustment correction has also been applied based on the model provided by Geruo et al [44].…”

Uncertainties of the Gravity Recovery and Climate Experiment time-variable gravity-field solutions based on three-cornered hat method

“…At a basin scale, irrespective of the size and relative signal amplitude, the solutions all vary from the ensemble mean (composed from CSR, JPL, GFZ, and GRGS) on the order of 10 to 15 mm. 18 Efforts have also been made to assess the GRACE-derived TWSA fields; for example, combining measurements and/or models in the context of the water-budget equations [19][20][21][22][23] or in terms of groundwater estimations. 8,[24][25][26] Additionally, direct comparisons with hydrology models, 27,28 remotely sensed rainfall data, 29,30 and ocean-bottom pressure products 31 have been reported.…”