Reconstructing annual groundwater storage changes in a large-scale irrigation region using GRACE data and Budyko model
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A two-parameter annual water balance model was developed for reconstructing annual terrestrial water storage change (Delta TWS) and groundwater storage change (Delta GWS). The model was integrated with the Gravity Recovery and Climate Experiment (GRACE) data and applied to the Punjab province in Pakistan for reconstructing Delta TWS and Delta GWS during 1980-2015 based on multiple input data sources. Model parameters were estimated through minimizing the root-mean-square error between the Budyko-modeled and GRACE-derived Delta TWS during 2003-2015. The correlation of ensemble means between Budyko-modeled and GRACE-derived Delta TWS is 0.68 with p-value <0.05. The Delta GWS was reconstructed by subtracting soil moisture storage change from the Budyko-modeled Delta TWS and was validated (i.e., r = 0.74, p-value < 0.05) against well observations during the pre-GRACE period (i.e., 1985-1994). The negative values of the cumulative sum of the reconstructed Delta GWS during 1980-2015 (i.e., -13.6 +/- 9.7 cm) indicate that the aquifer in Punjab has experienced depletion. The estimated depletion rate is -0.3 +/- 0.2 cm/year and it has a negative correlation (i.e., r = -0.70, p-value < 0.0001) with the total number of tube wells installed in Punjab. The integration of the developed Budyko model with GRACE data provides a new way for evaluating long-term groundwater depletion in large-scale irrigation regions with parsimonious models. (C) 2017 Elsevier B.V. All rights reserved.
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