Reconstructing annual groundwater storage changes in a large-scale irrigation region using GRACE data and Budyko model

Abstract

A two-parameter annual water balance model was developed for reconstructing annual terrestrial water storage change (ΔTWS) and groundwater storage change (ΔGWS). The model was integrated with the Gravity Recovery and Climate Experiment (GRACE) data and applied to the Punjab province in Pakistan for reconstructing ΔTWS and ΔGWS 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 ΔTWS during 2003–2015. The correlation of ensemble means between Budyko-modeled and GRACE-derived ΔTWS is 0.68 with p-value <0.05. The ΔGWS was reconstructed by subtracting soil moisture storage change from the Budyko-modeled ΔTWS 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 ΔGWS during 1980–2015 (i.e., −13.6±9.7cm) indicate that the aquifer in Punjab has experienced depletion. The estimated depletion rate is −0.3±0.2cm/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.