Downscaling GRACE-scale groundwater storage variations to aquifer scales: A linear regression approach based on the water balance conceptRéduction d’échelle des variations du stockage d’eau souterraine de l'échelle GRACE aux échelles des aquifères : une approche de régression linéaire basée sur le concept de bilan hydriqueVariaciones del almacenamiento de aguas subterráneas a escala GRACE a la escala de los acuíferos: Un enfoque de regresión lineal basado en el concepto de balance hídrico利用基于水均衡的线性回归方法的地下水储量从GRACE尺度到含水层尺度的降尺度Redução de escala de variações de armazenamento de água subterrânea em escala GRACE para escalas de aquíferos: Uma abordagem de regressão linear baseada no conceito de balanço hídrico

A method to downscale annual groundwater storage variations from large-scale, satellite-derived estimates to individual aquifers is presented, employing a simple linear regression approach based on the water balance principle. The method relies on groundwater storage changes derived from the gravity recovery and climate experiment (GRACE). Seven alluvial aquifers, ranging in area from approximately 145 to 1300 km2 in Fars Province, Iran, were selected as case studies to evaluate the applicability of the proposed downscaling method. The results indicate that groundwater storage at the GRACE scale (~ 31,416 km2) has depleted by 229 million cubic meters (MCM) per year during the study period (2002–2015). The correlation coefficients between downscaled and actual groundwater storage depletions varies from 0.655 to 0.891, with an average of ~ 0.82 across the seven aquifers, demonstrating the method’s ability to provide acceptable downscaling results. Downscaling results indicate that the alluvial aquifers of Aspas, Namdan, Beiza-Zarghan, Dehbid, Abadeh-Eghlid, Bakan, and Sidan-Farugh have experienced groundwater storage depletions of 17.71, 34.49, 46.21, 13.88, 14.11, 6.78, and 22.62 MCM per year, respectively, from 2002 to 2015, which correspond to water table declines of 0.915, 0.656, 0.822, 0.538, 0.725, 1.395, and 1.435 m/year, respectively. As a final point, this study proposes a downscaling method that can be applied to address groundwater storage variations at aquifer scales, particularly in regions with unavailable or limited data.