Estimation and Validation of Groundwater Storage Anomalies in the Kwale Aquifer, Kenya: A Case Study on the Applicability of GRACE and GLDAS for Monitoring Groundwater Temporal Variability in Small Coastal Aquifers of Data-Scarce Regions

Maman Moustapha Habiboulaye; John M. Gathenya; John K. Mwangi; Achieng Kevin Otieno

doi:10.48084/etasr.14103

Authors

Maman Moustapha Habiboulaye Department of Civil Engineering, Pan African University Institute for Basic Sciences, Technology and Innovation, Kenya
John M. Gathenya Department of Soil, Water & Environmental Engineering, Jomo Kenyatta University of Agriculture and Technology, Kenya
John K. Mwangi Department of Civil, Construction and Environmental Engineering, Jomo Kenyatta University of Agriculture and Technology, Kenya
Achieng Kevin Otieno Department of Civil Engineering, Dedan Kimathi University of Technology, Kenya

Volume: 15 | Issue: 6 | Pages: 29671-29679 | December 2025 | https://doi.org/10.48084/etasr.14103

Received: 15 August 2025 | Revised: 27 September 2025 | Accepted: 6 October 2025 | Online: 8 December 2025
Corresponding author: Maman Moustapha Habiboulaye

Abstract

Monitoring groundwater variability is essential for sustainable water resource management, particularly in regions with limited in-situ observations. This study evaluated the temporal consistency between Gravity Recovery and Climate Experiment (GRACE) derived Groundwater Storage Anomalies (GWSA) and in-situ measured borehole water levels in Kwale County, Kenya. Monthly GRACE Mascon data (CSR RL06.03) and borehole records (January 2007–December 2023) were standardized to z-scores to remove unit and baseline differences, enabling direct pattern-based comparisons. Pattern agreement was quantified using Pearson's correlation, Spearman's rank correlation, Nash–Sutcliffe Efficiency (NSE), and cross-correlation analysis. The results indicate a statistically significant and moderately strong linear relationship between GRACE and borehole anomalies (r = 0.578, p < 0.001), and a weak but significant monotonic association (ρ = 0.327, p = 0.0033). The positive NSE (0.156) demonstrates that GRACE is capable of capturing month-to-month variability in borehole water levels. Cross-correlation analysis identified the highest correlation at lag 0 months, showing that GRACE and borehole water level records respond concurrently to hydrological changes. The findings confirm that GRACE is capable of reproducing local groundwater variability patterns in Kwale County despite differences in the measurement scale and potential noise in borehole data. The demonstrated agreement supports the application of GRACE as a complementary groundwater monitoring tool in data-scarce regions, thus contributing to improved groundwater resource assessment, management, and protection.

Keywords:

borehole, GRACE, groundwater, GLDAS, satellite

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