A GLOBAL HOT SPOT ANALYSIS (GETIS-ORD GI*) OF GROUNDWATER STORAGE CHANGE USING GRACE SATELLITE AND GIS-BASED SPATIAL STATISTICAL ANALYSIS

Global groundwater is declining as a function of over extraction, pollution, and climate change effects on precipitation. While the dwindling of groundwater resources has been noticed, a holistic and accurate assessment of groundwater storage change (GWSC) patterns and distributions has never been conducted given the global scale of the assessment and the paucity of in-situ monitoring data worldwide. Therefore, in this study, alternative remote sensing approaches are utilized to not only delineate the distribution of global GWSC but to also observe the relationships between climatic factors and GWSC.

NASA’s gravity recovery and climate change experiment (GRACE) mission satellite was used to derive GWSC estimates for the purposes of identifying spatial clusters of hot spot (HS) and cold spot (CS) GWSC values. A 3° x 3° grid was utilized to generate GWSC estimates by isolating GLDAS - derived surface water parameters from GRACE-derived total water storage change signal. Resultant GWSC estimates underwent a hot spot (Getis-Ord Gi*) analysis to map statistically significant spatial clusters of GWSC HS/CS with a 99% confidence interval. Moreover monthly TRMM 3B43 were similarly analyzed to produce HS/CS precipitation areas that were compared to GWSC hot spot analysis results.

In Africa, CS were located in Madagascar and the Nile river basin (Z < - 4.1). Alternatively a HS area was established in Angola and Zambia (Z > 5.6). In Asia, CS were primarily centered in Iraq and western Iran, and in Northern India and Nepal (Z < -7.5); whereas HS domains were dispersed in western Turkey, southern India, central Asia region and southeast China (Z > 6). In Europe, CS regions were located in the British Isles, western French coast, eastern Ukraine, and southwestern Russia (Z < - 3.28). Contrastingly, HS areas were located primarily in southeast Europe, and in Portugal and southern Spain (Z > 4). In Australia, the CS area is in northwestern Australia (Z < - 8.3); whereas a HS area was established on the central eastern coast (Z > 7). Precipitation and GWSC HS analysis results displayed direct correspondence in several cases (e.g. Nile river basin and eastern Ukraine), while a few areas displayed a disassociation (e.g. Portugal and southern Spain, northwestern Australia), thus indicating an influence of anthropogenic factors on GWSC.