Characterizing rainfall-groundwater dynamics in a hard-rock aquifer system using time series, geographic information system and geostatistical modelling

The aim of this study was to investigate rainfall-groundwater dynamics over space and annual time scales in a hard-rock aquifer system of India by employing time series, geographic information system and geostatistical modelling techniques. Trends in 43-year (1965-2007) annual rainfall time series of ten rainfall stations and 16-year (1991-2006) pre-monsoon and post-monsoon groundwater levels of 140 sites were identified by using Mann-Kendall, Spearman rank order correlation and Kendall rank correlation tests. Trends were quantified by Kendall slope method. Furthermore, the study involves novelty of examining homogeneity of pre-monsoon and post-monsoon groundwater levels, for the first time, by applying seven tests. Regression analysis between rainfall and post-monsoon groundwater levels was performed. The pre-monsoon and post-monsoon groundwater levels for four periods - 1991-1994, 1995-1998, 1999-2002 and 2003-2006 - were subjected to geographic information system-based geostatistical modelling. The rainfall showed considerable spatiotemporal variations, with a declining trend at the Mavli rainfall station (p-value<0.05). The Levene's tests revealed spatial homogeneity of rainfall at =0.05. Regression analyses indicated significant relationships (r(2)>0.5) between groundwater level and rainfall for eight rainfall stations. Non-homogeneity and declining trends in the groundwater level, attributed to anthropogenic and hydrologic factors, were found at 5-61 more sites in pre-monsoon compared with post-monsoon season. The groundwater declining rates in phyllite-schist, gneiss, schist and granite formations were found to be 0.18, 0.26, 0.21 and 0.14myear(-1) and 0.13, 0.19, 0.16 and 0.02myear(-1) during the pre-monsoon and post-monsoon seasons, respectively. The geostatistical analyses for four time periods revealed linkages between the rainfall and groundwater levels. Copyright (c) 2013 John Wiley & Sons, Ltd.