The influence of drought and anthropogenic effects on groundwater levels in Orissa, India

Investigating the response of groundwater levels to the extreme weather events provides essential information for sustainable planning and management of water resources. The aim of this study was to identify and quantify the groundwater level trend of the state Orissa (India) to understand the forcing mechanism of droughts in conjunction with the anthropogenic pressure using the non-parametric Mann–Kendall statistical procedure. The pre- and post-monsoon groundwater level records of 1002 monitoring stations during the period 1994–2003 were analyzed. The results show that the drawdowns due to deficient rainfall during dry years, high temperatures, and anthropogenic pressure have not been recovered through the recharge in wet years. However, this study does not determine whether drought, high temperatures or anthropogenic effects have had largest influence on the groundwater levels decline. The cases of significant water table declines are higher in number than those expected to occur by chance. In the pre-monsoon season, 59% of the monitoring stations experienced groundwater declines as against 51% in the post-monsoon season for the study area as a whole. This could be interpreted that the fluctuation is not a part of noise, but that a signal is being identified. Further, the trend result showed wide spatial and seasonal differences. Irrespective of seasons, the consolidated rock formation that covers 80% of the geographical area experienced significant water table decline. However, the semi-consolidated and unconsolidated formations experienced water table decline in the pre-monsoon (summer) season only. The vulnerable sites where the groundwater-level declined significantly were identified so that recharge measures could be taken up.