Introduction

70% of earth is covered with water, but 1% of fresh water is readily accessible for human beings. For use of 1 % fresh water, 99% is available as ground water resource. When the replenishment amount of groundwater is less than the withdrawal amount, the area will experience the negative change of groundwater storage termed as Groundwater depletion. Due to lack of rainfall, different places of Globe are interacted through scarcity of groundwater. Several regions over the globe are depending on groundwater resources for usage of agricultural, industrial and domestic purposes. Groundwater depletion leads to water scarcity, land subsidence, increment of pumping costs, decrement of water quality, affecting environment, sea level rise. Groundwater replenishment depends on aquifer parameters, geology, soil structure, rainfall and surface water of a particular region. Growth of population and necessities demands preservation of the groundwater resources, which necessitates the groundwater storage. Places of Middle East region, North China, Colorado River basin, Bengal basin, Central valley of California and plain aquifer are experienced under Groundwater depletion since last 15 years. Many places of India are also interacted to deficiency of groundwater. According to Central Ground Water Board (CGWB), our country consuming 230 billion cubic meters of groundwater for irrigation, domestic and industrial purposes annually.
North western states (Rajasthan, Punjab and Haryana) are experienced 4.06±1.0 cm/year of groundwater depletion during study period of August 2002 to October 2008 [1]. The main reason of depletion through evapotranspiration loss is due to high temperatures and hot climatic conditions. Meerut and Lucknow regions have depletion rates of 2.76 ± 0.87 cm/year and 1.46 ± 0.74 cm/year respectively [2] due to the urbanization and land use changes. Kandivalasa River sub basin (Andhra Pradesh) experienced 5.6 MCM of groundwater depletion during 2013-2015 [3]. Depletion rate of groundwater in Tamilnadu during 2002-2012 was observed to be 21.4km3/year [4]. The depletion rate of groundwater happening in India majorly affected due to agriculture. The farmers are depending on groundwater for cultivation in post monsoon kharif and rabi seasons.
In present days, finding groundwater accessibility is not an easy process. It is partly due to the difficulties such as less observing stations, deficiency of insufficient measureable data. Therefore, many scientists have started researching on remote sensing methods to explore more about groundwater. Remote sensing has its own advantages and limitations over the local observed well data. In recent days, researchers using this type of approach and validating the results with local monitoring well data results to know how compatible it is. Most of the studies succeeded to correlate these two methods.
They estimated confining layer depletion, as well as procedures for approximating confining layer hydraulic conductivity and specific storage using geologic information [5]. [6] GRACE, Lake Altimetry, and model soil moisture are included to decrease scaling factor bias and compare estimated groundwater storage changes in East Africa. GRACE is applied to determine extract changes in groundwater storage [7]. Various time series models are applied to forecast groundwater level in Kashan plain, Iran [8]. They projected groundwater storage across Alberta river basin, Canada using an arrangement of GRACE, surface water and GWSAsat data [9]. [10] They highlighted uncertainties in GWD estimating and importance of incorporating prior information to refine spatial patterns of GRACE signals which could be more useful in groundwater resource management. [11] Long-term groundwater storage variation re-assessed in Northwest India using an extended record of GRACE time-variable gravity measurements method. [12] Ability of satellite measurements through GRACE is evaluated to trace seasonality and trend in groundwater storage for Bengal Basin of Bangladesh. [13] Soil moisture and snow by GLDAS is simulated to isolate groundwater storage from GRACE for the Mississippi River basin. [14] Feasibility of downscaling GRACE satellite data is investigated for prediction of changes in groundwater level. [15] Changes in regional groundwater storage in North China from GRACE satellites data and field data from 2003 to 2010 are estimated. [16] Monthly changes in total water storage via GRACE data is appraised across the Middle East.
In the current study, GRACE (as a remote sensing method) and GLDAS is used to evaluate variations in groundwater storing in the Bankura district region of West Bengal during for a period of November 2007 to January 2017.