Use of GRACE time-series data for estimating groundwater storage at small scale

Abstract

This study integrates the time series of satellite data, i.e. (terrestrial water storage (TWS) extracted from Gravity Recovery and Climate Experiment (GRACE), soil moisture (SM) from Global Land Data Assimilation System (GLDAS), rainfall from Tropical Rainfall Measuring Mission (TRMM)) with in-situ data, i.e. (groundwater (GW) observatory well data and surface water (SW) as reservoir level from Tamil Nadu Public Work Department (TN PWD)) to estimate the water storage of the study area for the period from 2002 March to 2016 December. The study area encompasses three districts of Tamil Nadu State – Chennai, Kancheepuram and Tiruvallur. It was previously observed that the groundwater level in this study area is decreasing at an alarming rate. Trends and residuals of the times series of all the previously stated components were analyzed. Negative trends were observed in the case of ΔSW, ΔSM, ΔGW, ΔTWS-GRACE, but rainfall shows a slight positive trend. Rainfall, being the input for water storage, a marginal increase in rainfall cannot affect the variability of ΔSM, ΔSW, ΔGW and ΔTWS-GRACE. ΔTWS decreases approximately 0.12 cm yr−1 averaged water level equal to a total volume −7.5 km3. The result of this study shows a decrease in the total storage of groundwater in the study area during the study period from 2002 March to 2016 December. Seawater intrusion due to an increase in sea surface height also shows an impact on ΔTWS derived from grace, in the form of anomalously elevated ΔTWS. A good agreement between ∆TWS-GRACE and ∆TWS-in-situ is found except where sea-water intrusion occurs.