remote sensing Article Groundwater Depletion in the West Liaohe River Basin, China and Its Implications Revealed by GRACE and In Situ Measurements Yulong Zhong 1,2 ID , Min Zhong 1,2, Wei Feng 1,* ID , Zizhan Zhang 1, Yingchun Shen 1,2 and Dingcheng Wu 1,2 1 State Key Laboratory of Geodesy and Earth’s Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China; [email protected] (Y.Z.); [email protected] (M.Z.); [email protected] (Z.Z.); [email protected] (Y.S.); [email protected] (D.W.) 2 University of Chinese Academy of Sciences, Beijing 100049, China * Correspondence: [email protected]; Tel.: +86-27-6888-1997 Received: 30 January 2018; Accepted: 19 March 2018; Published: 21 March 2018 Abstract: The West Liaohe River Basin (WLRB) is one of the most sensitive areas to climate change in China and an important grain production base in the Inner Mongolia Autonomous Region of China. Groundwater depletion in this region is becoming a critical issue. Here, we used the Gravity Recovery and Climate Experiment (GRACE) satellite data and in situ well observations to estimate groundwater storage (GWS) variations and discussed the driving factors of GWS changes in the WLRB. GRACE detects a GWS decline rate of −0.92 ± 0.49 km3/yr in the WLRB during 2005–2011, consistent with the estimate from in situ observations (−0.96 ± 0.19 km3/yr). This long-term GWS depletion is attributed to reduced precipitation and extensive groundwater overexploitation in the 2000s. Long-term groundwater level observations and reconstructed total water storage variations since 1980 show favorable agreement with precipitation anomalies at interannual timescales, both of which are significantly influenced by the El Niño-Southern Oscillation (ENSO). Generally, the WLRB receives more/less precipitation during the El Niño/La Niña periods. One of the strongest El Niño events on record in 1997–1998 and a subsequent strong La Niña drastically transform the climate of WLRB into a decade-long drought period, and accelerate the groundwater depletion in the WLRB after 1998. This study demonstrates the significance of integrating satellite observations, ground-based measurements, and climatological data for interpreting regional GWS changes from a long-term perspective. Keywords: groundwater storage; terrestrial water storage; satellite gravimetry; GRACE; reduced precipitation; groundwater overexploitation; West Liaohe River; ENSO 1. Introduction Groundwater, as an important component of total terrestrial water storage (TWS), plays a key role in the global water cycle. Overuse of groundwater has caused various environmental problems in many places globally, e.g., desiccation of Lake Urmia, groundwater depletion in Northwest India and in the California Central Valley, and land subsidence in the North China Plain [1–5]. However, monitoring groundwater storage (GWS) is limited in many regions [6]. The absence of in situ monitoring well networks, low-quality observation data, and uncertainties in storage coefficients (i.e., specific yield, Sy) for translating groundwater level changes to groundwater storage variations restrict our knowledge of GWS changes [7,8]. Remote Sens. 2018, 10, 493; doi:10.3390/rs10040493 www.mdpi.com/journal/remotesensing Remote Sens. 2018, 10, 493 2 of 16 Since its launch in 2002, the Gravity Recovery and Climate Experiment (GRACE) mission has provided a unique way to monitor TWS changes at a monthly scale and with a ~300 km footprint [9–11]. Furthermore,Remote Sens. it 2018 can, 10 be, x FOR used PEER to estimateREVIEW GWS changes when other TWS components can be removed2 of 16 or neglected. Many studies have compared the GRACE-derived GWS changes with independent in situ groundwater11]. Furthermore, monitoring it can observations be used to inestimate many partsGWS ofcha thenges world. when Atother the TWS early component stage, Rodells can et be al. [12] and Strassbergremoved or et neglected al. [13] found. Many good studies agreement have compared between the the GRACE GWS estimates-derived GWS from changes GRACE with and the Globalindependent Land Data in Assimilation situ groundwater System monitoring (GLDAS) observations model and in many those parts from ofin the situ world.measurements At the early in the Mississippistage, Rodell River et basin al. [12] and and the Strassberg High Plains et al. [13] Aquifer, found USA, good respectively.agreement between Subsequently, the GWS estimates a number of from GRACE and the Global Land Data Assimilation System (GLDAS) model and those from in situ studies have demonstrated the potential of GRACE to estimate GWS depletion in many regional basins, measurements in the Mississippi River basin and the High Plains Aquifer, USA, respectively. e.g., northwestern India [2,14–17], California’s Central Valley, USA [3,18,19], the North China Plain Subsequently, a number of studies have demonstrated the potential of GRACE to estimate GWS (NCP)depletion [20–22], in and many the regional Middle Eastbasins, [23 e.g.,]. northwestern India [2,14–17], California’s Central Valley, TheUSA West[3,18,19] Liaohe, the North River China Basin Plain (WLRB), (NCP) which[20–22], isand located the Middle in Northeast East [23]. China (Figure1) and is known asThe the West “Granary Liaohe of River Inner Basin Mongolia”, (WLRB) is, awhich major is grain-producinglocated in Northeast region China in China,(Figure with1) and a rapidlyis growingknown population as the “Granary since 1950 of Inner [24,25 Mongolia”,]. The basin is isa inmajor the transitiongrain-producing zone betweenregion in the China, Inner with Mongolia a Plateaurapidly and growing the Songliao population Plain. since The 1950 western [24,25]. partThe basin of the is in basin the transition is the south zone ofbetween the Great the Inner Khingan Mountains,Mongolia while Plateau the easternand the partSongliao is the Plain. plain The area western (Figure part1). Theof the WLRB basin isis alsothe south the upstream of the Great portion of theKhingan Liaohe Mountains River and, while overlies the aeastern Quaternary part is the loose plain rock area pore (Figure aquifer, 1). The where WLRB extensiveis also the upstream groundwater portion of the Liaohe River and overlies a Quaternary loose rock pore aquifer, where extensive exploitation occurs. Land use in the WLRB is primarily grassland and cropland, with some tree groundwater exploitation occurs. Land use in the WLRB is primarily grassland and cropland, with coveredsome land tree in covered the mountain land in the region mountain (Figure region S1). (Figure S1). Figure 1. Map of the West Liaohe Basin (WLRB, black boundary). The main rivers are shown in blue. Figure 1. Map of the West Liaohe Basin (WLRB, black boundary). The main rivers are shown in blue. The observation wells are shown as circles. The colors represent the groundwater level trends from The observation wells are shown as circles. The colors represent the groundwater level trends from 2005 to 2011. The insert map shows the location of the WLRB (red shade) in China. 2005 to 2011. The insert map shows the location of the WLRB (red shade) in China. The WLRB is located in a semi-arid region, with an area of 136,000 km2. It has a continental Theclimate WLRB that isexperien locatedces in dry a semi-arid and windy region, spring with conditions, an area ofhot 136,000 and humid km2. summers, It has a continental cool autumn climate that experiencesconditions, and dry cold and winters windy with spring little conditions, snow. As a semi hot and-arid humidregion, mean summers, annual cool precipitation autumn conditions,of the WLRB is 392 mm (1961 to 2015) and ranges from 260 to 540 mm. Annual precipitation is spatially and cold winters with little snow. As a semi-arid region, mean annual precipitation of the WLRB is variable, with less precipitation in the central plain (see Figure S2). About 80% of the precipitation 392 mm (1961 to 2015) and ranges from 260 to 540 mm. Annual precipitation is spatially variable, occurs in summer (June to September) [26,27]; while the potential evaporation ranges from 1190 to with1860 less precipitationmm, which greatly in the exceeds central precipitation plain (see [24,28] Figure. Since S2). 1980, About the 80% surface of theflow precipitation of the West Liaohe occurs in summerRiver (June began to to September) decline, and [26 it, 27nearly]; while dried the up potential since 2000 evaporation [24,29,30]. Water ranges storage from 1190in lakes to 1860 and mm, whichreservoirs greatly also exceeds decreased precipitation significantly [24 after,28]. 1999 Since [31] 1980,. Groundwater the surface has flow become of thea vital West resource Liaohe for River beganagricultural, to decline, industrial and it nearly, and drieddomestic up water since 2000use in [ 24the,29 WLRB,30]. Water[32]. Most storage area ins of lakes the andWLRB reservoirs are also decreasedequipped for significantly irrigation with after groundwater 1999 [31]. Groundwater[32], which accounted has become for ~80% a vital of the resource total water for agricultural,supply industrial,during and2005 domesticto 2015. Thus, water it is use crucial in the to ev WLRBaluate [the32 ].state Most of groundwater areas of the resources WLRB arein the equipped WLRB for irrigationfor the with development groundwater of sustainable [32], which agriculture accounted and for ~80%the preservation of the total of water terrestrial supply ecosystems. during 2005 to Groundwater level declines in the WLRB within the past two decades have been reported by several 2015. Thus, it is crucial to evaluate the state of groundwater resources in the WLRB for the development studies [33–36], e.g., with a rate of ~−0.18 m/yr from 1999 to 2010 [29]. Average groundwater levels in of sustainable agriculture and the preservation of terrestrial ecosystems. Groundwater level declines three main counties of the WLRB in 2006 decreased by 3.8 m, 2.8 m, and 1.9 m, respectively, when Remote Sens.