Quantifying the link between crop production and mined groundwater irrigation in China

Danielle S. Grogan, Fan Zhang, Alexander Prusevich, Richard B. Lammers, Dominik Wisser, Stanley Glidden, Changsheng Li, Steve Frolking
2015 Science of the Total Environment  
In response to increasing demand for food, Chinese agriculture has both expanded and intensified over the past several decades. Irrigation has played a key role in increasing crop production, and groundwater is now an important source of irrigation water. Groundwater abstraction in excess of recharge (which we use here to estimate groundwater mining) has resulted in declining groundwater levels and could eventually restrict groundwater availability. In this study we used a hydrological model,
more » ... Mplus, in conjunction with a process based crop growth model, DNDC, to evaluate Chinese agriculture's recent dependence upon mined groundwater, and to quantify mined groundwater-dependent crop production across a domain that includes variation in climate, crop choice, and management practices. This methodology allowed for the direct attribution of crop production to irrigation water from rivers and reservoirs, shallow (renewable) groundwater, and mined groundwater. Simulating 20 years of weather variability and circa year 2000 crop areas, we found that mined groundwater fulfilled 20% -49% of gross irrigation water demand, assuming all demand was met. Mined groundwater accounted for 15% -27% of national total crop production. There was high spatial variability across China in irrigation water demand and crop production derived from mined groundwater. We find that climate variability and mined groundwater demand do not operate independently; rather, years in which irrigation water demand is high due to the relatively hot and dry climate also experience limited surface water supplies and therefore have less surface water with which to meet that high irrigation water demand. -4 - [Molden et al., 2007] . Global multi-model projections of irrigation water availability show significant reduction in Northern China for irrigation potential from renewable surface water by 2100 due to climate change (using a scenario of high greenhouse gas emissions (RCP8.5) [Elliott et al., 2013]. Aquifer depletion could also significantly decrease irrigation water availability in the future. Despite the importance of groundwater and groundwater depletion for the future of Chinese agriculture, it is currently unknown how much food is produced as a direct result of irrigation with non-renewable groundwater mining. Konikow and Leake (2014) show that groundwater depletion is a combination of decreasing aquifer storage and capture of water from subsurface storage. Over time, the relative proportion of storage reduction to water capture changes, and increases in subsurface water capture can reduce baseflow in rivers [Konikow and Leake, 2014] . Previous research on groundwater in China has shown that groundwater pumping has indeed lead to capture of baseflow, with implications not only for water quantity but also water quality. In the Hai River Basin in northeastern China, groundwater depletion has been identified as the cause of 40% of waterways drying up, and the disappearance of 194 natural lakes and depressions [Jiang, 2009]. A multimodel study of the Baiyangdian Lake catchment in northern China shows that increased exploitation of water resources over the past 50 years has lead to depletion of both groundwater and surface water levels [Moiwo et al., 2010] . In the Shiyang River Basin in northwest China, localized regions have experienced groundwater level decreases of up to 14 meters, and seasonal drying up of river beds [Kang et al., 2009] . Downstream sections of this basin have become significantly salinized over the past 50 years, and measured total dissolved solids in well water has increased three-fold [Kang et al., 2009] . Salinization due to diminished groundwater Large-scale surface water balance models can simulate the use of both surface water and groundwater for irrigation. Several model-based estimates of irrigation water demand in China have been made, ranging from 220 to 850 km 3 yr −1 , circa 2000 [Wisser et al., 2008 , with most estimates in the range of 350 -500 km 3 yr −1 [Döll and Siebert, 2002; Siebert and Döll, 2007; Wada et al., 2012] . These estimates are from a range of hydrology model studies, which used the Water Balance Model [Wisser et al., 2008] , the Water-Global Assessment and Prognosis (WaterGAP) model [Döll and Siebert, 2002], the GID-based Environmental Policy Integrated Climate (GEPIC) model [Liu and Yang, 2010], the Global Crop Water Model (GCWM) [Siebert and Döll, 2010], and the PCR-Global Water Balance (PCR-GLOBWB) model [Wada et al., 2012]. The proportion of irrigation water demand fulfilled by mined groundwater pumping is less well constrained. Groundwater (both renewable and mined in excess of recharge) provides up to 40% of China's irrigation water, and model results from Wada et al. [2012] show that 20 km 3 yr −1 (5% of irrigation demand) is drawn from nonrenewable groundwater. Water supply alone does not determine food production; cropped areas, crop choice, soil quality, and management practices all contribute [Tilman et al., 2002; Foley et al., 2012]. Agriculture's vulnerability to changes in water supply will necessarily also depend on these factors, which all vary spatially across China.
doi:10.1016/j.scitotenv.2014.11.076 pmid:25544335 fatcat:ryw7xfxasrcqtnxjib44xjiuhm