According to legend, China was born in a huge flood—but today the northern part of the country is starved for water. Beijing, China’s capital city, is located in this arid region, and the megacity supports its 22 million residents with increasingly limited water sources. Only 100 cubic meters is available per person per year—anything less than 1,000 cubic meters per capita annually is considered “water scarce” by United Nations standards.
Beijing has come to rely more and more on groundwater, which currently makes up more than 70% of its total water supply. Because the population of the city is expected to rocket to more than 50 million by 2050, management of this subterranean resource is both critical and complex.
In a new study, Hyndman et al. provide a novel glimpse into the dynamics of the groundwater system beneath the megacity. The researchers created a model that takes into account Beijing’s developing landscape and found that urbanization has increased the recharge of groundwater.
The key factor is land use change. Urban development has edged large water consumers like agriculture and industry out of Beijing’s municipality. An urban landscape not only uses less water than agriculture but also loses less to evapotranspiration, the phenomenon that occurs when water evaporates from the soil or is drawn up from the ground by plants and transpired from their leaves.
The research team’s model of Beijing’s water system provides a better fit to observations than previous groundwater models. It integrates data on the water used by plants in different stages of growth, hydrology and topography, population growth, water use, temperature and precipitation, and other factors that influence groundwater recharge. Essentially, the researchers modeled the interactions between human water use and environmental factors to create a holistic picture of the real-world water system.
The researchers hope that their model, which may be applied to other groundwater systems around the globe, will inform policy makers about the long-term effects of policy decisions.
Although urbanization has improved Beijing’s groundwater recovery, it has not solved the megacity’s water woes. The greater recovery rate still does not ensure enough water to meet demand or even offset the steady decline of groundwater in the area. Further, runoff from city surfaces often contributes to the pollutants already troubling China’s water sources.
The city is desperately striving to meet its water demands through various methods, including improvement of wastewater treatment and engineering projects to divert water from the Yangtze River in the southern part of the country. As efforts to solve the water crisis continue, this model is a useful tool to better understand water conditions and changes in Beijing. (Geophysical Research Letters, https://doi.org/10.1002/2017GL074429, 2017)
—Elizabeth Thompson, Staff Writer