2.3 Groundwater Resources
The quantity of groundwater resources refers to the annual renewed quantity of groundwater in aquifers，i.e.，recharge from infiltration of precipitation and surface water.Quantity of groundwater resources in mountainous and hilly areas is calculated in terms of groundwater discharges，including river base flow，piedmont lateral seepage discharge，evaporation from water table and net consumption via groundwater abstraction，and total quantity of discharges is taken as the quantity of groundwater resources.The quantity of groundwater resources in plain areas is calculated in terms of groundwater recharges，including recharge by direct precipitation infiltration，recharge by surface water infiltration，recharge by piedmont lateral seepage and recharge by well irrigation，and total recharge minus recharge by well irrigation is taken as the quantity of groundwater resources.The quantity of groundwater resources in a water resources or administrative region is calculated by deducting the overlap between mountainous and hilly areas and plain areas in quantity of groundwater resources from the sum for the two kinds of areas.
In 2012，the national calculation area of shallow groundwater resources with a mineralization degree equal to or less than 2g/L was 8.41 million km2 and the annual quantity of groundwater resources was 829.64 billion m3，2.8%more than annual average.Among the annual quantity of groundwater resources，1.65 million km2 of calculated area of shallow groundwater in plain areas held 184.26 billion m3，and 6.76 million km2 of calculated area of shallow water in mountainous and hilly areas held 676.21 billion m3 and the overlap between them was 30.83 billion m3.
In 2012，the calculation area of shallow groundwater resources in Northern Six Regions in China took 91%of total plain area.The total groundwater recharge was 157.56 billion m3，providing an important source for water supply in northern China.The total groundwater recharges in the plain areas of the northern regions in 2012 were：28.6 billion m3 in the Songhua River；15.14 billion m3 in the Liaohe River；21.34 billion m3 in the Haihe River；15.72 billion m3 in the Yellow River；26.19 billion m3 in the Huaihe River；and 50.57 billion m3 in Northwest Rivers.Of the total groundwater recharge in the plain areas of the northern regions，recharge by direct precipitation infiltration accounted for 52.5%，recharge by surface water infiltration 35.3%，recharge by piedmont lateral seepage 7.5%，and recharge by well irrigation 4.7%.Recharge by direct precipitation infiltration is the major source of groundwater resources in the Huang-Huai-Hai（Yellow-Huaihe-Haihe rivers）plain and the Songhua-Liaohe plain，accounting for about 70%of total recharge；and recharge by surface water infiltration is the major source of groundwater resources in the Northwest Rivers plain，accounting for about 75%of total recharge.See Figure 8 for the composition of groundwater recharge in the plain areas of Northern Six Regions.
Figure 8 Composition of groundwater recharge in the plain areas of Northern Six Regions，2012