2.4 Total Quantity of Water Resources
Total quantity of water resources refers to the total quantity of surface water and groundwater yields formed by local precipitation，i.e.，sum of surface runoff and groundwater recharge by direct precipitation infiltration.It can be calculated either as the sum of quantities of surface water resources and groundwater resources minus the overlap between them，or as the sum of quantity of surface water resources and quantity of groundwater resources non-overlapping with surface water.
In 2012，the total quantity of water resources in China was 2，952.88 billion m3，6.6%more than normal.The quantity of groundwater resources non-overlapping with surface water was 115.55 billion m3，accounting for 13.9%of groundwater resources，which means that 86.1%of the groundwater resources overlapped with surface water.The total quantity of water resources accounted for 45.3%of the total precipitation，and the average water yield per square kilometer was 312，000 m3 in the country.
Table 5 shows total quantities of water resources in the Class Ⅰ WRR and Figure 9 shows comparison with normal.The total quantity of water resources in Northem Six Regions in 2012 was 563.9 billion m3，which was 7.2%more than normal and accounted for 19.1%of the national total；and the total quantity of Water resources in Southern Four Regions was 2，388.98 billion m3，which was 6.4%more than normal and accounted for 80.9%of the national total.
Table 5 Total quantities of water resources in Class Ⅰ WRR，2012 Unit：billion m3
Table 6 Total quantities of water resources in PAR，2012 Unit：billion m3
Figure 9 Total quantities of water resources and comparison with normal in Class Ⅰ WRR，2012
Note：The Yangtze includes the Taihu Lake Basin.
Figure 10 Total quantities of water resources and comparison with normal in PAR，2012
（Unit：billion m3）
Table 6 shows the 2012 total quantities of water resources in the PAR and Figure 10 shows comparison with normal.The total quantity of water resources in eastern China in 2012 was 688.58 billion m3，24.6%more than normal，accounting for 23.3%of the national total；that in central China was 735.19 billion m3，9.1%more than normal，24.9%of the national total；and that in western China was l，529.11 billion m3，1.0%less than normal，51.8%of the national total.
Figure 11 shows the variation processes of total quantities of water resources in China during 1997～2012.In China，the total quantity of water resources was 22.8%，11.5%and 6.6%more than normal in 1998，2010 and 2012，respectively，8.6%～16.1%less than normal in 2004，2006，2007，2009 and 2011，and within 3%of normal in the rest years；in Southern Four Regions，the total quantity of water resources was 20.9%and 10.7%more than normal in 1998 and 2010，respectively，and 13.0%～18.3%less than normal in 2004，2009 and 2011；and，in Northern Six Regions，except that 1998，2003，2005，2010 and 2012 saw a total quantity of water resources 7.2%～30.6%more than normal，all the other years experienced a total quantity of water resources less than normal to a varying extent，in which 2002 saw a total quantity of water resources 20.9%less than normal.
Figure 11 Variation processes of total quantities of water resources in China，1997～2012
