3 Water Storage
3.1 Large and Medium-sized Reservoirs
According to statistics on 583 large-sized reservoirs and 3，271 medium-sized reservoirs in China，the total year-end water storage in reservoirs was 365.62 billion m3 in 2012，or 29.76 billion m3 more than the year-beginning value，in which the large-sized reservoirs held 324.06 billion m3，which was 25.64 billion m3 more than the year-beginning value and the medium-sized reservoirs held 4 1.56 billion m3，4.12 billion m3 more than the year-beginning value.
Among the Class Ⅰ WRRs，the Huaihe and Northwest Rivers experienced decreased water storage by 2.54 billion m3 and 0.72 billion m3，respectively.The rest of 8 Class Ⅰ WRRs experienced increase to a varying extent，in which the Pearl and the Yangtze experienced increases of 12.08 billion m3 and 7.05 billion m3，respectively.The total year-end reservoir water storage in Northern Six Regions was 5.73 billion m3 more than the year-beginning value and that in Southern Four Regions 24.03 billion m3 less than the year-beginning value.See Figure 12 for the changes in water storage of large-and medium-sized reservoirs in Class Ⅰ WRR in 2012.
Figure 12 Changes in water storage of large-and medium-sized reservoi rs in Class Ⅰ WRR，2012
By comparing the year-end reservoir water storage with the year-beginning value by PAR，it can be seen that reservoir water storage increased in 19 PARs，including Guangxi，Hunan，Guizhou，Jilin，etc.，by a total quantity of 42.39 billion m3；decreased in 9 PARs，including Hubei，Henan，Shandong，Hainan，etc.，by a total quantity of 12.63 billion m3；and did not change in Tibet and Ningxia.See Figure 13 for the changes in water storage of large-and medium-sized reservoirs in PAR in 2012.
Figure 13 Changes in water storage of large-and medium-sized reservoirs in PAR，2012