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Several indices show that mean annual runoff in the periods of 1972–1994 and 1995–2010 was 57.25 and 36.03 mm, or 25.78% and 53.29% lower than the 1960–1971 period, respectively (Table 4). By contrast, the precipitation change was smaller, with reductions of 5.32% and 11.23% for the 1972–1994 and 1995–2010 periods, respectively. The variation coefficients of inter-annual (Inter-Cv) runoff and precipitation were not significantly altered, although the inter-annual variability of runoff was higher than that of precipitation. Based on the concentration degree (CD) (Zhang & Qian 2003) and intra-annual variation coefficients (Intra-Cv), there is little change in precipitation but a more obvious change in runoff.

Table 4

Changes of characteristics of runoff and precipitation in 1960–1971, 1972–1994, and 1995–2010 in the WRB

 Runoff
Precipitation
Index1960–19711972–19941995–20101960–19711972–19941995–2010
Average (mm) 77.13 57.25 36.03 585.64 554.49 519.86 
Inter-Cv 0.41 0.40 0.43 0.18 0.16 0.18 
CD (%) 28 32 34 35 35 36 
Intra-Cv 0.78 0.90 0.83 0.94 0.94 0.96 
 Runoff
Precipitation
Index1960–19711972–19941995–20101960–19711972–19941995–2010
Average (mm) 77.13 57.25 36.03 585.64 554.49 519.86 
Inter-Cv 0.41 0.40 0.43 0.18 0.16 0.18 
CD (%) 28 32 34 35 35 36 
Intra-Cv 0.78 0.90 0.83 0.94 0.94 0.96 

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