Projections of changes in precipitation Global climate modeling

The impact of human activities on precipitation in the 21st century is more complicated in comparison with temperature, due to a relatively lower capability of global climate models in simulating precipitation, and there are larger differences in the 21st century precipitation projections in China among different models under various emission scenarios.

However, there are also two main experiments to predict the future precipitation changes by Chinese scientists (Li et al, 1995; Chen et al, 1996; and Guo et al, 2001). Table 10.6 gives the predicted precipitation changes in East Asia at doubled CO2 scenario. It can be seen that annual rainfall is all projected to increase, with an averaged 9% increase in East Asia. Differences in projected seasonal precipitation changes show that remarkable increase occurs in the spring and the summer in studies before the mid-1990s, but in recently years, researches indicate the increase occurs mainly in the winter.

Table 10.6 Percentage changes in annual and seasonal precipitation in East Asia at doubled CO2 ( Based on Li et al, 1995; Chen et al, 1996; and Guo et al, 2001, Unit %)

Model

DJF

MAM

JJA

SON

YEAR

LASG/CGCM

-1.3

11.2

14.9

7.6

9.8

LASG/GOLAS

22.0

3.3

-2.1

5.5

5.0

OPYC

7.0

20.3

10.5

6.8

11.2

NCAR

4.8

12.3

13.1

6.9

9.3

MEAN

8.1

11.8

9.1

6.7

8.8

Table 10.7 summarizes projections of the linear trend of annual rainfall in East Asia and China in the 21st century by Chinese meteorologists using multiple climate models in the past 10 years (Luo et al, 2005; Xu et al, 2005; and Jiang et al, 2008a). In general, future precipitation projected by most models shows an increasing trend, but differences in the projections by different models are larger, the linear trends of precipitation changes in the 21st century range from -78 to 286 mm/100yr, and the standard deviation of the linear trends under the A2 scenario reaches 80.5 mm/100yr. However, differences in projections of the linear trends by IPCC AR4 models are obviously reduced, and the linear trends range from 4 to 190 mm/100yr, with a centurial average of 95mm/100yr, 86 mm/100yr, and 56 mm/100yr under the A2, A1B, and B1 scenarios, respectively. The maximum standard deviation of the linear trends under various emission scenarios is only 35mm/100yr. All those suggest that uncertainty in precipitation simulation has been improved in the IPCC AR4 models. According to projections of the IPCC AR4 models under the A2 scenario, the increasing trend of precipitation in China is 11%/100yr in the 21st century, and the annual rainfall increases by about 9% in the late 21st century (2071-2100) relative to the period of 1961 to 1990. And under the B1 scenario, the increasing trend is 7%/100yr. Most IPCC AR4 models project that winter rainfall increases remarkably, for example, under the A2 scenario, the rain fall in the late 21st century increases by an average 23% in winter, and by 4.9% in summer relative to the period of 1961 to 1990, and under the B1 scenario the rainfall increases by 15.3% and 4.5% in winter and summer, respectively.

Table 10.7 Projections of annual rainfall trends (mm/100yr) and their percentages (the ratio of annual rainfall in China to the long-term (1961-1990) averaged annual rainfall over the same region) (%/100yr; in parentheses) under various emission scenarios in China in the 21st century (for East Asia)

Source Model name

GG GS

A2

A1B

B2

B1

CCC

-78

-72

55

8

CCSR

144 84

153

107

88

Luo CSIRO

36

12

91

75

et al., DKRZ

84

48

2005 GFDL

72

36

231

115

HADL

120 120 286

187

NCAR

-48

108

ECHAM4-OPYC

-56

-48

Xu et al., 2005 NCC/IAP T63

24

-60

9.8%*

5.2%*

Above model mean

47

48

127

74

Above model SD

77

61

78

53

CGCM3.1

154 (19)

154 (19)

53 (7)

CNRM-CM3

85 (9)

87

40 (4)

CSIR0-Mk3.0

40 (7)

20 (3)

32 (5)

GFDL-CM2.0

116 (15)

137 (18)

98 (13)

GFDL-CM2.1

124 (16)

38 (5)

45 (6)

Jiang et al., GISS-ER

110 (10)

58 (5)

2008a INM-CM3.0

31 (3)

32 (3)

4 (0)

IPSL-CM4

44 (6)

68 (9)

52 (7)

MIROC3.2(medres)

136 (16)

109 (13)

ECHO-G

62 (9)

41 (13)

UKM0-HadCM3

190 (22)

162 (19)

132 (16)

ECHAM5/MPI-OM

41 (5)

58 (7)

7 (1)

PCM1

53 (6)

77 (9)

IPCC AR4 model mean

95 (11)

86 (10)

56 (7)

IPCC AR4 model SD

35 (6)

23(6)

26 (5)

Ensemble mean

47

48

103

86

74

58

Ensemble SD

77

61

81

23

53

37

Table 10.8 The multi-model ensemble projections of annual and seasonal precipitation percent changes in China for the years 2021 to 2050, 2071 to 2100 relative to the period 1961 to 1990 (Unit %) (multi-model standard deviation in parentheses)

Time period

Annual

A2

A1B

B1

2021-2050

2.8 (6.2)

3.7 (6.3)

3.9 (5.2)

2071-2100

9.0 (10.1)

9.8 (9.6)

7.2 (7.7)

Winter

A2

A1B

B1

2021-2050

11.5 (19.5)

11.9 (19.6)

10.2 (17.3)

2071-2100

22.6 (27.0)

23.2 (26.3)

15.3 (19.1)

Summer

A2

A1B

B1

2021-2050

0.3 (10.8)

1.4 (11.1)

1.3 (9.7)

2071-2100

4.9 (16.5)

6.0 (15.5)

4.5 (12.5)

The geographic distribution of projected precipitation (Fig. 10.5) shows that under different emission scenarios the annual rainfall increases remarkably in North China, Northwest China, and Northeast China, but changes a little in the Yangtze River basin and the region south of the Yangtze River. In the late 21st century (2071-2100), the annual rainfall under the A2 scenario will increase 15% to 21% relative to 1961-1990 in North China, Northwest China, the north of Northeast China, and the south fringe of the Tibetan Plateau and by less than 5% in the region south of the Yangtze River; and under the B1 scenario it increases by nearly 15%, 15%, and 10% in North China, Northwest China, and Northeast China, respectively, and by less than 4% in the south of the Yangtze River. With regard to seasonal changes of projected precipitation, the percentages of precipitation increase in the winter are higher than in the summer (not shown). Under the scenario A2 the winter rainfall increases by more than 30% in most areas north of 35oN, by about 10% in the middle-lower reach of the Yangtze River, and decreases in South China and the south fringe of the Tibetan Plateau; and the summer rainfall increases mostly in the south fringe of the Plateau and the north of Northwest China (10%), but slightly (less than 5%) in Eastern China, and reduces by 10% in the east of Northwest China.

80E 90E 100E 110E 120E 130E

80E 90E 100E 110E 120E 130E (b)

Fig. 10.5 As in Fig. 10.2 except for annual precipitation percentage changes

80E 90E 100E 110E 120E 130E

80E 90E 100E 110E 120E 130E (b)

Fig. 10.5 As in Fig. 10.2 except for annual precipitation percentage changes

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