中国科学院东亚区域气候 -环境重点实验室

Effects of Site-Change and Urbanisation in the Beijing Temperature Series 1977-2006

Li Zhen

Key Laboratory of Regional Climate-Environment in Temperate East Asia

Institute of Atmospheric Physics, Chinese Academy of Sciences

26 – 30 May 2008, Budapest, Hungary

Outline

Introduction Data sets Methods Results Conclusions

1. IntroductionThe Beijing station was moved from its suburban location (Daxing district) to an urban location (Beiwa road in Haidian district ) on 1/1/1981 and back on 1/7/1997.

The aims of the present study are:

Analyze and adjust site change effects in BJ temperature series

Estimate an urbanisation-related warming bias.

2.Datasets

1 1 5 . 6 1 1 5 . 8 1 1 6 1 1 6 . 2 1 1 6 . 4 1 1 6 . 6 1 1 6 . 8 1 1 7 1 1 7 . 2 1 1 7 . 4

3 9 . 6

3 9 . 8

4 0

4 0 . 2

4 0 . 4

4 0 . 6

4 0 . 8

4 1

T H

M S

Y QM Y

P G

H R

S Y

T ZC Y

D XF SX Y

Z T

C P

H D

F TM T

S JB J

M a p o f g r e a t e r B e i j i n g

2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 00

2 0

4 0

6 0

8 0

Figure 1. Locations of 19 stations in the larger Beijing area used in the present study.The bold are 4 core reference stations (CRS) , the Italic fonts indicate 5 rural stations.

Table1. Basic information of Beijing (BJ) and 18 nearby stations with daily temperature data back to 1977 or earlier. Italic are rural stations with less-than-18K population and bold are 4 core reference stations for site-change adjustments at BJ. Correlation coefficients with BJ for 3 sub-periods (c1 for 1977-1980, c2 for 1981-1997 and c3 for 1997-2006) are calculated based on seasonal mean temperature anomalies.

Abbrev.(name)

Lon.E / Lat.N/ Elev.m

Distance to BJ (km)

Population(K)

Correlation with BJ ( c1/c2/c3)

Relocation records

BJ (Beijing)

116.28° / 39.93°/ 54.7

- 1556 - Moved to Haidian on 01/01/1981Back to Daxing on 01/07/1997

FS(Fangshan)

116.00° / 39.7°/ 48.9

33.09 347 0.98/0.96/0.95 Moved within Fanshan District on 01/01/1965

TZ(Tongzhou)

116.63° / 39.92°/ 26.9

38.90 269 0.99/0.96/0.98 Moved within Tongzhou District on 01/01/1965

MY(Miyun)

116.87° / 40.38°/ 73.1

69.27 151 0.97/0.97/0.94 No change since 01/01/1957 but data are only available from 1971

PG(Pinggu)

117.10°/40.15°/ 29.4

91.78 4.1 0.98/0.95/0.90 Moved within Pinggu District on 01/01/1977

TH(Tanghekou)

116.63° / 40.73°/ 333.7

55.51 7.1 0.95/0.94/0.96 No change since 01/01/1974 in Huairou District.

XY(Xiayunling)

115.73° / 39.73°/ 409.1

61.89 10.3 0.96/0.89/0.89 No change since 01/02/1959 at Xiayunling, Fangshan District

ZT(Zhaitang)

115.68° / 39.97°/ 441.1

66.70 17.2 0.97/0.86/0.90 No change since 01/01/1974 at Zhaitang, Mentougou District

MS (MiyunShangdianzi)

117.12° / 40.65°/ 286.5

100.02 17.7 0.95/0.94/0.88 No change since the beginning on 01/01/1958

HD(Haidian)

116.28° / 39.98°/ 46.3

2.46 1807 0.98/0.99/0.91 Moved within Haidian District on 01/04/1974

FT(Fengtai)

116.25° / 39.87°/ 56.3

4.45 842 0.96/0.97/0.93 Moved within Fengtai District on 01/01/1978

DX(Daxing)

116.33° / 39.75°/ 41.3

10.46 227 0.96/0.99/0.80 Moved to Huangcun town, Daxing Disrict on 01/01/1978

SJ(Shijingshan)

116.18° / 39.93°/ 70.8

11.11 350 0.97/0.98/0.96 Moved within Shijingshan District on 01/01/1998

CP(Changping)

116.22° / 40.22°/ 79.7

15.74 257 0.96/0.96/0.96 Moved within Changping District on 01/01/1980

MT(Mentougou)

116.12° / 39.92°/ 93.6

17.79 177 0.98/0.97/0.95 Moved within Mentougou District on 01/01/1978

CY(Chaoyang)

116.48° / 39.95°/ 36.5

22.25 1556 0.98/0.98/0.96 Moved within Chaoyang District on 01/04/1961

SY(Shunyi)

116.63° / 40.12°/ 39.5

40.01 207 0.98/0.99/0.90 Moved within Shunyi District on 01/01/1999

YQ(Yanqing)

115.97° / 40.45°/ 489

42.83 97 0.95/0.94/0.96 Moved within Yanqing District on 01/01/1988 and 01/05/2000

HR(Huairou)

116.63° / 40.32°/ 60.6

43.42 107 0.97/0.97/0.94 Moved within Huairou on 01/07/1996

3.Methods

1 2 11 1

1( )

L n L

i ji L j L n

x xn

21 1

1( )

L n L

i ji L j L n

y yn

x denotes a daily temperature anomaly at BJ;

y denotes a (mean) daily anomaly at a (set of) reference station (s);

1 is the difference between the average of daily anomalies of a n-day-span after day L and that of the previous n-day-span at BJ;

is the same but at the reference station (s).2

The idea here is similar to that of Alexandersson (1986; 1995) . The ξ variable indicating possible site-change-induced bias is expressed as:

Adjustment scale:

Figure 2. Daily ξ series of (BJ vs mean of MT, MY and TH), from 1/1/1980 to 31/12/1981 (centred at the relocation date for BJ, 1/1/1981, as marked in the series), for n = 1, 30, 91, 366, 732, 1098 days.

1 day

- 4

- 2

0

2

4

1 92 183 274 365 456 547 638 729

℃

30 days

- 1

0

1

1 92 183 274 365 456 547 638 729

℃

91 days

- 1

- 0. 5

0

0. 5

1

1 92 183 274 365 456 547 638 729

℃

366 days

- 0. 20

0. 20. 40. 60. 8

1

1 92 183 274 365 456 547 638 729

℃

732 days

0. 3

0. 5

0. 7

0. 9

1 92 183 274 365 456 547 638 729

℃

1098 days

0. 5

0. 7

0. 9

1 92 183 274 365 456 547 638 729

℃

A site-change effect may be possibly estimated at the seasonal scale.

1

Adjustment variable:

1 21

( ) /m

m i ii

m

2

denotes the difference between the mean of daily anomalies during the 3 months of a certain season after the relocation day and that of the previous 3 months of the same season at BJ.

is the same but at a (set of) reference station (s).

i denotes the ith year after/before the relocation (1≤i≤m).

m is the number of years for calculating the multi-year mean adjustment.

4.Results

• Multi-year mean seasonal adjustments

Figure3. The m-year mean seasonal adjustment variables for BJ temperature records changing with m (MY and MS).

In the present analysis m is set as 3.

(a) Seasonal adjustments for 01/01/1981

-1.2

-1

-0.8

-0.6

1 2 3 4 5 6 7 8 9

m (years)

Δm（

℃）

sp

su

au

wi

(b) Seasonal adjustments for 01/07/1997

-1

-0.8

-0.6

-0.4

-0.2

0

1 2 3 4 5 6 7 8 9

m (years)Δ

m （

℃） sp

su

au

wi

• Core reference stations (CRS) for site-change adjustments

Figure 4. Three-year mean seasonal adjustments for BJ temperature records due to relocations in 1981/1997, based on records of different reference stations.

(a) Seasonal Adjustments for 01/01/1981

-1.8

-1.5

-1.2

-0.9

-0.6

-0.3

0

sp su au wi

Δ3

℃（

）

HD

CY

MT

TH

MY

PG

TZ

FT

FS

YQ

(b) Seasonal Adjustments for 01/07/1997

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

sp su au wiΔ

3 ( ℃

)

HD

CY

MT

TH

MY

PG

TZ

FT

FS

YQ

Eliminate obvious and less obvious ‘outliers’ stations, MY, PG, TZ and FS were chosen as the CRS .

Seasonal Adjustments for 1997

-1.5

-1

-0.5

sp su au w i

Δ3 (

℃)

MY

PG

FS

TZ

Seasonal Adjustments for 1981

-1.5

-1

-0.5

sp su au wi

Δ3

(℃

)

TZ

MY

PG

FS

• Site-change adjustments for BJ temperature records during 1981-1997

Table 2. Seasonal adjustments based on 4 CRS records and comparisons of three-year mean seasonal temperature anomalies before and after the relocation dates.

Relocation date Spring Summer Autumn Winter Annual

I January 1981 -0.95 -0.69 -0.73 -0.86 -0.81

1 July 1997 -0.73 -0.43 -0.72 -0.87 -0.69

Difference 0.22 0.25 0.01 -0.02 0.12

The two relocations induced larger biases for winter and spring than for summer and autumn.

The absolute values of biases for spring(0.22), summer (0.25) and annual(0.12) for 1981 are larger than for 1997 relocation.

A liner trend was used for adjusting the daily data at BJ during 1981-1997, for 4 seasons, respectively:

-0.95 + 0.22 * n / N-0.69 + 0.25 * n / N-0.73 + 0.01 * n / N-0.86 – 0.02 * n / N

spring

11

13

15

1977 1982 1987 1992 1997 2002year

℃

summer

23

25

27

1977 1982 1987 1992 1997 2002year

℃

autumn

10

12

14

16

1977 1982 1987 1992 1997 2002year

℃

winter

-5

-3

-1

1

1977 1982 1987 1992 1997 2002year

℃

10

11

12

13

14

1971 1976 1981 1986 1991 1996 2001 2006year

℃ Yan et al

Li et al

The present

original

Figure 5. Seasonal mean temperature series at BJ during 1977-2006 (adjusted: solid line; original: dashed line).

The annual plot includes for comparison the adjusted series from Li et al (2004) and Yan et al (2001).

The effects of site-changes on trends of BJ series

Table 3. Linear trends in the adjusted and original annual and seasonal temperature series during 1977-2006 (Unit: /decade)℃

Spring Summer Autumn Winter Annual

Original 0.685 0.53 0.541 0.736 0.618

Adjusted 0.868 0.672 0.697 0.885 0.781

Difference 0.183 0.142 0.156 0.149 0.163

After adjustments, the warming trends in the seasonal and annual series are enhanced.

Note that the adjusted series here retain an urban-related trends.

• Urban-related warming bias at BJ Figure 6. BJ adjusted annual temperature series in 1977-2006,

compared with those of 5 rural stations.

7

9

11

13

1977 1982 1987 1992 1997 2002year

℃

TH

MS

ZT

BJ

XY

PG

rural

The likely urban-related warming at BJ is of 0.54℃/decade , the possible upper limit of urban warming bias, about 69% contribution of the overall warming. This result coincided with Ren et al (2007).PG with a similar elevation to BJ presents 0.58 /decade w℃arming trend, and the firm bottom limit of urban warming bias is 0.20 /decade.℃

0.78 /decade℃ 0.24 /decade℃ 0.58 /decade℃

Table 4. Linear trends ( /decade) in annual temperature series for different periods. ℃Bracketed values are the differences of trend between BJ and the station for comparison. The numbers by each site name are elevation (m) and population of the site (K).

Period Station

1965-2006 1971-2006 1981-2006 1991-2006

BJ, 55m, 1556K 0.61 0.65 0.84 0.91

XY, 409m, 10K 0.05 (0.56) 0.05 (0.60) 0.12 (0.72) 0.15 (0.76)

MS, 286m, 18K 0.19 (0.42) 0.21 (0.44) 0.33 (0.51) 0.25 (0.66)

FS, 49m, 347K 0.34 (0.27) 0.37 (0.28) 0.50 (0.34) 0.72 (0.19)

TZ, 27m, 269K 0.70 (-0.09) 0.81 (-0.16) 1.06 (-0.22) 1.06 (-0.15)

Compared with FS, the urban warming bias at BJ is likely about 0.3 /decade.℃ This estimate coincides with what Portman (1993) concluded for larger cities in China.

5.Conclusion

Based on comparisons between 3-year- mean seasonal temperature anomalies at BJ and the mean of 4 CRS, the site-change-induced biases were between 0.43-0.95. The adjusted annual and seasonal mean series exhibited a slightly enhanced long-term warming trend in 1977-2006.

The annual mean UHI effect around the site change in 1981 was 0.12 larger than that in ℃1997. Urban-related warming bias was likely about 0.3 /decade, accounting for about 40% of the ℃overall warming at Beijing for the last 3-4 decades.