Effects of climate changes on the NDVI of vegetation in Asia
PANG Xin1(), LIU Jun2
1. Shanxi Conservancy Technical Institute, Yuncheng 044000, China 2. College of Mining Engineering, Taiyuan University of Technology, Taiyuan 030024, China
Based on the long-time-series (1982—2015) GIMMS NDVI3g and CRU Ts datasets of precipitation, temperature, and potential evapotranspiration (PET) of Asia, this study identified the spatio-temporal variations in the vegetation coverage and climatic elements in Asia in the past 34 years using the maximum-value composite procedure, Mann-Kendall trend tests, and correlation analysis. Furthermore, this study analyzed the response of vegetation coverage to climate changes and explored the influence mechanisms of climate changes on the dynamic changes of vegetation. The results show that the vegetation in Asia during 1982—2015 is as follows: ① the vegetation coverage was high (NDVI > 0.5) in Southeast Asia, Japan, India, and the southern coasts of China but low in most parts of central Asia; ② the NDVI in Asia showed an upward trend at an increasing rate of 0.000 7/a. Moreover, the vegetation coverage exhibited a significant seasonal increase, with spring contributing the most to the interannual NDVI; ③ The PET in Asia was high in the west but low in the east. For example, the PET was high (> 40 mm) in arid and semi-arid Central Asia and Western Asia; ④ The temperature in Asia was high in the south and low in the north. For example, in China, the temperature was higher than 15 ℃ in the south and lower than 15 ℃ in the north. Rainfall exhibited a similar but more significant spatial distribution compared to the temperature; ⑤ The temperature, rainfall, and PET showed regional effects on NDVI. For example, rainfall and PET served as the main factors influencing NDVI in northern Asia, while the temperature was the main factor influencing NDVI in central and southern Asia; ⑥ The effects of climate changes on NDVI were significant in spring and especially summer but were nonsignificant in autumn and winter; ⑦ The effects of climate changes on NDVI showed a significant time lag of one month.
Fig.2 Annual NDVI time series changes in Asia from 1982 to 2015
季节
线性回归方程
R2(n=34)
春
y = 0.000 8x + 0.373 5
0.658
夏
y = 0.000 5x + 0.429 9
0.463
秋
y = 0.000 5x + 0.409 1
0.414
冬
y = 0.000 2x + 0.310 1
0.101
Tab.1 Regression equation of seasonal variation trend of NDVI in Asia from 1982 to 2015
Fig.3 Average distribution of NDVI in Asia from 1982 to 2015
Fig.4 Four seasons distribution of NDVI in the study area
季节
各类所占像元百分比
非植被
稀疏植被
低植被 覆盖
中植被 覆盖
高植被 覆盖
春季
1.67
42.93
20.85
15.87
18.68
夏季
1.37
39.47
15.31
15.77
28.08
秋季
1.35
44.01
13.44
15.00
26.19
冬季
1.61
61.80
9.81
11.66
15.11
Tab.2 Statistics of NDVI change distribution(%)
Fig.5 Variation trend of NDVI in Asia from 1982 to 2015
分级标准
变化程度
Slope≤-0.1
严重退化
-0.1<Slope≤-0.05
中度退化
-0.05<Slope≤-0.01
轻微退化
-0.01<Slope≤0.01
基本不变
0.01<Slope≤0.05
轻度改善
0.05<Slope≤0.1
中度改善
Slope>0.1
明显改善
Tab.3 Vegetation coverage change classification
Fig.6 Statistical curve of climate factor M-K from 1982 to 2015
Fig.7 Distribution of interannual climate factors in Asia from 1982 to 2015
Tab.4 Seasonal variation distribution of meteorological factors in Asia from 1982 to 2015
Tab.5 Spatial distribution of NDVI-precipitation, NDVI-PET and NDVI-temperature correlation coefficients
月份
气温
降雨量
PET
同期
滞后1月
滞后2月
同期
滞后1月
滞后2月
同期
滞后1月
滞后2月
1
0.651
0.588
0.564**
0.654
0.592
0.557**
0.628**
0.596
0.515
2
0.618**
0.559
0.483
0.593
0.574
0.438**
0.490
0.574**
0.297
3
0.598
0.575**
0.294
0.476
0.585**
0.128
0.307
0.501**
-0.014
4
0.431
0.635**
-0.121
0.265
0.588**
-0.251
0.181
0.547**
-0.309
5
0.138
0.685**
-0.531
0.054
0.664**
-0.577
0.019
0.614**
-0.567
6
0.045
0.610**
-0.644
0.005
0.597**
-0.664
0.021
0.593**
-0.651
7
-0.077
0.533**
-0.674
-0.072
0.556**
-0.694
-0.012**
0.613
-0.696
8
-0.008
0.500**
-0.631
0.058
0.584**
-0.631
0.210
0.688**
-0.556
9
0.263**
0.668
-0.427
0.443
0.766**
-0.282
0.494
0.777**
-0.216
10
0.510
0.715**
0.059
0.578
0.756**
0.127
0.560
0.755**
0.127
11
0.554
0.574**
0.370
0.543**
0.621
0.362
0.5784**
0.630
0.405
12
0.573
0.563
0.610
0.588**
0.529
0.517
0.632
0.583
0.545**
Tab.6 Analysis of the response relationship of NDVI to climate factors in 1983
月份
气温
降雨量
PET
同期
滞后1月
滞后2月
同期
滞后1月
滞后2月
同期
滞后1月
滞后2月
1
0.648
0.491
0.559**
0.656
0.540
0.561**
0.639**
0.548
0.520
2
0.615**
0.552
0.453
0.592
0.554**
0.407
0.511
0.564**
0.314
3
0.585
0.601**
0.327
0.497
0.622**
0.221
0.268
0.522**
0.030
4
0.427
0.727**
-0.085
0.204
0.641**
-0.267
0.114
0.600**
-0.331
5
0.122
0.685**
-0.530
0.025
0.678**
-0.590
-0.002
0.629**
-0.580
6
0.033
0.595**
-0.644
0.006*
0.596
-0.655
0.025
0.613**
-0.653
7
-0.078
0.547**
-0.655
-0.071
0.597**
-0.687
0.008**
0.645
-0.676
8
0.020
0.584**
-0.630
0.102
0.658**
-0.623
0.237
0.730**
-0.538
9
0.232**
0.606
-0.443
0.430**
0.709
-0.336
0.488
0.745**
-0.226
10
0.475
0.673**
0.070
0.572
0.723 **
0.185
0.570
0.727**
0.191
11
0.607
0.545 **
0.440
0.60**
0.564
0.444
0.625**
0.583
0.459
12
0.596**
0.498
0.502
0.61**
0.527
0.517
0.634
0.534
0.536**
Tab.7 Analysis of the response relationship of NDVI to factors in 1996
月份
气温
降雨量
PET
同期
滞后1月
滞后2月
同期
滞后1月
滞后2月
同期
滞后1月
滞后2月
x1
0.622
0.526
0.508**
0.623**
0.554
0.500
0.589
0.600
0.440**
2
0.629**
0.488
0.488
0.593**
0.545
0.415
0.481
0.564**
0.293
3
0.539
0.591**
0.265
0.425
0.618**
0.122
0.187
0.544**
-0.084
4
0.356
0.685**
-0.143
0.134
0.608**
-0.327
0.035
0.553**
-0.374
5
0.102
0.689**
-0.543
0.006
0.664**
-0.579
0.007
0.647**
-0.572
6
-0.027
0.535**
-0.633
-0.048
0.548**
-0.668
0.000
0.553**
-0.649
7
-0.113
0.590**
-0.692
-0.048
0.548**
-0.668
-0.015
0.702**
-0.719
8
-0.013
0.583**
-0.660
0.055
0.656**
-0.657
0.169
0.686**
-0.592
9
0.268**
0.663
-0.474
0.403
0.741**
-0.395
0.471
0.772**
-0.317
10
0.399
0.667**
-0.023
0.478
0.724**
0.052
0.520
0.733**
0.110
11
0.544**
0.518
0.361
0.589**
0.540
0.413
0.622**
0.575
0.452
12
0.615
0.550
0.512**
0.645**
0.579
0.550
0.642
0.590
0.534 **
Tab.8 Analysis of the response relationship of NDVI to factors in 2010
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