Stronger Warming Amplification over Arid Ecoregions and Its Relationship to Vegetation Cover in China since 1982
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摘要: 利用归一化植被指数(Normalized Difference Vegetation Index,NDVI)将中国划分为不同的生态区,在此基础上分析夏季植被状况与不同生态区增暖之间的联系。研究表明,就多年平均而言,中国植被覆盖呈现自东向西逐渐减少的空间分布。1982年以来,植被稀疏的干旱生态区是夏季增暖最明显的区域,平均气温和平均最高气温增速大都位于0.6~1.0℃/10 a,而平均最低气温的升高达到0.8~1.4℃/10 a,明显高于中国其他区域。进一步分析发现,夏季气温的变化与其所处地区的植被疏密程度之间存在很好的负相关关系,即快速增暖主要发生在植被稀疏区,且这种负相关关系在夏季平均最低气温上最为显著。不同植被覆盖区中气温的长期变化趋势,受NDVI变化带来的地表反照率和云量变化的影响,但各生态区不尽相同,主要表现在:植被稀疏的干旱生态区,植被减少,引起地表反照率增加,感热输送增加而潜热输送减小,加速了该地区整体的增温速率;而在植被茂密地区,植被增加造成地表反照率减少,同时由于蒸发冷却,其整体增暖幅度缓于植被稀疏区。所以,植被活动对全球变暖背景下的区域气候变化具有重要作用,尤其表现在干旱生态区的陆面过程上,地表辐射平衡和能量收支的显著改变放大了干旱生态区的增暖速率。
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关键词:
- 夏季气温 /
- 归一化植被指数(NDVI) /
- 变暖趋势 /
- 干旱生态区
Abstract: To analyze vegetation variability and its relationship with summer air temperature variability in China, this study classifies various ecoregions based on the climatological Normalized Difference Vegetation Index (NDVI) values. Results show that there is a decreasing spatial distribution of vegetation from east to west in China. Arid ecoregions are the most obvious areas for summer warming since 1982. The warming rates over arid ecoregions for summer mean air temperature and mean maximum air temperature are 0.6-1.0℃/10 a and that for summer mean minimum air temperature is 0.8-1.4℃/10 a. Furthermore, summer air temperature variations have a significant negative correlation with vegetation conditions since 1982. In other words, the lower the vegetation greenness is, the stronger the warming trend is. It is worth noting that the negative correlation is most significant between mean minimum air temperature and vegetation conditions. In each ecoregion, the long-term trend of temperature is largely affected by changes in albedo and clouds. In the sparse vegetation regions, the increased albedo leads to a decrease in latent heat transport and increases the sensible heat flux, which intensifies the warming trend. In the dense vegetation regions, the decline in albedo leads to increases in evaporative cooling, which slows the rate of increase in the air temperature. Overall, vegetation activities play an important role in regional climate change, especially over the arid regions, where significant changes in surface radiation balance and energy flux amplify the rate of warming. -
图 1 中国地区夏季植被覆盖气候态的空间分布:(a)依照NDVI指数值划分的6种生态区(生态区标号见表 1); (b)依照土地覆盖类型划分的10种区域
Figure 1. Spatial patterns of climatological summer vegetation in China: (a) Classification map of the six ecoregions defined based on NDVI (Normalized Difference Vegetation Index) for the period 1982-2012 (same as Table 1); (b) classification map of the ten regions defined based on land cover type for period 2000-2012
图 2 1982~2012年中国地区夏季气温和植被覆盖变化趋势的空间分布(打点区域表示通过95%信度检验):(a)平均气温;(b)平均最高气温;(c)平均最低气温;(d)NDVI指数
Figure 2. Spatial patterns of temperature trend for (a) summer mean air temperature, (b) mean maximum air temperature, (c) mean minimum air temperature, and (d) NDVI trend for the period of 1982-2012. Stippling indicates regions where (a-c) temperature trend or (d) NDVI trend is statistically significant at the 95% confidence level
图 3 1982~2012年气温变化趋势与植被覆盖散点分布(虚线为用最小二分法进行的线性拟合):(a)气温变化趋势与各区域NDVI指数的散点分布;(b)气温变化趋势与不同土地覆盖类型的散点分布
Figure 3. Relationship between temperature trend and the climatological (a) NDVI over different ecoregions or (b) land cover type for the period of 1982-2012. Dashed lines are the least square fittings of linear function
图 4 1982~2012年各生态地区区域平均气温距平(折线图,虚线表示1982~2012年气温趋势)和降水距平百分率(柱状图)的时间序列。(a)-(f)所代表的生态地区NDVI值依次升高,即分别为表 1中所划分的6个生态区
Figure 4. Regional mean temperature anomalies (solid lines, dashed lines show the temperature trends for 1982-2012) and percentage precipitation anomalies (bars) for the period of 1982-2012. NDVI values are same as Table 1 and increased from (a) to (f) sequentially
图 5 不同植被覆盖度区域中(a、b、c)夏季平均气温、夏季平均最高气温、夏季平均最低气温以及(d、e、f)云量、地表反照率和NDVI指数的标准化距平时间序列:(a、d)稀疏植被地区;(b、e)中等植被地区;(c、f)茂密植被地区
Figure 5. Regional mean anomalies of (a-c) temperature (mean, max, and min), (d-f) cloud cover, albedo, and NDVI for the period of 1982-2012: (a, d) The least vegetation regions; (b, e) the medium vegetation regions; (c, f) the dense vegetation regions
表 1 不同生态区的划分标准
Table 1. Classification of different ecoregions
生态区标号 NDVI范围 1 NDVI≤0.15 2 0.15<NDVI≤0.30 3 0.30<NDVI≤0.45 4 0.45<NDVI≤0.60 5 0.60<NDVI≤0.75 6 NDVI>0.75 注:生态区标号1~6表示植被从稀疏植被到茂盛植被的分级。 表 2 依照NDVI值划分的6个生态区1982~2012年间气温变化趋势和标准差
Table 2. Linear trends and standard deviations of summer air temperature over the six eco regions defined based on NDVI in Table 1 for the period 1982-2012
平均气温 最高气温 最低气温 生态区标号 变化趋势
/℃(10 a)-1标准差
/℃变化趋势
/℃(10 a)-1标准差
/℃变化趋势
/℃(10 a)-1标准差
/℃1 0.55** 0.686** 0.53** 0.697** 0.70** 0.769** 2 0.54** 0.661** 0.50** 0.671** 0.67** 0.722** 3 0.50** 0.605** 0.49** 0.664** 0.62** 0.659** 4 0.33* 0.453* 0.34 0.508 0.41** 0.487** 5 0.28* 0.377* 0.34 0.467 0.33** 0.395** 6 0.31 0.449 0.41 0.709 0.35 0.500 *表示通过90%的信度检验,**表示通过99%的信度检验。 表 3 1982~2012年不同生态区区域平均气候因子变化(标准化趋势)
Table 3. Changes in climate elements in each individual ecoregions for the period 1982-2012
标准化趋势 平均气温 最高气温 最低气温 云量 NDVI 地表反照率 稀疏植被地区 0.062 0.054 0.073 -0.010 -0.008 0.010 中等植被地区 0.055 0.045 0.069 -0.004 0.024 -0.009 茂密植被地区 0.044 0.040 0.057 0.008 0.005 -0.004 -
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