黄土高原不同生态类型NDVI时空变化及其对气候变化响应

了解植被的时空变化及其气候主控因子可为植被保护和恢复提供重要的理论依据。基于MOD13A1和气象数据,分析了黄土高原Normalized Difference Vegetation Index （NDVI）时空变化特征,探讨了NDVI对水热条件在不同时间尺度的响应特征。结果表明：黄土高原植被覆盖状态正在不断的改善,气候呈暖湿的发展趋势;83.77%的植被退化区（退化区面积占研究区总面积的5.79%）海拔<2000 m且退化类型以不显著减少为主,不同覆被类型的退化区海拔分布及退化比例差异明显,湿地的退化面积比最高（23.91%）、其次耕地（11.88%）。年尺度上,NDVI与降水呈正相关的面积高于气温,约75.06%的区域受水分条件控制;灌木地（海拔分布<2200 m）、耕地（<3000 m）、草地（<3000 m）和裸地（600~3700 m）等植被生长受水分条件影响;森林（<1000 m、1700~3700 m）和湿地（>2500 m）的植被生长受热量影响。月尺度上,黄土高原植被NDVI对热量响应以滞后1个月为主,不同植被对水热响应的滞后性差异明显,草地、湿地、耕地和裸地对热量响应以滞后1个月为主;森林和灌木地则表现水热同期的特征。伴随滞后时间的推移,水分主控面积逐渐降低,热量成为影响植被生长的主要因素,水热主控及响应滞后性分布受海拔影响明显。

Spatiotemporal variation of NDVI in different ecotypes on the Loess Plateau and its response to climate change

Understanding the spatio-temporal changes of vegetation and its climatic control factors can provide important theoretical basis for the protection and restoration of ecological vegetation. Based on MOD13A1 and meteorological data, the spatial patterns and trends of Normalized Difference Vegetation Index (NDVI) in the Loess Plateau were analyzed. The response of NDVI to temperature and precipitation was analyzed on the annual and monthly scales. The results showed that the vegetation coverage in the study area was improving continuously, and the climate showed a warm and wet trend. Of the degraded areas in the Loess Plateau, some 83.77% (area only 5.79%) was below 2000 m and the number of vegetation degradation types were not significantly reduced. The altitude distribution and degraded proportion of different vegetation degraded areas were significantly different. The degraded area ratio of wetland was the highest (23.91%), followed by cultivated land (11.88%). On the annual scale, the area with positive correlation between NDVI and precipitation was higher than that of temperature, and about 75.06% of the area was affected by precipitation. Precipitation was the main factor affecting the growth of shrub land (altitude distribution < 2200 m, the same below), cultivated land (< 3000 m), grassland (< 3000 m) and bare land (600-3700 m). Temperature was the main factor affecting the growth of forests (< 1000 m, 1700-3700 m) and wetlands (>2500 m). On the monthly scale, the overall response lag period of the Loess Plateau to temperature was one month, and there was no response lag period to precipitation. The response lag period of different vegetations to hydrothermal conditions was obvious. Grassland (lagging altitude distribution 710-3800 m, the same below), wetland (> 860 m), cultivated land (< 150 m, 350-2250 m, 2550-2900 m, 3430-3560 m) and bare land (760-2100 m) had a one month lag effect on temperature response, while forest (< 2900 m, > 3450 m) and shrub land (< 1270 m, > 1860 m) had no lag effect on temperature response, and six types of vegetation had no lag effect on water condition response. With the time lagging, the proportion of precipitation control gradually decreases. Temperature becomes the main factor affecting vegetation. The main control of water and heat and the lagging distribution of response are obviously affected by altitude. The proper vegetation type should be selected in different areas and altitudes, and water resources should be used reasonably for vegetation restoration.