1982-2006年加纳植被覆盖时空变化及其气候影响

非洲陆地生态系统是气候变化的高敏感区,研究该区域植被覆盖变化及其控制因素,对深刻认识气候变化的影响具有重要意义。本文利用1982-2006年植被指数（NDVI）数据,研究位于非洲西部热带地区的加纳共和国植被覆盖的时空变化特征,结合同期的气温和降水量数据,分析其植被活动对气候变化的响应特征。研究结果表明,加纳86.4%的植被覆盖区NDVI在25 a间都呈现不同程度的增加趋势。20世纪80年代初和21世纪初这2个时期,NDVI值大于0.4的面积百分比呈增加趋势;NDVI值大于0.5的面积百分比从26%增加到38.2%;NDVI值在0.4-0.5之间的面积百分比从47.5%增加到51.9%。NDVI受降水量控制的区域占总区域面积的57.2%,而受气温控制的面积占总区域面积的42.8%。总的来看,加纳植被覆盖对降水量变化的敏感程度强于气温变化。

Spatiotemporal Variation of Vegetation and Climate Impacts on It in Ghana from 1982 to 2006

As African terrestrial ecosystem is highly sensitive to climate change, considerable researches during the past several decades have focused on monitoring vegetation activity and its responses to climate change, thus we can thoroughly understand the progress of climate change. It's significant to study the vegetation variation and its control factors in this area.We combined datasets of the satellite-derived Normalized Difference Vegetation Index (NDVI),whose spatial resolution is 8 km, and climate factors (temperature and precipitation) to detect vegetation activity change. Additionally, we analyzed the spatial correlations among NDVI, temperature, precipitation on the spatio-temporal patterns from 1982 to 2006 in Ghana. In order to conduct certain spatial correlation analysis, we interpolated the temperature and precipitation data from Climatic Research Unit (CRU3.0) datasets with respect to the spatial resolution of NDVI. At the regional scale, the results from this study showed the different increase trends occurred in the vegetation area of Ghana in the recently 25 years, which suggested that the vegetation activity has been strengthened. Compare the spatial distribution of NDVI in the early 1980 s (1982-1986) with the early 21st century (2002-2006), we found that the areas whose NDVI value is greater than 0.5 and whose value is between 0.4 and 0.5 all show a trend of increase; area percentage with NDVI value greater than 0.5 had increased from 26% to 38.2%, and the area percentage with NDVI value between 0.4 and 0.5 had increased from 47.5% to 51.9%.Spatial correlation analysis showed that the area with precipitation governed NDVI accounted for 57.2% of the total area, and the area with NDVI controlled by the temperature accounted for 42.8% of the total area. In summary, the vegetation of Ghana is more sensitive to the rainfall changes than the temperature changes.