研究气候变化背景下植被变化趋势及其与水热因子的关系, 对于黄河源区的生态恢复和生态建设具有重要意义。采用基于FAO Penman-Monteith的降水蒸散比来描述区域的干湿状况, 划分了黄河上游地区的干湿气候区。在此基础上, 利用AVHRR归一化植被指数(NDVI)和GLOPEM净初级生产力(NPP)数据集和同期的气候资料, 分析了黄河上游植被覆盖、植被生产力和气候变化的趋势, 探讨了不同干湿气候区影响植被变化的主要气候因子。结果表明, 研究区域东南部为半湿润气候区, 其余为半干旱气候区, 干湿气候分界线与450 mm降水等值线较接近; 1981-2006年区域气候趋于干暖化, 尤其是气温的升高趋势明显; 半湿润地区NDVI和NPP显著增加, 半干旱地区略有增加; 半湿润地区的NDVI多与气温显著正相关, 与降水量的相关性较弱, 气温是植被生长的主要气候制约因素; 半干旱地区的NDVI则与降水量的正相关性更强, 对降水量的变化较为敏感。NPP对气候变化的响应模式与NDVI相似。植被对气候变化的响应部分依赖于研究区域所具备的水热条件, 干湿气候划分有助于更好地解释植被对气候变化响应的空间差异。

Aims Precipitation and temperature are considered the limiting factors to vegetation growth in arid and cold areas, respectively. Our objective was to study the trends in vegetation cover and productivity and their relationships with prevailing hydrothermal factors in order to better understand climatic constraints on regional vegetation dynamics.
Methods We zoned dry and wet climates using daily meteorological data from 1959 to 2008 at 16 locations in the headwaters of the Yellow River Basin to calculate the ratio of precipitation to evapotranspiration estimated with the FAO Penman-Monteith model. Based on this zoning, the temporal dynamics of vegetation and changes in climate were analyzed using the normalized difference vegetation index (NDVI) obtained from the NASA AVHRR sensor (1982-2006) and the GLOPEM net primary productivity (NPP) (1981-2000) and corresponding annual meteorological data. Then we developed the relationships between NDVI and NPP and climatic factors.
Important findings The region studied is semi-humid in the southeast and semi-arid elsewhere, with a boundary nearly matching the 450 mm rainfall contour. The weather became wetter and especially warmer in most parts of the region during 1981-2006. The regional average NDVI and NPP markedly increased in semi-humid areas and slightly increased in semi-arid areas. Overall, NDVI had a significantly positive correlation with mean annual air temperature and a mainly negative correlation with mean annual precipitation in most semi-humid areas. The most important factor influencing NDVI was heat. In contrast, the key climatic factor affecting vegetation changes in the semi-arid areas was water, the relationship between NDVI and precipitation was strong and vegetation was more sensitive to changes in precipitation. The impact of climate change on NPP was similar to that on NDVI. Findings suggest that the responses of vegetation to climate change depend in part on the hydrothermal conditions of the region, and the zoning of dry and wet climate illustrates the spatial difference of vegetation feedback to climate change.