黄河源区植被生长季NDVI时空特征及其对气候变化的响应

利用黄河源区MODIS/NDVI数据、1∶100万植被类型图和气象资料,分析了该区不同植被类型生长季NDVI时空特征以及与气候因子的关系。结果表明,1）2000—2011年,黄河源区植被生长呈改善趋势,生长季NDVI年际变化率每10 a为＋2.75%,高寒草原、高寒草甸、高寒灌丛生长季NDVI年际变化率分别为每10 a＋2.84%、＋2.65%、＋2.77%。2）黄河源区植被改善面积占全区总面积的29.39%,主要分布在卡日曲和玛曲上游、扎曲流域、布青山南麓、扎陵湖北部和鄂陵湖周边地区。植被退化面积仅占全区总面积的0.98%,主要分布在约古宗列曲东南部山地和卡日曲北部山地。受水热条件控制,植被改善表现为：①植被改善面积南坡大于北坡;②植被改善面积随海拔升高先增加后减小;③植被改善面积随坡度增加迅速减小。3）黄河源区植被生长季NDVI与同期气温和降水分别存在显著正相关性,其中高寒草原和高寒草甸生长受降水影响更为明显,而高寒灌丛生长受气温影响更为明显。气候的暖湿化趋势可能是促使黄河源区植被生长改善的主要原因。

Spatial-temporal variation of growing-season NDVI and its responses to climate change over the source region of the Yellow River

The spatial-temporal distribution of vegetation variation in the source region of the Yellow River was investigated by using the MODIS/NDVI data from 2000-2011.Combining the vegetation maps at a scale of 1：1 000 000 and meteorological data,we discussed the relationship between growing-season NDVI and climatic variables.The results were shown as follows： 1） NDVI increased at a rate of 2.75%/10a in the source region of the Yellow River since 2000.Inter-annual variations in NDVI of alpine grassland,alpine meadow,alpine shrub were ＋2.84%/10a,＋2.65%/10a and ＋2.77%/10a respectively.2） NDVI increased and decreased area covered about 29.39% and 0.98% of the whole study area.The increased area was mainly distributed in upper reaches of Kariqu River and Maqu River,Zhaqu watershed,south of Buqing Mountains,north of Zhaling Lake and the surrounding areas of Eling Lake.NDVI decreased area was mainly distributed in the southeastern mountains of Yueguzonglie River and northern mountains of Kariqu River.Controlled by thermal and hydrological conditions： ①Amelioration area was more in the sunny slope than in the northern slope.②Amelioration area firstly increased and then decreased while the elevation rose up.③Amelioration area rapidly decreased while the slope increased.3） There was a significantly positive correlation between NDVI and climatic factors（temperature and precipitation）.The results also revealed that a correlation between NDVI and precipitation in alpine grassland and alpine meadow zone was stronger than temperature,and NDVI had a closer correlation with temperature than with precipitation for the alpine shrub.The main reasons for the positive change of vegetation in the source region of the Yellow River were the heat and wet tendency of climate.