基于MODIS数据的海河流域植被覆盖度估算及动态变化分析

Monitoring and Dynamic Analysis of Fractional Vegetation Cover in the Hai River Basin Based on MODIS Data

本文以MODIS-NDVI时间序列数据为基础,利用像元二分模型对海河流域2000年-2007年的植被覆盖度(fc)进行了估算,分析了年最大植被覆盖度的时空变化特征,并对植被覆盖度与降雨量之间的响应关系进行了深入探讨。结果表明:①海河流域2000年-2007年平原农业区植被覆盖度整体较高,fc介于60%～80%之间;永定河上游区域植被覆盖度较低,fc小于30%;②近8年来海河流域植被覆盖度整体呈增加趋势,只有东南部的部分农田及城市扩展区,植被覆盖度有所减少;③海河流域植被覆盖度与当年3至8月的降水总量相关性最高,相关系数为0.687,该时段内的降雨量与植被覆盖度年际变化总体趋势较为相似,在绝大多数年份,两者的增减具有一致性。

Fractional vegetation cover（fc） is a critical indicator for vegetation and the eco-environment.It is frequently as a basic input for hydrology,meteorology and water-soil protection studies at regional or global scales.Fractional vegetation cover estimation from remote sensing would serve as a basis for integrated assessment of the environmental effects of the Hai River basin.The Hai River basin,lies in North China,covering an area about 31.78×104 km2（accounting for about 3.3% of the total area of China） and ranging in the latitude approximately between 35° and 43° N and in longitude between 112° and l20°.The Hai River basin encompasses the Hai River,Luan River and Tuhai-Majia River.In this paper,the Hai River was investigated,which belongs to the temperate climate zone（semiarid monsoon）,showing a mean annual temperature of 10.4℃ and a mean annual precipitation of about 547.8 mm,in which roughly 75% - 85% are concentrated in the months of 6-9.Continuous 16-days composites of Moderate Resolution Imaging Spectroradiometer（MODIS）-Normalized Difference Vegetation Index（NDVI） images of 1 km spatial resolution were acquired for this study.Fractional vegetation cover of the Hai River basin was estimated using a dimidiate pixel method based on the MODIS-NDVI data from 2000 to 2007.It is a demonstration of application of the long time series fc monitoring at a regional scale.Spatiotemporal changes in the annual maximum fc in this study area for the period of 2000 to 2007 were analyzed using the slope method.Results showed that the fc of cropland in the plain is generally higher,varying between 60% and 80%.It is relatively lower in the upper basin of the Yongding River,fc was found to be less than 30%.During recent 8 years,the fc of the Hai River basin has shown an increasing trend in general but decreased in some cropland areas over the east-south of the study area and the urban expanded areas.For better understanding effects of precipitation on fc,their correlation coefficients in different temporal durations were calculated.Results suggested that the annual maximum fc is significantly related to accumulated precipitation from March to August,showing a correlation coefficient of 0.687.Changes in fc in the last nine years were essentially consistent with changes in precipitation.The increasing trend of the fc in the Hai River basin is likely caused by increased precipitation,which would also be indicative of the benefits from application of eco-protection policies.