Application of remote sensing time-series data to investigate the relationship between vegetation change and climatic factors:A case study of Circum-Bohai Sea area
Vegetation is one of the most important components of terrestrial ecosystem. The dynamics of vegetation is affected by climate factors and human activities. Generally, natural vegetation is mainly affected by climate factors, especially temperature and precipitation. Presently, global climate change has occurred. To predict the influence of global climate change on vegetation, reduce the unfavorable or adverse effect and protect the ecosystem environment, it is necessary to study the correlation between vegetation and climate factors. Normalized difference vegetation index (NDVI) is generally regarded as a good indicator of terrestrial vegetation. In this study, ten-year MODIS NDVI time-series data and temperature, precipitation data from 2000 to 2009 in Circum-Bohai Sea area were used. A modified SPLINE method was adopted to remove the effect of noise and to reconstruct NDVI time series. On the basis of these data, the temporal and spatial dynamics of NDVI were analyzed through least-square regression. The correlation and lagged correlation coefficients between NDVI and temperature, precipitation were calculated. The results showed that an increasing trend in NDVI was found in the study area, but there was an obvious heterogeneity. The areas with significant increase and decrease in NDVI were small. In the Circum-Bohai Sea area, the development of vegetation was driven by temperature and precipitation, and the correlation coefficients between vegetation NDVI and temperature were greater than those between vegetation NDVI and precipitation in the same period. The response of vegetation to temperature and precipitation lagged and the lag period was about 16 days. Inter-annual NDVI change in the Circum-Bohai Sea area was mainly influenced by precipitation and human activities, and a positive correlation between precipitation and annual NDVI was found. Human activities influenced vegetation dynamics through changing land use. Urban sprawl led to decrease in NDVI, but the effort to return farmland to forest increased NDVI.