| Based on the SPOT VGT/NDVI dataset from 2000 to 2013,temperature and precipitation data of 30 typical meteorological sites in the Haihe river basin,statistical data and other data,with the support of ArcGIS technology,by using Slope trend analysis,Hurst index,partial correlation analysis,buffer analysis and other methods,the spatial and temporal dynamic characteristics of vegetation coverage in the Haihe river basin in recent 14 years were analyzed at first.Then,the correlation and lag of NDVI with temperature and precipitation were analyzed comprehensively from annual and monthly scales.Furthermore,the impact of human activities on vegetation change in the Haihe river basin were analyzed from the aspects of land use,ecological construction project and urbanization effect.The main conclusions were as follows:(1)From the spatial distribution,the vegetation coverage in the Haihe river basin was generally in good condition in the 14 years,and the vegetation coverage in bad condition only appeared in the Bohai Bay area and some urban central areas.From the interannual variation,the vegetation coverage during the 14 years has been significantly improved as a whole.From the monthly variation,the vegetation change was only degraded in March,while the vegetation change in the remaining months tended to improve.From the spatial change,the vegetation in the study area has been improved as a whole,and the vegetation in most regions has been significantly improved.But the degradation of vegetation in the peripheral areas of urban center was serious.From the sustainability of vegetation change trends,the vegetation in the Haihe river basin would continue to improve in the future,and the persistent significantly improvement was dominated.Furthermore,the improvement for woodland and grass were the most obvious.While the persistent significantly degradation area of wetland and construction land accounted for the highest proportion.(2)From the annual scale correlation between vegetation and temperature and precipitation,the vegetation change in most areas was negatively correlated with temperature and positively correlated with precipitation,and the correlation between precipitation and vegetation change was more significant,indicating that the precipitation change had a greater impact on the vegetation change.From the monthly scale correlation between vegetation and temperature and precipitation,according to the partial correlation between the NDVI of each month and temperature and precipitation of the first 0-3 months,the response of vegetation change to temperature and precipitation changes were delayed by 1-3 months.The temperature of March,July and November had the greatest impact on monthly vegetation change.The precipitation of January,July and September had the greatest impact on monthly vegetation change,and especially the impact of precipitation in July on vegetation change was the most obvious.(3)Land use,ecological construction projects and urbanization effects had some effects on vegetation change in varying degree.The relationship between land use and vegetation change in the study area during 14 years was that the vegetation improved area of forest land and grassland was biggest,while the vegetation degenerated area of construction land and wetland was biggest.In the context of ecological restoration,the implementation of ecological construction projects has played a positive role in improving vegetation coverage in the study area,which had played a significantly positive effect on the regional ecological environment.There were obvious spatial differences in the effect of urbanization on regional vegetation change.Under the guidance of the concept that constructing ecological livable city,human interference with vegetation was associated with urbanization,making the vegetation changes showed a double feature that vegetation degenerated outside the city center while vegetation improved in the downtown area. |
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