| Vegetation,as the main component of terrestrial ecosystems,plays an important role in the terrestrial carbon cycle and global climate stability.Large-scale vegetation changes represent the effect of nature and human activities on the ecological environment.The Huang-Huai-Hai River Basin is an essential ecological barrier,economic development area and agricultural production base in China,but the regional ecological environment is fragile with serious soil-water loss.With the global warming,the regional climate has changed significantly.To improve the regional ecological environment,a great ecological restoration projects were implemented by Chinese government.Under the multiple influences of climate change and human activities(ecological projects and urbanization construction,etc.),regional vegetation variations and its driving mechanisms are more complex.With ecological protection and high-quality development in the Yellow River basin becoming a national policy,it is necessary to monitor the spatial and temporal of vegetation and its driving mechanism in recent 34 years.The research has important significance for ecological environmental protection and economic and society sustainable development in the Huang-Huai-Hai River Basin.Based on normalized difference vegetation index(NDVI)from 1982 to2015,climate data,land use data,defense meteorological sate-llite program/operational linescan system(DMSP/OLS)satellite imagery,regionalization of soil and water conservation,using trend analysis,land-use transition matrix,partial correlation analysis,and residual analysis,we investigated the NDVI variations in the Huang-Huai-Hai River Basin and its driving mechanisms from the inter-basin,sub-basin,province and pixel scale.The results indicated the following:(1)Vegetation variations was increasing in the Huang-Huai-Hai River BasinOver the past 34 years,The NDVI showed an increasing trend on the inter-basin scale,with a growth rate of 0.0139/10a(P<0.05).NDVI had a change point in 2006.On the sub-basin scale,NDVI showed an increasing trend,and the Huaihe River Basin had the greatest growth rate and the highest average value,with a significant increasing trend in 80.55%of the regions.On the provincial scale,NDVI showed an increasing trend,with the greatest growth rate and the highest average in Anhui province,and 94.76%of the regions showed a significant increasing trend.On the pixel scale,the area where the NDVI significantly increased covered 73.72%of the total area,mainly distributed in eastern Gansu province,northern Shaanxi province,southern Inner Mongolia autonomous region,northern Shandong province,southern Henan province,and Anhui province.(2)Precipitation and temperature in the Huang-Huai-Hai River Basin showed a fluctuant rising trendOn the inter-basin scale,precipitation and temperature in the study area showed an increasing trend from 1982 to 2015,and the increasing trend of precipitation was slower than that of temperature.The annual growth rates were 8.6586 mm/10a(P=0.39)and 0.4142?/10a(P<0.05),respectively.On the sub-basin scale,the precipitation growth rate was the fastest and the highest in the Huaihe River Basin.The fastest temperature growth rate was in the Yellow River Basin and the highest average was in the Huaihe River Basin.On the provincial scale,the fastest precipitation growth rate was in Shandong province,and the highest precipitation mean value was in Hubei province.The fastest temperature growth rate was in Qinghai province,and the highest temperature mean value was in Anhui province.On the pixel scale,precipitation was reduced from northwest to southeast,and temperature increased from west to east.(3)Land use types and DMSP/OLS nightlight values had changed significantly in the Huang-Huai-Hai River Basin,and the soil and water conservation measures in the key areas had a positive effectThe land use changes from 1980 to 2015 showed that the built-up land and woodland increased.In addition,cropland,grassland,water body,and unused land all showed a decreasing trend.The highest conversion sources of woodland were grassland and cropland,which was about 3022 km~2.The main conversion source of built-up land was crop land,which were about 19159 km~2.The DMSP/OLS satellite imagery showed that the nightlight values of the study area were increasing,and the urbanization processes were accelerating.Before 2002,urbanization speed of the provinces was fast which mainly located in the Huaihe River Basin,and after 2002,they were mainly located in the Yellow River Basin.The soil and water conservation measures analysis showed that,under the background of severe vegetation damage,soil and water conservation projects such as small watershed management and slope farmland control program,and measures such as afforestation and enclosure implemented by the government had a positive impact in vegetation coverage changes.(4)NDVI was more susceptible to temperature than to precipitation.Human activities had played a positive role in increasing regional vegetation changesVegetation changes were influenced by climatic factors and human activities.The changes of land use types showed that ecological engineering measures had a positive effect on vegetation variations.The changes driven by urban expansion had a negative effect on vegetation variations.The changes of DMSP/OLS nightlight values also indicated that urbanization had a negative effect on vegetation coverage,and urban expansion had resulted in a decline in surrounding vegetation variations.The soil and water conservation measures results showed that human activities were the mainly promoted for vegetation changes in the plain.The implementation of soil and water conservation measures had played a role in promoting vegetation variations in hilly and gully regions.Soil and water conservation measures in the loess hilly and gully regions of Shanxi province,Shannxi province and Inner Mongolia autonomous region had the most obvious effects.The Zoige-Headwater Region was significantly affected by climate change,and the trend of degraded alpine grassland had not been effectively curbedThe results enriched the understanding of the long-term vegetation changes and driving mechanisms in the Huang-Huai-Hai River Basin,and promoted the sustainable development and the ecological protection for the basin.Moreover,these findings provided a reference for the protection and management of vegetation by local authorities. |
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