Study On The Spatiotemporal Of NPP And Its Response To Driving Factors In Anhui Province,China

Anhui province is located in the eastern monsoon region of China,where the combination of water and heat is superior.In recent years,the economy of Anhui province is in the period of rapid development and the concept of national environmental protection is increasingly strengthened.Among the many influencing factors of NPP?Net Primary Productivity?,climate and human activities play a dominant role.However,the impacts of the two factors on NPP are different from each other.In this paper,based on the CASA model,MODIS 13A1-NDVI remote sensing data,precipitation,temperature and solar radiation data in 2001-2016 were used and domestic land use and cover change?LUCC?data was combined to simulate the terrestrial ecosystem and analysis long time series of NPP in the area of time and space distribution pattern and dynamic change characteristics.Besides,the driving force factors of changes in NPP were explored and the relative contribution of influencing factors was quantitatively analyzed.The results are as follows:?1?From 2001 to 2016,the inter-annual variation of NDVI in Anhui province was generally on the rise,and its fluctuation ranged from 0.46 to 0.53.The change trend of the year was“bimodal”with the highest peak and the second peak appearing in July and April respectively.The NPP of the four seasons all showed a slight upward trend,generally speaking,from high to low,it was summer,spring,autumn and winter.During 16 years,there was significant in the spatial heterogeneity of the vegetation NDVI in Anhui province.The areas of high value were mainly distributed in the south and west of Anhui province,namely the south Anhui mountains and the Dabie mountains in the west of Anhui.The areas of median value were mainly distributed in the north and central part of Anhui,such as the northern plain of Anhui and the Jianghuai hills.The areas of low value were mainly distributed along the Yangtze river,Chaohu lake and Huai river.However,there was no significant difference in the annual variation of the spatial distribution.During the study period,vegetation NDVI increased in most areas of Anhui province?11.37×10⁴km²,81.18%?,indicating that vegetation growth conditions improved significantly.The area of NDVI positively correlated with precipitation and temperature accounted for the majority of the study area.The average annual correlation between NDVI of vegetation and precipitation and temperature was about 0.44 and 0.60,respectively,showing a decreasing trend on the whole.However,the correlation between NDVI and temperature in Anhui province was higher than that of precipitation.?2?From 2001 to 2016,except for urban/built up land in Anhui province,the value of vegetation NDVI of the other 7 types of land use from high to low were forest land>grassland>cropland/natural vegetation mosaic>cropland>wetland>low vegetation cover land>water bodies,and they all showed a slight rising trend.Compared with that of2001,the average NDVI of vegetation in the three regions of Anhui increased by different ranges in 2016;In the correlation coefficient with precipitation,the areas of northern regions of Anhui showed an obvious downward trend,while central and southern regions of Anhui showed a slight upward trend and vice versa in other two regions.In general,the correlation between vegetation NDVI and temperature in the three regions was higher than that of precipitation,except the situation happened in northern regions of Anhui in 2001.?3?From 2001 to 2016,the mean value of NPP and the total amount of NPP in Anhui province showed an upward trend in the interannual changes.The mean value of NPP increased from 206.20gC/?m²·a?in 2001 to 226.21gC/?m²·a?in 2016.The total NPP of vegetation increased from 288.75×10¹¹gC/a in 2001 to 316.77×10¹¹gC/a in 2016.During the change of the year,the average NPP of the vegetation in Anhui province showed a"single peak",and the highest peak occurred in July.In the four seasons,the total NPP of vegetation in the whole province was sorted from high to low as summer>spring>autumn>winter.In the inter-annual change of four seasons,the total NPP of summer vegetation showed a slight downward trend,while the other three seasons showed a slight upward trend.?4?From 2001 to 2016,the vegetation NPP was higher in the north and south,and lower in the middle of Anhui province,while the inter-annual variation was not significant during the study period..From the value range of NPP ineach year,the percentage of NPP in the high-value areas such as 200?250,250?300 and>300gC/?m2·a?showed an increasing trend,while the percentage in other low-value areas showed a decreasing trend.In the spatial distribution of annual changes of vegetation NPP,the whole region of Anhui province had a distribution process from low to high and then to low due to the influence of phenological law.The most obvious area was the Huaibei plain with crops as the main cover type,while the southern Anhui mountainous area with natural forest as the main cover type had the least change range.In the variation of vegetation NPP in Anhui province during the study period,the total area of the three growth zones of vegetation NPP?79.71%?was far more than that of the areas with declining NPP Among them,the area with the growth of NPP in 0?50gC/?m2·a?was the largest,which was reaching about91769km²,accounting for 65.53%of the total area of the province,and distributed all over the province.?5?The trend fluctuation range of vegetation NPP in the study area during 2001-2016 was between-18.67and 14.78.In Anhui province,the areas with increased NPP reached96091.25km²,accounting for 68.70%of the total area of the province.Most of them?67.23%?were slightly increased.The areas of NPP under the trend of decreasing was relatively less,mainly distributed along the Yangtze river,while the plain area of Huaibei,the hilly area of central Anhui and the mountainous area of southern Anhui were scattered.The influence of precipitation and temperature on NPP in Anhui province fluctuated during the study period.In general,the consistency between NPP and annual average temperature was higher than that between NPP and annual average precipitation.Compared with annual precipitation,the correlation between vegetation NPP and temperature was slightly higher in Anhui province.During the study period,relative to precipitation,the correlation between NPP and temperature in Anhui province was slightly higher,and the Pearson correlation coefficient of both showed a decreasing trend in interannual variation,with the multi-year mean values of 0.54 and 0.79,respectively.However,the decline associated with precipitation was slightly larger than that associated with temperature.?6?During 2001-2016,the land use types with increased areas in Anhui province were mainly forestland,urban and construction land and wetland with the increase amount of1687.75,1007.00 and 754.00km²,respectively.The land types of NPP reduction were mainly cropland,cropland/natural vegetation mosaic and grassland,where the reduction was 2025.25,908.00 and 548.75km² respectively.During the study period,the total NPP of vegetation of different land use types in Anhui province was ranked from high to low:cropland>grassland>forestland>cropland/natural vegetation mosaic>water bodies>wetland>low vegetation cover land.Compared with 2001,the land use and cover change area in northern regions of Anhui was the least in 2016,more in central and southern regions of Anhui.Among them,the increased areas in northern regions of Anhui was mainly urban/built up?239.25km²?and wetland?122km²?,while the decreased areas were mainly cropland?275.50km²?and grassland?104.00km²?.The increased areas in central regions of Anhui were mainly forest?580.00km²?,urban/built up?450.50km²?and wetland?417.00km²?,while the decreased area was mainly cropland?785.25km²?,cropland/natural vegetation mosaic?369.00km²?and grassland?307.00km²?.The areas increased in southern regions of Anhui were mainly forestland?1105.25km2?,urban/built up?316.75km2?and wetland?21.75km²?.Among the decreased areas,cropland?945.25km²?,cropland/natural vegetation mosaic?551.50km²?and grassland?137.00km²?were the main ones.?7?Climate change with increasing warming and wetting and human behavior with increasing environmental protection promoted the increase of NPP in Anhui province.However,in terms of relative contribution,climate change had a greater impact on the increase of vegetation NPP in Anhui province.The reason was mainly related to the acceleration of urbanization,which makes the regional climate change in a warm and humid manner.