| Vegetation is the most important part of land cover and a key part of the ecological function of terrestrial ecosystems.As a living system for human survival and development,terrestrial ecosystems have many responses to global climate change.Plants covered by the ground can slow down the kinetic energy of raindrops,reduce flood peaks,relieve runoff,and have ecological functions such as optimizing soil resistance to erosion and alleviating soil erosion.so starting from the research and evaluation of vegetation changes,can effectively evaluate the quality of the regional environment,and provide guidance on measures to maintain the balance of regional ecosystems.Rao River Basin is located in the northeast of Jiangxi Province,with rich vegetation types in the basin,and "one lake and five rivers" is an important part of the basic pattern of ecological protection red line in Jiangxi Province,which is an important basin to promote the construction of ecological civilization and effectively protect the "clear water of Poyang Lake" with the efforts of the whole province.It is an important watershed of Jiangxi Province.Therefore,choosing Rao River Basin as a typical area can not only further grasp the condition of "one lake and five rivers" ecosystem in Poyang Lake Basin and provide data support for ecological restoration of Rao River Basin,but also has great significance for understanding the quality of regional ecological environment and maintaining regional ecological balance in the context of global change.Based on the ecological theory of the river basin,based on the MODIS NDVI data and natural society survey data of the river basin from 2000 to 2020,this study uses trend change analysis,Theil-Sen Median method,Mann-Kendall trend test method and geographic detector model to study the temporal and spatial variation characteristics of NDVI in the Rao River Basin in the past 21 years,and analyzes the influencing factors of vegetation cover change in the river basin.In addition,the main influencing factors or extent of vegetation cover in the Rao River Basin are identified.The conclusions of the study are as follows:(1)The NDVI in the Rao River Basin is well,and the overall trend of regional NDVI showed a slow increase trend,and there are differences in NDVI at different time scales and different spatial distributions.Among the inter-annual changes,NDVI in the Rao River Basin show a significant increase trend from 2000 to 2020,with a growth rate of 4.5×10-3yr-1,and show a slow fluctuation increase and a large increase in 2000-2007 and 2008-2018,respectively.In the seasonal changes,NDVI in the Rao River Basin show an increasing trend in spring,summer,autumn and winter,which is summer> autumn> spring > winter.Among the monthly changes,NDVI show a unimodal growth trend,with February being the lowest value,and the unimodal growth began to decline in August.In the interannual spatial distribution,the NDVI distribution trend in the Rao River Basin was high in the northeast and low in the southwest,and the high vegetation coverage area increasfrom 0.14% to30.25%.The spatial distribution characteristics of NDVI in all seasons are similar to those in the Rao River Basin,and the NDVI values in different seasons varied according to the time of vegetation growth and biological characteristics.The average CV coefficient of NDVI in the Rao River Basin is 0.062,indicating that the stability of vegetation growth in the basin is high.The Hurst index indicates that the NDVI in the Rao River Basin is mainly weakly sustained and will show a weak upward trend in the future.(2)In terms of natural factors,the temperature and precipitation in the Rao River basin show an increasing trend from 2000 to 2020,the average seasonal temperature and the average annual temperature both show an increasing trend,the growth rate of the four seasons is summer > spring > autumn > winter,the average seasonal precipitation and the average annual precipitation also show an increasing trend,the growth rate of the four seasons is the same as the temperature;and the spatial pattern of the four seasons temperature is similar,and the eastern temperature is lower than the western temperature in the east-west direction,and the central temperature is higher.In the north and south upwards,the overall temperature is lower in the north than in the south;The spatial pattern of precipitation in the four seasons is similar in spring and winter,high in southeast and low in northwest,similar in summer and autumn,and gradually decreasing from east to west.NDVI in the Rao River Basin showed dynamic changes under the combined influence of temperature and precipitation factors,and temperature played a leading role in the meteorological factors of the basin.The partial correlation coefficient between NDVI and temperature in the four seasons is spring> summer> autumn > winter.The temperature of spring,summer and autumn is positively correlated with NDVI,and the temperature in winter is negatively correlated with NDVI.The average partial correlation coefficient between NDVI and precipitation in different seasons is from high to low in autumn> spring> summer > winter.Spring and autumn precipitation are positively correlated with NDVI,and summer and winter precipitation were negatively correlated with NDVI.In terms of altitude,NDVI decrease with the increase of altitude,and in terms of slope,NDVI gradually increase with the increase of slope,and the change of NDVI is not significant with the slope,with the largest NDVI in the northeast slope and the smallest NDVI in the western slope.(3)In terms of social factors,from 2000 to 2020,the land use of the Rao Rive Basin changed significantly,the area of water and construction land in the Rao Basin increased,and the area of cultivated land,forest land,grassland and unused land decreased in turn.The expansion of construction land is distributed in areas with a high level of urbanization.The mode of land use conversion is mainly to shift forest,grassland and arable land to construction land.Among the different land use types,forest land has the highest NDVI and construction land have the lowest NDVI.The population of the Rao River Basin is concentrated in Zhushan District,which is also the region with the highest GDP,and the negative impact of residual analysis on human production and life is also concentrated here,and the NDVI of the basin decreases with the growth of population density and GDP.(4)Natural factors play a major role in the NDVI change in the Rao River Basin,followed by social factors.The most influential factors were temperature and slope,and the most significant interaction factors are temperature and slope,which are two-factor interaction enhancements,and the distribution of driving factor interaction results are as follows: two-factor nonlinear enhancement accounted for 23.5%,and two-factor interaction enhancement accounted for 76.5%.The largest driver grading range or type of NDVI are as follows: temperature is 15.4-15.9°C,precipitation is 1527-1682 mm,soil type is simplified highly active strong acid soil,land use type is woodland,altitude is 450-600 m,slope is 25-40.58°Vegetation type is broadleaf forest,population density is 75-350 people/square kilometer,GDP is 300-20000 yuan/person.In summary,there are differences in time scale and spatial distribution of NDVI in the Rao River Basin from 2000 to 2020.The future basin NDVI show a slight upward trend.Natural factors and human factors jointly affect the NDVI of the river basin,and natural factors have a greater influence on the change of vegetation NDVI in the Rao River Basin.This study provides data support for vegetation monitoring and ecological restoration in the Rao River basin base on the analysis of the relationship between vegetation and its drivers. |
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