Study On Spatiotemporal Evolution And Influencing Factors Of Carbon Sink In Ningxia From 2000 To 2019

The continuous increase in carbon dioxide（CO₂）concentration has led to a continuous increase in global average temperature,which has caused a series of climate and environmental problems,and has had a significant impact on human survival and development.The terrestrial ecosystem is the main exchange site for CO₂and also the site with the most drastic changes in CO₂.Ningxia Hui Autonomous Region is located in the northwest inland of China and is a key ecological fragile area of concern to China.This article takes Ningxia Hui Autonomous Region as the research area.Based on remote sensing data,meteorological data,and land use data,the CASA model and regression model were used to estimate the monthly net primary productivity（NPP）of vegetation and soil microbial respiration（Rh）in Ningxia Hui Autonomous Region from 2000 to 2019.The difference of the above two was the net ecosystem productivity（NEP）.This thesis analyzed the spatio-temporal distribution and change patterns of carbon sink in Ningxia Autonomous Region,and explored the effects of meteorological and terrain factors,and human activities on carbon sinks in Ningxia.The main research content and conclusions are as follows:（1）With the CASA model and regression model,this thesis estimated the carbon sink in the study area.From an interannual perspective,the overall distribution of NEP in Ningxia Autonomous Region is high in the north and low in the middle,with the southern mountain areas>the Yellow River-irrigated>the center-dried.As a whole,the southern mountain areas and the Yellow River-irrigated are carbon sinks,while the central arid zone is carbon source.From 2000 to 2019,the overall capacity of carbon sequestration of Ningxia was enhanced.In 2000,75.22%of Ningxia’s regions were carbon sources,24.77%were carbon sinks,and in 2019,50%of the regions were carbon sources and carbon sinks.Among them,the number of carbon sinks in county-level administrative regions increased from 8 to 12,and the number of carbon sources decreased from 14 to 10.（2）From 2000 to 2019,there were significant differences in the distribution of NEP among different months in Ningxia.NEP was high in summer and low in winter,with the highest in August and the lowest in December.From October to April,only Helan Mountain,Luoshan Mountain,and Liupan Mountain showed carbon sinks.From May to September,the distribution of NEP in Ningxia was relatively similar to the annual distribution.（3）The influence of meteorological and topographic factors on NEP was explored through correlation analysis.There is a positive correlation between temperature,precipitation,solar radiation and NEP.The areas with positive temperature correlation are mainly distributed in the central and southern regions of Ningxia,while the areas with negative temperature correlation are mainly distributed in high-altitude areas and urban construction areas.The positive correlation areas of precipitation are mainly distributed in irrigation areas such as the Yellow River-Irrigated and Qingshui River-Irrigated,as well as in the southern mountain areas,while the negative correlation areas are mainly distributed in artificial irrigation areas such as Shapotou District.The positive correlation areas of solar radiation are mainly distributed in the Yellow River-Irrigated and Qingshui River-Irrigated,while the negative correlation areas are mainly distributed in the arid areas of the center-dried.As the elevation continues to rise,the NEP in Ningxia shows a trend of first decreasing,then increasing,and then decreasing.NEP exhibits the same variation pattern with slope changes at different periods.There is no significant correlation between NEP and slope orientation,with lower vegetation NEP on the southwest slope and higher vegetation NEP on the northwest slope.（4）Using the human activity intensity index,it was analyzed that the human activity intensity in Ningxia is 0.26,which is at a low level and shows a distribution pattern of strong in the north and weak in the south.High value areas are mainly distributed in the Yinchuan Plain.Taking the Hongsibao area as the boundary,there is a negative growth relationship between NEP and human activity intensity to the north.The Hongsibao District and the areas south of it have increased with the strengthening of human activity influence.