A Numeric Study On The Impact Of Climate Change On Ecosystem Carbon Dynamics And Productivity In China's Arid And Semi-arid Regions

As an important part of the global land,the arid and semi-arid areas are the most significant areas of temperature increase in the past 100 years.Although these areas only account for 30%of the global land,however,they contribute 50%to global warming,which is an important part of the study that cannot be ignored.The arid ecosystem carbon cycle is sensitive to climate,but the impact of severe climate change on carbon stocks in China's arid and semi-arid regions in recent decades remains unclear.In particular,there are large uncertainties in climate change data,which makes it difficult to evaluate carbon stocks in arid and semi-arid regions of China.In response to this problem,we used three climate reanalysis datasets(MERRA?Modern-Era Retrospective Analysis for Research and Applications?,ERA-Interim?European Centre for Medium-Range Weather Forecasts?ECMWF?Interim Re-Driven and CFSR?Climate Forecast System Reanalysis??to drive an Arid Ecosystem Model?AEM?,which we used to assess the impact of climate change and CO₂ elevation on carbon dynamics in China's arid and semi-arid regions from 1980 to 2014.The relative contribution rate of different environmental factors?precipitation,temperature,CO₂?to net primary productivity?NPP?in arid areas and their interaction effects were discussed.The influence of uncertainty of meteorological driving data on regional carbon dynamic assessment was discussed.The main work of this research:?1?Construction of standardized ecological and geographic GIS datasets that drive AEM modelsAt the site and regional scales,the key physiological and ecological parameters of the main vegetation types in arid and semi-arid regions of China were optimized,and localized assessments were carried out for the main vegetation types in the study area.Three sets of data for driving numerical simulations were constructed.Scale space meteorological dataset?including precipitation,relative humidity,short-wave radiation,maximum temperature,average temperature and minimum temperature?,and the accuracy of three of datasets.?2?Compare the organic carbon pool driven by three sets of meteorological reanalysis data and analyze its temporal and spatial characteristicsComparative analysis of three datasets of reanalyzed data simulation results,analysis of the total dynamics of regional organic carbon and its spatial pattern over the past 35 years.?3?The quantification the impact of climate change on regional NPPBased on regional scale sensitivity test and multi-scenario factor analysis,to quantify contribution of each climatic factor to NPP were quantified.Analysis of the impact process of climatic factors was carried out,and countermeasures and suggestions for sustainable development were also given.The main innovations of this research:?1?The effects of uncertainties of meteorological driving data on regional ecosystem productivity and carbon dynamic assessment were discussed by using multi-source meteorological data to drive numerical simulations.?2?Using numerical simulation experiments to isolate and quantify the effects of climate effects and different climate?and CO₂?change factors on ecosystems.The major controlling factors of productivity and NPP were identified as referential to regional ecological management for climate change.The main conclusions of this study are as follows:?1?Under the combined influence of climate and CO₂ changes,the study found that the three arid meteorological data in China showed carbon sinks in the past 35 years?1980-2014?,with a total growth of 0.75-1.23 Pg.The fluctuation of soil carbon pool?SOC?is the main factor in the dynamics of total organic carbon pools throughout the study area.?2?From the perspective of interannual variation,in 2012-2014,the carbon pools simulated by the three sets of datasets showed a significant growth trend with high consistency,indicating that the uncertainty of climate change data during this period was small.Between 1987 and 1990,the total carbon pool?TOTC?of MERRA and ERA-Interim showed a downward trend,while CFSR showed an upward trend with high uncertainty.From the perspective of spatial pattern,the TOTCs simulated by the three sets of datasets show that the northwestern part of Inner Mongolia has remained basically unchanged for the past 35 years,and the Ordos Plateau has shown an increase in TOTC,indicating that the uncertainty in these two regions is small.The three sets of data sets also differ in space.The TOTC simulated by the MERRA data set shows carbon loss?>-2 Kg C/m²?in the northeastern part of Daxinganling,while the ERA-Interim and CFSR simulated TOTC are in the area.The performance is increased by carbon?>1 Kg C/m²?,and the TOTC simulation in the MERRA dataset in the Qinghai-Tibet Plateau is slightly reduced?>-0.5 Kg C/m²?,while the other two sets of datasets show a slight increase in carbon pools in this region?>0.5 Kg C/m²?,indicating that the uncertainty in these two areas is higher.?3?Between 1980 and 2014,the average annual net productivity?NPP?simulated by MERRA,ERA-Interim and CFSR was 1579±16 Tg C or 301.667±3 g C/m²,1595±16 Tg C or 304.94±3 g C/m² and 1674±31 Tg C or 320.88±6 g C/m².In the past 35 years,NPP in China's arid and semi-arid areas showed a trend of growth.The NPP of MERRA simulation increased by 3.14g C/m²/year.The growth of ERA-Interim was obvious?12.15 g C/m²/year?,and the growth of CFSR was weak?0.33 g C/m²/year?.?4?NPP increased from 305.82g C/m²/year in the first half of the study period?1980-1997?to 311.03 g C/m²/year in the latter 18 years?1997-2014?,which is basically stable.However,this relatively stable pattern is the result of the offsetting effects of climate change and CO₂ fertilization.During the 35 years,the CO₂concentration increased by 18%,which led to an increase of 5.2%in NPP.However,climate change caused NPP to decrease by 5.3%.Among them,NPP decreased by 4.9%due to precipitation change?-0.2mm/year?,and temperature change caused NPP to decrease by 0.4%.There is only a weak interaction between climate factors.?5?The environmental main controlling factors of NPP in arid and semi-arid regions of China have high spatial heterogeneity,and about 60%of the regional NPP dynamics are mainly controlled by precipitation changes,especially in the northeastern part of Daxing'anling,the northwest and the central desert area of the Qinghai-Tibet Plateau.About 14%of the area is mainly affected by the CO₂ effect,including the North China Plain,the eastern Inner Mongolia and the northwest desert oasis and mountainous areas;12%of the area is mainly affected by temperature,mainly distributed in the northeast and southwest of the Qinghai-Tibet Plateau.The complex pattern of regional climate response is due to the spatial heterogeneity of climate change in arid and semi-arid regions of China,and the differential response characteristics of major vegetation types to climatic factors in different regions.Adapting to the environmental main control factors in different regions is an important guarantee for maintaining ecosystem productivity and promoting sustainable development in arid and semi-arid regions under the background of climate change.This study can commend countermeasures to provide decision-making advice for regional strategies to address climate change.?6?The use of three sets of data sets can help to analyze the uncertainty caused by meteorological factors in the study area.It can also be seen from the research results that the carbon sink pattern caused by different data sets has significant heterogeneity?carbon sink 0.75-1.23Pg?.Further accurate quantification of meteorological factors in the study area is the focus of the next step.The soil carbon pool is the main carbon pool in the arid area,accounting for more than 80%of the total carbon pool.The study found that soil carbon pool fluctuations are the main cause of carbon sinks in the study area.