Assessment Of Impacts Of Extreme Droughts On Gross Primary Productivity Of Terrestrial Ecosystems In China

The gross primary productivity(GPP)of terrestrial ecosystem is the sum of photosynthetic carbon uptake by vegetation in terrestrial ecosystem,the starting point of carbon biogeochemical cycle,and the main index reflecting the carbon flux in the biosphere.As an extreme climate event,drought can have an important impact on the carbon cycle process of ecosystems,which affects the productivity of terrestrial ecosystems by affecting photosynthesis.However,China is located in the Asian monsoon climate zone and is sensitive to global changes,which in essence makes China change one of the countries with the highest frequency and the most severely affected drought disasters.Therefore,it is of great significance to carry out the spatial and temporal pattern of the vegetationa gross primary productivity(GPP)and drought in China and the influence of the typical drought years on the vegetationa gross primary productivity in China.Based on two sets of GPP of revised light energy utilization model(EC-LUE)and bayesian multi-algorithm integration simulation(GLASS),meteorological data of China’s618 meteorological stations from 1982 to 2017,using trend analysis and GIS spatial statistics technology quantifies the spatial and temporal pattern of GPP and drought in China from 1982 to 2017,and discuss the response characteristics of GPP on drought in different time scales and different vegetation types.The main conclusions are summarized as follows:(1)Temporally,the two sets of GPP showed an increasing trend year by year from1982 to 2017,1998 year and 2002 year were significantly higher than the average over the study period,1989 year and 1992 year were significantly lower than the annual average GPP;spatially,the spatial distribution characteristics of GPP in China during 1982-2017 showed a downward gradient from southeast to northwest,the areas with larger annual fluctuation of GPP are mainly distributed in the south of southwest China and the north of central China;the two sets of GPP in four seasons showed an obvious upward trend in most areas of China,and the proportion of regions with significant increase was 75.7%(EC-LUE GPP)and 73.0%(GLASS GPP)(p<0.05),respectively;in different vegetation type regions,the highest value of GPP is in the R7(tropical monsoon rainforest,rain forest regions),followed by the R1(subtropical evergreen broad-leaved forest region).GPP anomalies with the larger change range of fluctuation are in R1 and R3(warm temperate deciduous broad-leaved forest region)and R7.The spatial distribution and variation trend of the two sets of GPP in four seasons are consistent with the annual scale.(2)From 1982 to 2017,China’s annual SPEI showed a fluctuating downward trend,and its linear change rate was-0.0232/10 a.SPEI decreased in spring and summer,and SPEI increased in autumn and winter,so drought decreased during vegetation growth;spatially,the low value of SPEI from 1982 to 2017 appeared in the southeast of the Southwest China and the southeast of the Northwest China,and the regions of the high value appeared in most regions of the Northwest China.The distribution regions of the high and low values of summer in the four seasons is similar to the year scale;from 1982 to 2017,the central part of the Southwest and Northwest China and the eastern region of the country showed a humid trend,while the northwest and southeast of the Northwest China,southwest and southeast of the Northwest China,and southeast of the North China showed a drought trend.The SPEI did not change significantly in most regions of the country,while the proportion of significant changes of SPEI from 1982 to 2017 was15.18%.The distribution areas of dry and wet trend in summer are basically consistent with the annual scale.(3)From 1982 to 2017,the most significantly affected by different levels of drought in China were 2001 year and 2011 year respectively.Overall,whether it is the annual,seasonal or monthly scale,the rate of GPP decline caused by drought increases as drought level increases.Specifically,at the annual scale,the areas affected by drought in 2001 year were mainly in North China,Northeast China and the north of the Middle East.Extreme drought caused decline rate of 21.77% and 16.01% in EC-LUE GPP and GLASS GPP,respectively.The areas affected by drought in 2011 year were mainly in the southeast of Southwest China and the Middle East.Extreme drought caused decline rate of 9.69% and6.72% in EC-LUE GPP and GLASS GPP,respectively.At the seasonal scale,summer GPP has the most loss rate caused by different levels drought in 2001 year.Extreme drought caused decline rate of 19.96% and 15.57% in EC-LUE GPP and GLASS GPP,respectively.Spring GPP has the most loss rate caused by different levels drought in 2011 year.Extreme drought caused decline rate of 14.32% and 8.75% in EC-LUE GPP and GLASS GPP,respectively.At the monthly scale,extreme drought caused decline rate of22.91% and 15.43% in EC-LUE GPP and GLASS GPP in May 2001 year,respectively.Extreme drought caused decline rate of 97.91% and 97.89% in EC-LUE GPP and GLASS GPP in January 2011 year.The most areas affected by drought in 2001 year and 2011 year were temperate grassland areas and subtropical evergreen broad-leaved forest areas,respectively.The results of this paper allow us to have a deep understanding of the changing law of gross primary productivity and drought in China in the past 36 years,and further understand the impact of great drought on the gross primary productivity of vegetation in China,which provide an important scientific basis for China to deal with the impact of drought on carbon cycle.