| This study analyzed climate change in Chinese ecologically fragile zones characteristics from 1982 to 2017,compared the latest version of the GLASS and GLOBMAP LAI data,analyzed the main characteristics of time and space changes of leaf area index(LAI)in the ecological fragile area,and discussed the main meteorological factors affecting changes of the LAI changes in the ecological fragile zone.The main conclusions of this study are as follows:(1)The annual mean and trend of the latest version of GLASS LAI and GLOBMAP LAI in China and the world are relatively close,with the annual mean difference between-0.5 and 0.5 m~2/m~2,and the annual trend difference between-0.03and 0.03 m~2/(m~2ˇyear);The annual mean LAI value of GLOBMAP in tropical rainforest area is significantly higher than that of GLASS,while that of non-forest area is lower than that of GLASS.Compared with GLOBMAP LAI,GLASS LAI has a higher spatial integrity,and there is no large area of missing data in the world and China.Since the same data source was used for the inversion of LAI from 1982 to2017,the time consistency of GLASS LAI was relatively good,while the data source inconsistency existed in GLLOBMAP LAI around 2000.In general,GLASS LAI data are more suitable for subsequent studies of this paper on long-term LAI changes and leading factors of climate.(2)Daily mean temperature increases significantly in the Chinese ecologically fragile zones.Nearly 97%of the lattice temperatures rise above 2?/100a,and 10%of the lattice temperatures rise greater than 5?/100a.The temporal variation of the whole mean temperature is dominated by the ecologically fragile zones in the north.The spatial and temporal variation characteristics of daily maximum and minimum temperature are similar to that of daily mean temperature.But for the frequency of increase above 4.0?/100a,the daily minimum temperature is greater than daily maximum temperature,which is greater than the daily mean temperature,and their frequencies are 52%,45%and 38%,respectively.Compared with the daily mean and minimum temperature,the daily maximum temperature rises more obvious in the ecologically fragile zones in southern China(especially in the agricultural and pastoral areas in southern China).(3)The regional differences of precipitation trends in Chinese ecologically fragile zones are significant,and the precipitation increase is very obvious in ecologically fragile zones in the arid and semiarid areas and loess plateau;while relative humidity generally shows a significant downward trend,more than 60%of the grid points with a declining trend above 10%/100a.After the 21st century,the precipitation in the ecologically fragile zones in the north basically showed an increasing trend;while the average relative humidity in Chinese ecologically fragile zones basically shows significantly downward trends.(4)From 1982 to 2017,LAI in Chinese ecologically fragile zones was mainly on an upward trend,and the number of grid points for LAI growth accounted for 80%of all unmeasured grid points in ecologically fragile zones.in ecologically fragile zones of karst in southwest China,the growth trend of average LAI was the largest,which was 0.9m~2/m~2/100a,followed by the loess plateau.LAI growth in the fragile region of the loess plateau started at the earliest time,and has been growing steadily and continuously since 1982.(5)The growth trend of LAI in ecologically fragile zones in the northern agriculture,animal husbandry,forest and grass are dominated by the west and northeast,while the growth trend of LAI in ecologically fragile zones in the southern farming and pastoral areas is dominated by the north and southeast.However,the spatial and temporal consistency of LAI changes in ecologically fragile zones of loess plateau?arid and semi-arid area?the Tibetan plateau and karst in the southwest China is relatively good,and LAI PC1 is consistent with the time variation characteristics of regional mean LAI,basically.(6)The dominant meteorological factor for LAI growth in Chinese ecologically fragile zones is temperature.Daily average temperature is the dominant meteorological factor for LAI growth in most ecologically fragile zones,while daily maximum temperature and minimum temperature are the dominant meteorological factors for LAI growth in ecologically fragile zones in southern agricultural and pastoral areas and western arid and semi-arid areas,respectively.Except for ecologically fragile zones in arid and semi-arid areas,LAI changes in Chinese ecologically fragile zones are more affected by the daily maximum temperature than the daily minimum temperature.(7)Compared with precipitation,LAI changes in ecologically fragile zones of agriculture,animal husbandry,forestry and grass in the north and southern farming and pastoral areas have a better relationship with relative humidity,probably because it can better reflect the actual dry and wet conditions in these regions.This enlightens us that in today's increasingly intensified climate change and human activities,the study of vegetation meteorological impact factors cannot be limited to temperature and precipitation. |
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