Spatial-temporal Variation Of Extreme Precipitation Index And Its Influence On Vegetation In Inner Mongolia

The fifth assessment report of the United Nations Intergovernmental Panel on Climate Change(IPCC)pointed out that the global average surface temperature increased by about 0.85°C between 1880 and 2012.In the context of global warming,the frequency and extent of extreme weather events have increased significantly.The suddenness and extreme nature of extreme weather have exerted greater impacts than average temperature and annual precipitation have done on plants and plant communities,resulting in severe degradation or loss of vegetation habitats and changes in vegetation ecosystems.Based on the daily precipitation data of 100 meteorological stations in Inner Mongolia from 1960 to 2014 and the GIMMS-NDVI remote sensing data from 1982 to 2014,thesis analyzes the extreme precipitation indices,NDVI time evolution trend and spatial variation characteristics.And then based on different time and space scales and different vegetation types area,the thesis explores the response characteristics of the annual/monthly variation of vegetation NDVI in Inner Mongolia to extreme precipitation indices.The results show:(1)From 1960 to 2014,all extreme precipitation indices in Inner Mongolia showed different degrees of decline,and their trends were not significant,but the characteristics of interannual fluctuations were obvious.According to the spatial variation trend of extreme precipitation indices,the annual average trend of continuous drying index(CDD)decreased from west to east,and the average annual trend of other indices decreased from east to west.The spatial distribution trend of extreme precipitation indices in the region,the number of heavy precipitation days(R10),continuous wetness index(CWD),heavy precipitation(R95),monthly maximum 1-day precipitation(Rx1day),simple daily intensity index(SDII)and annual total precipitation(PRCPTOT)uptrend site is higher than the downtrend site,and the continuous dryness index(CDD),monthly maximum consecutive 5-day precipitation(Rx5day),and the wet days(NW)are the opposite.From the spatial distribution characteristics of the trend of extreme precipitation indices,the regional differences are significant.The stations with a general decreasing trend are mainly distributed in the eastern and central regions of Inner Mongolia,while the stations with increasing ternd are mainly distributed in the northeastern and western regions of Inner Mongolia.(2)The annual maximum NDVI of vegetation in Inner Mongolia from1982 to 2014 has a non-significant increasing trend,and its rising rate is0.003/10a,which is slow before 2010,but more obvious after 2010.The NDVI interannual volatility was obvious in each month.The NDVI in June,showed a decreasing trend;In April-May,July-October NDVI has an increasing trend,of which NDVI showed a very significant increasing trend in October(P<0.01),and the trend was 0.01/10a.(3)The interannual spatial distribution of NDVI from 1982 to 2014shows that the NDVI of the eastern part of Xing'an League,the southern part of Tongliao City,the southern part of Chifeng City,the southern part of Hohhot City,the eastern part of Erdos City,and the southern part of Bayannaoer City have a large increasing trend.The rate is between 0.1/10a and 0.2/10a;In the southwest of Xing'an League,the northern part of Tongliao City,the northern part of Chifeng City,the central part of the eastern part of Xilingol League,and the small part of northern part of Hohhot City,the NDVI declines greatly,and its decline rate is between-0.09/10a and-0.05/10a.Overall,the area of having the NDVI decline trend in the study area is larger than the area of having the increasing trend.In most areas,the NDVI showed a decreasing trend in each month,and only a small part of the area showed an increasing trend.(4)According to the correlation between the extreme precipitation indices and NDVI,the correlation coefficients of R10,R95,Rx1day,Rx5day,SDII and PRCPTOT with NDVI are 0.64,0.66,0.59,0.53,0.72 and 0.62,both greater than 0.5(P<0.01),significantly greater than the correlation coefficient of other indices and NDVI.The correlation coefficient between NW and NDVI was 0.42(P<0.05).There is a spatial difference in the response of vegetation NDVI to the annual extreme precipitation index,but most regions have a high positive correlation with NDVI and extreme precipitation indices.According to different vegetation types,the vegetation of typical steppe,desert steppe,steppe desert and meadow stepland gave greater response to the extreme precipitation indices.The NDVI of each vegetation type area was significantly correlated with most extreme precipitation indices.(5)The correlation and hysteresis of NDVI and the monthly precipitation of extreme precipitation indices indicate that Rx1day and Rx5day have the greatest impact on vegetation in July,and the correlation coefficients are 0.55and 0.54,and showed highly significant correlation.Secondly,Rx1day and Rx5day have a significant impact on vegetation in June,which is significantly correlated.From April to October of the past 33 years,NDVI had significant correlation with Rx1day and Rx5day,and its decision coefficient R~2 was above 0.75,and its monthly scale correlation coefficient was higher than the annual scale.Rx1day and Rx5day had the greatest impact on NDVI in the current month and the first two months,and the correlation coefficient was above 0.85(P<0.05).Vegetation in meadow grassland,desert steppe,desert,agricultural area and grasslandized desert area was significantly affected by the extreme precipitation indices of current month,and the typical grassland was significantly correlated with the extreme precipitation indices of current month.Extreme precipitation in the first two months had the greatest impact on NDVI in each vegetation type area.