Effects Of Global Sea Surface Temperature On The Seasonal Severity Rating Of Wildfires In East Asia

Wildfires include forest fire,brush fire,and grassland fire.East Asia is rich in forest and grassland resources.Forest is the main body of terrestrial ecosystem,which is the largest,most complex,multi-species,multi-function and multi-benefit ecosystem on the land.Grassland is an important part of the terrestrial ecosystem and plays an important role in the ecosystem.As the emissary of human civilization,wildfire plays an important role in the natural ecosystem.Each occurrence of wildfires causes incalculable damage to natural resources such as forest resources,grassland resources,economic losses and human lives.The occurrence and spread of wildfires are influenced by many factors,among which climate plays an important role.The frequency of climate anomalies has increased significantly in recent decades,with wildfires increasing in size and severity in many parts of the world.Both sea surface temperature and pressure anomalies affect climate change,which in turn affects regional temperature and precipitation.Changes in regional temperature and precipitation affect the humidity and amount of combustible material,and finally affects the occurrence of wildfires.Correlation analysis,regression analysis,empirical orthogonal function analysis,singular value decomposition and other methods was used to analyze the impact of global sea surface temperature anomalies on the seasonal severity rating of fire in East Asia under each climate zone from 2000 to 2017.The main findings are as follows:(1)It was observed that wildfire point of East Asia had a negative trend from 2001 to 2017 and mainly in spring,and wildfires are mostly in the east.The spatial and temporal distribution of each climate zone also have their own characteristics.In the tropical or subtropical humid climate zone,the wildfire points had a decreasing trend,and wildfires mainly in winter;in the tropical or subtropical arid winter climate zone,the wildfire points had a decreasing trend,and wildfires are mainly in January to March;wildfire point in the temperate monsoon climate zone had a positive trend,and wildfires are mainly in March to April;in the temperate semi-arid climate zone,wildfire had a creasing trend,and wildfires are mainly in June to July.(2)It was observed that SSR of East Asia had a negative trend from 2000 to 2017,and temperate monsoon areas and temperate semi-arid areas have the highest risk of wildfires.Taking the peak time of wildfires as the research time,the SSR of tropical or subtropical humid climate zone,tropical or subtropical arid winter climate zone,temperate monsoon climate zone and temperate semi-arid climate zone all had a negative trend.(3)Using a linear regression to analysis SSR data and wildfire point times in four climatic regions,it was observed that the correlation coefficients of tropical or subtropical humid climate regions and tropical or subtropical arid winter climate regions were 0.85 and 0.71,it shows that the SSR is increased,the number of wildfire points is also increasing.The number of wildfire occurrences in temperate monsoon climate zone and temperate semi-arid climate zone has a good correlation with the second mode after EOF decomposition of SSR.(4)Analyzing the obtained SST data after excluding the freezing point data,and obtain the global sea temperature distribution,time coefficient of variation and trend from 2000 to 2018.It was observed that the time coefficients of variation of global SST are all positive,and the regions with the highest variability are high latitudes,the equatorial Middle East Pacific,and the Peruvian coast.The sea surface temperature in most sea areas of world were increasing,especially in the South Indian Ocean and the Middle East and Pacific.SST in the North Pacific and North Atlantic was decreasing.The first mode of the EOF of SST is the main mode,indicating the change in temperature increase(decrease)in the northern hemisphere and temperature decrease(increased)in the southern hemisphere;the second mode discovered El Ni?o incident and found 2002,2005,2010,2012,2016 is the El Ni?o year;the third mode discovered the La Nina incident.(5)This study analyzed the interactions between global sea surface temperature(SST)and fire seasonal severity index(SSR)of climatic regions of East Asia using singular value decomposition(SVD)to identify key sea areas affecting the SSR of terrestrial climatic regions and quantify the impact periods of SST on SSR.The results showed that: In the tropical or subtropical humid areas,significant positive correlations were found between winter SSR and SST of the Pacific Ocean around central and western Equatorial of last March to May.While,in the tropical or subtropical arid areas,strong negative correlations were found between SSR from January to March of the current year and SST of the North Atlantic from last April to June.In temperate monsoon climate regions,the SSR from March to April shown significantly negative correlations not only with SST from last September to November in the eastern Pacific Ocean,but with SST from last April to June in the North Pacific Ocean.Likewise,in the temperate semi-arid climate regions,the SSR from June to July was negatively correlated with not only SST from last October to December in the eastern Pacific Ocean,but SST from last June to August in the Indian Ocean.Together these results indicated that sea surface temperature anomalies have a significant impact on the severity of fire season in East Asia,which provided an important basis for the prediction of the SSR in the study area.(6)To find out the influence of distribution pattern of the key sea zones on each climate region,SSR of each climatic zone is coupled with its key sea.From first mode of SVD analysis in tropical or subtropical humid areas and the Western and Central Pacific SST critical areas,it is observed that SST in the key sea is high,SSR in the southeast,South and west of the tropical or subtropical humid areas is high,and vice versa;the second mode indicates that when SST in the Western and Central Pacific SST critical areas increases,SST in the southeast of the tropical or subtropical humid areas is high.The first mode of the SVD analysis of the tropical or subtropical arid winter climate zone and the key area of the North Atlantic sea temperature shows that when the SST warms up in the key area of the North Atlantic sea temperature from April to June of the current year,the SSR is low in most areas of the study area,on the contrary high.The first mode of SVD analysis of the temperate monsoon zone and the key zone of the East Pacific SST shows that when the SST of the key zone of the East Pacific SST increases from September to November of the previous year,SSR will decrease from March to April of that year the northeast and north and most of Japan of the temperate monsoon zone,and vice versa;the first mode of SVD analysis with the key area of the North Pacific SST shows that the SST in the key area of the East Pacific sea temperature had increased(cooled)from March to May of the current year at that time,the SSR in the northeast south,west northeast,north China of the temperate monsoon zone,and Japan increased(lower).The first modal results of the SVD analysis of the temperate semi-arid climate zone and the critical zone of the SST in the East Pacific indicate that when the SST warms up in the East Pacific zone from October to December of the current year,the SSR in most regions of the temperate monsoon zone will decrease,and vice versa;the first mode of the SVD analysis with the key area of the Indian Ocean shows that when the SST of the North Indian Ocean SST decreases from June to August of the last year,the SSR in most areas of the temperate monsoon area is high,and vice versa low.