Multicentury Wildfire And Climate In The Daxing'an Mountains,China

Wildfire is in many ecosystems a central organizing disturbance process,affecting biogeochemical cycles,biodiversity and ecosystem structures,and hydrological processes.Wildfire also often has profound social and economic impacts,which are forecast to increase with future intensification of human land use and anthropogenic climate change.Increased wildfire sizes and severities in recent decades in many locations around the world have focused attention on potentially severe consequences of warmer temperatures,changes in rainfall patterns,earlier spring snow melt,and longer fire seasons.Wildfires are strongly affected by changes in weather and climate,but on varying spatial and temporal scales.The occurrence,spread,and intensity of any single wildfire is mainly dependent on weather patterns that vary on daily to monthly time scales.However,there is increased understanding of linkages between wildfire synchrony over regional scales and inter-annual to multi-decadal patterns in climate variation influenced by global teleconnections such as the El Nino-Southern Oscillation(ENSO)and other coupled ocean-atmosphere temperature and pressure patterns.These patterns affect regional droughts that,in turn,affect local patterns in fuel moisture and lightning ignitions.We crossdate 207 fire-scarred trees from the six sites sampled in the Daxing'an Mountains,with individual wildfire dates extending from 1693 to 2007.Wildfires were frequent occurrences in all sites,although there was a decline in both local and regional wildfire frequency after 1947.We identified 31 regional wildfires(recorded at 2 or more sites)from the first recorded in 1774 to the last in 1987.Regional wildfires occurred on average every 7 years from 1774 to 1947.We did not calculate fire frequency after 1947 because of the obvious change in wildfire frequency after this date.Only three regional wildfires were recorded after 1947:in 1974,1977,and 1987.Fire scars were generally recorded as dormant(before growth began for the year)or early in the ring for any one year.Regional wildfires exhibit consistent and significant relationships with regional drought during the 20th century and with atmospheric circulation patterns since 1774.Regional wildfires typically occurred during years of low PDSI,El Nino years(positive Nino3 and negative SOI),positive phases of the PDO,and negative phases of the NAO.We also find in the chi-square contingency test of expected vs.observed wildfire dates that contingent combinations of years when El Nino,positive PDO,and negative NAO occurred led to more wildfires than expected if wildfire occurred by chance.Correlations between seasonal meteorological station parameters and large-scale climate oscillations over the common period 1957-2009 support linkages seen in the historical wildfire data.Previous winter PDO and temperature anomalies(0.28;p<0.05,n = 53).NAO was negatively correlated with spring temperature anomalies(-0.41;p<0.015 n = 53)and positively correlated with precipitation anomalies(0.39;p<0.01,n = 53)in summer.We performed the rotated principal components analysis and identified 16 PC axes with Eigenvalues>1 that explain a total of 84.3%of spatial variance in Aprial to October(A-O)instrumental PDSI across eastern China.PC1,PC2,and PC3 explain 23%,12%,and 11%of the variance,respectively.The correlation between PC1 scores and mean A-O NAO for the period 1925-2014 is-0.33(p<0.01,n=90),correlation between PC1 and A-O Nino3 is 0.26(p<0.05,n=90),and correlation between PC3 scores and A-O PDO indices is 0.31(p<0.01,n=90).No teleconnection was related to PC2 scores.The spatial pattern of PC1 and PC3 loadings of gridded A-O PDSI strongly resemble the spatial correlation patterns of A-O PDSI with A-O NAO,Nino3,and PDO,respectively.At last,we analyze the fire history in Zion Nationa Park,the results are generally the same compared with the Southwest USA,we also explore the differences between Northeast China and Zion National Park of fire history.We create the database of fire history in China,and found the driving forces of the fire in China is still the climatic conditions.