Historical Temperature And Runoff Recorded By Tree-ring In The Daxing’an Mountains

Climate warming has caused irreversible effects on the natural world and human living environment.The Sixth Assessment report of IPCC points out that it is urgent to mitigate global climate change and adapt to climate warming.With the continuous development of society,water shortage and other problems are becoming increasingly serious,and climate change has become a hot issue.The characteristics of tree-ring,which can qualitatively and quantitatively indicate environmental changes,make up for the shortage of modern instrumental data,and have become an important tool for reconstructing paleoclimate,research on using annual rings to reveal hydroclimatic changes in long historical periods is urgently needed and is important for understanding the historical hydroclimate of the region.The complex climatic conditions and geographical location of the Daxing’an Mountains make it one of the sensitive zones for climate change,and the study of the spatial and temporal characteristics of hydroclimatic elements here is representative.In this study,Larix gmelinii,a dominant tree in the northern virgin forest of the Daxing’an Mountains,and Picea koraiensis,a precious tree in the southern reserve,were selected.The standardized chronology(STD),the residual chronology(RES)and the autoregressive chronology(ARS)of Larix gmelinii and Picea koraiensis were constructed.Based on an in-depth analysis of the response relationship between tree growth process and hydroclimatic factors,the long-term historical series of annual mean temperature and annual runoff in the Daxing’an Mountains over the past two centuries were reconstructed by using the optimal regression model.The variation characteristics of the hydrological climate in this region are analyzed,and the variation rules of temperature and runoff in the past are revealed.The main conclusions are as follows:1.This study established STD,RES,and ARS for Larix gmelinii from 1749 to 2020 and Picea koraiensis from 1813 to 2016.All statistical characteristics of the chronologies are in accordance with international standards for tree chronology and can be used to reconstruct historical hydrological climate change in the Daxing’an Mountains.2.The radial growth of trees in the Daxing’an Mountains is closely related to temperature and runoff,with temperature inhibiting the radial growth of trees and runoff promoting the growth of annual rings width.The optimal regression model was selected to reconstruct the historical series of annual mean temperature and annual runoff in the southern part of Baiyinaobao and the northern part of Mangui for 172 a and 223 a.The results of the segmental test method can be used to study the changes of temperature and runoff in the long historical period in the Daxing’an Mountains.The regression model is accurate and reliable,and can be used to study the changes of temperature and runoff in the Daxing’an Mountains in long historical periods.3.The annual mean temperature in the Daxing’an Mountains showed an increasing trend.In the past 172 years,the southern Baiyinaobao area has experienced 6 cooling and8 warming periods,with the highest and most dramatic changes in the decadal mean temperature in the study area from 2005 to 2016,experiencing 2 warming and 3 cooling periods,with the longest-lasting cold period occurring from 1909 to 1918.In the northern Mangui region,there were 2 cooling and 3 warming periods in the past two centuries,with the longest duration warming period occurring from 1978 to 2020,during which the interdecadal mean was the highest,with 2 cold periods and 8 warm periods,and abrupt temperature changes occurred in 2000 and 2009.The average annual temperature in the southern part of the Daxing’an Mountains is higher than that in the northern part as a whole.In the past two centuries,cold years were concentrated in the 1910 s and warm years were frequent in the early 21 st century,and the temperature series showed significant cycles of3 a,7 a,10-11 a,15-22 a and 35 a.PDO has the greatest influence on temperature change in the Daxing’an Mountains.4.The annual runoff in the Daxing’an Mountains showed a decreasing trend.There are obvious changes of dry and abundant water in the runoff series of the southern Gonger River since 1845,which has experienced 8 periods of abundant and 7 periods of dry runoff,and the period of rising runoff with longer duration occurred from 1880 to 1914,with 4periods of wet water and 2 periods of dry water,and in 2016 runoff reached the abundance year standard.The Northern Ji Liu River Basin experienced more frequent runoff abundance conversions before 1838,with the long-duration variable abundance period occurring from 1888 to 1942,and a total of 38 wet years and 25 dry years over the last 2centuries,with 2020 being the year with the least reconstructed runoff.The annual runoff in the north is much higher than that in the south,and the changes fluctuate more gently.The wet years appeared more frequently in the 1910 s,and the dry years occured in the early 21 st century.The runoff series showed significant cycles of 3 a,10-11 a and 20-22 a.The variation of runoff in the Daxing’an Mountains was closely related to the largescale climate circulation activities.This study uses the environmental "recorder" tree-ring to reveal the changes of temperature and runoff in the Daxing’an Mountains,providing a theoretical reference to explore the impact of climate change on the long history of hydroclimate in the area,and providing a basis for the rational development and utilization of water resources in the area.