Study On The Variation Characteristics Of Extreme Climate Events On The Qinghai-Tibet Plateau During 1961-2016

In recent years,global warming and frequent extreme climate events have attracted wide attention of governments and international organizations.The Qinghai-Tibet Plateau has unique geographic characteristics and ecological environment system.It is sensitive to climate change and extreme climate events,and has poor ability to resist natural disasters.Explore the characteristics of extreme climate events in the QinghaiTibet Plateau under the background of global change has a practical significance for the protection of ecological environment and resources in the region and for coping with extreme climate events and secondary disasters.Based on the daily temperature and precipitation data of 67 meteorological stations in the Qinghai-Tibet Plateau from 1961 to 2016 and 13 extreme temperature and 10 extreme precipitation indices commonly used in the world,the spatiotemporal variability and probability distribution characteristics of extreme climate events over the Qinghai-Tibet Plateau were discussed in detail on the basis of analyzing the characteristics of climate change in the region.The main conclusions are as follows:(1)From 1961 to 2016,the temperature of Qinghai-Tibet Plateau has increased obviously.The average linear warming rate was 0.32 ?/10 a.There were significant spatial differences in the annual average temperature distribution,showing higher in the southeast and Qaidam basins and northeastern Qinghai,and lower in other regions.The first eigenvector of EOF indicated the consistency of temperature change in the whole region of the Qinghai-Tibet Plateau,showing a fluctuant rising trend.The second eigenvector indicated the difference of temperature change between the north and the south of the Qinghai-Tibet Plateau.The main feature was that the main warming stages were different in the north and south of the region.From 1961 to 2016,the precipitation of the Qinghai-Tibet Plateau showed a trend of fluctuating growth.Increase and decrease occurred alternately,with an increased rate of 7.2 mm/10 a.There were significant spatial differences in the distribution of annual average precipitation,which showed the decreasing regulation from southeast to northwest.The first eigenvector of EOF mainly represented the North-South difference of precipitation change in the central and eastern part of the Qinghai-Tibet Plateau,and the main feature was the difference of precipitation increase stages in the region.The second eigenvector mainly represented the consistency of the main regions of precipitation change.The main feature was that the increase of precipitation in the plateau was mainly caused by the increase of the region,and the main increase stage was in the 1990 s and after.(2)From 1961 to 2016,the extreme temperature cold indices and daily range of temperature(DTR)in the Qinghai-Tibet Plateau showed a significant decreased trend,while the warm indices showed a significant raised trend.Among them,the change trend of cold index was obviously higher than that of warm index,especially the minimum of minimum temperature(TNn),which showed the cold-warm asymmetry of temperature increasing.Compared to other regions in China,the trend of extreme temperature indices in the Qinghai-Tibet Plateau was consistent with that in other regions.Except for the daily range of temperature(DTR),the warm spell duration index(WSDI)and the cold spell duration index(CSDI),the range of other indices was obviously larger than that in other regions,especially the relative indices.The "amplifier" effect of climate change in the Qinghai-Tibet Plateau was extremely obvious.Similar to the Qinghai-Tibet Plateau,the range of night indices in other regions was larger than that of day indices,and the minimum of minimum temperature(TNn)was much larger than the other three extreme temperature indices.The asymmetric warming characteristics were widespread under the background of global warming.Except for the daily range of temperature(DTR),the other extreme temperature indices in the Qinghai-Tibet Plateau had high correlation.The correlation between annual average temperature and extreme temperature indices was good,and the change of extreme temperature indices can better reflect the climate change trend of the QinghaiTibet Plateau.(3)The total precipitation amount(PRCPTOT),simple daily intensity index(SDII),heavy precipitation(R95p),extremely heavy precipitation(R99p),weak precipitation days(R10mm),weak or moderate precipitation days(R20mm),maximum 1-day precipitation(RX1day)and maximum 5-day precipitation(RX5day)of the Qinghai-Tibet Plateau all showed an increasing trend.The increase of heavy precipitation(R95p)and extremely heavy precipitation(R99p)were more than half of the total precipitation,which were the main source of precipitation increased in the Qinghai-Tibet Plateau.The maximum consecutive dry days(CDD)and maximum consecutive wet days(CWD)tended to decrease.In recent decades,the precipitation in the study area became more homogeneous,and the drought events were reduced.The spatial distribution pattern of extreme precipitation index changed in the study area was more complex and the difference was greater.The increased extreme precipitation index generally increased in the study area,but only fewer stations which amount below 30% of the total stations passed the significance test.Consistently,except for extremely heavy precipitation(R99p),the stations with significant increases in these indices were concentrated in the Qilian Mountains in the northeastern part of the plateau,and the precipitation variations in this region were relatively large in recent decades.(4)The optimal distribution of extreme temperature events in the Qinghai-Tibet Plateau was the Generalized Extreme Value Distribution(GEV),and the second dominant distribution was Weibull Distribution(Weibull(3P)).The optimal distribution and the second dominant distribution had high spatial coincidence.The optimal distribution of extreme temperature events had spatial differences,and the Generalized Extreme Value Distribution(GEV)was relatively suitable for the northern QinghaiTibet Plateau.The optimal distribution of extreme precipitation events was also Generalized Extreme Value Distribution(GEV),and the second dominant distribution was Logarithmic Logistic Distribution(Log-Logistic(3P)).Unlike extreme temperature events,the optimal distribution of extreme precipitation events and the second dominant distribution had strong spatial complementarity.The optimal distribution of extreme precipitation events also had spatial differences.Generalized Extreme Value Distribution(GEV)had relatively good applicability in the central Qinghai-Tibet Plateau.For extreme temperature and precipitation indices,the Generalized Extreme Value Distribution(GEV)and Logarithmic Logistic Distribution(Log-Logistic(3P))had spatial complementarity in fitting probability distribution in the study area.