| Under the background of global warming,the phenomenon of "Karakoram anomaly",in which glaciers in the Karakoram mountains retreat or even leap,has attracted scholars’ attention.The Karakoram-West Kunlun region is located in the northwest of the Qinghai-Tibet Plateau,and there is a lack of observational data.How to scientifically explain the phenomenon of "Karakoram anomaly" and uncover the characteristics of climate change behind it has become a hot spot and trouble in current research.Utilizing the Weather Research and Forecasting(WRF)model,a mesoscale meteorological model for the Karakoram-West Kunlun region has been established through sensitivity tests of simulated area setting,initial field data and parameterization scheme optimization.Based on the local WRF model,dynamic downscaling simulation and analysis of the space-time characteristics of climate change in the study area from 1992 to 2021 were conducted.On this basis,the effects of topography and circulation factors on climate change in the study area are discussed.The main conclusions are as follows:(1)After the optimization of the simulation test scheme,the established local WRF model can objectively and accurately simulate the spatial-temporal variation characteristics of air temperature and precipitation in the study area.In the validation period,the correlation coefficients between simulated temperature and observed temperature were 0.87(p < 0.05)and 0.99(p < 0.05),respectively.The correlation coefficients of precipitation were 0.69(p < 0.05)and 0.67(p < 0.05),respectively.Spatially,the correlation coefficients between the simulated and observed fields of annual mean temperature reached 0.94 during the three-year validation period,and the precipitation also reached 0.66,0.62 and 0.64,respectively,p < 0.05.(2)The temperature in the study area from 1992 to 2021 mainly shows a warming characteristic.The trend rate of annual mean temperature was 0.18 ℃/10a(p< 0.05).Among the four seasons,the warming trend was most significant in autumn(0.29 ℃/10 a,p < 0.01),followed by spring(0.29 ℃/10 a,p < 0.01),while the warming trend was not significant in summer and winter.Spatially,92.85% of the study area showed a warming trend of annual mean temperature,with the southeast region showing the most significant warming.The warming area in spring and autumn showed a significant trend(p < 0.05),and the warming area in spring was concentrated in the northern part of the study area,while the warming area in autumn was concentrated in the southern part of the study area.(3)Precipitation in the study area increased from 1992 to 2021,but there were significant differences among different regions and seasons.The annual precipitation(5.23 mm/10a),summer(4.83 mm/10 a,p < 0.05)and autumn(2.92 mm/10 a,p < 0.05)increased significantly.The precipitation in winter(-1.39 mm/10a)and spring(-0.87mm/10a)showed an insignificant decreasing trend.The areas with annual precipitation increase accounted for 73.08% of the whole region,and the central Kunlun Mountains and the southwestern Karakoram region had more precipitation and more intense precipitation change.The spatial distribution characteristics of the trend rate of precipitation change in spring were similar to that of annual precipitation.The areas with significant precipitation change in summer and autumn(p < 0.05)were mainly distributed in the areas with increasing precipitation,and the areas with significant precipitation decrease in winter.(4)Both temperature and precipitation in the study area show a certain degree of "altitude dependence".There was a significant "elevation dependent accelerated warming" phenomenon in autumn and winter(p < 0.01),and the most significant one was in autumn(r = 0.60).There was a negative correlation between spring,summer and annual mean temperature tendency rate and altitude(p < 0.05),and the correlation between spring and altitude was the strongest(r =-0.86),especially in 1-4.5km altitude range(r =-0.88).The tendency rate of precipitation change was significantly correlated with altitude(p < 0.01),and there was a negative correlation between spring(r =-0.30)and winter(r =-0.34),and a positive correlation between summer(r= 0.54)and autumn(r = 0.52).(5)There was a weak negative correlation(p < 0.01)between annual mean,spring and summer temperature trend rate and slope,and the correlation coefficients were-0.33,-0.46 and-0.39,respectively,which mainly occurred in the range of 0-30°slope(r =-0.33,r =-0.51,r =-0.31).On the whole,there was a positive correlation between the trend rate of precipitation change and slope in spring,summer and autumn(p < 0.01),and a negative correlation in winter(p < 0.01).The temperature change is more obvious in the flat area,especially on the southern slope in summer and autumn,and on the Northern Slope in spring and winter.The change of precipitation at all time scales was more obvious on the southern slope,and the change of interns and summer precipitation was also more obvious on the flat land.(6)There is a positive correlation between annual mean and autumn temperature and the Atlantic Multidecadal Oscillation index(AMO)(r = 0.37,r = 0.44;p < 0.05),summer temperature is positively correlated with North Pacific Index(NPI)and Arctic Oscillation Index(AO)(r = 0.42,r = 0.46;p < 0.05),winter temperature had the closest relationship with NPI index(r = 0.52;p < 0.01).The annual,spring and summer precipitation are negatively correlated with the East Atlantic/Western Russian Remote correlation index(EAWR,East Atlantic/Western Russian)(r =-0.42,r =-0.38,r =-0.43;p < 0.05).Precipitation in summer and autumn was negatively correlated with WP(West Pacific)(r =-0.38,r =-0.44;p < 0.05).There was a close relationship between the Global Mean Lan/Ocean Temperature Index(GTI)and the Temperature and autumn precipitation on all time scales(p < 0.01). |
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