Past And Future Climatic Changes On The Tibetan Plateau And The Response Of The Nam Co

The Tibetan Plateau,known as “the third pole of the earth”,affecting the global circulation.It stores abundant resources of glaciers and permafrost,nurtures numerous lakes and large Asian rivers,and it is the water source of Asian countries..Under the background of global warming,it is of great significance to analyze the climate past change,predicted the future trend and further explore its possible influence to the lake ice on the Tibetan Plateau,for adapting to the global climate and guaranteeing the water security of Asian countries.To this end,using the long-time and high spatial resolution monthly datasets(0.5? spatial resolution from 1901 to 2017),the spatiotemporal characteristics of precipitation and air temperature on the Tibetan Plateau were analyzed.The relationship between climate and large-scale circulation factors was discussed based on multi-wavelet coherence.Then used temperature and precipitation data from 1979 to 2015 in the CMFD data set were used as the baseline data to statistical downscaling for the three selected Earth System Models(GFDL-ESM2 G,IPSL-CM5R-MR,MIROC5)datasets.Analyzed spatiotemporal characteristics of temperature and precipitation and the difference of cool and warm season air temperature and precipitation trend on the Tibetan Plateau of the 21 st century.Taking Nam Co as an example,the response of freezing-thawing process to climate change of lakes on the Tibetan Plateau was studied through the lake model.The main results are as follows:(1)The relationship between the Tibetan Plateau climate change and atmospheric circulation factors from 1901 to 2017 was analyzed.The long-term averages of precipitation and temperature varied spatially because of the terrain effects.The climate for 1901-2017 was overall getting wetter and warmer,but its significant interannual variability split the whole study period into three sub-periods:drier and warmer for 1901-1940,wetter and colder for 1941-1966,and wetter and warmer for 1966-2017.For a single atmospheric circulation index,ENSO was found to have the greatest impacts on the climate change at the scale of 8-16 months over the whole study period.However,if additional atmospheric circulation index was considered for the simultaneous effects,the combination of AO-ENSO was likely to have important impacts on climate at a newly added scale of 64-128 months.The interannual variability of climate can be attributed to that of a single or combined atmospheric circulation indices.These results provide fundamental information forstudies of climate change on the Tibetan Plateau and the globe,and the multivariate wavelet analysis is promising in interpreting the impacts of atmospheric circulation on climate change.(2)Predicted the future climate change uesd CMIP5 climate model downscaling on the Tibetan Plateau.For temporal changes,annual average air temperature and precipitation were increasing significantly over time.But the change magnitudes varied with space.The increase in temperature was larger in the west and southeast than that in the central part.And the extremum of precipitation trends increases with the increase of simulated emission concentration.The projected climate changes were related to emission scenarios with change magnitudes in the order of,RCP2.6 < RCP4.5 < RCP8.5.The changes of temperature and precipitation in the warm season were generally greater than those in the cold season.Meanwhile,the differences between cold and warm seasons were increasing with the increasing emission concentration.The downscaled climate data can be used as inputs of climate,hydrological and crop models for scenario analysis,and the obtained results provide important information for the study of future climate change and hydrological cycle.(3)Nam Co as an example,explored the response of the freezing-thawing process of lake on the Tibetan Plateau to climate change.This study intends to simulate lake ice freezing and breakup dates for the Nam Co lakes in the Tibetan Plateau with a one-dimensional and physically based model using enthalpy as the prognostic variable.Based on the model of Ren,we improved the schemes for heat transfer within the lake ice,surface albedo,roughness,air density,added the process for lake ice sublimation,and considered the effect of lake salinity on freezing point for the Tibetan Plateau lake ice.Further,we simulated the seasonal and interannual variations in lake surface temperature,lake ice thickness,and lake ice phenology for Nam Co in the Tibetan Plateau.The improved model could better reproduce the observed lake surface temperature,lake ice thickness,and lake ice freezing and breakup dates.However,the simulation accuracy of lake ice in the eastern part was better than that of the western part because of the Tibetan Plateau reanalysis data and the impacts of westerly prevailing in winter.Moreover,we found that the thin air density on the Tibetan Plateau can amplify the store heat ability for the lake,which caused the lake ice freezing date to be delayed and the melting date to be slightly advanced.This study improved the understanding of the freeze-thaw processes of theTibetan Plateau lakes,makes up for the simulation biases from the other model of the Tibetan Plateau lakes during the cold season,and its simulation results can also supplement and verify remote sensing observations.