Spatio-temporal Patterns And Comprehensive Clustering Analysis Of Climatic Change Risk Sources In Qinghai-Tibet Plateau

Climate change has been the focal point of scientific research in recent years. Scientists have been exploring on aspects from performances of climate change to attribution analyses, from assessments on current situations to simulation of the future. The Intergovernmental Panel on Climate Change (IPCC) emphasized the importance of the adoption of systematic risk assessments and management methods in the research on climate change in the fourth Climate Change Assessment Report. Risk management process includes approximately four procedures, which are risk identification, risk estimation, risk assessment, and risk disposition. Moreover, the most fundamental and essential work is to identify and analyze the risk source which induces risks during the risk identification stage. Based on this, this research chose the Qinghai-Tibet Plateau, the sensitive and typical area of climate change, as research case area, identified the characteristics of strength and spatio-temporal patterns of the key risk sources of climate change from 1971 to 2008, based on the analyses on climate change background and using various methods such as space interpolation, wavelet analysis, and M-K inspection, etc., and comprehensively analyzed the risk sources by means of Self-Organizing Feature Map, to establish the research foundation of the future risk assessment and risk management.First of all, this research analyzed the background of basic climate change of the Qinghai-Tibet Plateau area, which indicates that the majority of the area experienced temperature rise and precipitation increase during 1971 and 2008, except that the small eastern and western areas underwent precipitation decrease. What's more, the analysis tells us the four seasons changed mainly towards warm and humid type which increased temperature and humidification with few exceptions in fall. Also, judging from interdecadal change, the climate change type of the decade of 1970s was markedly different from other decades'. During the four decades, the Qinghai-Tibet Plateau area went through the overall process of temperature and humidification increase with different change situations on different stages, however. Then, based on the clear understanding of climate change background, the research analyzed the risk sources which aroused climate change risks, such as drought and flood, snowstorm, and windstorm one by one. Both the total amount and frequency of rainstorm risk source which aroused flooding presented a fluctuation ascendant trend during the critical period of crop growth (May to September) from 1971 to 2008. There were some mutations during recent 38 years and there was a large-scale cycle of about 26 years. From the perspective of precipitation time, the total amount and number of the precipitation in July were the most, and the single rainfall in May was the most. The definition took the relative intensity of precipitation background value into account and analyzed the rainstorm situations in a more objective manner. The surface dryness degree of drought risk source was measured by drought index. Based on the calculations and analyses of space-time structure of potential evapotranspiration, the research took the precipitation background value into account, calculated drought index, and conducted discussions by standard on spatio-temporal patterns of zoning dryness like hyper-arid, arid, semi-arid, semi-humid, and humid. The risk source of snowstorm was mainly represented by snow depth and snow days. There was a cycle of about 18 years of snow change in recent 38 years known from satellite inversion data. The spatial distribution pattern and spatial variation characteristic of annual snow depth and annual snow days were alike, but the interdecadal changes were very different. The average wind speed of the whole Qinghai-Tibet Plateau area presented a gradually declining trend, and there was no mutation but a cycle of about 27 years. From the perspective of spatial pattern, the wind speed gradually reduced from the central area to southeastern and northwestern areas respectively. The annual tendency rates and the four seasons tendency rates of most sites were negative, spatial variation characteristics were almost similar, and the interdecadal changes had major difference.This research obtained the comprehensive analysis results of 91 sites of the Qinghai-Tibet Plateau area from 1971 to 2008, using the relative intensity of annual rainfall, surface dryness index, annual snow depth, annual snow days, and annual average wind speed as clustering variables and Self-Organizing Feature Map with number of categories of 4. The conclusion can be described as four types, namely snowing leading, elements equilibrium, rainstorm leading, and dryness and average wind speed leading.