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This thesis confirms many changes, including sharp temperature rise, interannual variability of precipitation, extreme climate events and significant decreases of sunshine duration and wind speed in southwestern China, and systemically explores the action mechanism between large-scale atmospheric circulation systems, the complicated topography, human activities and regional climate changes. This study also analyzes the response of glaciers to climate change so that on the one hand it clearly reflects the relationship between glacier morphologic changes and climate change; on the other, it reveals the mechanism of action of climate warming as a balance between energy and matter. The achievements of this study reflect a significant contribution to the body of research on the response of climate in cold regions, glaciers and human activities to a global change against the background of the typical monsoon climate, and have provided scientific basis for predictions, countermeasures against disasters from extreme weather, utilization of water and the establishment of counterplans to slow and adapt to climate change.

Zongxing Li works at the Cold and Arid Region Environmental and Engineering Research Institute, Chinese Academy of Sciences, China.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
Southwestern China includes the Sichuan, Yunnan, and Guizhou Provinces, the Xizang Autonomous Region, and Chongqing Municipality, with an area of 2.333×106 km2, accounting for 24.5 % of the total land area of China. The topography declines from west to east and from north to south. There are four geomorphic units: the Xizang Plateau, the Hengduan Mountains, the Sichuan basin, and the Yunnan–Guizhou plateau. Southwestern China is a typical monsoonal climate region, controlled by the South Asian monsoon but also influenced by the East Asian monsoon. In addition, it is influenced by the Xizangan Plateau monsoon and the Westerlies. According to the Chinese Glacier Inventory, there were 23221 glaciers in southwestern China, covering an area of 29,523 km2, which is 50.16 % of the total glacier number and 49.69 % of the total glacier area in China. Climate research has concentrated mainly on sub-regions or single districts over the study region, however, there has been little systematic analysis of climate change in the whole region. Here, the temporal–spatial variation and its causes of climate change and the glaciers’ response in southwestern China during 1961–2008 have been analyzed, based on meteorological data from 110 stations, NCEP/NCAR reanalysis data and, and the records of glacier changes from field observations and previous studies.
Zongxing Li

Chapter 2. Data and Methods

Abstract
The observation data of ground stations is the main data source of this study. The data about the daily mean temperature, daily minimum temperature, daily precipitation, daily wind speed, and daily sunshine hours are from the meteorological observation database of National Meteorological Information Center in China Meteorological Administration (http://​www.​nmic.​gov.​cn/​). The time span of meteorological data is mainly set from January 1, 1961 to December 31, 2008 in order to ensure the length of all data uniform and stable. It is necessary to select qualified observation data by the data quality control before analysis in order to ensure the accuracy of the results of the study. The quality control of meteorological observation data in this study is to examine the date of the daily mean temperature, daily minimum temperature, daily maximum temperature, and daily precipitation by using the international test method and software nonuniformity: RclimDex and RHtest, and to find out the station having data quality problems, then to delete them from the original data, finally, to select the qualified observation stations and to make a statistics and analysis on the basis of this data.
Zongxing Li

Chapter 3. Spatial and Temporal Variation of Temperature and Precipitation in Southwestern China

Abstract
Annual and seasonal warming trends in southwestern China during 1961–2008 were significant. About 77% of the 110 stations displayed statistically significant increases of annual temperature. The increase was more apparent in higher altitude areas than in lower ones. Warm–dry flow in summer affected the study region, and the southern extent of the winter monsoon has also been weakened, which in part accounts for some of the climate warming experienced especially in the warmest years in southwestern China. Sunshine hours have a crucial influence on the SB temperature especially during spring and summer, whereas this influence mainly is effective in winter at the Xizang Plateau–Hengduna Mountains and Yunnan–Guizhou Plateau. In addition, the increased net longwave radiation flux over the most areas in the study region and sea surface temperature in Western Pacific may have also made some contributions to temperature rise. Precipitation variations were less marked than those of temperature, generally showing weak decreasing trends during 1961–2008. About 53% of the stations experienced a trend of increasing annual precipitation. Stations with precipitation increases were also mainly at higher altitudes mainly owing to the more water vapor flux, but the significance level was low. Northward penetration of the summer monsoon is limited by an increasing northeasterly air flow over the region, and northwesterly winds in the north are preventing southward transportation of water vapor from the ocean in summer. In addition, the water vapor flux showed a weak variation from the most precipitation years to the least years. These characteristics suggest a weakened monsoonal flow and vapor transportation in recent years, and also partly explain the inconspicuous precipitation variations over southwestern China. In addition, the strengthening Western Pacific Subtropical High also has had some influence on precipitation variations.
Zongxing Li

Chapter 4. Spatial and Temporal Variation of Climate Extremes in Southwestern China

Abstract
Analysis of changes in twelve indices of extreme temperature and eleven of extreme precipitation at 110 meteorological stations in southwestern China during 1961–2008 revealed statistically significant increases in the temperature of the warmest and coldest nights, in the frequencies of extreme warm days and nights, and in the growing season length. Decreases of the diurnal temperature range and the number of frost days were statistically significant, but a decreasing trend of ice days was not significant. At a large proportion of the stations, patterns of temperature extremes were consistent with warming since 1961. Warming trends in minimum temperature indices were greater than those relating to maximum temperature. Warming magnitudes were greater on the Xizang Plateau and the Hengduan Mountains than on the Yunnan–Guizhou plateau and in the Sichuan basin, as confirmed by the decrease of the regional trend from west to east. Changes in precipitation extremes were relatively small, and only the regional trends in consecutive wet days, extremely wet day precipitation and maximum 1-day precipitation were significant. These trends are difficult to detect against the larger interannual and decadal-scale variability of precipitation. On the whole, the number of rainy days increased on the Xizang Plateau and in the Hengduan Mountains, but the rainy strength has also increased at lower altitude areas. Analysis of large-scale atmospheric circulation changes reveals that a strengthening anticyclonic circulation, increasing geopotential height, weakening monsoonal flow and vapor transportation over the Eurasian continent have contributed to the changes in climate extremes in southwestern China. The spatial distribution of temporal changes of all climate extreme indices in southwestern China reflects the obvious altitude dependence. Trend magnitudes of temperature extremes are significantly higher for flat stations, and followed by summit, intermountain basin, and valley stations. It is obvious that the larger decreasing trend in summit station, and following is flat stations; whereas the greater increasing trend mainly occurred in valley stations in southwestern China, and the intermountain stations also showed the lower decrease or increase. In addition, the mean contribution of the UHI effect to regional trends of urban stations for cold extremes and warm extremes were 16.0 % and 7.9 %, respectively, based on the preliminary evaluation.
Zongxing Li

Chapter 5. Spatial and Temporal Variation of Sunshine Hours in Southwestern China

Abstract
Sunshine hours is one of the most important factors affecting climate and environment. Trends of temporal and spatial patterns in sunshine hours and associated climatic factors over southwestern China are evaluated for the period 1961–2008 based on data from 110 meteorological stations. The results show that southwestern China is experiencing statistically decreasing sunshine hours with rate of 31.9h/10a during 1961–2008, and the statistically significant decrease of sunshine hours mainly occurred in lower altitude regions, especially in Sichuan basin and Guizhou plateau. It showed the closely temporal and spatial correlation between wind speed and sunshine hours, and the larger decreasing trend displayed declining trend in nonwindy days than that in windy days. This is strongly suggestive of the fact that stronger winds lead to longer sunshine hours, further validating that wind speed directly and strongly influences sunshine hours in southwestern China. The relative humidity also has a great influence on sunshine hours reflected by the significant correlation and the similar trend between the two variables. Sunshine hours also has a high correlation with precipitation and surface downwards solar radiation flux, whereas the effect from urbanization on regional-scales trend was inconspicuous. The increased total cloud cover and cloud water content from 1960s to 1970s, and the decreased relative humidity and increased surface downwards solar radiation flux between 1980s and 1990s have also influenced the variation of sunshine hours. In addition, the clear local influence of topography can be reflected by the decreasing magnitudes increased from summit to flat stations.
Zongxing Li

Chapter 6. Spatial and Temporal Variation of Wind Speed in Southwestern China

Abstract
Daily wind speed data from 110 stations in southwestern China were analyzed to determine trends, spatial differences, and possible causes. There was a statistically significant decrease of 0.24m/s/10a in the annual mean wind speed during the period 1969–2008. The decreasing trend was faster (0.37m/s/10a) during 1969–2000. Between 2001 and 2008, there was a significant increase. The pattern of seasonal changes was similar. Stations with stronger, significant decreasing trends were mainly on the Xizang Plateau, the Hengduan Mountains, and the Yunnan Plateau, and stations with significant increasing trends were mainly in the Sichuan basin, indicating the influence of altitude on wind speed. Surface wind speeds in southwestern China have been affected in recent years by both the changed large-scale atmospheric circulation and the regional and global warming. The analysis have confirmed that the decreasing wind speed during 1969–2000 was caused mainly by the decreasing monsoonal circulation and Westerlies, and the strengthening latitudinal wind speed has made some contributions on the increasing wind speed after 2000. And what’s more, the strengthening Xizang monsoon has also made some contributions to wind change, and it indicated lower wind speeds related to increased temperatures, particularly to a rise of the minimum temperature in recent years. The weak wind speed may also be caused by the asymmetric decreasing latitudinal gradients of surface temperature and pressure gradient during 1969–2008. The data indicated a positive correlation between wind speed and sunshine hours suggesting another possible influencing factor. Topographical influences are evident in the higher annual and seasonal trends at summit and intermontane basin stations and the lower trends at valley stations. In addition, a minor influence from urban effect on wind speed also has been founded.
Zongxing Li

Chapter 7. Glaciers Response to Climate Change in Southwestern China

Abstract
Glaciers are distributed in Nyainqêntanglha Mountains, Himalayas, Tanggula Mountains, Gangdise Mountains, and Hengduan Mountains in southwestern China. Under temperature rise, especially the increasing warming with altitude recorded by 110 stations, ice cores and tree rings in southwestern China, four characteristics of glacier variations occurred during recent decades: the fronts of 32 glaciers and areas of 13 glacial basins have retreated, mass losses of 10 glaciers have been considerable, glacial lakes in six regions have expanded and melt water discharge of four basins has also increased, the typical glacier showed the accelerative ablation. The remarkable regional differences of glacier change in southwestern China may be caused by the two following factors: differences in temperature and precipitation; and differences of glacier location, scale, and frontal altitude. As response to climate change, eight monsoonal temperate glaciers were stationary or advancing between the 1900s–1930s and the 1960s–1980s, and were in retreat from the 1930s to the 1960s and from the 1980s to the present. In a world, it is evident that the glacier retreat stages are in the warm and wet phases, and vice versa. The accumulated mass balance in Hailuogou basin is -10.83 m water equivalent in the past 45 years, an annual mean value of -0.24m water equivalent, and 29 years are negative mass balance year, show that it suffered a sustained mass loss of snow and ice in the period 1959/1960–2003/2004. And what's more, the warming climate has had an impact on the hydrological cycle at glacial area. As the glacier area subject to melting has increased and the ablation season has become longer, the contribution of meltwater to annual river discharge has increased, which can be reflected by the increased runoff in the downstream region of the glacial area of the Yanggongjiang basin during 1979–2003 and Hailuogou basin during 1999–2004, and the mean contribution of the runoff in the downstream region of the glacial area to the whole basin are 35.8% and 54.7%, respectively. The earlier onset of ablation at higher elevation glaciers has resulted in the period of minimum discharge occurring earlier in the year, and seasonal runoff variations are dominated by snow and glacier melt. The increase amplitude of runoff in the downstream region of the glacial area is much stronger than that of precipitation, resulting from the prominent increase of meltwater from glacial region in two basins. As the acceleration of ablation velocity, the lengthening of ablation period, and the extension of ablation area, changes of internal and upper surface morphology also occurred and characterized by many ice clefts, glacier collapses, decrease of thickness, enlargement of glacial caves, and reduction of the size of seracs, providing evidence of the response to climatic warming in recent years. However, it is difficult to discuss the quantitative relationship between climate change and glacier behavior in southwestern China owing to the limited observation in the glacial accumulation areas and the complexity of climate change and glacier dynamic response.
Zongxing Li

Chapter 8. The Main Conclusion and Prospect

Abstract
Based on the observation data of 110 meteorological stations and the NCEP/NCAR reanalysis data, this study systematically researched the spatial and temporal variations of annual mean temperature and precipitation in southwestern China and its influencing factors and further analyzed the interannual variation, spatial distribution of extreme temperature and precipitation as well as the correlation with atmospheric circulation, altitude, urban heat island, and some by combining some research materials and using a variety of analysis methods. This study also explored the characteristics and reasons of spatial and temporal variations of sunshine hours from wind speed, relative humidity, urbanization process, cloud water content, local terrain, and so on, and revealed the influences of the large-scale atmospheric circulation, regional climate warming, horizontal pressure gradient, and plateau monsoon on the temporal and spatial variation of wind speed. On the basis of this, this study analyzed and summarized the response characteristics of glaciers in studied area to climate changes and the correlation with glacier length, material balance, galcier runoff, surface morphology change, and the climate change.
Zongxing Li
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