Monitoring Glacier Change Based On Remote Sensing In The Hengduan Mountains For The Last Four Decades

The Hengduan Mountains is located in eastern of the Tibet Plateau. It is the most south and east glacier region in China, and is one of the main distributions of the maritime type glacier. The Hengduan Mountains is the only area that affected by both Pacific as well as Indian Ocean water system and the boundary between the Indian monsoon and the East Asian monsoon. There is a remarkable difference in this region. Studying glaciers in this region has important scientific significance and social significance.This paper selected three typical sample regions in the Hengduan Mountains as study area: the Gangrigabu range, the Mainri Mountain range and the Gongga Mountain range. Data source is Landsat series satellites remote sensing images of MSS, TM, ETM+, and OLI. Aided by Digital Elevation Model, we delineated the outlines of glaciers in years 1974/1976,1989/1993/1994, 2001/2005 and 2010/2013.We used the character point method to analyze the changes of seven classical glacier terminuses. Combinding our results with previously published results, we calculated maritime type glacier area change in China. Finally we analyzed the temperature and precipitation of the three meteorological stations which are the nearest from the sample regions, and discussed the relationship between climate change and glacier variation:we analyzed the influence factors of glacier variations among the sample regions. In addition, we analyzed the influence factors of glacier change in each period. We used the fractal theory to analyze the space morphology change of the glaciers in this region, and made a preliminary forecast of the future glacier change. The main conclusions are as follows:Characteristics of glacier distribution and change1. The glaciers area shrunk in the three sample regions. The shrinking trends become more obvious from east to west. The glacier in the Gangrigabu range has retreated by 1.13%·a-1 from 664.22 km2 in 1976 to 386.65 km2 in 2013; In the Mainri Mountain range has decreased by 0.46%·a-1 from 172.30 km2 in 1974 to 141.42 km2 in 2013; In the Gongga Mountain range has shrunk by 0.33%·a-1 from 254.91 km2 in 1974 to 224.45 km2 in 2010. Considering the process of change, glacial retreat rate was significantly accelerated in the last ten years.2. The glaciers in each aspect of the sample regions are retreating. Glaciers shrinkage is greatly affected by the source of the water vapors. Glaciers shrunk faster in leeward slope than windward slope, and faster in north-facing aspect than in south-facing.3. Affected by mountain elevation, the height of glaciation is gradually increasing, from west to east. The rate of glaciers retreat decreased with the increasing height of glaciation. Glaciers shrunk faster at low elevation than at high elevation.4. The retreat rate is different in different scales. Larger glaciers divided into two or more smaller glaciers, leading to the number and area of smaller glaciers increasing. In general, with the increasing scale of glaciers the retreat rate is reduced and trend to be stable.5. The glaciers in each slope of the sample regions followed a normal distribution, and the retreat rates had no significant difference in different slope.6. The retreat rate of seven classical glacier terminuses and glacier area showed that there were slowed down in the second period and going quicker in the last period.7. The retreat rate of maritime type glacier area change has no obvious difference. So glacial recession is a complex problem, the rate of retreat was influenced by the interaction between the terrain and climate.The influence factors of the glacier changes1. Average temperature in the study area experienced a clearly warming trend in recent 40 years. The Gangrigabu range and the Gongga Mountain range showed warming rates are higher in winter. Annual rainfall fluctuation changed significantly, but the linear increasing trend is not very significant. The summer precipitation accounts for more than 90% of annual rainfall.2. The rate of retreat was decided by the interaction between the terrain and climate. The rate of glaciers retreat decreased with the increasing height of glaciation or the increasing of glacial scale; The slight temperature rises caused little glacial recession; And affected by the source of the water vapors, glaciers shrunk faster in leeward slope than windward slope.3. There is a good response relationship between the glacier variation and the climate change. The increased precipitation can cause the deceleration of the glacial shrinking, and the temperature rising mainly caused the glacial shrinking.4. Analysis the space morphology change of the glaciers in the three sample regions found that, there has been a slight decrease in the glacier stability index in recent 40 years, which shows that the speed of glacial melting would slightly higher than existing.