GISdevelopment.net ---> AARS ---> ACRS 1992 ---> Water Resources Studies of Glacier Change during Quaternary Period in Tibet by using Remote Sensing and GIS Techniques Sh1 Changan, Liu Jiyuan Institute of Remote Sensing Application, CAS Beijing 1000101 P.R. China Tibet plateau was bulged with strong plate tectonics in Quaternary period, and put lots of towering mountains beyond snow line. Therefore, it developed a large areas of glacier. Since then glacier has begun formed. Its change has been having a close relationship with environment changes analyzed from geological time scale have a possible relationship with Tibetan geological structure and climate change with is still very active now: From decade scale, however, it reflects the change of ecological environment of human being. For this reason, it has an important significance to understand and predict the glacier change. “ Three Rivers” region located in central Tibet consisting of Lhasa River, Nian Chu River basin and the middle reaches of the yalu tsangpo River. Although its areas only occupies 5.8% of the whole Tibet territory, it has been playing an very important role in the social and economic development of Tibet. Therefore, it is very important to deeply study environment background change of the region for its further agriculture development and economic construction. Based on above consideration, we chose Karila glacier as a test site which is located in central parts of Three Rivers . Through studying its dynamic changes under the support of modern GIS and remote sensing technique, finally access a thorough understanding for the region’s environment background. Glaciologists have early paid attention to galcier change during Quaternary period. Shi Yafeng et al. in 1980, Zheng Bengxing et al. in 1965, Zhang Xiangshang et al. in 1975, who had successfully done a plenty of research work on glacier dynamic changes in Mt. Qi Lian, Mt. Tian and Mt. Himalaya region, have provided lots of scientific evidences for studying time and space law of galcier change in China. Their data sources mainly come from : (1) field surveying and mapping and calculating from the relics of former glacier ; (2) aerial surveying topographic map ; (3) comparative analysis of aerial photography and early satellite image. Those data obtained by the methods mentioned above have some limitations for quantitative analysis. Since 1980s satellite remote sensing has been developed rapidly and has a periodical and commercial services. Undoubtedly, new generation Landsat TM data with high resolution under the support of GIS technique, have provided a powerful tool for studying glacier change. Introduction to Testsite The testsite locates in central and southern Tibet, at the northern foot of the Himalaya Mountain, to the southwest side of Yang Zhouyong Lake. It covers the range from E90 10’ to E90 50’ and from N28 46’ 30’ to N28 53’ ‘ (Fig 1.) Here mountain body was bulged strongly with an elevation from 4000 meters to 7000 meters, relative altitude reaches 3000 meters: and terrain is very suitable for galcier development. Earila galcier and Qiang Yong glacier locate in northern and southern test site respectively, occupies 45% and 35% of total area: Both are continental glaciers, which are hardly affected by ocean moisture; rainfall mainly depends on the supply of summer convective rain: both change slowly and have high stability. Data and Mehodology The data used for galcier change analysis in this paper mainly come from: Maps edited from ground close-shot photogrammetery data of Karila glacier in 1979. Karila Landsat TM images in 1989: Climate and hydrological data of Tibet Autonomous Region from 1953 to 1988. Fig. 3 has shown the research procedures. ARC/INFO and other software made by ourselves have been used in the study. Results and Discussion 1. Glacier and glacier lake change analysis at different elevation zone The glacier change analysis for this region is carried out under the support of GIS software by making the glacier distribution maps of two dates. Comparative analysis for two date data. The major glacial bodies in study area have no marked advance and recession coverage changes were quite unbalanced; disappeared in some place and grew in other place, but receded ice-snow coverage is more than advanced (Fig. 4) Karila glacier in the northern region, for instance, which western ice-snow coverage has made great recession and eastern marked advances; Bit middle part of Qiang Yong glacier located in south of the region has been prolonged greatly. It must be noticed that these changes did not take place on the major body of Karila and Qiang Yong glaciers. We can not confirm the advances and recessions of two glacial bodies with the 30m resolution of Landsat TM imagery. Bit final comparison of two glacial coverage is in a receded state; From 1979 to 1988. total ice-snow area of the region has been shrunk back by 11.1%. Analysis on ice-snow coverage change within different elevation zone. Ice-snow coverage changing with elevation is in normal distribution state by analyzing the relationship between ice-snow coverage and its corresponding elevation zone. Maximum value is 6200 meters, ice-snow areas changes dramatically. Following conclusions can be deduced: snow line or equilibrium line of the region must have existed in this elevation zone. Above the line glacial material is in a accumulation state, and terrain is favorable to glacial development. Under the line, the glacial is in a relatively melting state. Analyzed from glacial recession rate of two dates at different elevation zone, the largest change is still around 5600 meters snow line. Under the elevation zone, the glacial recession rate increases with gradually with elevation, stops at 6000 meters elevation zone, even appears negative increase. It shows that galcier change is complex. This negative recession is possible material accumulation for glacial advance in the next decade. Recession of glacial lake. It is easy to interpret and locate glacial lake on TM imagery because plateau glacial lakes which have low temperature and strong reflection features and two date glacial lake area data, glacial lake areas of the region is shrinking back by almost 50%. There are two explanations for this phenomenon: one is that climate is becoming dry, air moisture decreasing and evaporation increasing; the other is that glacial recession speed began to slow down and melting water supply was not enough. Analyzed from elevation zone (Fig. 7), Because front edge of one glacier tongue has melted and become a lake at 5000 meters elevation zone, it made glacial lake area increase 80% within the zone; and 5200 meters elevation zone , all glacial; lakes have almost obviously disappeared. Glacial lake area change is an indirect reflect of the glacial body which is decreasing its melting speed. Ice-snow change analysis on different slope aspect. In mountainous region, slope aspect has an great effective on local micro-climate, and made different glacial change on different slope aspect; The slope aspect map of Karila region was produced by its DEM: Slope aspect was classified according to the angle degree which is formed by the compass’s direction and the direction of the slope vertical projects. Because the studying area is located in N28—N30 area, it is easy for us to define the sunny aspect and shadow aspect. Tab 2. is analysis results from slope aspect map with two dates glacial maps. It shows that Although absolute value of glacial recession and glacial recession rate on sunny slope aspect has greater change than that on shadow aspect, the different is not very remarkable and only has about 7%. It is explained that slope aspect in high mountainous region has no a significant function for glacial change because altitude has reduce the slope aspect function for temperature. 2. Climate analysis for glacier change Climate change is fundamental for glacier change. Generally speaking, short term climate change has no great effect on glacial tongue body’s advance and recession, but has an impact on ice-snow coverage rate. Lon term climate system change has a significant influence on glacial advance and recession. In order to explain and analyze the glacial change in Karila region. We choose climate data lasting about 30 years from our meteorological stations near Karila region. The meteorological stations can basically represent ground and mountain climate change in Karlia and its nearby region. Temperature change. Long term temperature change is one of the most important factors which affect glacial melting. Analyzed from those data collected from four meteorological stations nearby Karila region, the Different of average temperature of two decades ( 1971 -- `1980’s average value minus 1961—1970’s average value ) are all positive. That is to say, climate trend of the region is becoming warm; and the different value from Lang Kazhi station which have the closest distance to Karlia is the largest, it is raised 0.4 C, obviously, temperature is one reason to effect ice-snow melting. Different seasonal temperature changes also have great effect on glacial melting. In the past two decades, spring and winter temperature rose 0.3 C and 0.7 C respectively. It is obviously disadvantageous to glacial material accumulating. Summer average temperature which is advantageous to melt ice-snow is decreasing 0.4 C ( later decade minus former decade). Therefore, seasonal temperature change has made the region glacial in a state which advance and recession existed together. It is same with conclusions Mr. La jun et al. had achieved. Fig. 9 is a figures of summer ground temperature change in 1970s at Lang Kazhi station. It shows 1972 to 1976 and from 1977 to 1979. It is clear that the decreasing temperature has blocked up the glacial melting procedure in Karila region in 1970s. Change of precipitation Precipitation change in mountainous region of Karila has no regular change law because of no long term time data. Taking the year of 1970 as middle point, the difference of average annual precipitation between the two decades is not very large, and increase, but change range is not very large ( see Tab. 4). Summer precipitation has been played an important role in Karila region, nearly occupied 60-70% of all –around year precipitation : Therefore, glacial supplying state controlled by monsoon climate mainly depends on the change of summer precipitation. In recent twenty years, although the precipitation changed a very large, the temperature has decreased during same period which has a fairly great effect on glacial material balance. Conclusions Permanent snow area’s recession and glacial lake’s shrinking back have shown that climate in the region is becoming dry. But glacial tongue of main glacier bodies in the region have appeared an obvious change on TM imagery, which proved that there has been no dramatic climate change in the region. Studying change low at different elevation zone through using DEM analysis, is a practical and effective means in modern glaciology research. We can get the following results from the research. Ice-snow coverage rate has an positive relationship with the elevation. At snowline, there is a turning point on ice-snow coverage rate curve. We also discovered that ice-snow dynamic change concentrates on the elevation zone interpreted from TM image. Slope aspect has no effective function on the glacial recession. Modern remote sensing and geographical information system is an effective method to analyze modern glacier change.