Overall and local changing patterns of main glaciers and their responses to climate change in Geladandong area of Yangtze Headwater region during 1969-2012
Studies on glacier change can provide profound implications to understand ecosystem response to global climate change at regional scale. Geladandong area,as the Yangtze headwater region with restricted environmental conditions,is largely in the absence of scientific attention,especially that focusing on changing pattern of glaciers. This study aims to reveal the overall and local changing patterns of the main glaciers and their responses to climate change. Repeated aerial photographs and satellite images taken in 1969,1973,1992, 2001 and 2012 were used to analyze overall changing patterns of the Gangjiaquba glacier and the Jianggudiru glacier. Field photographs of the glaciers taken in 1986,1994,1999 and 2003 were compared with repeated ones taken in 2010 to analyze local changing patterns of the Gangjiaquba glacier and the Jianggudiru glacier. Meteorological data at the Tuotuohe Town during 1970-2009 were used to analyze changing trends and interdecadal variations of temperature and precipitation. Software for image processing and editing (Adobe Photoshop CS3 Extended) was used to measure and calculate glacier outline difference between each of repeated aerial photographs and satellite images. Field measurement was conducted to locate the geographical coordinates of the past and present edges of glaciers based on historical photographs,and then to calculate retreating distances of glaciers. Software for statistical analyzing and image processing (OriginPro 8.6.0) was used to analyze the changing trends and interdecadal variations of meteorological variables. The response of glaciers to climate change was explored by discussing possible linkages between changing patterns of main glaciers and meteorological variables. Results show as follows: (1) the Gangjiaquba glacier and the Jianggudiru glacier retreated at both overall and local levels during 1969-2012; (2) local temperature rose during 1970-2009 with the most significant increase in 2000s;and (3) local precipitation exhibited no significant changing trend during 1970-2009 but with the highest mean annual precipitation in the 2000s. Generally, changing patterns of main glaciers are correlated to temperature and precipitation in study area,representing a clear response of glacier variation to changing climate. Furthermore,the climate-driven glacier variation produces considerable impacts on basin area at ecological,economic and social perspectives. This study provides sound explanation for the response of glacier variation to climate change. Historical photographs taken in the field are very rare and then meaningful in understanding glacier variation at local level,especially considering the field work in locations like study area,which is very time- and money-consuming. Geladandong area of the Yangtze headwater region is largely ignored due to topographic isolation and complexity,but the unique environmental characteristics make this region an ideal place for studying regional responses to global climate change. This study is a useful attempt, based on graphical analysis method, to demonstrate changing patterns of main glaciers at both overall and local levels.