青藏高原东南部来古冰湖变化及其溃决洪水评估

冰湖溃决洪水(Glacial lake outburst flood,简称GLOF)灾害是冰川区最常见、危害最大的灾害类型之一,历来是国内外学者研究的关键科学问题。在全球变暖的大背景下,冰川退缩加剧,其下游冰湖扩张快速,湖面升高,溃决风险提高。青藏高原尤其是东南部地区孕育着大量的冰湖,在过去的几十年间,冰湖溃决洪水威胁着当地人民的生产生活。基于LANDSAT遥感影像,本文获取了青藏高原东南部雅弄冰川和来古冰湖1986年、1990年、1994年、1997年、2000年、2003年、2005年、2011年、2013年和2017年共10期湖面面积,并结合实地测量的冰湖水深资料,计算了冰湖对应年份的储水量,建立冰湖面积与储水量变化序列;结合野外调查从冰湖面积与水量变化趋势和突发事件两方面探讨冰湖溃决可能性;利用BREACH模型和SMPDBK模型估算和模拟来古冰湖溃决洪水,做灾害预警分析。结果表明,1986~2017年冰湖上湖变化不大,而来谷下湖处于持续扩张中,面积由1986年的1.151±0.070 km^2扩张至2017年的3.148±0.097 km^2,水量由0.645×10^8 m^3增加至2.143×10^8 m^3,雅弄冰川在1986~2013年持续后退,在2013~2017年突然前进;经讨论其溃决风险得出冰川滑动入湖导致湖水瞬时涌出从而造成溃坝的可能性较高;利用BREACH模型及SMPDBK模型对来古冰湖溃决洪水模拟结果表明,当来古下湖湖水受冰体挤压抬升发生溃决时,溃决洪水将严重威胁然乌镇及其上游居民的生命和财物安全。

LAIGU GLACIAL LAKE VARIATION AND ITS OUTBURST FLOOD RISK IN SOUTHEAST TIBETAN PLATEAU

Glacial lake outburst flood (GLOF) is one of the major disasters in glaciated regions. The GLOF risk is increasing due to glacier retreat and expansion of glacier lake surface area under global warming. There are plenty of glacial lakes in southeast Tibetan Plateau (TP) where frequent GLOF events were observed over the past several decades. The Laigu glacial lake (29°18.5'N, 96°50'E) is located on the upstream of Ranwu Town with dense population. Therefore, it is of importance to monitor this lake and evaluate the GLOF risk as the lake may provide threat to the local people. In this study, we found that the area of Laigu lake No.1 is expending continuously from 1.151±0.070 km2 in 1986 to 3.148±0.097 km2 in 2017, while surface area of the Lake No.2 had no significant variation, based on LANDSAT images achieved in 1986, 1990, 1994, 1997, 2000, 2003, 2005, 2011, 2013 and 2017. The lake No.1 water storage was calculated based on bathymetric data and lake area. The results showed that the water storage increased from 64.5×10^6 m^3 in 1986 to 214.3×10^6 m^3 in 2017 at a rate of 48.0×10^6 m^3/a. Yarlung glacier which related to Laigu lake No.1 retreated continuously in 1986~2013 while advanced suddenly in 2013~2017. The lake No.1 glacier surging may create a high possibility of the GLOF risk over the region. The GLOF risk of Laigu glacial lake No.1 was evaluated using BREACH model and SMPDBK model. The results showed the villages located in the valley and the Ranwu town is in serious threat from GLOF.