1979-2018年藏东南典型冰川泥石流流域极端气候事件分析

Climate Extremes in a Typical Glacier-related Debris Flow Watershed of Southeast Tibet During 1979-2018

强降雨和高温是冰川泥石流的主要诱发因素,深入理解小流域冰川泥石流的孕灾气象条件变化规律,可为冰川泥石流的预警预判和灾害防治等工作提供依据和基础数据。基于中国区域地面气象要素驱动数据集(1979-2018年),利用Sen’s斜率法、Mann-Kendall趋势及突变检验法、滑动t检验法、Mor‐let小波变换法、变异系数(CV)和降雨集中指数(PCI)多种方法和指标,详细分析了藏东南典型冰川泥石流流域卡达沟的降雨量、气温和极端气候指数近40年的变化特征。结果表明:(1)年均气温和暖昼日数分别以0.05℃·a^(-1)和1.46 d·a^(-1)的速率显著上升,暖昼日数年际波动极大。两者均具有32 a准周期以及中短尺度周期。(2)春、夏、秋、冬季气温分别以0.044℃·a^(-1)、0.039℃·a^(-1)、0.049℃·a^(-1)和0.06℃·a^(-1)的速率显著上升。所有月份气温均呈显著升高趋势,其中3月和11月气温波动极大。(3)年降雨量下降趋势不显著。极端降雨日数无明显变化趋势,但年际波动较大,于1988年发生了突变。年降雨量和年极端降雨日数均具有16~22 a、8~10 a、4~6 a、2~5 a和2~3 a的多尺度周期。(4)降雨的年内分配总体上较均衡。除6、7月降雨量以1.44 mm·a^(-1)和1.15 mm·a^(-1)的速率呈显著减少趋势外,季节降雨和月降雨总体变化趋势不显著。总体来看,卡达沟流域正处于湿热向干热的过渡期,目前还处于阶段性的高温期和多周期强振幅中心叠加的丰水期。同时暖昼日数、极端降雨日数以及月降雨存在中等及以上变异,容易发生极端旱涝事件。极端水热条件组合增加了卡达沟冰川泥石流未来暴发的风险。

Heavy rainfall and high air temperature are the main factors inducing glacial debris flows.In-depth understanding of the variation of disaster-pregnant meteorological conditions of glacial debris flows in small watersheds can provide basis and basic data for early warning and disaster prevention of glacial debris flows.Based on the China Meteorological Forcing Dataset(CMFD)(1979-2018),the inter-annual and intra-annual variation characteristics of rainfall,air temperature,and extreme climate index in Kada valley are analyzed using several methods,including Sen's slope,Mann-Kendall trend and mutation test,Sliding t-test,Morlet wavelet transform,coefficient of variation(CV),and precipitation concentration index(PCI).The results show that:(1)Both the average annual air temperature and the warm days showed a significant rising trend at rates of 0.05℃·a^(-1) and 1.46 d·a^(-1),respectively,but the inter-annual variance of the warm days was very high.Both the average annual air temperature and the warm days exhibited quasi-periods of 32 a and mid to short-term scale periods.(2)The air temperature in spring,summer,autumn and winter increased significantly at rates of 0.044℃·a^(-1),0.039℃·a^(-1),0.049℃·a^(-1) and 0.06℃·a^(-1),respectively.The air temperature increased significantly in all months,with March and November showing significant inter-annual fluctuations.(3)The decreasing trend of annual rainfall was not significant.Although no significant trend in extreme rainfall days was observed,it fluctuated considerably from year to year,with a sudden change occurring in 1988.Both annual rainfall and extreme rainfall days exhibited multiscale periods of 16~22 a,8~10 a,4~6 a,2~5 a and 2~3 a.(4)The intra-annual distribution of rainfall is generally more balanced.The overall changing pattern of seasonal and monthly rainfall was not significant,except for a noticeable decline in rainfall during June and July,at rates of 1.44 mm·a^(-1) and 1.15 mm·a^(-1),respectively.In general,the climate in the Kada valley is transitioning from hot and humid to dry and hot.Additionally,it is in the rainy period of multiscale periodic strong amplitude centers superposition of 2~3 a and 4~6 a,as well as the high air temperature period of 8~11 a.At the same time,the warm days,extreme rainfall days,and monthly rainfall have moderate or greater variation,increasing the likelihood of extreme drought and flood events.The combination of extreme hydrothermal conditions raises the risk of glacial debris flow outbreak in the Kada valley.