“7.23”水城特大滑坡事件的降水背景分析

Analysis of precipitation background of"7.23"Shuicheng landslide

2019年7月23日21时20分贵州省水城县鸡场镇坪地村岔沟组发生特大山体滑坡(简称“7.23”水城特大滑坡),21栋房屋被埋,42人遇难、9人失联。本文利用高空及地面常规观测资料、地面加密观测资料、FY-2G相当黑体亮温(TBB)、NCEP/NCAR FNL格点再分析资料对此次特大滑坡的气象背景进行了诊断分析,得到如下结论:(1)“7.23”水城特大滑坡出现在降水停止后16 h,滑坡前一晚22日夜间降水局地性较强,主要降水时段出现在22日20-23时,距滑坡时间24 h左右。距滑坡点960 m处最大雨强为19.5 mm·h^-1(20-21时),距滑坡点2.7 km处最大雨强为56.9 mm·h^-1(21-22时)。(2)滑坡前一周当地出现了三场降水,分别为两场大雨及一场暴雨。大雨以上较强降水对100 cm以上土壤体积含水量变化影响大,较强降水使100 cm以上土壤含水量增加迅速,但对100 cm以下的渗透作用微弱。(3)滑坡前一晚22日夜间的降水发生在副热带高压西侧西低东高的背景下,水汽条件充沛并具备一定的不稳定能量条件,但触发抬升能力偏弱。(4)22日20时地面中小尺度低涡的生成激发了分裂后的对流云团的重生和发展,重生后的β中尺度低涡云团在发展最强阶段造成了滑坡点附近的局地强降水,是22日20—23时滑坡点附近降水增强的直接影响系统。(5)22日多个要素分析显示,弱冷空气接近水城时激发了初始对流和降水。弱冷空气维持少动期间,降水在其南侧的暖区一侧加强。(6)较强降水使土壤表层增湿、含水量增加,但仍难以判断降水是滑坡的主要诱因,山坡岩体结构改变、重力与支持力之间的平衡被打破可能才是滑坡的重要原因。

A huge landslide occurred in Chagou group,Pingdi village,Jichang Town,Shuicheng County in Guizhou Province(referred to as"7.23"Shuicheng landslide)at 21∶20 on 23 July 2019.Houses were buried,42 people were killed and 9 people were missing.In this study,the conventional observation data,the encrypted observation data,the FY-2G blackbody temperature(TBB)and the NCEP/NCAR FNL grid⁃ded reanalysis data are used to diagnose and analyze the environmental conditions of this event.Conclusions are as follows.(1)The landslide occurred 16 hours after the precipitation stopped,with the characteristics of precipitation lag.The main precipitation period occurred at 20-23 BT on 22 July.The maximum rain intensity at 960 m away from the landslide point is 19.5 mm·h^-1(20-21 o'clock),and the maximum rain intensity at 2.7 km away from the landslide point is 56.9 mm·h^-1(21-22 BT),which occurred about 24 h before the landslide.(2)There were three rounds of precipitation in the area one week before the landslide,which contributed to the increase of soil water content in the top 100 cm layer,but had weak infiltration effect below 100 cm.(3)The precipitation occurred in the night of 22 July was under the condition of the west-low and east-high on the west side of the subtropical high.Water vapor was abundant and it has some unstable energy.But the abil⁃ity of triggering uplift was weak.(4)The Meso-βscale convective cloud clusters are the direct influence system of precipitation,which in⁃creased from 20 to 23 BT on 22 July.The formation of surface Meso-βscale vortex stimulates the regeneration and development of the split convective cloud clusters.(5)The initial convection and precipitation are excited when the weak cold air approachs Shuicheng.The heavy precipitation strengthens on the warm region on the south side of the slow-moving weak cold air mass.(6)The local heavy rain increased the soil soil moisture content,but it is still difficult to judge whether the precipitation is the main cause of the huge landslide.The main cause of the landslide is likely the change of the rock structure of the hillside,which breaks the balance between gravity and supporting force.