2002年8月湖南致洪强降水过程与成因分析

Analysis of Flood-Producing Rainfall Events over Hunan Province during August 2002

利用 2 0 0 2年 8月的常规观测资料 ,1°× 1°的NCEP逐日再分析资料 ,1°× 1°的云顶黑体亮度温度 (TBB)逐时资料 ,水利部发布的 2 0 0 2年 5～ 8月水情资料 ,以及 1 960～1 997年中国 31 5站的逐日降水资料 ,对 2 0 0 2年 8月中下旬湖南百年难遇的大洪水发生原因以及致洪强降水进行分析。发现 :( 1 ) 2 0 0 2年 8月受 1 2、 1 4号台风影响的湖南南部大暴雨和 8月中旬持续高空槽前的大面积强降水 ,是引起 8月中下旬湖南严重洪涝灾害的直接原因之一 ;( 2 ) 2 0 0 2年 4～ 5月以及梅雨期湘南地区的强降水使得土壤水份饱和 ,江河湖库维持较高的水位 ,导致 8月上中旬先后 3次强降水过程产生的雨水只能作为径流流入洞庭湖水系 ,使洞庭湖水系的来水与长江上游的洪峰来水遭遇 ,造成 8月中下旬洞庭湖水系的严重洪涝灾害 ;( 3) 8月上中旬的强降水过程中 ,中尺度对流系统 (MCS)十分活跃 ,而MCS的发生、发展又与有利于出现对流活动的大尺度环境场有关。

The reasons causing the record floods and the heavy rainfalls in Hunan province in August 2002 have been studied by using conventional and special observational data, including the NCEP/NCAR reanalyzed daily 1°×1° data, 1°×1° hourly T BB data in August 2002, hydrological data from the Ministry of Water Resources o f the People's Republic of China in May-August 2002, and daily precipitation dat a of 1960-1997 The main conclusions are as follows: (1) Unusual large scale ci rculation, for example, the maintenance of block high near Baikal and West Pacif ic Subtropical High, is very favorable to formation and development of the heavy rainfalls and flash flood (2) Landing typhoons and upper troughs in early and middle August result in persistent severe rainfall, and then, reduce to flash f lood in Hunan Province (3) During anomaly precipitations, soil saturated, rive rs and lakes had higher water level in Hunan Province in April—July The flood s in the rivers and lakes encountered the floods coming from the upper reaches o f the Yangtze River, which brought severe damage in middle and later August Sat urated soil, higher water-level of the middle reaches of the Yangtze River and Dongting Lake are already produced by heavy rainfall during April-July Therefo re, the heavy rainfall of August in Hunan Province becomes run-off to the water system of Dongting Lake Further more, disasterous flood of Hunan Province hap pened because of the encounter of high water-level of Dongting Lake and floods from the upper reaches of the Yangtze River (4) Mesoscale convective systems ( MCSs) affected by favorable large-scale conditions are active in August Conse quently, it is very important to focus on favorable large-scale conditions and activities of MCSs for studying and forecasting of heavy rainfall