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1 洪涝灾害成因1.1 气候影响全市降雨量年内分配极不均匀,7～9月占年降水总量的70%以上,而全市的致灾暴雨又多发生在这期间的1～2次降雨过程。同时,全市处于同一个雨区,暴雨成因以南北向切变走向与河流走向一致,造成上下游洪水迭加,加重灾情,且致灾往往是一条线。从而加剧了洪灾程度和抗洪抢险的艰巨性。降水量年际间差异很大,相差2～4倍,时常发生旱涝灾害。而且有连续干旱和连续丰水的特点。1.2 地形影响全市地势自西向东倾斜,西部为山区,东部为平原。市境东西长不足200km,但高差却达2000多米。从山地到平原,中间丘陵地带很短,洪水无缓冲余地,基本是一泄直下。
1 Causes of Flood Disaster 1.1 Climatic Impacts The distribution of rainfall throughout the year is extremely uneven during the year, accounting for more than 70% of the total annual precipitation in July-September. However, the heavy rainstorms in the whole city occurred once or twice during this period. In the meantime, the whole city is in the same rain area. The cause of the heavy rain is changing from north to south toward the same direction as that of the river, resulting in the superimposition of floods in the upper and lower reaches of the city, which aggravates the disaster and the disaster is often a line. Thus exacerbating the degree of floods and the arduousness of flood control. Precipitation is very different from year to year, a difference of 2 to 4 times, frequent droughts and floods. And continuous drought and continuous abundance of water features. 1.2 topography affect the city’s topography from west to east tilt, the western mountainous areas, the eastern plain. City long things less than 200km, but the height is up to more than 2,000 meters. From the mountains to the plains, the middle of the hilly area is very short, no buffer for the flood, the basic is a vent down.