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我国是一个暴雨频繁、洪涝灾害比较严重的国家。降雨和河川径流在地区上分布很不均匀,降雨量和年际、年内变化都很大,南方汛期降雨量约占全年降雨量的50％～60％,而北方汛期降雨量约占全年降雨量的70％～80％。在一次暴雨中,其中连续几小时的降雨量,有时竟可占一次降雨总量的60％以上。许多经常发生大暴雨的地区,因受自然地理和地形条件的影响,汇流很快,有的十多小时甚至几个小时洪就可到达,给
Our country is a country with heavy rainfall and serious floods and disasters. Rainfall and river runoff are unevenly distributed in the region. Rainfall, interannual years and years vary greatly. Rainfall in the southern flood season accounts for about 50% -60% of the annual rainfall, while precipitation in the northern flood season accounts for about the whole year 70% ~ 80% of the rainfall. In a torrential rains, where the rainfall for several hours, sometimes even accounted for more than 60% of the total rainfall. In many areas where frequent heavy rains occur, confluence occurs rapidly due to the effects of physical geography and topography, and more than 10 hours or even hours can be reached