1月4日上午，安徽合肥多个公交站台被积雪压塌，导致多人伤亡。此外，多地还发生多起厂房、大棚、菜市场顶棚被积雪压塌的情况。看似蓬软的雪为何有此威力?
雪是水汽在空中凝结而成再落下的自然现象，雪本身是有重量的。为了便于理解，我们从降水量的角度来估算一下雪的重量。
通常情况下，在北方，1平方米面积上8～10毫米的降雪厚度融化成水相当于降水1毫米;而在南方，1平方米面积上6～8毫米的降雪厚度融化成水相当于降水1毫米。同样厚度，南方含水量较高的雪比北方的重。
根据水的密度，我们不难得出，在北方，1平方米面积上，8～10 毫米的积雪的质量\[m=\rho Sh=1000\times 1\times 0.001=1\rm (kg)\]，那么100平方米面积上8～10毫米的积雪就重100公斤;在南方，100 平方米面积上6～8毫米的积雪也就重100公斤。
此外，含水量较高的是湿雪，更容易黏在一起;含水量较少的是干雪，就像沙子一样，比较松散，不容易黏在一起。南方地区下雪温度并不是很低，所以雪的水含量很大，落下的都是湿雪，这些湿雪在建筑物上面更容易堆积起来，不容易滑落松散。
不仅是雪的重量，建筑物还需要考虑压强的问题。我国建筑设计上规定雪压为一般空旷地水平面积上30年一遇的最大积雪重量。一般而言，北方容易遭受大雪灾害，所以北方的建筑物一般会考虑雪压。南方一些不常降大雪地区的临时建筑，如大棚、临时简易棚等，则很少考虑雪压的问题。因此，降下的湿雪给建筑物造成的雪压很大，甚至将建筑物压垮。
中国气象局介绍，通俗地说，100平方米的平面屋顶如果积雪一尺厚（333毫米），就会承受超过3至5吨的重压，可想而知雪花有多重。
【综合《新京报》1月5日邓琦、戴轩文，中国科技网】
On the morning of January 4, several bus platforms in Hefei, Anhui province were crushed(压塌) by snow, had causing many casualties(伤亡). There are also a lot of factories, sheds, vegetable market had been collapsed(压塌) by the snow. Why the soft snow have such power?
Snow is a natural phenomenon(现象) which water congeal(凝结) in the air and then falls, it has weight. In order to let you understand, let’s count the weight of snow from precipitation(降水量).
Normally, In the northern China, 8 to 10 millimeters snow in 1 square meter amounts to 1 millimeter precipitation; but in the southern China, 6 to 8 millimeters snow in 1 square meter amounts to one millimeter. In the same thickness, the snow in the south is heavier than the north.
According to the density(密度) of the water , It’s not hard to figure out, in the north, 1 square meter of 8 to 10 millimeters snow is\[m=\rho Sh=1000\times 1\times 0.001=1\rm (kg)\] So 100 square meters of 8 to 10 millimeters snow weighs 100 kilograms. In the south, 100 square meters of 6 to 8 millimeters snow weighs 100 kilograms.
In addition, the wetter the snow is, the easier it sticks together; Dry snow likes sand, is looser(蓬松的) and less sticky. The temperature in the south is not very low, So the snow is not so dry, there’s all wet snow, The wet snow is easier to pile up(堆积) on the building and not to slide down.
It’s not just the weight of the snow to let the platform down, but the building also needs to think about the pressure. In our country’s building design, the maximum pressure buildings can held is the maximum ground snowfall in 30 years. Generally, the north is prone to suffer from snow disasters, so designer in the north usually consider snow pressure. Some temporary(临时的) buildings such as greenhouses in the southern part of the country that do not have heavy snow seldom consider the snow pressure. As a result, the wet snow was so heavy that crushed the building.
According to the China Meteorological Administration, a flat roof of 100 square meters will bear more than 3 to 5 tons of snow if the snow is one Chi (333 mm) thick.
[According to Deng Qi and Dai Xuan’s article on January 15’s New Peking and China Technology]