There is growing evidence that urbanization has a sharp impact on climate, causing changes that can wreak havoc on precipitation patterns that supply the precious resource of water. The heavy amounts of heat and pollution rising from cities both delay and stimulate the fall of precipitation, depriving some areas of rain while drenching others. Cities are on average one to ten degrees warmer than the surrounding undeveloped areas. Cities also produce large amounts of pollutants called aerosols, gaseous suspensions of dust particles or byproducts from the burning of fossil fuels. Both heat and pollutants change the dynamics of clouds. When hoisted up in the sky, the microscopic particles act as multiple surfaces on which the moisture in clouds can condense as tiny droplets. This can prevent or delay the formation of larger raindrops that fall more easily from the sky, or it can cause the rain to fall in another location. In California, pollution blows eastward and causes a precipitation shortage of around one trillion gallons a year across the Sierra Nevada mountain range. By contrast, in very humid cities, such as Houston, heat and pollutants seem to invigorate summer storm activity by allowing clouds to build higher and fuller before releasing torrential rains.

1.B.proved

2.D different precipitation patterns

3.A.heat and pollutants

4.C.cause damage to

5.A.To give an example of an area affected by heavy rain