Floods

Examine the flood images.

Floods happen when normally dry areas are covered in water. Floods often occur when rain falls or snow melts faster or in greater amounts than the ground can absorb water or rivers can carry it away, or when storm winds push seawater onshore.

Questions

1. Explain how higher temperatures could locally influence the water cycle and lead to flooding. (Hint: Think about the processes that put water in the air and take it out again.)
   Check Answer
   Big wet storms seem more likely than small storms to overwhelm the rate of infiltration and the capacity of rivers to carry runoff, and cause flooding. Heating encourages the development of big storms. Hotter temperatures put more water vapor in the atmosphere - the supply of vapor would increase due to increased evaporation, and the warmer air would allow greater amounts of vapor to build up. When all that water finally condenses, enormous clouds will form, and produce similarly enormous amounts of rain and snow.
   
   Also, global warming raises sea level, because ice melts and liquid water expands when temperature rises. So areas that used to be far enough inland or high enough above sea level to escape flooding may now be drowned when hurricanes force seawater onshore.
2. How would flooding and the associated impacts on the water cycle affect people and property?
   Check Answer
   During floods, buildings and crops are washed away and people are drowned. In the aftermath, famine strikes because fields and livestock were destroyed. Pests and diseases may proliferate in waterlogged areas. Paradoxically, flooding often leads to water shortages - debris, toxic chemicals, and sewage picked up by the flood runoff into and contaminate rivers, and some of these pollutants can be injected into the groundwater during infiltration. Increased runoff causes greater riverbank and soil erosion.