5.5 flooding

• what is a flood

  When discharge in a river exceeds the river's capacity due to a surplus in the hydrological cycle
• what are the 4 meteorological causes of a flood

  -intense storms leading to flash flooding

  -snowmelt

  -extreme monsoonal rainfall

  -heavy or prolonged rainfall
• why do intense storms cause flooding


  because intense rainfall increases surface run off (shorter lag time) leading to a flashy river.

  infiltration capacity is reached more quickly
• what is monsoonal rainfall


  seasons of heavy rainfall in the summer months in Asian countries; high temps cause fast evaporation rates leading to high precipitation
• example of extreme monsoonal rainfall causing flooding

  pakistan 2022
• outline the causes of the extreme monsoonal rainfall in Pakistan 2022

  -climate change caused a heatwave (made it 30x more likely) which brought 8 monsoonal depressions to the southern Provence

  -La Niña effect brings warm ocean surface waters
• how much more rainfall did Pakistan receive in August 2022 than normal

  190% more rainfall
• how many people were affected by the monsoonal rainfall in Pakistan

  33 million
• what was the financial loss of the monsoonal rainfall in Pakistan

  $30 billion
• why were the monsoonal depressions so devastating


  all 8 hit the southern Provence when they normally travel north over the monsoonal period
• explain snowmelt as a cause of flooding

  -snow in the upland, high altitude areas melts first

  -downstream remains frozen and this forms ice dams, with glacial lakes behind

  -when the ice eventually melts downstream, large volumes of water released quickly from behind dam causing a flood
• what are 2 human causes of flooding


  -mismanagement of rivers

  -change of land use in the river catchment area
• explain how humans can mismanage rivers


  -channel straightening

  -building dams

  -embankments
• how does channel straightening cause floods

  increases rate off channel flow which displaces flood risk downstream
• how does building embankments cause floods

  increases capacity of river so more water available to flood land
• example of humans exacerbating flood risk


  Carlise Floods (storm Desmond) and Boscastle flood
• how did humans impact the Boscastle flood


  -urbanisation as land use for car parks/roads

  -poor drainage systems as old town
• how did humans impact the Carlisle Flood


  -build embankments upstream of up to 2m

  -channel straightening upstream contributed to the 30% inundation of Carlisle
• outline the environmental impacts of the Carlisle flood

  -soils nutrients washed away decreasing land productivity

  -soils washed into rivers became polluting which decreased water quality

  -this harmed aquatic wildlife

  -other ecosystems such as worms and badgers living in the soil were drowned

  -trees that lined the rivers ripped from river banks
• outline the economic impacts of the Carlisle flood


  -4000 businesses both directly and indirectly flooded

  -road closures prevented people going to work

  -farming sector lost tens of millions
• outline social (including infrastructure) impacts of the Carlisle flood


  -19,000 homes flooded leaving many homeless

  -22 bridged damages or destroyed, preventing children going to school and people going to work

  -2 main hospitals cancelled routine appointments and operations
• long term effects of Pakistans floods

  pushed a further 6 million people into poverty