4. Causes of excess run off (Human causes of excess runoff (river…
4. Causes of excess run off
Pakistan floods 2010
unlike India and Bangladesh, monsoons are less relied on in Pakistan.
twice the normal amount of rainfall occurred, covering 30% of the country at its peak
Destroyed over 5000 schools
coincided with the start of the 2010-11 La Nina episode, contributing to heavier than normal rainfall.
warm air from Central Asia rises, bringing much cooer and wetter air from the Indian Ocean. It is blocked by the Himalayas (worlds tallest mountains) and falls in India. :!:
Yorkshire 2007 extreme rainfall
over 3 times the national average fell
Widespread , intense rainfall in two episodes over the month. The second was more severe and followed a flood because the ground was previously saturated.
Could have occurred due to anthropogenic climate change, or random variability of natural forces in the atmospheric system. Sea level pressure lower than average,
In Hull, 30,000 people had to leave their homes at the height the flood.
3 people drowned.
Human causes of excess runoff
changing land use
caused by excess overland flow generated by deforested hills
1919 forest land hit a low of 3%, but it is currently at 10%. Mainly thanks to the Forestry Commission.
less transpiration and irnterception without land vegetation, yet more runoff can be expected
In Amazonia, 20% of the forest has been destroyed in the last 50 years, a combination of cattle ranching and large-scale agribusiness.
decreased effectiveness of infiltration, through flow and storage
renders surfaces impermeable
drainage systems increase infiltration rates
Afforestation and seeding
- humans reducing flood risk
not wide enough
no engineering strategies
dredging to increase channel capacity
Ganges delta flooding
Aral Sea basin
90% reduction due to over use of crop production and irrigation systems
Tempe Town Lake 2017
Rising water pulled in vegetation growing along portions of the river
Oe of the four reservoirs created by diversion dams on the Salt River and now 60% full, compared with 34% full in December.
dams were made to handle over 200,000 cubic feet of warm water per second
. Mountains and glaciers act as natural resoviors for water, until the summer when they melt and are released into rivers.
South Platte River in Colorado and Nebraska
- snowmelt is responsible for stem flow. in recent decades irrigation water from field replenishes the alluvial aquifer.
essential for summer irrigation season and too supply cities/people