5.4 Deficits Within the Hydrological Cycle Flashcards
5.4a Causes of drought
types of drought
- meteorological drought
- hydrological drought
- agricultural drought
- famin drought
5.4a Causes of drought
meteorological drought
shortfalls in precipitation as a result of short-term variability within the longer-term average overall, as shown in many semi-arid and arid regions
rainfall deficit due to: low precipitation high temperatures strong winds increased solar radiation reduced snow cover
major impacts:
loss of soil moisture
supply of irrigation water declines
5.4a Causes of drought
hydrological drought
associated with reduced stream flow and lower groundwater levels, which decrease because of reduced inputs of precipitation and continued high rates of evaporation.
it results in reduced storage in lakes and reservoirs, often with marked salinisation and poorer water quality
stream flow deficit due to :
reduced infiltration
low soil moisture
little percolation and groundwater recharge
major impacts:
reduced storage in lakes and reservoirs
less water for urban supply and power generation - restrictions
poorer water quality
threats to wetlands and wildlife habitats
5.4a Causes of drought
agricultural drought
the rainfall deficiency from meteorological drought leads to deficiency of soil moisture and soil water availability, which has a knock-on effect on plant growth and reduces biomass
soil moisture deficit due to: low evapotranspiration plant water stress reduced biomass fall in groundwater levels
major impacts: poor yields from rain-fed crops irrigation systems start to fail pasture and livestock productivity declines rural industries affected some government aid required
5.4a Causes of drought
famine drought
a humanitarian crisis in which the widespread failure of agricultural systems leads to food shortages and famines with sever social, economic and environmental impacts
food defect due to: loss of natural vegetation increased risk of wild fires wind-blown soil erosion desertification
major impacts: widespread failure of agricultural systems food shortages on seasonal scale rural economy collapses rural-urban migration increased malnutrition and related mortality humanitarian crisis international aid required
5.4a Causes of drought
El Niño Southern Oscillation (ENSO) cycles
NEED TO ADD TO THIS
normal conditions in the Pacific Basin:
trade winds blow from east to west along the equator, the air pushes warm water westwards
the shallow position of the thermocline allows winds to pull up water from below
upwelling
warm, moist air rises, cools and condenses, forming rain clouds
conditions during an El Niño event:
the trade wind pattern is disrupted- it may slacken or even reverse- having a knock-on effect on the ocean currents
air circulation loop revered
triggers very dry conditions throughout the world in the second year
conditions during a La Niña event:
extremely strong trade winds
very strong air circulation
low pressure develops with strong convectional uplift as very warm water heats the atmosphere, leading to heavy rain in Southeast Asia
increases in the equatorial undercurrent and very strong upwelling of cold water off Peru results in strong high pressure and extreme drought
5.4b Human Activity and Drought
human factors
Human factors act like a feedback loop. Humans enhance the impacts of drought by the over-abstraction of surface water from rivers and ponds, and of groundwater from aquifers.
key factors are population growth, overgrazing, over cultivation and deforestation
5.4b Human Activity and Drought
population growth
rapid population growth puts pressure on the land to grow more food
migrants fleeing from one disaster area help to make another
5.4b Human Activity and Drought
overgrazing
too many goats, sheep and cattle destroy the vegetation cover
5.4b Human Activity and Drought
overcultivation
intense use of marginal land exhausts the soil and crops will not grow
5.4b Human Activity and Drought
deforestation
trees are cut down for fuel, fencing and housing
the roots no longer bind the soil, and erosion ensues
when deforestation passes a tipping point, hydrological and climate cycles change permanently
deforestation acts in a positive feedback loop
5.4c Impacts of drought on ecosystem functioning and resilience
ecological resilience
what is ecological resilience?
ecological resilience is the capacity of an ecosystem to withstand and recover from a natural event (e.g. drought or flooding) or some from of human disturbance
5.4c Impacts of drought on ecosystem functioning and resilience
wetlands
what are wetlands?
wetlands are an area of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt
5.4c Impacts of drought on ecosystem functioning and resilience
wetland functions
temporary water stores:
temporary water stores within the hydrological cycle, thus mitigating river floods downstream, protecting land from destructive erosion by acting as wastelands and recharging aquifers
maintain water quality:
wetlands act as giant water filters by trapping and recycling nutrients, as well as pollutants to maintain water quality
high biological productivity:
wetlands support a very diverse food web, providing nursery areas for fish and refuges for migrating birds
the functions of wetlands contribute towards their value for human society, as providers of resources (fish, fuelwood, etc), for services in terms of hydrology within the water cycle, and as carbon stores (peat) pithing the carbon cycle
5.4c Impacts of drought on ecosystem functioning and resilience
impacts of drought on wetlands
drought can have a major impact on wetlands- with limited precipitation, there will be less interception as vegetation will deteriorate, and less infiltration and percolation to the groundwater stores, causing water table levels to fall
the precipitation will continue and might increase from the less-protected surface, while transpiration rates will decrease, making the wetlands less functional
desiccation (extreme dryness) can also accelerate destruction by wild fires
drought increases tree mortality, which in turn reduced habitats for wild animals- as well as for cattle ranching and ecotourism
