Water Cycle EQ2 Flashcards
Drought
This is a very complex geographical phenomenon, whereby there is a deficiency of water over an extended time period
Meteorological drought
- Shortfalls in precipitation as a result of short-term variability within long-term average
Agriculture drought
- The rainfall deficiency from meteorological drought leads to deficiency of soil moisture and soil water availability, which effect plant growth and reduces biomass
Hydrological drought
- Associated with reduced stream flow and groundwater levels, which decrease as a result of reduced inputs of precipitation and high rates of evaporation
Famine drought
- A humanitarian crisis in which the widespread failure of agricultural systems causes food shortages, with severe social, economic and environmental impacts
Physical factors affecting drought
ENSO cycles:
- This is a naturally occurring mass of warm water located in the Pacific Ocean
- It is located in the Western part, where it is pushed by trade winds and ocean currents
- El Niño occurs when these winds are reduced, allowing the mass of water to move more Eastwards towards South America, which can cause drought in the Western pacific. An example is the Millennium drought that was caused by a strong El Niño
- La Niña occurs when the winds are stronger than usual, pushing the mass of warm water even further westwards, towards Australia. The severe East African drought of 2011 was attributed to La Niña
Anticyclones:
- When the loops of the jet streams break up or stabilise, anticyclones can be formed due to the high pressure
- These bring little rainfall and heatwaves. These can block weather systems, such as depressions and cause low precipitation, creating vulnerability for drought
Human influences on drought
- Abstracting water from groundwater and rivers reduces the local supply, as well as building dams and reservoirs
- Deforestation and overgrazing reduced vegetation cover, and in turn evapotranspiration rates are lowered, which lowers atmospheric moisture and precipitation
- The removal of vegetation also changes soil conditions through compaction and reduced soil moisture retention, causing reduced infiltration and greater run-off. This reduced soil moisture content and water storage in case of a drought
- The production of clothes (especially cotton) uses intense levels of water. It can take 2700 litres of water to produce cotton to make 1 t-shirt
Drought in the Sahel- human influence on drought impacts
- This study highlights that human activity may not directly cause droughts, but plays a large role in making the impacts of drought more severe
- Sahel has a high variability of rainfall, making it a drought sensation area. The mean annual rainfall can vary from 100mm to 800mm
- In the 1999-2000 drought, 10 million people needed food assistance. This was due to rural population densities had grown rapidly, agriculture mostly being rain-fed making it especially vulnerable to drought, and the Ethiopian-Eritrean war blocking food access for many people
Ecological impacts of drought
Wetland ecosystem:
- As the supply of water is reduced, areas of open water shrink or dry up altogether, resulting in loss of habitat
- As soil moisture is reduced, extended drying can lead to soil erosion, which reduces it’s ability to store water in times of floods
- Droughts can alter communities by eliminating some species and creating gaps in food webs
Forest ecosystems:
- Forests are highly valued for their ecological services and functions such as hydrologic processes, timber production and wildlife habitats
- Research shows that it takes 2-4 years to recover from a drought to resume normal growing rates
- Long-term harm to drought stressed trees include impaired growth, impaired water transport ability, vulnerability to pests and diseases
- Between 2000-2003 drought caused warm conditions which allowed pests and diseases to accumulate in parts of Canada, for example the pine bark beetles. As a result 90% of piñon pine trees were killed off in some area
Meteorological causes of flooding
Flash floods:
- They may be caused by heavy and intense rainfall associated with tropical storms
- Much of the UK is at risk to flooding due to mid-latitude depressions
Snowmelt:
- Snow and ice are responsible for flooding in areas of higher latitudes/altitudes
- The melting of snows and ice in late spring causes flooding in Asia and America
- The ground may still be frozen in the spring when the snow and ice melt. This causes little to no interception, with the discharge running directly into nearby water sources to cause floods
- Rain may also fall on melting snow, combining to cause heavy flooding
Monsoons:
- This is a seasonal change in the direction of the prevailing winds of a world. The causes wet and dry in the subtropical areas
- In Pakistan, in 2010, 9000mm was received in one week
Impacts of flooding (socio-economic)
- Between 1990 and 2010, there were 200,000 killed from floods and 3 billion adversely affected
- Flood depth has a link to mortality as many people in developing countries cannot swim. Children and young people are particularly vulnerable
- Water-borne diseases are likely in developing countries
- Psychological stress is very common amongst victims in developed countries
- Where farming is subsistence and agricultural infrastructure is damaged, there is a direct loss of food supply and famine may occur
- Direct structural damage is the most tangible flood loss
- Reduced property values for housing in flood prone areas can negatively impact the economy (possibly deter tourists)
- In more developed countries, floods can lead to escalating food prices due to shortages
- Due to storm Desmond in 2015, a McVities factory had to close down in Carlisle, leading to the loss of 1000 jobs
- Anually, Australia spends almost A$ 400 million on flood reparations
- About 90% of all flood deaths occur in Asia
Impacts of flooding (environmental)
-Flood can recharge groundwater systems, fill wetlands and increase connections between aquatic habitats
- Intense flooding can over supply sediment and nutrients resulting in possible eutrophication (dense growth of plant life causing death of animal life from lack of oxygen)
- Pollutants may be washed into water supplies and degrade aquatic supplies
