Short And Long Term Influences On Hydrological System Flashcards
Name four types of drought
Meteorological drought
Agriculture drought
Hydrological drought
Socio-economic drought
Define meteorological drought
Occurs when long term precipitation trend is below the long term average. This type of drought is region specific to its atmospheric conditions
Define agricultural drought
When there is insufficient soil moisture to meet the demands of crops at a particular time. Can be caused by water shortage, evapotranspiration, reduced groundwater supply. Usually occurs after a meteorological drought.
Define hydrological drought
When there are deficiencies in sub/surface water supplies (rivers, groundwater) to meet the needs of vegetation. Originates because a lack of precip
Define socio-economic drought
When water demand for social purposes exceeds water availability. Result from lack of precip or exploitation of water supplies
Define ITCZ
Intertropical convergence zone
A belt of low atmospheric pressure around the equator.
Here air rises due to intense heating from sun causing high evaporation (ocean). Causing alternating wet season
Example: Africa Sahel lower humidity=less evap. High pressure blocks ITCZ (wet season) could cause a drought
Define mid latitude blocking cyclones
Occurs in mid latitudes
Anticyclone forms (area of high pressure) where air descends to ground causing the increase in pressure.
Anticyclones brings stable conditions able to block low pressure systems from the west up to two weeks. Multiple blocking anticyclones can cause drought
Define El-niño southern oscillation ENSO cycles
Naturally occurring phenomenon that involves movement of a mass of warm water in Pacific. Because the changes in surface trade winds, atmospheric circulation and ocean currents.
Causing cooler ocean to replace warmer ocean= less evap and precip leading to drought
Naturally occurs every seven years
Name the three physical causes of drought
Intertropical convergence zone
Mid latitude blocking anticyclones
El Niño southern oscillation cycles
Examples of human activities that increase drought risk
Over abstraction of groundwater- causes water deficit
Building reservoirs/water transfer- alters natural course/hydrological cycle (China, 600 rovers dried up)
Deforestation- reduced vegetation cover reducing evapotranspiration levels
Overgrazing- removal of vegetation changes soil conditions reducing infiltration increasing runoff and decreasing soil moisture content
Case study: Sahel region
Vast arid region across 11 African countries. Regular droughts
Most severe drought 2011-12 causes:
Air pollution generated by EU/USA cashed atmospheric cooling changing global heat and circulation. So tropical rains didn’t arrive=drought
Higher sea surface temperatures caused by global warming. Rain bearing winds fail when sea temperatures are warmer over Sahel
El Niño event could increase water stress in western sahel
Sahel has one of highest poverty rates and lowest development levels. High pop growth from 2.5-4%
Over cultivated land causes desertification increasing vulnerability to drought
Case study: Millennium Drought
Southern Eastern Australia 1997-2009 (longest drought)
Annual rainfall 97-09 12.4% below 20th century mean
El nino events in 2002-03 and 2006/07 partly responsible. Estimated for 80% of rainfall decline in Australia.
Ridge of high pressure also blocked depression reducing rainfall
Global warming intensifies sea surface temperature
Impact of drought on a wetland ecosystem
Wetland- area of land saturated with water permanently/seasonally (Everglades)
Supply of water reduced, flooded areas shrink/dry up causing progressive loss of habitat
Soil moisture reduces, extended period leads to soil erosion (loss of nutrients)
Aquatic species decline
Meteorological causes of flooding
Flash flooding due to thunderstorms/tropical storms. 2013 Island of Sardinia flash floods killed 18 people $1.14 billion damage
Mid-latitude depressions causes flooding in UK, each depression brings rain. Multiple depression cause flooding, as grounds already saturated
Monsoons (seasonal change in direction of prevailing winds) India Sri Lanka warm climate with torrential rain because of the ITZ moving north. Myanmar caused 103 deaths and affected 1mill+
Snow melt from mountain areas. Red River North Dakota USA
Impact of drought on forest ecosystems
Forests are valuable due to their ecological function/services/regulation of hydrological cycle
Species become less resilient to droughts and take years to recover
foliage loss/increase number of pests (hot conditions= pine bark bettle attacks USA) causing major ecosystem changes
Forest important for carbon sequestration, average 0.73 tonnes of carbon per hectare per year
