Enquiry 2 What Factors Influecne The Hydrological System Over Short And Long Term Timecales ? Flashcards
Droughts
Long period of time with below average precipitation
Meteorological causes of drought
Short term precipitation deficit
ENSO cycles
Anticyclones (Air does not rise so condensation and cloud formation does not occur)
Changes in the ITCZ
El Niño
Reverse of walkers cell
High pressure accumulates above Australia, causing drought whilst s America becomes a low pressure centre (at risk of flooding and intense rainfall)
La Niña
Intensification of walkers cell
Australia has a low pressure system and s America experience drought due to high pressure
Desertification in Sahel
Causes are essentially naturally
Set in motion a downward spiral:
Changing rainfall patterns (less reliable)
Vegetation cover becomes stressed and dies
Bare soil eroded by wind and occasional intense rain
Human factors act as a feedback loop for drought
Pop growth- rapid puts pressure on land to grow more food
Overgrazing- too many goats
Over cultivation- intense use of marginal land exhausts the soil and crops will not grow
Deforestation- trees are cut down for fuel- roots not longer bind the soil and erosion ensues
Wetlands
50 years ago were considered as wastelands
Act as temporary water stores
Recharge aquifers
Giant filters trapping pollutants
Drought- less precip=,less infiltration and percolation
Water table fall
Evap increase= decrease transpiration = reduce valuable functions
Main challenge to then is artificial drainage
Forests
High levels of transpiration
Coniferous forest- susceptibility of pines to fungal diseases
Tree mortality increase (also affect carbon stores)
Tropical rainforests- greater impact on large trees
Ecological resistance
Physical causes of flooding
Intense storms- lead to FLASH FLOODING (exceptionally short lag time)
Prolonged, heavy rain (deep depressions across uk)
Rapid snowmelt- (plains of Siberia)
Bangladesh
Flood prone country
Land of flood plains and deltas built up by might rivers (Ganges, Parma and Meghna)
Rivers swollen twice a year by meltwater from himilayas
hilly tracts Bayern rivers often flash flood victims
Tidal flooding
Resulting from storm surge
Or when high river flows meet particularly high spring tides in estuaries
Likelihood of flooding also increased by:
Low lying areas with impervious surfaces
Ice dams melt suddenly and water in glacial lakes is released
Volcanic activity generate meltwater beneath ice sheets that is released
Earthquakes cause failure of dams or landslides
Human activity and flood risk
Combo of economic and pop growth during 20th caused many flood plains to be built on
Natural landscapes modified for agriculture/ industrial
Sprinkling ground water on arable crops
Ploughing compacts soil
Sewers feed water into channel
River mismanagement:
Channelisation
Dams
River embankments
Channelisation
Effective way of improving river discharge and reducing flood risk- simply displaced that risk downstream (location overwhelmed with increased discharge)
Dams
Block the flow of sediment down a river so the reservoir gradually fills up with silt- downstream there is increased river bed erosion
River embankments
Designed to protect from floods of a given magnitude
Can fail when flood exceed capacity
Socioeconomic impacts of flooding
Death and injury
Spread of water borne diseases
Trauma
Damage to property
Destruction of crops
Environmental impacts of flooding
There are many positives:
Recharged groundwater stores
Increase connectivity between aquatic habitats
Soil replenishment
Eutrophication
Process of nutrient enrichment that ultimately leads to the reduction of oxygen in rivers, lakes and ponds and the consequent death of fish and other species
Caused by removal of soil and sediment by floodwaters
Impacts of climate change on inputs and outputs (precipitation)
Water atmos has water holding capacity
Precipitation increase in tropics and high latitudes
Climate warming means more precipitation in northern regions is falling as rain rather than snow
Impacts of climate change in inputs and outputs (evaporation and evapotranspiration)
Evap over large areas of Asia and n America appears to be increasing
Transpiration linked to veg changes which in turn is linked to changes in soil moisture and precipitation
Impacts of climate change in inputs and outputs (soil moisture)
Uncertain as soil moisture depends on many factors
When precipitation is increasing it is likely that soil moisture will be increasing
Impacts of climate change in stores and flows
Surface runoff- more low flows (droughts) and high flows (floods)
Permafrost- deepening of active layer is releasing more groundwater and Meghan released from thawed lakes may be accelerating change
Glacier ice- strong evidence of glacier retreat and ice sheer thinning since 70s and less accumulation as more precip is falling as rain= decreasing store
Oceans- more data on surface temp needed
Where ocean is warming there will be evap
Storage capacity being increased by meltwater
Rising sea level
Concerns about short term term oscillations (ENSO CYCLES)
Problem with forecasting- distinguishing between impacts of long term climate change and short term oscillations (el Nino events)
Further complication- ENSO cycles associated with extreme flooding in some parts of world and extreme drought in others
Short term climate changes on global water supplies (some of impacts are possible rather than probable)
Diminishing supply, increased uncertainty-
Depleted aquifers leads to groundwater problems
Increase intensity and frequency of droughts as result of global warming and oscillation is issue for rainfed agriculturalists
Greater rates of evapotranspiration- desiccation of forest stores
More frequent cyclone and monsoon events threaten water supplies intermittently
