W - 2.1 -> 2.4 Flashcards
meteorological drought definition
occurs when LT precip much lower than normal.
- region specific, as atmospheric conditions that result in deficiencies of precipitation are highly variable between climate types
agricultural drought definition
insufficient soil moisture to meet the needs of the agriculture in the area.
hydrological drought
deficiencies in surface and subsurface water supplies as measured in rivers, lakes + groundwater, etc. originates with a deficiency of precipitation.
socio-economic drought
when the water demand for socioeconomic purposes exceeds the water availability.
drought in California
- 34% less rainfall in 2013
- 13 consecutive months of drought by 2014
- some rain in Dec 2014 improved this, but needed 5x more to recover
- climate variability accounted for 8-27% of this
- drought = farmers must over extract water - exacerbating the drought
meterological causes of drought
ENSO leads to La Nina, which reduces rainfall
longer trends
- 5 prev periods in last 500 years where snowpack levels have been equivalent to today
Short term precipitation deficit
- south cali consistently below average rain from 13-16
- north has varied, but mostly lower than average
hydrological causes
- CA relies on snowfall/ melt for its water supply
- Snowpack has reduced from above average - 136% in 05, to 5% in 15
Millenium Drought - Australia
97- 09
- annual rainfall was 12.4% below 20th century mean
- disastrous impact on wheat, wool and meat exports
- prevailing El Nino conditions explain 2/3 of rainfall deficit, but human causes played a role
Physical causes
- australia lies on sub tropical ridge - high pressure belt
- el nino events in 02/03 + 06/07, and natural climate change cycles (sunspots) enhance dry conditions
- current warming trend is reducing temp gradient between equator and poles - less energy for mid latitude storms
- 15% drop in rainfall by 2030
deforestation
- 90% of basin original veg removed since 1800s
- reduces transpiration/ precipitation
- increases GW consumprion
- added 2 weeks per year onto drought period
emissions
- anthropogenic greenhouse gas emission adding to natural variabilities
- climate model evidence most plausible
surface water
- 94% of all rainfall evaporates from surface water
- 42% of leftovers are diverted/ pumped for human use through damns and reservoirs
groundwater overextraction
- groundwater accounts for 17% of total accessible water resource and 30% of total water use - concentrated in certain areas of basin
- crops (nuts) and herds (cows) increase water demand
resulting conflict
- 3.5 million people depend on limited water supply - 32.5k GL a year
- introduction of water cap and Murray-Darling Bain plan overshadowed by illegal over use from farmers above quota
- conflict with environmentalists over wetland water availability
- 16mil Kangaroos have died
Mesopotamian marshes
- alluvial fan on Tigris-Euphrates rivers
- habitat for marsh-arabs
- drained from 50s-70s, then eviction of Shia Muslims in 80/90s
- in 03: 10% original size, 500k reduced to 20k
- 16: UNESCO world heritage site
- but turkey still dams the river
key physical changes
- dams
- less infiltration
- less percolation
- less GW recharge
- evaporation increases
- transpiration increase
- aquatic + veg die
In Iraq
- 250k marsh Arabs part of resistance movement
- lived in south
- Hussein cut off water supply from Tigris-Euphrates
- desertification
- since 03 recovery started
why are they not resilient
- soil erosion removes key nutrients, so veg difficult to recover
- new water encourages more soil erosion
- vegetation cant establish itself and begin seres of succession
Malaysia Floods 2014
- 200k affected, 21 dead
- NE monsoon heavy rain on 17th Dec
- by 20th dec, most rivers affected
- then road closures + foreign tourists stranded
- 21st dec, heavy rains, Padras river 9.26m above danger level, with heavy overflow
flash floods
- intense rainfall, thunderstorm or tropical storm with no warning
- small basins - short lag time
- ground saturated quickly
monsoons
- specific heat capacity differences between land and sea
- summer: LP over land, HP over sea, winds blow HP-LP, dragging moisture-laden wind from Indian Ocean
prolonged rainfall
- mid latitude depressions queued up over the same place - result of jet stream sinuosity
- UK: two bands of rain
- Ground OK at first, then saturated, surface runoff
- capacity of river fills, then spills over the flood place
- worst in urbanised floodplains
