Climate Variation and Drought

what is the walker circulation?

what is the walker circulation?

• an atmos circulation in the equatorial regions of the pacific ocean

• warmer water in the western Pacific → causing pow-p, warmer air

• cooler ocean water in the east pacific → causing high-p, cooler air

• winds blow surface ocean water westward (increase sea lvl). cool deep ocean water wells-up along the west coast of South america bringing deep, nutrient-rich seawater to the surface, allowing fish pop to thrive

what is la Nina?

• more amplified ‘normal’ condition leading to direr and cooler conditions in south america and more rainfall in indonesia

what is el nino?

• occurs when surface winds weaken

  • tilted sea surface flattens n warm pacific water flows to the eat → water flows back to equilibrium

  • water on coast of south america become nutrient poor and impacts fish pop

  • droughts occur in australia/indonesia while storms n flooding occur on the coast of the americas

Enso conditions

• ENSO = el nino/southern oscillation

• sea surface temperature anomalies in the mid-pacific ocean for 1900-2003

• el nino has warm temperature anomalies

global impact el nina/nino

what are monsoon?

• seasonally changing air circulation in the world’s tropical n subtropical regions in which summer winds blow from the ocean toward the land, bringing heavy rain inland

  • in summer, land heats faster than ocean; most ocean flows inland

• in winter, winter winds blow from the land toward the ocean, causing drier weather inland

  • land cools faster than ocean; air flows toward ocean

• winter n summer r opp

monsoons in south asia

• normally bring 2 months of flooding

• agriculture depends on regular monsoon rain

• economic disaster occurs when monsoon rains fail

• droughts occur if rains do not arrive → no crops = no feeding

what is drought?

• a deficiency of freshwater within a region lasting long enough to harm normal vegetation, crops, livestock, surface n underground water supplies, human health, and human activities

Dust bowl

• decade long drought in the 1930s led to severe drought

• soil has no vegetation, so lifted into clouds

• dust storms carried away topsoil

what are the 3 types of drought?

• meteorological drought

• agricultural drought

• hydrological drought

  → they r sequential

what is a meteorological drought?

• precipitation is less than normal for weeks or yrs

what is agricultural drought?

• low soil moisture

• inhibits crop germination or growth

• may be caused by human activity

what is hydrological drought?

• insufficient water flows into lakes, streams, or reservoirs

• surface-water lvl drop

• water table drops

drought positive feedback

• hot, dry weather increases evaporation, causing ground to dry out

• dry ground contributes to less moisture to air

• plants die, contributes less moisture (evaporation) to air and less shade on the ground

what does the palmer drought index measure?

• moisture deficiency, relative to avg conditions

• compares 2 variables:

  • water supply from precipitation n reserves

  • water depletion from evaporation, infiltration, n runoff

• allows scientists to visualize cumulative changes over time

what are droughts in cali caused by?

• insufficient snow in Sierra Nevada created low water supplies

when was cali’s worst drought in 1,200 yrs?

• 2011-2017

  • devasted crops

  • inconvenienced millions of peep

  • killed millions of trees

• reservoirs dropped to all-time low lvls

what does monsoonal climate have?

• have wet n dry seasons

• heavy rain falls during wet season

• little/no rain falls during dry season

→ risk of famine

when do droughts occur?

• if rain f n intensity drop

  • reservoirs n streams rapidly dry out

  • crops n livestocks die as soil dries

• densely pop areas r at high risk of famine

in a monsoonal climate zone, the shift from drought conditions to flood conditions can happen ____________

• rapidly

→ shown by precipitation records from east-central africa and madagascar

droughts in africa

• poor dev n poverty increases drought risk in africa

• horn of africa has been n a drought since 2011

• 17 million peep face water stress n food insecurity

• 5.5 million peep have access to only contaminated water

• lack of infrastruct n poor security hamper relief efforts

drought effect on lake chad

• hydrological drought has led to the progressive shrinkage of lake chad, central africa

• formerly the world's 6th largest lake

• lake chad has decreased by 90% due to climate change, pop growth n irrigation

video

• el nino effect

• lack of rain + sever drought

• cow death (livestock in general)

• poor government intervention

• food security at risk

• people starving to death

what are the impacts of drought?

• severe natural hazard in many areas of the world often accompanied by famine n starvation

• often called a ‘creeping’ phenomena until conditions have deteriorated

• costs r more difficult to assess than other hazards

  • China, 1928: 3 million deaths

  • NE Africa, 1983:150,000 deaths

  • Somalia, 2017–2018: Food shortages for 6 \n million