heatwaves and drought

john

heatwave def

period of high temperatures relative to typical seasonal conditions for a location

anticyclones

• large scale high pressure systems

• light winds

• descending air inhibits cloud formation

heat stress

• humans need to shed 90W heat or core temperature rises leading to organ damage or death

• lower temps- radiation, conduction, convection, perspiration

• high temps- perspiration only

heatwaves and air pollution

• temperature inversions inhibit connective mixing and trap emissions

• clear skies- strong radiation enhance ozone production

• 2003- 21-38% of the total excess deaths due to “elevated ambient ozone and PM10 concentrations”

heatwaves and soil moisture

• soil moisture deficits can increase the frequency, duration and severity of hot spells in moisture limited areas (S Europe)

• In wetter climates, this relationship is weaker

• low air humidity- reduced heat stress- mild reduction in heatwave mortality

2003 EU heatwave

• over 25 degrees average temps

• daily recorded deaths peaked at 4,500

• 16 EU countries including France, UK, Italy- >80,000 excess deaths

Vulnerability

VULNERABLE AGE GROUPS

• >65 years

• <5 years

OTHER

• pre existing medical conditions

• housing

• economic circumstances

Mitigation: UK

• heatwave alert levels (1-4)

• ‘beat the heat’

Mitigation- long term

• urban green spaces

• 30-40% reduction of heat-related diseases

• cool infrastructure

Global effects

drought def

a moisture deficit relative to the average water availability at a given location and season

meteorological drought

period of lower rainfall

drought occurence

• occurs globally

• more common in areas with low rainfall levels

• areas of tropics and subtropics experience distinct dry and wet seasons

environmental drought impacts

• loss of wetlands

• drying of seasonal water bodies

• reduced vegetation cover

• loss of wildlife habitat

• soil erosion

• wildfires

• wildfire migration

• disease

socio-economic drought impacts

• (cash) crop failure

• loss of livestock

• irrigation costs

• reduced water quality

• (clean) water scarcity and supply disruptions

• decreased water supply for energy sector

• decreased soil fertility

• unemployment

• increased food (production) prices

• risk of disease

• mass migrations

• hunger and famined

drought in the sahel- facts

• semi arid 100-800mm/yr

• dry and wet seasons

• rainfall driven by tropical convection, west african monsoon, el nino

drought in the sahel- causes

REGIONAL FORCING

anthropogenic-

• overgrazing, deforestation for agriculture

• increased surface albedo, less solar energy absorbed

• reduced moisture supply to atmosphere, less rainfall

• unfavourable conditions for vegetation growth

REMOTE FORCING

changes in sea surface temperatures-

• changes in SST

• monsoon circulation weaker

• drier, less vegetation

• higher albedo, decrease in water input

other-

• atlantic multidecadal oscillation

• dust feedbacks

• aerosol related forcing

Ethiopia

• droughts related to existing vulnerability

exacerbated by:

• rural destitution

• environmental degradation

• war and conflicts

1999-2000 crisis: 10 million in need of food assistance

mitigation and adaptation- droughts

• collective transboundary management of grazing systems

• conservation of rangelands and forests

• community level soil and water conservation actions

• agroforestry

• irrigation improvements (drip irrigation, drought resistant crops)

difficult dur to conflicts

climate change

• human influence has increased the chance of compound extreme events since the 1950s

• including increases in frequency of heatwaves and droughts globally

• every 0.5 degree of global warming increases the intensity and frequency of heatwaves and heavy precipitation as well as droughts