W3 Heat Waves

what is a heatwave?

prolonged perios of extreme heat both longer and hotter than normals

UK Met Office - a period of at least 3 consecutive days with daily maximum temperatures meeting or exceedign the heatwave temperature threshold

How heatwaves affect the body

• dizziness and faint feelings from not drinking enough water

• heart rate increases as the body works harder

• heat rashes as body loses heat from the skin

• skin produces → sweating cools the skin by losing heat through evaporation

• ankles can become swollen from increased blood flow

Heatwave impacts

• Health

• Agriculture

  • crop failure

  • death of poultry animals

  • increased food prices

• Environment

  • widlfires

  • air, water and soil pollution

• Water

  • lack of drinking water

  • irrigation and groundwater depletion

• Transport

  • melting of roads

  • trainline faults

  • low river water levels affecting inland waterways

• Energy

  • high demand and more power cuts

  • hazards - ACs blasting during the summers

  • two nuclear power plants were shut down in Germany

Criteria for Issuing Heatwave Warnings

most warning systems use a heatwave index

SIMPLE:

• Specific temp threshold + duration for which this threshold is exceeded, work well for dry regions

COMPLEX:

• Humidity

• wind speed

• vapour pressure

• incoming solar radiation

• better for wet regions

Heat-Health Watch Levels

1. Preparedness

2. Alert + Readiness

3. Heatwave Action

4. Emergency

Record-breaking UK 2022 Heatwave

• UK’s first ever red warning alert - national emergency

• 40 degrees first-time record in the UK

• spatially-extensive - covered in almost all of UK + large parts of mainland Europe

Explain jet streams

North of the Jet has colder weather and the south has warmer and settled weather

Heat-Dome Explanation

Hot air is lighter and therefore expand vertically; but there is high pressure aloft, so air has nowhere to escape, but being forced downwards. Sinking air acts like ‘lid on a pan,’ and keeps the warm ground air in place. This force prevents air near surface.

Philippines Heat-Index Warnings

• Service provided by the PAGASA (The Philippine Atmospheric, Geophysical and Astronomical Services Administration) - National Weather Agency

• Uses an index based on temperature and humidity for heatwave warnings

Singapore Heat-Stress Warnings

Focuses on action: simple tips for members of the public to adjust their activities, take protective action, and wear appropriate attire depending on the prevailing heat stress levels.

What is Wet Bulb Globe Temperatures?

WBGT - provides an indication of heat stress by taking into account the combined effects of:

• Air temperature

• Humidity

• Wind speed

• Solar radiation

WGBT Formula

WBGT = 0.7 Tnwb + 0.2 Tg + 0.1 Td

Td definition

= temperature of the ambient air measured in the shade (typical air temperature values people are familiar with)

Tg definition

= Dry bulb thermometer that is inserted into a standard black metal globe and it represents the integrated effect of air temperature, wind speed, and radiant heat.

Tnwb definition

= Natural Wet Bulb temperature. The thermometer is covered by a wet cotton wick that is exposed to the natural prevailing air movement as well as radiation. It represents the integrated effect of air temperature, humidity, and wind speed. Tnwb < dry bulb temperature. The closer together the values are, the more humid it is. At 100% relative humidity, the Tnwb is equal to the dry bulb temperature.

Prolonged Siberian Heat of 2020 Key Facts:

• From Jan to May 2020 - the avg. temperatures ranked as the 2nd warmest on record.

• Russia: recorfd high temperatures in 2020, Jan to May avg. being 5.3 degrees above the 1951 - 1980 average.

Impacts of the Prolonged Siberian Heatwave in 2020

• High temperatures and dry conditions increased the wildfires

• About 7900 sq miles of Siberian territory burned as of June 25

• Air pollution and GHG emissions: 45 of these fires led to a release of 56 megatons of CO2 in June 2020

• Health impacts on the population

• Melting of permafrost - leading to high damages inc. environmental pollution

Explain how this heatwave is an example of a positive feedback loop

Over this region there is low pressure → cloudy skies → warm temperatures → early snow melt → bare soil → bare soil absorbs more solar radiation and hence causes higher temperatures.

Regional Warm Period future expectations?

By 2050 we expect such a regional warm period in the first 6 months of the year to be at least another 0.5 °C warmer, and possibly up to 5 °C warmer