About Evaporative Demand:
- Evaporative demand is a measure of how thirsty the atmosphere is.
- It determines the near-maximum of how much water will evaporate from a given piece of land if sufficient water is available.
- It does not necessarily relate to actual evaporation rate, as if there is little water supply there can only be a small evaporation rate, no matter how large the demand.
- It is driven by atmospheric factors including temperature, wind speed, humidity and cloud cover.
- Periods of high evaporative demand are connected to droughts and increased fire danger.
- Tracking extended periods with above normal evaporative demand can be a useful way to detect drought onset, drought intensification, and elevated fire danger.
- Above normal temperatures, clear skies, and wind speed, and below normal humidity all drive evaporative demand up and lead to quicker drying at the surface.
- Soil moisture is reduced which leads to less water available for plants and vegetation becomes stressed and more flammable.
- When extended periods of below normal precipitation overlap with extended periods of above normal evaporative demand fuels become critically dry favoring rapidly spreading wildfires.
What is a Thirstwave?
- It denotes three or more contiguous days of intense evaporative demand.
- While heat waves are caused by particular temperature and wind patterns, a thirstwave is the product of temperature, humidity, solar radiation, and wind speed.
- When temperatures rise, the consequences include more heat as well as the mechanics of water exchange between land and atmosphere, which in turn alters humidity, wind, and solar radiation.
- In a warming world, the researchers found that thirstwaves have grown more intense, are more frequent, and are lasting longer.
