07/12/2023
By Troy King

The Kennedy College of Sciences, Department of Environmental, Earth and Atmospheric Sciences, invites you to attend a Master’s thesis defense by Troy King on "An Analysis of Extreme Evaporation Events, and the Role of Extreme Evaporation in the Climate System.”

Candidate Name: Troy King
Degree: Master’s
Date: Tuesday, July 25, 2023
Time: 10 a.m. to 1 p.m.
Location: Olney Science Center Room 312, North Campus

Thesis/Dissertation Title: An Analysis of Extreme Evaporation Events, and the Role of Extreme Evaporation in the Climate System

Committee:

  • Advisor Christopher Skinner, Department of Environmental, Earth and Atmospheric Sciences, University of Massachusetts Lowell
  • Mathew Barlow, Department of Environmental, Earth and Atmospheric Sciences, University of Massachusetts Lowell
  • Frank Colby, Department of Environmental, Earth and Atmospheric Sciences, University of Massachusetts Lowell

Brief Abstract:

The evaporation of water from Earth's surface to Earth's atmosphere plays a key role in the hydrologic cycle, influencing temperature, humidity, precipitation, and ultimately water availability across the globe. Evaporation rates are controlled by the availability of water at the surface to evaporate, and the atmospheric evaporative demand which is influenced by temperature, humidity, solar radiation, and wind speed. Large evaporation rates can cause or intensify various atmospheric and climate phenomena, including the onset of flash drought, the intensification of extratropical cyclones, and heavy precipitation. Despite the importance of extreme evaporation in influencing these phenomena, there has been a relative lack of work done on instances of extreme evaporation. Using the ERA5 reanalysis data base with data from 1979-2019, we define an "Extreme Evaporation Event " (EEE) as an instance where the daily evaporation at a given location exceeds the climatological 95th percentile of evaporation at that location. This definition provides flexibility in the areas in which an EEE can occur, as opposed to different definitions where a threshold value must be met, often limiting "Extreme Evaporation" to the oceans. Using this method, we find that evaporation has increased over much of the globe, particularly over the oceans, albeit not uniformly. We also find that EEEs are more common over the oceans during the winter months, and more common over land surfaces during the summer months. When investigating the causes of EEEs, we find that EEEs over land surfaces tend to occur when there is anomalously high water available to evaporate, and anomalously high evaporative demand and more moist air. Over the oceans, while there is always a supply of moisture to be evaporated, EEEs also tend to happen with anomalously high evaporative demand, but with drier than average air often present. The findings of this study help to better illustrate the role of extreme evaporation in our climate system as the planet warms.