What is a wet bulb temperature?

What is a wet bulb temperature?
Posted on 02-07-2023

What is a wet bulb temperature?

The wet-bulb temperature is a meteorological term used to describe a measure of the lowest temperature that can be achieved by evaporating water into the air at constant pressure. It is a crucial parameter in understanding and predicting weather conditions and assessing the impact of heat stress on humans, animals, and the environment. In this response, I will provide a comprehensive explanation of wet-bulb temperature, its calculation, significance, applications, and its role in climate change.

Temperature is a fundamental parameter used to characterize the state of the atmosphere. It provides insight into the heat energy present in the air and affects various aspects of weather and climate. However, dry-bulb temperature alone does not account for the influence of humidity on thermal comfort and heat stress. The wet-bulb temperature, on the other hand, provides a more comprehensive understanding of the thermal conditions by considering the effects of evaporation.


Definition and Measurement:

The wet-bulb temperature represents the temperature at which the air would be cooled to by evaporating water into it, with the process occurring at a constant pressure. To measure the wet-bulb temperature, a wet-bulb thermometer is used. It consists of a thermometer with a moistened cloth covering the bulb. When the thermometer is exposed to air, the moisture on the cloth evaporates, causing the temperature to decrease due to evaporative cooling. This wet-bulb temperature is then recorded.



The calculation of wet-bulb temperature involves several meteorological parameters, including dry-bulb temperature, relative humidity, atmospheric pressure, and wind speed. Various equations have been developed to estimate wet-bulb temperature accurately, such as the Magnus formula, the Goff-Gratch equation, and the Bolton formula. These equations incorporate the psychrometric properties of air, which describe the relationship between temperature, humidity, and water vapor pressure.


Significance and Applications:

  1. Heat Stress Assessment: Wet-bulb temperature is a critical parameter in assessing heat stress on living organisms, including humans and animals. It reflects the combined effects of temperature and humidity, which significantly impact the body's ability to cool itself through evaporation. High wet-bulb temperatures indicate increased risk of heat-related illnesses and heatstroke, especially in hot and humid climates.

  2. Thermal Comfort: Wet-bulb temperature plays a vital role in determining human comfort levels. The comfort index, such as the Wet Bulb Globe Temperature (WBGT), is used in various fields like sports, occupational health, and building design to assess thermal comfort and guide necessary precautions to prevent heat-related illnesses.

  3. Weather Forecasting: Wet-bulb temperature is an essential input for weather forecasting models. By considering the evaporation process, these models can more accurately predict cloud formation, precipitation, and the potential for severe weather events.

  4. Agriculture: Understanding wet-bulb temperature helps in assessing crop water requirements, irrigation scheduling, and managing plant stress. It is particularly crucial for crops sensitive to high humidity levels, as excessive moisture can lead to disease outbreaks and reduced productivity.

  5. Energy Demand: Wet-bulb temperature affects energy demand and usage, especially in regions with high cooling requirements. It is used in the estimation of cooling load requirements for air conditioning systems, ensuring energy-efficient designs and operations.

  6. Climate Change: Wet-bulb temperature is a significant indicator of climate change impacts. As global temperatures rise, the increase in humidity amplifies the effects of heat stress. Monitoring wet-bulb temperature trends helps in understanding the evolving climate patterns and projecting future changes.


Climate Change and Wet-Bulb Temperature:

Climate change is altering weather patterns and exacerbating heat stress conditions worldwide. Rising greenhouse gas emissions contribute to the warming of the Earth's surface, leading to increased air temperatures. As temperatures rise, the atmosphere's capacity to hold moisture increases, resulting in higher absolute humidity and potentially elevated wet-bulb temperatures.

Elevated wet-bulb temperatures have severe implications for human health, agriculture, ecosystems, and infrastructure. Regions already experiencing high temperatures and humidity may face more frequent and intense heatwaves, making outdoor activities dangerous and challenging. Moreover, elevated wet-bulb temperatures can impact the viability of certain crops and livestock, disrupt ecosystems, and threaten the integrity of infrastructure and buildings not designed to withstand extreme heat and humidity conditions.

Efforts are underway to study wet-bulb temperatures in the context of climate change and develop adaptation strategies. Scientists use climate models to project future wet-bulb temperature trends under various emission scenarios. This information helps policymakers and communities to anticipate and mitigate the impacts of rising temperatures and humidity, ranging from urban planning and heatwave early warning systems to improving cooling infrastructure and public health preparedness.



The wet-bulb temperature provides a more comprehensive understanding of thermal conditions by considering the effects of evaporation. It plays a crucial role in assessing heat stress, determining thermal comfort, weather forecasting, managing agriculture, estimating energy demand, and studying climate change impacts. The measurement and calculation of wet-bulb temperature involve considering meteorological parameters such as dry-bulb temperature, relative humidity, atmospheric pressure, and wind speed. Monitoring wet-bulb temperature trends helps in understanding climate change and its implications for various sectors. By considering wet-bulb temperature, we can make informed decisions and take necessary precautions to ensure human well-being, safeguard ecosystems, and build resilient infrastructure in a changing climate.

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