The Intergovernmental Panel on Climate Change’s (IPCC) sixth assessment report recently shed light on the increasing ‘Wet Bulb’ Temperature trend in South Asia, specifically focusing on its potential impact on health due to a combination of heat and humidity. This article will delve deeper into the topic, explaining the concepts of Wet Bulb, Dry Bulb and Dew Point temperatures, and their implications on the environment.
Understanding Wet Bulb Temperature
The Wet Bulb temperature is the lowest temperature achievable by evaporating water into the air at a constant pressure. Essentially it presents a boundary beyond which humans struggle to tolerate high temperatures due to combined heat and humidity. It signifies the temperature indicated by a moistened thermometer bulb exposed to the air flow during an adiabatic process – a process during which no heat is gained or lost. This can be measured by using a thermometer with the bulb wrapped in wet muslin, with the level of evaporation from the bandage and temperature difference between the dry and wet bulbs dependent on air humidity. The wet bulb temperature is always lower than the dry bulb temperature, except at 100% relative humidity. For human health, wet bulb temperatures exceeding 31°C are extremely harmful, while a temperature of 35°C is unsurvivable for more than six hours.
Dew Point and Dry Bulb Temperatures Explained
Dry Bulb Temperature, often termed as “air temperature”, is commonly referred to when discussing the temperature of the air and essentially points to the ambient air temperature. It maintains this name as the temperature is indicated by a thermometer unaffected by air moisture and can be measured using a standard thermometer freely exposed to air but shielded from radiation and moisture. This serves as an indicator of heat content.
On the other hand, the Dew Point Temperature is the temperature at which water vapour begins to condense out of the air, making the air completely saturated. Above this temperature, the moisture stays in the air. If the dew-point temperature is close to the dry air temperature, the relative humidity is high, and if it’s far below, the relative humidity is low. Similar to the wet bulb temperature, the Dew Point temperature is always lower than the Dry Bulb temperature and matches it at 100% relative humidity.
Impact of this Trend on India
The implications of the rising Wet Bulb temperature are alarming, especially for densely populated countries like India. Cities such as Lucknow and Patna are projected to reach wet bulb temperatures of 35°C if emissions continue to rise. Other cities like Bhubaneswar, Chennai, Mumbai, Indore, and Ahmedabad are deemed ‘at risk’ of reaching 32°C-34°C under maintained emissions. Large sections of central India, including Vidarbha, also face the risk of exceeding wet bulb temperatures of 32-34°C under the current emission scenario.
This growing trend could potentially result in an increase of heat-wave related deaths or a decrease in productivity due to the extreme heat conditions. Furthermore, the dependence on artificial cooling mechanisms to manage the heat would inflate energy demand, exposing many to the dangers of power failures and disregarding the most susceptible individuals in society who must venture outdoors. Therefore, it is clear that the escalating Wet Bulb temperatures present both an environmental and societal challenge that needs immediate attention.
