Description

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Context

Rising evaporative demand in India has highlighted significant gaps in the country's climate data and research.

What is Evaporative Demand?

Evaporative demand, also known as potential evapotranspiration (PET) or "atmospheric thirst," measures the atmosphere's ability to draw moisture from the land surface and vegetation via evaporation and transpiration.

Evaporative Demand	Also known as Potential Evapotranspiration (PET) or "atmospheric thirst"; measures the atmosphere’s ability to pull moisture via evaporation and transpiration.
Evaporation	Water changes from liquid to vapor, removing moisture from soil or water bodies.
Transpiration	Plants release water vapor through leaf pores after absorbing it from roots.
Factors Increasing Evaporative Demand	High temperature, low humidity, strong winds, and high solar radiation.
Factors Decreasing Evaporative Demand	Cool temperatures, high humidity, calm winds, and cloud cover.
Thirstwaves	A term for prolonged periods (e.g., ≥ 3 days) of unusually high evaporative demand; considers multiple atmospheric conditions beyond just temperature.

Link to Droughts and Water Stress

High evaporative demand makes a significant contribution to

Drought Onset and Intensification: When evaporative demand is high, water quickly evaporates from soil and water bodies, and plants transpire more, causing the surface to dry faster. If this coincides with low precipitation, drought conditions worsen.
Reduced Soil Moisture: Quicker surface drying reduces soil moisture, leaving less water available for crops and natural vegetation, resulting in plant stress and increased flammability, increasing the risk of wildfires.
Exacerbated Water Scarcity: India is already experiencing significant water stress, with millions of people lacking access to safe drinking water. Rising evaporative demand depletes surface and groundwater supplies, exacerbating the water crisis. The per capita water availability has decreased dramatically, from 5100 cubic meters in 1951 to 1545 cubic meters in 2021, crossing the water stress threshold.

Source: The Hindu

Practice Question:

Q. With reference to Evaporative Demand, consider the following statements:

It refers to the amount of evaporation that would occur if water is unlimited.

It is influenced by temperature, wind speed, solar radiation, and humidity.

Higher evaporative demand during drought conditions leads to increased soil moisture.

Which of the statements given above is/are correct?

A) 1 and 2 only

B) 2 and 3 only

C) 1 and 3 only

D) 1, 2 and 3

Answer: