Syllabus:

GS3: Conservation, environmental pollution and degradation, environmental impact assessment.

Context: 

A recent research statement, published in Earth's Future, indicates that "Thirstwaves," periods of high atmospheric water demand, are not only becoming more intense but also occurring more frequently

More on the News 

• University of Idaho and University of Colorado and the U.S. National Oceanic and Atmospheric Administration coined the term “Thirstwave” which they recently found to be increasing over the U.S.

• In a warming world, the researchers found that “Thirstwaves” have grown more intense, are more frequent, and are lasting longer, especially in seasons when crops are grown. 

• This significantly impacts agricultural practices and water availability. 

Evaporative Demand 

• It determines the near-maximum of how much water will evaporate from a given piece of land if sufficient water is available. 

• It is measured by standardized short-crop evapotranspiration, the water used by a 12 cm grass surface with full water access and no stress, combining evaporation and plant transpiration.

• Evapotranspiration refers to the two processes by which water moves from land to the atmosphere: evaporation from surfaces and transpiration from plant leaves.

Thirstwave

• It denotes three or more contiguous days of intense evaporative demand.

• It is the product of temperature, humidity, solar radiation, and wind speed. 

• Rising temperatures affect heat levels and land-atmosphere water exchange, altering humidity, wind, and solar radiation.

 Evaporation and Evapotranspiration in India

• Historical Trends in Evaporation and Evapotranspiration:

• Both evaporation and potential evapotranspiration (PET) decreased in India over 30 years, contrary to expectations that warming should increase evaporation.
• Humidity played a crucial role in offsetting the temperature-driven increase in evaporation.
• However, future warming (as projected by global circulation models) is expected to override humidity’s dampening effect, leading to higher potential evapotranspiration (PET).

• Recent Changes in Evaporative Demand(ED)

• A 2022 study (IIT-Roorkee, NIH, and European collaborators) found increased actual evapotranspiration (AET) in Northern India, the Western Himalayas, and parts of the Eastern Himalayas.
• This could be due to agricultural expansion or increased vegetation, but exact causes need further investigation.

• Lack of Data on Extreme "Thirstwaves"

• Unlike heatwaves, India lacks systematic data on extreme evaporative demand events (thirstwaves).
• Different crops and ecosystems respond differently to evaporative stress, but this remains understudied.

• Global Implications and Future Research

• The first study on thirstwaves was conducted in the U.S., but similar research is needed in the Global South, where societies are more vulnerable to climate impacts.
• Researchers are now investigating thirstwaves in South Asia, with implications for food and water security.
• Surprisingly, the worst thirstwaves occur in regions not experiencing the highest evaporative demand, suggesting a need for reevaluating climate adaptation strategies.

Way Forward

• Upgrade and expand weather stations to monitor all key ED-related parameters effectively.

• Invest in dedicated research programs to study long-term ED trends, its drivers, and regional variations across India.

• Encourage micro-irrigation, precision farming, and drought-resistant, low-water crops.

• Formulate national and state-level policies that acknowledge and address the challenges posed by rising ED.

• Educate farmers and the general public about the concept of evaporative demand and its implications for water availability. 

• Integration of thirstwave analysis into climate adaptation and water management policies.