Increased marine heat waves affect summer monsoon rains in India

An increase in marine heat waves in the northern Indian Ocean, which have been shown to affect monsoon rainfall in a recent study, has focused on accurate heat wave monitoring and forecasting. marines in the region.

In the study, scientists showed that the western Indian Ocean region experienced the greatest increase in marine heat waves at a rate of about 1.5 events per decade, followed by the northern Gulf. of Bengal at a rate of 0.5 events per decade. The Western Indian Ocean has seen 66 events while the Bay of Bengal has seen 94 over the past four decades, between 1982 and 2018.

Marine heatwaves in the Western Indian Ocean and the Bay of Bengal are “the ocean’s erratic response to increased warming waters”. They appear as periods of extremely high temperatures in the ocean and cause drying conditions in the central Indian subcontinent. At the same time, there is a “significant increase in rainfall over the southern peninsula of India in response to heat waves in the northern Bay of Bengal”, the study authors said in a press release. .

“We need dedicated marine heatwave forecasts for the Indian Ocean, as this is a region with the warmest waters, where marine heatwaves are expected to increase further, said the lead author. of the study, Roxy Mathew Koll, of the Indian Institute of Tropical Meteorology, Pune. He added that the US government agency National Oceanic and Atmospheric Administration, for example, provides a Coral Reef Watch, which monitors the global reef environment.

Peak of heatwave

The proposed roadmap emphasizes four major improvements to the current observing system of the Indian Ocean observing system, including the scaling up of biogeochemical measurements. Key recommendations are more chemical and biological measurements in ecosystems and fisheries at risk, expansion into the western tropics to improve understanding of the monsoon, better resolved upper ocean processes to improve predictions of precipitation, drought and heat waves and expansion in key coastal regions. and the deep ocean to better constrain the energy budget at the basin scale.

Long-term warming of waters due to soaring greenhouse gas emissions, overfishing, marine pollution, habitat destruction and acidification are straining global ocean systems. The Intergovernmental Panel on Climate Change‘s special report on the oceans and cryosphere in a changing climate indicates that marine heat-related events have increased globally and that over the period from 1982 to 2016, they doubled in frequency and became longer lasting, more intense and more extensive.

It is very likely that between 84% and 90% of marine heat waves that occurred between 2006 and 2015 are attributable to human-caused temperature increase, he pointed out.

Recently, a global network of scientists proposed a roadmap for upgrading the Indian Ocean Observing System, a multinational ocean monitoring network, to track changes in the Indian Ocean, making pressure for the urgent development of a more resilient ocean observing system capable of taking into account the accelerating rate of climate and ocean change.

The observation system is supported by a set of instruments such as floats, drifting buoys and moored buoys which monitor temperature, salinity, seawater currents as well as conditions such as humidity , winds from the atmosphere above.

Trends in marine heatwaves in the western Indian Ocean and northern Bay of Bengal. Graph from Koll et al

Ocean monitoring

Ocean modeling and analysis expert Prasad Bhaskaran, who was not associated with the study, also pointed to the “prioritization” of marine heatwave prediction and groundwater monitoring. He recommends using data from Australia’s Integrated Marine Observing System and ocean gliders which are autonomous underwater vehicles to shed light on unknown parts of the ocean.

The Integrated Marine Observing System deploys a nationwide range of equipment to monitor the open oceans and coastal marine environment around Australia, covering physical, chemical and biological variables. “It contains data from field observations, in situ observations and satellite measurements,” explained Bhaskaran from the Department of Ocean Engineering and Naval Architecture at the Indian Institute of Technology, Kharagpur. “We also need the data to be collected by the gliders. Gliders are very commonly used in the United States for research applications.

“This technology is very advanced there and has been used for some time to understand the physical properties of seawater,” Bhaskaran said. “Studies have been attempted in the United States using gliders to understand Gulf Stream circulation dynamics and also improve hurricane intensity forecasts.”

Gliders are remotely piloted, travel long distances and cover a wide range of depths. They serve as a platform for a variety of ocean sensors, such as temperature, conductivity, dissolved oxygen, and various bio-optical measurements. “Data collection using gliders is lacking for the Indian Ocean region, and there is a need to deploy more gliders in the future in this region, which can help improve model predictions and to better understand the physical properties of the upper ocean layer and the associated dynamics,” Bhaskaran said. . “Gliders can play a crucial role in improving the current understanding of marine heat waves in the Indian Ocean region.”

According to M Ravichandran, Secretary of the Ministry of Earth Sciences, ocean gliders will be deployed in the Indian Ocean as part of India’s Deep Ocean Exploration mission as part of the mission’s ocean climate advisory services, in addition to a new generation of autonomous floats (Argo floats) which will measure temperature and salinity in real time throughout the entire ocean volume (beyond 2,000 meters).

“In addition, moored instruments or buoys deployed in the Indian Ocean will also support ocean surface biogeochemical measurements, in addition to collecting information on physical parameters such as surface temperature and salinity. of the sea,” Ravichandran said. Mongabay-India.

A 2019 paper by scientists from the National Institute of Ocean Technology of the Department of Earth Sciences which started the moored buoy program in 1997, says the buoys were established for the primary purpose of supporting marine services. Early Warning for Cyclones and Tsunamis in the Northern Indian Ocean. .

Currently, there are 20 functional buoys that record surface meteorological and oceanographic parameters such as air temperature, relative humidity, wind, sea level pressure, waves, sea surface temperature, sea, sea surface salinity and surface current in real time.

“In India’s Deep Ocean Mission, a key program is to monitor and better understand the ocean and improve forecasting, including marine heat wave monitoring, modeling and forecasting,” added Ravichandran.

“Our understanding of sea waves is still a gray area,” Bhaskaran said, adding that improved ocean observations will fill the gaps in understanding sea heat waves.

“Oceans support significant primary productivity and also regulate the degree to which rainfall amounts in an area vary across seasons and within a year,” he said. “We need to study in more detail (how marine heat waves affect biodiversity and precipitation).”

Effect on monsoon

The effect of climate change that is already rooted in the Earth and the human-induced effect on the characteristics of marine heat waves and its implication on the food cycle is another research gap that needs to be filled.

Expanding on the mechanism by which marine heatwaves appear to influence Indian summer monsoon rainfall, Koll explains that warming of the earth in summer creates low pressure on the Indian subcontinent. Consequently, the winds blow from the Indian Ocean towards the land, carrying moisture for the monsoon rains. When marine heat waves occur, winds are drawn to these regions over the ocean (instead of over land), reducing precipitation over land.

Although there are differences in how heat waves are created in the northern Bay of Bengal and the western Indian Ocean, both influence monsoon rains. One difference is that ocean currents also play a key role in shaping marine heat waves in the western Indian Ocean.

Reduced transport of water from the equatorial region to the north leads to an accumulation of warm water in the western Indian Ocean. Another difference is that while the Western Indian Ocean events cover a larger area and are long-lived, the Bay of Bengal events cover a relatively smaller area and are short-lived.

Weather and climate extremes researcher Krishna Achuta Rao said the present paper is a “good preliminary study” to show maybe there is an influence, but “an analysis of the contribution of marine heat waves and what is the contribution of other factors influencing monsoon rains”.

Rao, professor and director of the Center for Atmospheric Sciences, IIT-Delhi, said mongabay india, “We have to know who is a small player… who is a big player. If we are to use marine heatwaves as an indicator of what will happen to monsoon rainfall, then the contribution of marine heatwaves will need to be separated from the influence of long-term steady warming of Indian Ocean waters because that there are so many elements that influence the summer monsoon in India.

This article first appeared on Mongabay.

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