Amplified Rossby Waves and Climate Change: Key Drivers of Intensifying Heatwaves in India

Recent research by Indian meteorological and climate institutes highlights that amplified Rossby waves and regional factors, like the Bay of Bengal’s cyclonic activity, significantly intensify heatwaves in India. Understanding these dynamics is crucial for developing effective heatwave prediction and mitigation strategies in a warming climate.

Heatwaves in India have become more intense, causing severe health impacts and drawing significant attention from researchers at the India Meteorological Department, the Indian Institute of Tropical Meteorology, and Savitribai Phule Pune University. Recent studies have highlighted the critical role of amplified Rossby waves in this intensification. Over the years, India’s temperature variability has exhibited two dominant modes: dry (mode-1) and moist (mode-2) heatwaves. These modes are influenced by midlatitude Rossby waves that intrude into the Indian region. However, the specific regional and teleconnection factors contributing to the intensification of these heatwaves had not been thoroughly examined until the present study. This research delves into the dynamics behind the intensification of the moist heatwave mode (mode-2) using a barotropic vorticity equation model, which reveals that cyclonic vorticity over the Bay of Bengal combines with mid-latitude anticyclonic vorticity. This combination leads to an amplified and persistent anticyclonic phase over Northwest India, intensifying the heatwaves significantly.

Unraveling the Heatwave Puzzle: Key Influences

The increase in the intensity and frequency of heatwaves in India can be attributed to various factors, including large-scale climate variability, synoptic-scale features like Rossby wave activity, and local factors such as land use changes and soil moisture conditions. For instance, the influence of the El-Nino Southern Oscillation (ENSO) and the impact of the Indian Ocean on heat extremes have been recognized as significant contributors. Over the past decades, the Indian region has witnessed a notable increase in heatwave frequency and intensity, with these events often leading to severe health impacts, especially when combined with high humidity levels, which exacerbate heat stress conditions. These trends are consistent with global patterns, where heatwaves are becoming more frequent, intense, and prolonged.

The Role of Rossby Waves in Heatwave Intensification

Previous research has identified two dominant modes of temperature variability in India, linked to different types of heatwaves. Mode-1 is associated with dry conditions, while mode-2 is linked to moist heatwaves. Mode-2, in particular, has shown an increasing trend, with its development influenced by Rossby waves propagating through specific pathways. This study employs a barotropic vorticity equation model to explore the intensification mechanisms of these heatwaves. The findings indicate that the interaction between cyclonic vorticity from the Bay of Bengal and anticyclonic vorticity from mid-latitudes leads to intensified circulation patterns. This superimposition results in amplified and persistent anticyclonic phases over the Northwest Indian region, which in turn intensifies the heatwaves.

Climate Change and Heatwave Dynamics

To analyze these dynamics, the study utilizes observational data from the India Meteorological Department and NOAA, focusing on temperature patterns and moisture fluxes over the Indian region. The barotropic model experiments simulate various scenarios to understand the propagation and intensification of Rossby waves. The results reveal that local heat sources, such as warm sea surface temperatures in the Bay of Bengal, play a crucial role in the intensification process. These local conditions, combined with the broader climatic patterns, create a conducive environment for the development of severe heatwaves.

Understanding Local and Global Influences

The research also considers the impact of climate change on these processes, noting that different circulation regimes characterized by jet speed and wave numbers can favor the intensification of heatwaves. Climate change scenarios indicate a rise in temperature and changes in moisture supply over the Indian region, which could further influence the behavior of these heatwaves. The interaction between these factors and the resultant extreme events are complex and highly non-linear, requiring a comprehensive understanding to improve prediction and mitigation strategies.

Implications for Public Health and Safety

The study highlights the complex interplay of regional and teleconnection factors driving the intensification of heatwaves in India. By using a barotropic vorticity equation model, the research provides insights into the mechanisms behind the amplification of the moist heatwave mode (mode-2). The findings underscore the importance of understanding these dynamics to develop effective heatwave prediction and mitigation strategies, particularly in the context of a warming climate. As climate change continues to alter global weather patterns, such studies are crucial in preparing for and responding to the increasing threat of extreme heat events. This research not only advances the scientific understanding of heatwave dynamics but also has practical implications for public health and safety in India and other regions experiencing similar climatic challenges.