Climate Change Alters Western Disturbances and Weather

Recent unseasonal heavy rainfall and strong winds across Delhi and surrounding regions, while offering temporary respite from early summer heat, point to a more profound meteorological shift. These weather events, attributed by the India Meteorological Department (IMD) to a fresh Western Disturbance, are increasingly indicative of a larger pattern: the significant alteration of these crucial weather systems due to rising global temperatures. New analyses and scientific studies indicate that climate change is not only increasing the frequency of Western Disturbances but also changing their behavior, leading to more intense weather events and unseasonal occurrences.

Understanding Western Disturbances

Western Disturbances (WDs) are essentially eastward-moving weather systems laden with moisture that originate in the Mediterranean region and travel across Iran and Afghanistan before reaching the Indian subcontinent. These systems draw moisture from the Mediterranean Sea, Black Sea, Caspian Sea, and, increasingly, the Arabian Sea. Classified as extra-tropical cyclones, they form due to the interaction between cold polar air and warmer tropical air masses. Their path and intensity are significantly influenced by the subtropical westerly jet stream—a powerful current of high-altitude winds flowing west to east over the Himalayan and Tibetan highlands. Traditionally, WDs are most active during the boreal winter months (December to March), playing a critical role in the weather patterns of northwestern India, Pakistan, Afghanistan, and Tajikistan by bringing vital winter precipitation.

Climate Change's Impact

Mounting evidence suggests that climate change is fundamentally altering the established characteristics of Western Disturbances:

• Increased Winter Intensity and Frequency: Research, including a 2024 study in the journal Weather and Climate Dynamics, indicates a significant rise in winter WDs over the western and central Himalayas and the Hindu Kush over the past seven decades. Experts like Dr. K J Ramesh, former Director General of the IMD, attribute this to the direct impact of climate change, noting that WDs have been "dumping more rainfall over the Himalayan region." This intensification is linked to a strengthening of the subtropical westerly jet stream, a phenomenon scientists suggest is fueled by warmer global temperatures.
• Altered Seasonality and Monsoon Interactions: The same 2024 study highlights a concerning trend: WDs are becoming more common outside their typical winter window, with increased occurrences in May, June, and July. This shift is potentially due to a "delayed northward retreat of the subtropical jet," which historically recedes before the summer monsoon's onset. Consequently, the overlap of active WDs with the monsoon period is leading to a higher incidence of extreme weather events, including devastating heavy rainfall and floods.
• Enhanced Moisture from a Warming Arabian Sea: The intensity of precipitation associated with WDs is also increasing. A key factor is the rapid warming of the Arabian Sea. A 2022 study in Earth Science Reviews found that sea surface temperatures in the Arabian Sea have risen by 1.2 to 1.4 degrees Celsius in recent decades compared to forty years prior. This warmer sea surface releases more moisture into the atmosphere, providing WDs with more "fuel" for heavier and more frequent precipitation.
• Broader Reach and Increased Variability: An analysis by Climate Trends, a Delhi-based research organization, suggests that soaring global temperatures have broadened the subtropical westerly jet stream. This expansion allows WDs more room for "meridional oscillations," meaning they can now travel further north and south within the jet stream's influence. As noted by experts (quoted in the Climate Trends analysis), this greater oscillation capacity leads to more varied temperature and precipitation patterns across a wider area.

Consequences and Outlook

The changing patterns of Western Disturbances are already having tangible effects. The increased frequency and intensity, particularly during March and April this year, have been linked to heavy rainfall, flash floods, and landslides in Himalayan states such as Jammu & Kashmir, Himachal Pradesh, and Uttarakhand. Paradoxically, this increased WD activity also contributed to keeping prolonged heatwaves at bay in the northwestern plains during the same period.

However, the overall trend is towards greater weather unpredictability and an increased risk of extreme events. Western Disturbances used to be fairly predictable. Now, they are becoming more intense, erratic, and unseasonal. This is creating a new normal. This change brings major challenges for agriculture, water resource management, and disaster preparedness across the affected regions. Understanding and adapting to these climate change-induced shifts in major weather systems like Western Disturbances is becoming increasingly critical.

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