Smoke emitted thousands of km’s away by the unprecedented Canadian wildfires in 2023 contributed to the anomaly in the Indian summer monsoon in August that year. It was the driest monsoon of August in recorded history, a new study has found.
“We have tested the hypothesis that the 2023 Canadian extreme wildfire emissions can indirectly contribute to Indian rainfall anomalies of similar record-breaking magnitude to those found in August 2023 by weakening the monsoon westerlies through wind patterns generated by a pressure gradient, which was in turn created by smoke-related cooling in the Eurasian region,” the researchers said.
The model data does also seem to suggest that a shift in the Madden Julian Oscillation (MJO), an eastward moving atmospheric disturbance towards a phase favouring a decrease in precipitation did occur, and that this was produced via the induced pressure gradient which intensified the northern part of the MJO, thus decreasing its propagation speed, the study found.
“This points to a robust connection between the introduction of Canadian wildfire emissions and the Indian monsoon precipitation anomaly of August 2023, which is mediated by a main and a secondary mechanism,” the researchers said.
The study, undertaken by five experts from the Imperial College London, UK and the Technical University of Crete, Greece, has been published by Springer’s Natural Hazards, an international peer-reviewed journal, on February 21.
Wildfires, the researchers said, are becoming more severe with climate change, and the study highlights the potential for large-scale wildfire events to impact crucial meteorological phenomena in regions very far away from the emission source.
The Canadian wildfires in the summer of 2023 were unprecedented in scale and intensity, with a recorded 15 million hectares burning across the country from British Columbia and Yukon on the western Coast to Nova Scotia and Newfoundland on the easternmost edge. Different studies have pointed towards persistent, intense and widespread summer surface warming along with pronounced reductions in precipitation and soil moisture as the cause of the fires that produced the highest carbon emissions recorded since 2003.
Given the fact that the MJO moves eastwards, the resulting weather disturbances would have travelled across the Canadian mainland, crossed over the Atlantic and traversed parts of Europe, northern Africa and west Asia to impact the Indian subcontinent.
Observing that the Indian monsoon can respond to changes in anthropogenic aerosols across the northern hemisphere, the study shows that emissions following significant wildfire events in this hemisphere can affect the Indian monsoon in the same manner.
The researchers conducted ensemble simulations with a state-of-the-art Earth System Model and a very similar precipitation anomaly during the Indian monsoon was observed when accounting for the Canadian fire smoke, as opposed to when not accounting for it.
The mechanism proposed for this anomaly based on model findings is the generation of a pronounced low-level pressure anomaly over the Asian continent following smoke-related cooling, which led to weakened monsoonal winds and reduced moisture transport in the region, thus diminishing Indian monsoon precipitation, they concluded.
