May 22 - July 31
Investigating The Probability of Compounding Heatwave and Extreme Rainfall Events in Brazil
Javier Sanchez and Elinor Martin
What is already known:
- The frequency of heatwaves has been gradually increasing throughout the world due to climate change
- Heatwaves can enhance the probability of extreme rainfall following a heatwave termination in certain regions of the world.
- Extreme rainfall events following heatwaves are most commonly found in the mid-latitude areas of the world, including regions such as the Eastern United States, Central Europe, and Japan.
What this study adds:
- The southern, more temperate regions of Brazil are significantly more likely to experience heatwaves compounding extreme rainfall events.
- Sao Paulo, Brazil is five times more likely compared to daily average to receive an extreme rainfall event after a heatwave terminates.
- Brasilia, Brazil is twice as likely compared to daily average to receive an extreme rainfall event after a heatwave terminates.
- Extreme rainfall events are likely to increase for Brasilia and Sao Paulo as heatwave frequency increases.
- Heatwave terminations have no noticeable impact in the probability of extreme rainfall in Manaus.
Abstract:
Heat waves and flooding events are deadly weather events that are expected to become more impactful as climate change continues to increase the frequency and intensity of these events, which makes it essential to better understand the relationship between heat waves and extreme rainfall events that lead to flooding. This study investigates the probability Brazil will experience an extreme rainfall event within 48 hours after a heatwave terminates. A ~10 km gridded, spatial daily temperature and precipitation dataset from 1961-2020 was used to identify heatwaves and extreme rainfall events. A heat wave is a period where the maximum daily temperature exceeds the 90th percentile for at least 3 consecutive days, while an extreme rainfall event is defined as an event where the daily precipitation accumulation exceeds the 95th percentile. São Paulo, Brazil showed the strongest compounding heatwave-extreme rainfall relationship, where the likelihood of extreme rainfall following a heatwave is increased nearly six times over the probability of extreme rainfall in general, with the extreme rainfall probability increasing from 4% to 23% following a heatwave. Brasilia displayed a slight increase in extreme rainfall probability following heatwave terminations, with the probability increasing by over twice as much compared to the climatological average probability. In contrast, for Manaus extreme rainfall very rarely occurs shortly after heatwave terminations, where only 5% of heatwave terminations are followed by extreme rainfall, which isn’t higher than the general daily average of 5%. This suggests that heatwave terminations don’t affect the probability of extreme rainfall events in Manaus. These heatwave-compounding extreme rainfall episodes are more prominent in the Southern cities of Brazil where the climate tends to be more seasonal with a stronger amount of temperature variability between seasons. This suggests that the southern portions of Brazil will likely experience severe impacts associated with climate change as the frequency of heatwaves continues to rise, further compounding potential extreme rainfall events in the future.