- By Mark Poynting and Esme Stallard
- BBC News Climate & Science
More than 70 million people in the US are under heat alerts this week, with extreme temperatures as high as 105F (41C) forecast in some areas.
Scientists say many extreme weather events are becoming more frequent and intense as a result of climate change.
1. More extreme rain
This can result in more droplets and heavier rainfall, sometimes in a shorter space of time and over a smaller area.
It says this pattern will continue with further warming.
Heavy rain in this region is rare, which offers researchers fewer historical comparisons.
The Rio Grande do Sul region that was hit is particularly vulnerable to heavy rains, as it is the meeting point of tropical and polar air masses.
But climate expert Francisco Eliseu Aquino told the AFP news agency that “these interactions [have] intensified with climate change”.
2. Hotter, longer heatwaves
Even a small increase in average temperatures makes a big difference to heat extremes.
As the range of daily temperatures shifts to warmer levels, hotter days are more likely and more intense.
In April 2024, temperatures in Mali hit 48.5C during an extreme heatwave across the Sahel region of Africa, which was linked to increased hospitalisations and deaths.
This can happen as a result of heat domes, which are areas of high pressure where hot air is pushed down and trapped, causing temperatures to soar over large areas.
Forecasters predict temperatures to be 5.5-11C (10-20F) above normal, potentially posing a risk to human health and the environment from resulting wildfires.
3. Longer droughts
Linking climate change with specific individual droughts can be difficult.
But heatwaves fuelled by climate change can worsen droughts by drying out soil. This makes the air above warm up more quickly, leading to more intense heat.
During periods of hot weather, increased demand for water, especially from farmers, puts even more stress on the water supply.
4. More fuel for wildfires
But climate change is making the weather conditions needed for wildfires to spread more likely, the IPCC says.
Extreme, long-lasting heat draws more moisture out of soils and vegetation.
These tinder-dry conditions provide fuel for fires, which can spread at an incredible speed, particularly if winds are strong.
Climate change more than doubled the likelihood of the extreme “fire weather” conditions in eastern Canada in May and June 2023, which helped fires to spread, the WWA says.
The combined effects of shifting land use and climate change mean extreme wildfires are projected to become more frequent and intense in future globally, according to the UN Environment Programme (UNEP).
The number of the most extreme fires may rise by up to 50% by 2100, UNEP suggests.
