For some time now, parts of Brazil have been experiencing extreme heat combined with very high humidity. This combination leads to a higher "perceived temperature" and increases heat stress for people and the environment. Just last week, perceived temperatures of over 62°C were recorded in Rio de Janeiro. According to the Heat Index, such temperatures correspond to the highest possible danger level.
meteoblue offers a variety of weather maps for free use. With the help of some of these maps, the prevailing conditions in Brazil can be analysed. The image shows the average daily temperature in degrees Celsius (left map) for 2024-03-20. As already mentioned, however, temperature alone is not necessarily decisive for the well-being of people and nature. Humidity also plays a decisive role, as can be seen in the humidity map for 2024-03-20.
High temperatures in combination with high humidity are also known as sweltering heat. If both factors are present, this has an impact on a person's thermoregulation. In the worst case, this can lead to circulatory collapse or heat death. As this is an important combination, there are also variables and indices that take this relationship into account.
The right map shows the apparent temperature from 2024-03-20. This temperature figure reflects the temperature perceived by humans and considers factors such as wind, temperature and relative humidity. More precisely, it is made up of the heat index and the wind chill factor. As temperature and humidity rise, it becomes increasingly difficult for the body to dissipate excess heat through perspiration (sweating). Wind, on the other hand, has a cooling effect. There are other ways of describing the "felt" temperature. For example, the wet bulb temperature, also known as the cooling limit. This temperature also serves as a measure of heat stress, whereby the human body is barely able to maintain all its systems once the threshold value of 35°C is exceeded.
As many regions of Brazil are currently experiencing both high temperatures and high relative humidity, it is no wonder that the apparent temperature is higher than the actual temperature. When looking at the wind animation map (see screenshot from 2024-03-20) there is no dominant atmospheric circulation pattern over Brazil. Due to low pressure differences over the country, there are no strong wind currents that contribute to a cooling effect.
Just last week, perceived temperatures of over 62°C were recorded in Rio de Janeiro. According to the Heat Index, this value corresponds to the highest danger level, meaning heatstroke is extremely likely (NOAA).
Although the strong warming of the ground during the day leads to the formation of pronounced thunderstorm cells, these can only provide short-term relief. This is because the soil water present due to the precipitation begins to evaporate again immediately and thus continues to contribute to the high humidity. This cycle of warming, evaporation, convection, condensation, and precipitation is a characteristic feature of tropical and subtropical climate zones, where high temperatures and humidity often come together and lead to intense rainfall.
According to the IPCC, the intensity and frequency of heat extremes will continue to increase with increasing global warming, regardless of the climate scenario selected or the region. It also mentions that the global water vapour content in the atmosphere will increase (absolute humidity), while the relative humidity will remain more or less constant. This is caused by the fact that warm air can absorb more water vapour before condensation occurs. Finally, the IPCC's 6th Assessment Report (AR6) emphasises that there will also be an intensification of heavy precipitation. According to the IPCC, the realisation of the statements mentioned here is described as "extremely likely". Nevertheless, it is important to note that there are spatial differences and not all areas are equally affected by different risks. For more details and further information, we recommend the following IPCC sources: Headlines AR6, Synthesis Report
The scorching conditions experienced in Brazil serve as a stark reminder of the risks posed by extreme weather patterns. Despite the formidable challenge, our comprehensive weather and climate data offer a beacon of understanding, helping individuals and communities to anticipate and prepare for such harsh conditions. With the ingenuity of human adaptation and the power of predictive analytics, there is a path forward to navigate these climatic adversities, ensuring safety and resilience for the future.
