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The document describes a 'hazard synthesis' method developed by World Weather Attribution to combine different lines of evidence into a single number representing the influence of climate change on an extreme event's intensity and likelihood. It notes that while this approach is more realistic than using models or observations in isolation, it faces limitations when events would have been impossible in a cooler world or when climate models contradict basic physics, such as the Clausius-Clapeyron relationship. The author emphasizes that human expertise and experience are necessary to evaluate these results, as automated or AI-driven analysis cannot yet account for model deficiencies or data discrepancies.

The study finds that heavy precipitation events leading to severe flooding in Sudan are no longer rare in a climate 1.3°C warmer than pre-industrial levels, with such events now expected approximately every three years. Climate models indicate that human-induced warming has roughly doubled the likelihood of these events and increased their intensity by about 10%, with observed 30-day rainfall intensity in the study region increasing by 18% since 1981. The report emphasises that these climate risks are compounded by 'risk multipliers' including ongoing conflict, poverty, rapid urbanisation, and ageing infrastructure, which have created a displacement crisis in Sudan, Chad, and Nigeria. The authors argue that the transboundary nature of river systems in sub-Saharan Africa necessitates improved international coordination for flood management and early warning systems to mitigate future disasters as warming reaches 2°C.

The study finds that human-induced climate change has increased the intensity of heavy 3-day rainfall events in Nepal by approximately 10% and their likelihood by about 70% compared to a 1.3°C cooler climate. These climate drivers combined with rapid urbanisation in the Kathmandu Valley—which saw a 386% increase in built-up areas between 1990 and 2020—and a 28% reduction in forest cover from 1989 to 2019, significantly increased flood exposure and disrupted natural drainage. The analysis notes that the 2015 Gorhka earthquake and the COVID-19 pandemic acted as compounding factors that increased vulnerability. While the Department of Hydrology and Meteorology provided forecasts, the Kathmandu Valley has historically not been the focus of flood risk management, which typically prioritises the Terai region.

The report finds that human-induced climate change increased the intensity and likelihood of heavy rainfall associated with Hurricane Milton in central Florida. Using the IRIS model, the analysis indicates that climate change increased the frequency of storms with Milton's wind speeds by approximately 40%, meaning the storm would have likely made landfall as a Category 2 rather than a Category 3 hurricane without global warming. Additionally, sea surface temperatures along Milton's track were 1°C warmer than in a world without climate change, making such temperatures 400 to 800 times more likely. The report also assesses Florida's adaptation measures, noting that while building codes are among the toughest in the US, the state's planning remains largely reactive and fails to adequately address social vulnerabilities in low-income and minority communities.

The analysis finds that climate change made rainfall approximately 10% heavier in both the coastal and inland regions affected by Hurricane Helene and increased the likelihood of such rainfall totals by 40% and 70%, respectively. The study also indicates that climate change increased the number of storms with similar wind speeds by about 150% and made the record-hot sea surface temperatures over the storm's track 200-500 times more likely. While the storm was well-forecast, high death tolls occurred inland due to mountainous terrain, poor infrastructure, and a lack of experience with hurricanes.

An attribution study on the September 2024 Central European floods finds that human-induced climate change roughly doubled the likelihood of such an event and increased its intensity by 7%. While improved forecasting and emergency management reduced fatalities compared to the 1997 and 2002 floods, the scale of the event overwhelmed infrastructure in several urban centres, causing damages estimated at several billion Euros.

The study finds that climate change increased rainfall intensity in Taiwan and Hunan province and contributed to a 7% increase in maximum wind speeds for similar storms in the Western North Pacific basin. While sea surface temperatures as hot as those observed during Typhoon Gaemi were "almost impossible without climate change", the analysis did not identify a significant trend for rainfall in the northern Philippines. The report highlights that existing urban plans and flood infrastructure are unable to withstand climate-driven extreme floods, particularly in areas of unplanned urban development like Metro Manila.

The study analyzes severe flooding in Afghanistan, Pakistan, and Iran during April and May 2024, which caused hundreds of deaths and significant infrastructure damage. While the event occurred outside the typical winter rainfall season, researchers found that a declining El Niño increased the likelihood of such rainfall by approximately two times and intensity by about 8% compared to neutral years. The analysis concludes that human-induced climate change cannot be definitively attributed as the main driver due to discrepancies between observational data and climate model signals, although a 40-year observational trend shows an increase in heavy rainfall. The report emphasizes that high vulnerability—driven by deforestation, unplanned urban expansion, and limited water management—exacerbated the disaster's impact.

The study finds that human-induced climate change, driven by the burning of fossil fuels, made the extreme rainfall events in Rio Grande do Sul more than twice as likely and increased their intensity by 6-9%. The El Niño Southern Oscillation also played a significant role, increasing the likelihood of such events by a factor of 2-5. The floods affected over 90% of the state, causing 169 deaths and displacing over 580,000 people, with impacts exacerbated by poverty, failing flood protection infrastructure in Porto Alegre, and inconsistent enforcement of environmental protection laws.

A World Weather Attribution study found that human-caused climate change increased the likelihood of extreme heat for 6.3 billion people globally, adding an average of 26 extreme heat days per location over the last year.

A World Weather Attribution study found that human-induced climate change significantly increased the frequency and intensity of April 2024 heatwaves across Asia. In the Philippines, the event would have been "impossible" without climate change, while in West Asia, the probability increased by a factor of 5. In South Asia, extreme temperatures were found to be about 45 times more likely and 0.85ºC hotter. The report highlights disproportionate impacts on vulnerable groups, including 1.7 million displaced people in Gaza and outdoor workers, and notes that existing heat action plans often lack mandatory workplace regulations and retrofitting for informal settlements.

The analysis concludes that El Niño is a key driver of the 2024 drought in Southern Africa, making such events twice as likely to occur. Conversely, human-induced climate change did not emerge as a significant driver of the low rainfall observed between December and February, with data suggesting that rainfall in this period actually increases as global temperatures rise.

A World Weather Attribution analysis concludes that the extreme heatwave affecting the Sahel in early 2024, which coincided with Ramadan and power cuts, would have been impossible without the 1.2°C of global warming caused by human activities. The event was particularly severe in Mali and Burkina Faso, where 5-day maximum temperatures had a return time of 200 years. The study finds that human-induced warming increased 5-day maximum temperatures by 1.5°C in Mali/Burkina Faso and 1.4°C across the wider Sahel, while the current El Niño event contributed only a small amount (approximately 0.2°C). In Bamako, Mali, the Gabriel Touré hospital reported 102 deaths between 1-4 April, significantly exceeding the 130 deaths recorded for the entire month of April 2023.

A study of heavy rainfall in eastern Mindanao (Caraga and Davao regions) between December and February found a strong upward trend in extreme rainfall in observations, though climate models failed to replicate this trend, preventing a quantified attribution to human-induced climate change. The analysis notes that El Niño typically reduces rainfall in this region during the Northeast monsoon, suggesting rainfall could have been more extreme without it. High vulnerability to flooding is attributed to poverty, protracted conflict, deforestation, urban wetland loss, and stalled disaster risk management policies, including the failure of automated sensors since 2022.

An attribution study by the World Weather Attribution initiative found that human-induced climate change doubled the likelihood of the heavy precipitation associated with Storm Bettina and increased its intensity by approximately 5 percent. In contrast, the study found no clear evidence that climate change influenced the wind speeds of the event, attributing observed decreases in wind speed to natural variability. The analysis notes that warming increases the proportion of precipitation falling as rain rather than snow, exacerbating flood damages, and that the ongoing Russia-Ukraine war increased the vulnerability of affected populations.

The study finds that human-induced climate change and a positive phase of the Indian Ocean Dipole (IOD) contributed approximately equally to the magnitude of extreme rainfall in the Horn of Africa during the 2023 OND season. While the IOD is a natural oscillation, the warming of 1.2C from fossil fuel combustion approximately doubled the rainfall magnitude. The researchers report high confidence that climate change increased rainfall intensity, though they have low confidence in the specific quantification due to limited model correlation and short records. The impact was compounded by previous droughts, unsustainable land management, and systemic challenges in early warning systems, leading to over 300 deaths and the displacement of more than one million people in Kenya and Somalia.

A study by World Weather Attribution found that human-induced climate change significantly increased the intensity and likelihood of an early spring heat event in South America, which affected Argentina, Brazil, Paraguay, and Bolivia. The event, occurring approximately once every 30 years in the current climate, would have been 1.4 to 4.3 °C cooler without human-caused warming. The study notes that the likelihood of such an event has increased by at least 100 times due to climate change. Future warming of 2°C above pre-industrial levels is projected to make similar events five times more likely and 1.1 to 1.6 °C hotter. The researchers highlight a lack of heat action plans in the affected region, which increases vulnerability for the urban poor and ecosystems, despite the fact that adaptation can reduce morbidity and mortality.

A World Weather Attribution study found that human-induced climate change significantly increased the likelihood and intensity of extreme rainfall events in the Mediterranean region in September 2023. In Libya, a 1-in-300 to 600 year event became up to 50 times more likely and 50% more intense compared to a 1.2C cooler climate. In a region encompassing Greece, Bulgaria, and Türkiye, similar events became up to 10 times more likely and 40% more intense. The study highlights that while climate change exacerbated the weather, the scale of the disaster—particularly in Libya—was compounded by state fragility, lack of dam maintenance, and inadequate emergency communication.

The research finds that human-induced climate change significantly increased the intensity and probability of extreme fire weather in eastern Canada in 2023, particularly in Québec, where the cumulative severity of the fire season was approximately 50% more intense and at least seven times more likely to occur.

A collaborative study by international scientists found that the extreme heatwave in the Western Mediterranean from 26-28 April 2023 was likely made at least 100 times more probable by human-induced climate change. The event, which saw temperatures up to 20 degrees higher than normal and broke national records in Spain and Portugal, would have been at least 2°C cooler in a world 1.2°C colder. The researchers note that climate models likely underestimate the increase in extreme heat in Western Europe, suggesting their findings are conservative.