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The study finds that while human-induced climate change did not significantly alter the likelihood of the overall 24-month rainfall deficit, it drastically increased drought severity through higher temperatures and evapotranspiration. In a world 1.2°C cooler, the combination of low rainfall and high evapotranspiration observed would not have led to drought; however, in the current climate, it is classified as an 'exceptional drought'. The researchers estimate that such droughts have become approximately 100 times more likely due to climate change.

The study analysed peak 48-hour rainfall in Te Matau-a-Māui and Te Tairāwhiti during February 2023. Historical weather station data (1979-2023) suggests the 2-day maximum rainfall is now approximately 30% more intense and four times more likely to occur than if the climate had not warmed by 1.2C. However, climate models showed a much smaller change in likelihood and intensity, creating a discrepancy that prevents the researchers from quantifying the overall role of human-induced climate change with certainty. The report notes that 225,000 homes lost power and the event caused multi-billion dollar damages, comparable to the 2011 Waitaha earthquakes.

The analysis finds that while the low rainfall during the October-December 2022 period in Central South America cannot be attributed to climate change and is partly driven by La Niña, human-induced climate change likely reduced water availability by increasing temperatures and evapotranspiration. This exacerbates the agricultural drought, which has already caused severe crop losses in Argentina and water shortages in Uruguay.

The document explains attribution studies—which use climate models to determine if and how much human-induced climate change affected a specific event—and provides guidance on reporting various extreme phenomena. It details how global warming increases the probability and intensity of heatwaves and heavy precipitation globally, while the effects on droughts, wildfires, and tropical cyclones vary by region or specific metric. It emphasizes that while climate change influences the risk and intensity of these events, human factors like land use and water management also contribute to whether an event becomes a disaster.

The 2022 rainy season in West Africa saw above-average rainfall and devastating floods, particularly in Nigeria and Niger, where fatalities reached at least 612 and 195 respectively. An attribution study found that climate change made the seasonal rainfall over the Lake Chad region approximately 80 times more likely and 20% more intense, while the 7-day maximum rainfall over the lower Niger Basin became about twice as likely and 5% more intense. Beyond climate change, the flooding was driven by the release of the Lagdo Dam in Cameroon and exacerbated by high poverty rates, political instability, and the location of infrastructure and settlements on flood plains.

World Weather Attribution (WWA) reports on its activities from October 2021 to October 2022, during which it published eight rapid analyses and several peer-reviewed papers. These studies examined the role of human-induced climate change in events such as heatwaves in India, Pakistan, and the UK, as well as flooding and droughts in various regions. The organization emphasizes that while climate change is a major driver for heatwaves, its role in other events like tropical cyclones can be less clear, often compounding with high levels of vulnerability to increase human impacts.

The 2022 monsoon rainfall in Pakistan, particularly in Sindh and Balochistan, resulted in catastrophic flooding that affected over 33 million people and caused damages likely exceeding US$30 billion. Attribution analysis indicates that 5-day maximum rainfall in Sindh and Balochistan is now approximately 75% more intense than it would have been without a 1.2C warming, while 60-day rain across the Indus basin is about 50% more intense. While high regional variability and model discrepancies make exact quantification of the human-induced role difficult, most models and observations show that intense rainfall has increased as Pakistan warmed, with future projections suggesting further significant increases in rainfall intensity at 2 °C of warming.

The analysis finds that human-caused climate change made the July 2022 UK heatwave, which saw record temperatures of 40.3°C, at least 10 times more likely. Observational data suggests such a heatwave would have been approximately 4°C cooler in preindustrial times, while model-based estimates suggest a 2°C difference in a 1.2°C cooler world. The event was extreme even in the current climate, with some 1-day maximum temperatures having return periods of 1 in 1000 to 1500 years.

An event attribution study found that human-caused climate change increased the likelihood and intensity of the extreme rainfall that hit eastern Northeast Brazil in May 2022, causing over 133 deaths and displacing at least 25,000 people. While the events were exceptionally rare—with a 1-in-500 to 1-in-1000 annual chance in the current climate—they would have been approximately 20% less intense in a world without human-induced warming. The study highlights that pre-existing structural vulnerabilities, such as unplanned urbanization in low-income neighborhoods and an infrastructure deficit, exacerbated the disaster's impact.

A collaborative scientific study found that human-induced climate change approximately doubled the probability of the extreme 2-day rainfall that caused devastating floods in eastern South Africa in April 2022, increasing the event's intensity by 4-8%.

A collaborative scientific analysis concludes that greenhouse gas and aerosol emissions contributed to the increased likelihood and intensity of heavy rainfall during Tropical Storm Ana and Tropical Cyclone Batsirai in early 2022. While Tropical Storm Ana was a rare event for Malawi and Mozambique (1 in 50 years), Cyclone Batsirai was more common for Madagascar (1 in 2 years). The study highlights that existing vulnerabilities, including prior flooding, conflict in northern Mozambique, and drought in southern Madagascar, exacerbated the humanitarian impacts.

The document explains 'event attribution' as a scientific method to determine how much human-induced climate change affects the probability and intensity of specific weather extremes. It provides a detailed breakdown of how climate change influences heatwaves, floods, tropical cyclones, snowfalls, droughts, and wildfires, while cautioning against oversimplifying these events as having a single cause. The guide emphasizes that while some trends (like heatwaves) are globally certain, others (like floods or droughts) vary by region and are influenced by local human factors such as land use and water management.

The analysis finds no significant evidence that human-caused climate change altered the probability or intensity of the October 2020 heavy rainfall events in Central Vietnam. While observations suggest a 1-in-80 year event, the uncertainty ranges for both observational and model-based data are too large to establish a significant climate change signal. The study concludes that natural variability currently outweighs climate change impacts for multi-day precipitation in the region, emphasizing the need for improved disaster risk reduction measures regardless of climate trends.

The study finds that human-induced climate change did not significantly increase the occurrence of the poor rains observed in southern Madagascar between July 2019 and June 2021, as trends remain overwhelmed by natural variability. While the region experienced a 1-in-135 year dry event with only 60% of normal rainfall, the resulting severe food insecurity was driven primarily by high pre-existing vulnerability, poverty, COVID-19 restrictions, and pest infestations rather than climate change.

A rapid analysis of the June 2021 Pacific Northwest heatwave concludes that the event was virtually impossible without human-caused climate change. The study estimates the event as a 1-in-1000-year occurrence in the current climate, noting it was approximately 2°C hotter than it would have been before the industrial revolution. Projections indicate that with 2°C of global warming, such events could occur every 5 to 10 years.

The analysis finds that while human-caused climate change made the absolute temperatures of the April 2021 frost event less cold, it simultaneously triggered an earlier start to the growing season. This shift exposed young leaves to winter-like conditions, making the 2021 event 20% to 120% more likely. The study notes that in a 2°C warming scenario, such frost events are projected to intensify further by 0.2°C to 0.5°C.

The report concludes that the June 2021 Pacific Northwest heatwave was virtually impossible without human-caused climate change, estimating it as a 1-in-1000 year event in the current climate. The analysis indicates the event was approximately 2°C hotter than it would have been in a pre-industrial climate and would have been at least 150 times rarer without anthropogenic warming. Future projections suggest that in a world with 2°C of global warming, such an event would occur every 5 to 10 years and be another degree hotter. Meteorological drivers included an 'omega-block' high-pressure system and dry antecedent soil conditions, while natural variability modes like ENSO and PDO played little to no role.

The July 2021 floods in Western Europe were driven by extreme rainfall from the low-pressure system 'Bernd', compounded by pre-existing wet soil conditions. While attribution for small catchments like the Ahr and Erft is challenging due to high natural variability, a broader 'Pooling Region' analysis indicates that climate change increased the intensity of maximum 1-day rainfall by 3-19% and its likelihood by a factor of 1.2 to 9 compared to a climate 1.2 °C cooler. Future projections suggest further increases in intensity and frequency in a 2 °C warmer climate.

The report concludes that the prolonged regional heat in Siberia from January to June 2020 was effectively impossible without human influence, with a best estimate probability ratio of 99,000 compared to a 1900 climate. Such events would have been at least 2°C cooler without anthropogenic influence. For the specific record of 38°C at Verkhoyansk, the study found a confident anthropogenic shift in intensity of 1.5°C, although the probability ratio for this specific station event is of lower confidence. By 2050, the regional heat is expected to be further intensified, with a synthesis change in intensity of 4.85°C compared to 1900.

The analysis finds that anthropogenic climate change has significantly increased the probability of extreme fire weather and heatwaves in southeastern Australia, while having no attributable trend in dry extremes. Specifically, the probability of a Fire Weather Index as high as in 2019/20 has increased by more than a factor of four since 1900. Heatwaves of similar intensity are now approximately 10 times more likely than they were around 1900. While climate change increased the overall risk, the specific severity of the 2019 event was further amplified by natural variability, specifically the Indian Ocean Dipole and the Southern Annular Mode.