2021 Climate and Health Review – Uncharted Territory: Extreme Weather Events and Morbidity

Economic Damage Largely Reflects Flood and Storm Impacts in High-Income Urban Areas

Total damages of $215 billion were reported for the 30 events, with floods and storms representing 70% (see Table 1). Three North American events (Storm Uri, Hurricane Ida, and the Pacific Northwest heatwave) accounted for half of the total, while major floods in Henan, China, and Germany accounted for a further 28%. The fact that many EWEs affected one or more populous, middle- or high-income city—among them Houston, Madrid, New Orleans, New York City, Shanghai, Sydney, Vancouver, and Zhengzhou—increased their potential for economic impact. Insurance coverage for all EWEs was 43% of total, indicating large gaps; 55% of damages from Hurricane Ida were insured ²² , 33% of flooding damages in Germany ²³ , and only 17% of total EWE damages in Asia ²² . The cost of damages in low-income countries is not well-captured; of the 12 EWEs without cost estimates, 10 were in LMICs, and none of the droughts had cost estimates. Data from the United States suggest droughts are the second costliest disaster, after hurricanes ²⁴ . Re-insurer estimates of total damages from all natural disasters in 2021 (including earthquakes) was $280 billion ²² ; at 77%, the 30 EWEs represent a large fraction of this estimate.

Mortality Has Declined and Is Now Led by Extreme Heat, But Reports Do Not Likely Reflect True Impact

A total of 3,490 casualties were reported for the 30 major events of 2021. Nearly one-third (1,037 deaths) were attributed to a single event, the June–July heatwave in the Pacific Northwest (see Table 1), when a wobble in the jet stream facilitated a persistent “heat dome” over the region—deemed by a rapid attribution study to be “virtually impossible” without climate change ²⁵ . Storms and flooding accounted for more than half of reported deaths, often from drowning; while the extreme cold of the Texas winter storm led to a reported 246 deaths, mostly from hypothermia. Death toll reports often change over time, due to additional information, missed counts or classifications, or other reasons. For example, one re-analysis found that as many as 750 may have died in the cold spell in Texas ²⁶ . Droughts and floods caused the lion's share of EWE-linked deaths in the past; however, early-warning systems and preparedness have led to a decline over several decades ²⁷ . Heatwaves are now the deadliest extreme event, estimated by the Lancet Countdown to take the lives of an estimated 345,000 older adults globally in 2019 ¹⁹ . This review has captured only a small portion of likely actual deaths associated with the full range of EWEs in 2021.

Displacement, Driven Mainly by Floods and Storms, Affects Those Least Equipped to Adapt

Floods, cyclones, and droughts affect large numbers of people through temporary evacuation and/or longer-term internal displacement; this is of particular concern because displacement affects disproportionately “those least equipped to recover and adapt,” as noted by the WMO ²⁷ . Displacement of more than 4.5 million people was reported for the 30 EWEs in 2021 (see Table 1). Flooding in China and in South Sudan accounted for most displacements reported. Inconsistencies and gaps in the data are apparent, however, with estimates available for only 17 of the 30 events (particularly lacking for droughts). The United Nations High Commissioner for Refugees suggests that storms, droughts, and sea-level rise lead more than 20 million people to move within their countries annually ²⁸ . The Internal Displacement Monitoring Center reported that 30 million people left their homes due to weather-related disasters in 2020; floods (14 million) and storms (14.6 million) were by far the largest causes of displacement ²⁹ . The data reviewed here capture only a small share of the likely 2021 total.

Wildfire Smoke: “Airpocalypse”

With extreme heat and dry conditions, wildfires in 2021 were intense, fast-moving, and difficult to extinguish, and they generated toxic, traveling smoke plumes. The largest fires by area burned (18 million hectares) occurred in Siberia ³⁰ and generated one of the most toxic air pollution episodes on record—an “airpocalypse” of smoke containing ammonia, benzene, and hydrogen cyanide—forcing the 320,000 residents of the city of Yakutsk indoors as PM_2.5 exceeded 1,000 micrograms/m³ (10-fold the levels of some of the world's most polluted cities); the smoke plume reached Ulaanbaatar, Mongolia, 2,000 miles away ³¹ . The North American wildfires occurring in the same season burned at least 3 million hectares in the Western United States and Canada ³² . One of largest, the Dixie fire in California, was so intense that it generated its own weather system of storm clouds and lightening, carrying a smoke-wave to major urban centers on the East Coast, nearly 3,000 miles away ³³ . Heatwaves in 2021 also led to wildfires across the Mediterranean Basin. In Turkey, an inadequate public emergency response left residents fighting the blazes on their own ³⁴ , while fires brought Greece its “greatest ecological disaster in decades,” and more than two dozen firefighters were among the victims in Algeria's wildfires ³⁵ . Wildfire PM_2.5 was elevated throughout much of this populous region for weeks ³⁶ .

Wildfire smoke PM_2.5 is known to worsen respiratory conditions, including asthma and chronic obstructive pulmonary disease (COPD) ³⁷ , and to increase risk of lower respiratory infections such as bronchitis and pneumonia ³⁸ . Research in 2021 contributed to strengthening the evidence that PM_2.5 from wildfire smoke—which may contain residue from burned buildings and other materials—is also more toxic than ambient PM_2.5. A review highlighted that wildfire smoke contains many of the carcinogenic components of cigarette smoke ³⁹ , and an experimental study found it to induce both oxidative stress and DNA damage ⁴⁰ . An observational study in Southern California found 10-fold more respiratory hospitalizations in those exposed to wildfire PM_2.5 compared to those exposed to the same amount of ambient PM_2.5 ⁴¹ . Another study examining crowdsourced-data in California found PM_2.5 was three times higher indoors during wildfires, indicating the challenge of sheltering ⁴² . A review of wildfire smoke exposure found increased risk of COVID-19 infection ⁴³ ; firefighters were observed to have greater risk of COVID-19 severity ³⁸ ; while tens of thousands of COVID-19 cases in the U.S. West in 2020 were likely attributable to exposure to wildfire PM_2.5. ⁴⁴ _. With the Siberia, Pacific Northwest, and Mediterranean wildfires, tens of millions were likely exposed to wildfire PM_2.5, often in tandem with COVID-19 pandemic waves, suggesting a large global disease burden of new or worsened respiratory illness.

Extreme Cold: “Everything Gets Worse If You Don’t Have Electricity”

In February, the Northern Hemisphere jet stream veered dramatically south, bringing Arctic freeze to parts of Southern Canada, the United States, and Northern Mexico and giving Texas its coldest spell in four decades ⁴⁵ . The “deep freeze” led to the worst power outage in the state's history, largely due to inadequately winterized natural gas infrastructure, which left more than 10 million homes without power and heat and many without water ⁴⁶ . “Catastrophes…compounded one another in a true humanitarian crisis” as water pipes burst, shelters filled, and under-resourced communities felt the brunt of the impact ⁴⁷ . More than 500 people were treated for carbon monoxide (CO) poisoning in Houston hospitals alone as people turned to generators and cars for warmth ⁴⁸ . At the same time, millions of Mexicans experienced extreme cold and power outages, as a result of the country's reliance on frozen Texas natural gas pipelines. “Catastrophic weather wasn’t contemplated in Texas or Mexico,” according to one observer ⁴⁹ . Spain experienced similar extreme cold and snow in January, leading to power outages in Madrid, and hospitals filled with injuries ⁵⁰ . In Cañada Real, Europe's largest informal settlement on the outskirts of Madrid, these conditions brought respiratory infections and CO poisoning to those least able to protect themselves, with one person observing that “everything gets worse if you don’t have electricity” ⁵¹ .

As experience with polar vortex shifts grows, awareness of the harms from such devastating cold spells is increasing. Evidence suggests extreme cold increases risk of illness, particularly among the elderly and those with pre-existing cardiovascular disease (CVD) and respiratory illness ⁵² . In China, where cold is an ongoing health concern in some regions, studies found respiratory emergency department visits were more frequent ⁵³ , as were asthma and upper respiratory infections in children ⁵⁴ , during cold spells. A systematic review found cold exposure associated with poorer cognitive function and memory in the elderly ⁵⁵ . Winter storms in New York State were associated with increased morbidity from CVD, respiratory illness, and food- and water-borne diseases (stronger effects jointly with power outages) ⁵⁶ and with higher COPD hospitalizations (power outages mediating a large share of the effect) ⁵⁷ . A review found loss of power in ice storms to be the weather disaster most associated with negative birth outcomes ⁵⁸ . With the cold disasters in Texas, Mexico, and Spain, many millions were likely exposed to days of extreme cold weather—including many days without power, heat, or water—suggesting risk of injuries and respiratory illness, as well as infectious disease, cognitive impairment in the elderly, and adverse birth outcomes.

Extreme, Precipitation-Related Flooding: “Stunned Scientists”

Intense rainfall in July in Henan Province, China—home to 100 million people—buried this vast region under water; homes, infrastructure, and industry, including Apple and Nissan factories, were badly damaged ⁵⁹ . An unprecedented 20 centimeters of rain fell in 24 hours in the capital Zhengzhou, exacerbating drainage vulnerabilities, flooding the subway, displacing more than 1 million ⁶⁰ , and challenging the city's nature-based “sponge-city” drainage infrastructure ⁶¹ . In the same month, intense rain fell across parts of Germany and Belgium, with up to 15 centimeters in 24 hours causing flash flooding and leaving residents and climate scientists alike “stunned” at the quantity of rain. Despite ample warning, “we weren’t expecting this amount of water,” as one resident observed ⁶² . People found themselves “knee-deep in sewage” ⁶³ ; in some towns, 80% of houses were uninhabitable, with mold-covered walls, and residents had to choose whether to rebuild or move ⁶⁴ . The next month, Hurricane Ida rapidly intensified over a 24-hour period from a Category 1 to a Category 4 storm as it struck New Orleans, creating power outages affecting 1 million homes, putting tens of thousands under evacuation orders, and leading to a curfew to protect people from theft ⁶⁵ . The hurricane then tracked northward, flooding populous urban areas in the Northeast United States, including New York City, where tens of thousands were displaced or had no running water, and half a million were under boil-water orders ⁶⁶ .

In 2021, research added to knowledge of morbidity impacts from intense rainfall and rapid flooding in part through examination of experience with similar previous events. For example, studies of Hurricane Harvey in Houston found flooding was associated with increased emergency department visits for CO poisoning, insect bites, dehydration, hypothermia, intestinal infections, and pregnancy complications ⁶⁷ ; greater risk of upper respiratory and asthma symptoms, both a month and a year after the event ⁶⁸ ; and greater risk of hospitalization for toxicological emergencies, trauma, and skin rashes in children ⁶⁹ . A survey in Detroit found recurrent flooding to be common and household factors (eg, roof condition, foundation structure), particularly in rental units, to be important predictors of asthma ⁷⁰ . A meta-analysis found flooding significantly increased risk of bacillary dysentery in China ⁷¹ . A systematic review of floods and mental health in LMICs found an association with post-traumatic stress disorder ⁷² , while a comprehensive review found a more than 90% likelihood of experiencing any psychosocial impact from all EWEs, particularly for those involving property damage and losses ⁷³ . The widespread catastrophic flooding in populous areas of China, the Eastern United States, and North-Central Europe—including the low share of damages insured—suggest dozens of millions of people may have been exposed to risk of mental health effects, in addition to injury, asthma and other respiratory illness, gastrointestinal and skin infections, and pregnancy complications.

Drought: “The Next Pandemic”

Today, drought is already widespread, affecting 19% of the global land surface ¹⁹ . Without more intentional water and land management, “drought will be the next pandemic,” according to the United Nations ⁷⁴ . In 2021, drought on the Colorado River, which supplies water to 40 million people across seven U.S. states and Mexico, may have become the most severe in the last millennium; in August, the United States declared a water shortage on this lifeblood tributary of the American West, triggering mandatory water cuts ⁷⁵ . A similar situation evolved in the Paraná River Basin, which provides water to 40 million people in Argentina, Brazil, and Paraguay ⁷⁶ , with the latter particularly hard-hit due to its dependence on the river for its export-led agriculture ⁷⁷ . Megacities such as São Paulo are promoting conservation to avoid crisis and rationing ⁷⁸ . But droughts in low-income countries carry a higher burden: In Southern Madagascar, lack of rain this year may create the world's first climate famine, as more than 1.1 million subsist on foraged locusts, termites, and cactus leaves ⁷⁹ ; Médecins Sans Frontières has reported tens of thousands of malnourished children with bilharzia, malaria, and respiratory infections ⁸⁰ . In Cameroon, in the Lake Chad region, conflict over water has erupted between herders and farmers in an area plagued by drought for decades ⁸¹ . In China, the worst sandstorm in a decade reached Beijing from Mongolia in March, worsening air quality and forcing residents indoors ⁸² .

In 2021, rural and agricultural populations felt drought effects most acutely. In a review of health effects of drought in high-income countries, associations included water- and vector-borne disease, respiratory disease from airborne dust, and mental health effects ⁸³ . For example, farmers in the United States facing drought felt that job strain increased substantially, driven by psychosocial stress factors ⁸⁴ . On the other hand, a review of drought impacts on health in Africa found increased anemia, cholera, scabies, dengue fever, and child nutrition-related disabilities, including stunting and wasting ⁸⁵ . Drought was associated with lower odds of completing childhood BCG, DPT, and polio vaccines, suggesting risk of future disease outbreaks ⁸⁶ . In a systematic review, during droughts in India, the work burden on women and children increased, along with malnutrition and anemia ⁸⁷ . Meanwhile, a review of experimental studies found a likely harmful effect of desert dust on asthma and respiratory infections, suggesting dust may be a platform for other chemicals that enhance its pulmonary toxicity ⁸⁸ . Mega-droughts in the Colorado and Paraná River basins are bringing mental health-affecting water shortages to farming communities and threat of water rationing to urban dwellers, impacting 80 million people. Droughts in Madagascar, East Africa, and Lake Chad add millions to those likely exposed to risk of malnutrition and anemia, respiratory illness, infectious and vector-borne disease, and the dangers of armed conflict. The China sandstorm exposed millions to enhanced risk from respiratory illnesses.