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Northern hemisphere summer marked by heat and fires

Source:WMO16-09-2020

The Northern hemisphere just had its hottest summer and hottest August on record, according to the US National Oceanic and Atmospheric Administration.

At global level, it was the second warmest August on record and 0.94°C (1.69°F) above the 20th-century average of 15.6°C (1.69°F), according to the NOAA dataset. The Copernicus Climate Change Service implemented by the European Centre for Medium-Range Weather Forecasts ranked it as the fourth warmest August on record globally. WMO consolidates different international datasets for its reports on the state of the global climate.

Air quality USA September 2020

August 2020 marked the 44th consecutive August and the 428th consecutive month with temperatures, at least nominally, above the 20th-century average. The 10 warmest Augusts have all occurred since 1998. The five warmest Augusts have occurred since 2015, according to NOAA.

The most notable temperature departures from average during August 2020 included the western contiguous United States, which is suffering a destructive fire season.

Record-breaking fires

The states of California, Oregon and Washington have been worst hit, with dozens of casualties, razing entire neighbourhoods to the ground and forcing the evacuation of thousands of people.

The fires have impacted air quality for millions of people and turned skies orange. Clouds of smoke have billowed over the western Pacific and, according to satellite images, travelled more than 1,300 miles.

As of 13 August, nearly 16,500 firefighters continue working to gain containment on the 28 major wildfires across California. Since the beginning of the year, wildfires have burned over 3.2 million acres in California. Since August 15, when California’s fire activity elevated, there have been 24 fatalities and over 4,200 structures destroyed, according to Cal Fire.

Causes

According to thUS drought 2020e US National Interagency Fire Center, of the 41,599 fires to date this year, 36,383 were human-caused, burning a total of 2,510,743 acres across the United States. California remained in the first spot, with 7,072 human-caused fires reported.

Weather, climate and water-related conditions were also conducive to rapid wildfire growth.

Drought: The western United States has seen an expansion of drought conditions over the first half of 2020. In August, the dry conditions and high temperatures continued and worsened drought across the West. The percent area of the contiguous United States experiencing some level of drought increased by 7 percentage points in August, leaving nearly 40% of the country in drought.

Heatwave: A record-breaking heatwave settled over the Western USA during the middle of August. Temperatures soared to a recorded 54.4°C (130°F) in Death Valley, California. A WMO team of experts will verify this temperature reading.

Strong winds fed off the heat and low humidity and fanned the flames.

US temperatures August 2020Moisture from a rapidly weakening tropical storm to the south resulted in strong thunderstorms moving into coastal California accompanied by thousands of lightning strikes. According to CalFire, between August 15 and the end of August, more than 14,000 lightning strikes occurred.

Connection to climate change

Six of the top 20 largest wildfires in California history have occurred this year, according to Cal Fire. In Cal-Fire’s list of the top twenty largest wildfires, eight of the top ten have occurred in the last ten years, and seventeen of the top twenty have occurred since 2000. Seven of the top ten most destructive wildfires have occurred since 2015.

Wildfires are a part of the natural cycle of life in many ecosystems across the western United States. As a fire blazes, it kills pests, while germinating a generation of new seedlings, and the forest growth cycle begins anew. But too many wildfires potentially permanently altering the ecosystem.

The Fourth National Climate Assessment, a US government inter-agency report, notes that from 1984 to 2015, climate change led to twice as much land being burned than if climate change had not occurred. And even though there are other factors involved in the acreage wildfires burn—like fire suppression and local fire management practices—from 1916 to 2003, the area burned by wildfires was likely also driven by climate factors.

According to the Fourth National Climate Assessment, climate change has led to more intense droughts, especially across California. These droughts, combined with increased temperatures, have desiccated forests, making them tinderboxes.

The report said that the 2011–2015 meteorological drought in California, combined with future warming, will lead to long-term changes in land cover, leading to increased probability of climate feedbacks (e.g., drought and wildfire) and in ecosystem shifts.