Heavy rainfall events setting ever new records have been increasing strikingly in the past 30 years.

While before 1980, multi-decadal fluctuations in extreme rainfall events are explained by natural variability, a team of scientists of the Potsdam Institute for Climate Impact Research detected a clear upward trend in the past few decades towards more unprecedented daily rainfall events. They find the worldwide increase to be consistent with rising global temperatures which are caused by greenhouse-gas emissions from burning fossil fuels. Short-term torrential rains can lead to high-impact floodings.

Extreme rainfall in Pakistan 2010 caused devastating flooding which killed hundreds and lead to a cholera outbreak. Other examples of record-breaking precipitation events in the period studied include rainstorms in Texas in the US, 2010, which caused dozens of flash-floods. And no less than three so-called “once-in-a-century” flooding events in Germany all happened in just a couple of years, starting 1997.

“In all of these places, the amount of rain pouring down in one day broke local records – and while each of these individual events has been caused by a number of different factors, we find a clear overall upward trend for these unprecedented hazards,” says lead-author Jascha Lehmann.

The average increase is 12 percent globally – but 56 percent in South East Asia

An advanced statistical analysis of rainfall data from the years 1901 to 2010 derived from thousands of weather stations around the globe shows that over 1980-2010 there were 12 percent more of these events than expected in a stationary climate, a scenario without global warming. “Due to the upward trend, the worldwide increase of record-breaking daily rainfall events in the very last year of the studied period reaches even 26 percent,” Lehmann adds.

The record-breaking anomaly has distinct patterns across Earth’s continents with generally wet regions seeing an over-proportional increase and drier regions less so. In South East Asian countries, the observed increase in record-breaking rainfall events is as high as 56 percent, in Europe 31 percent, in the central US 24 percent. In contrast, some regions experienced a significant decrease of record-breaking daily rainfall events. In the Mediterranean, the reduction is 27 percent, and in the Western US 21 percent. Both regions are at risk of severe droughts.

The link to climate change: warmer air can hold more water

While a statistical analysis of course cannot provide direct physical cause-effect relations, the scientists compared their findings to existing knowledge about how much more water can be stored in the atmosphere when temperatures rise, as given by the well-known Clausius-Clapeyron equation. This additional moisture can be released during short-term heavy rainfall events. The scientists show that the observed increase in unprecedented heavy rainfall events generally fits with this thermodynamically expected increase under global warming.

“One out of 10 record-breaking rainfall events observed globally in the past 30 years can only be explained if the long-term warming is taken into account,” says co-author, Dim Coumou. “For the last year studied, 2010, it is even one event out of four, as the trend is upward.”

Up to now, studies could add up to only medium confidence on how human induced greenhouse gases have contributed to changes in heavy precipitation events at the global and regional scale. The new analysis now helps to fill this research gap. Building on previous work on extreme precipitation, it is the first to study worldwide observational data of record-breaking daily rainfall events in this context.

“The recent upward trend is worrying”

The scientists considered that the quality of historic weather data differs from one place to another. For instance, rainfall measurements from the Sahara Desert are scarce which inhibits making any conclusions for this region. Other regions like Europe or the US are well covered with rainfall measurements stretching back over a century which enables the authors to draw conclusions with high levels of confidence.

“The pronounced recent increase in record-breaking rainfall events is of course worrying,” Coumou concludes. “Yet since it is consistent with human-caused global warming, it can also be curbed if greenhouse gas emissions from fossil fuels are substantially reduced.”

Stefan Rahmstorf, Earth System Analysis research domain co-chair at the Potsdam Institute for Climate Impact Research (PIK) and Professor at the University of Potsdam, said: “Our Earth is once again being hit by extreme weather, including extreme heat with wildfires in California and devastating floods of rain in Japan. Based on the laws of physics, due to global warming we must expect more frequent and worse heat waves as well as extreme precipitation events.

“Weather data already show a significant worldwide increase in both types of events in recent decades. Climate researchers have warned about this for a long time. This trend can only be halted if the Paris Agreement for stabilising our climate is rapidly and fully implemented.”

The World Meteorological Organisation (WMO) has said that high impact weather, including extreme heat and disastrous precipitation, marked the early part of summer in the northern hemisphere.

Japan has suffered the worst flooding and landslide in decades, with many daily rainfall records broken. According to official government figures on Tuesday, July 10, 2018, more than 150 people have lost their lives and the casualty toll is expected to rise. Around 10,000 houses have been destroyed and/or inundated houses.

Between June 28 and July 8, there was extraordinary heavy rainfall caused by huge amount of water vapor provided by a stationary rainy front in addition to damp air remaining from Typhoon Prapiroon. West Japan and Hokkaido experienced record precipitation during the period, according to the Japan Meteorological Agency (JMA).

Total precipitation at many observation sites reached two-to four times mean monthly precipitation for July. For instance, 1,800 mm of rain fell in Shikoku, 1,200 mm in Tokai, 900 mm in North Kyushu, 600 mm in Kinki, and 500 mm in Chugoku. This triggered many landslides, inundations and flood events.

Japan is one of the world’s best prepared countries for disaster risk reduction and disaster management. JMA issued emergency warnings in advance targeting as many as 11 prefectures in the country to alert people to the significant likelihood of catastrophes.  The emergency warning system was launched by JMA in 2013, based on lessons from the major tsunami caused by the 2011 Great East Japan Earthquake. In addition, JMA dispatched its experts as the JMA Emergency Task Team or JETT, to local governments in the region to best support this multi-hazard disaster prevention activities. It set up a web portal dedicated to the heavy rain event.

Typhoon Maria

On July 10, Typhoon Maria is impacting the southern Japanese Ryukyu Islands. Northern Taiwan is bracing itself for winds of 175 km/h and gusts of 250 km/h (the equivalent of a category 3 hurricane on the Saffir Simpson scale).  China’s National Meteorological Centre issued red warning of typhoon in the morning. Typhoon Maria is expected to move towards west by north at the speed of 30 kilometres per hour, skim over northern Taiwan Island on the early morning of July 11, and make landfall in the coastal regions from Fuqing, Fujian to Cangnan, Zhejiang on the morning of July 11. After landing, it will continue to move towards northwest.

Extreme and unusual temperatures

On June 28, Quriyat, just south of Muscat, on the coast of Oman, recorded a 24-hour minimum temperature of 42.6°C, meaning that the coolest overnight temperature did not drop below. Although highest “low” temperature is not currently monitored as a category in the WMO Weather and Climate Extremes Archive, it is believed to be the highest such temperature ever recorded by a thermometer.

Ouargla, in Algeria’s Sahara Desert, reported a maximum temperature of 51. °C on July 5. It is likely that this is the highest reliable temperature ever recorded in Algeria. WMO’s Weather and Climate Extremes Archive currently lists Kebili, Tunisia, as being Africa’s highest temperature with 55°C recorded in July 1931. However, there have been questions about the reliability of colonial era temperature records in Africa.

The station of Furnace Creek in Death Valley national park in California, USA, recorded a temperature of 52.0°C on July 8. The station holds the record for the highest recorded temperature on Earth at 56.7°C (134°F), on July 10, 1913.

Other parts of California were also gripped by extreme heat. Downtown Los Angeles set a new monthly July minimum overnight record of 26.1°C on July 7. Chino, near Los Angeles, saw a record temperature of 48.9°C (120°F). Burbank Airport set a new absolute record of 45.6°C (114°F) on July 6, beating 45°C in 1971, and Van Nuys Airport saw a record temperature of 47.2°C (117°C), according to the US National Weather Service.

In Canada, a heatwave combined with high humidity in the province of Quebec contributed to dozens of deaths, especially among the vulnerable and elderly.

At the same time, parts of Eastern Canada saw a brief return of wintery weather, with snow in parts of Newfoundland and Cape Breton (Nova Scotia), and temperatures of -1C, in St John’s and Halifax. Winter weather this late in the year is rare, this being the first since 1996.

Western Siberian Hydromet Centre of Russia issued a storm warning due temperatures of more than 30°C for more than five days, expected to last between July 9 and 16. This creates high risks of wildfires as well as of power supply, transportation, and utility services disruptions and drowning of people escaping the heat in water.

Krasnoyarsk Region reports daily anomalies of 7°C above average, with fires already impacting about 80,000 hectares of forest.

Drought and heat in parts of Europe

In Europe, WMO’s Regional Climate Centre on Climate Monitoring, operated by the German Weather Service, DWD, issued a Climate Watch advisory with guidance on drought and above normal temperatures valid until July 23. The guidance product, used by National Meteorological Services to issue national warnings and forecasts, referred to a continuation of the drought situation and above-normal temperatures for northern Europe (from Ireland to the Baltic States and southern Scandinavia). The weekly temperature anomalies are forecasted with up to +3 – +6°C. The probability that precipitation will be below the lower tercile is more than 70%. This drought may be accompanied by water scarcity, local thunderstorms, risks of wildfires and harvest losses, it said.

For some parts of northern Europe, June was one of the driest, warmest on record.

After an unusually warm June, the heatwave in the United Kingdom continued into July. On July 10, the UK’s Met Office said that somewhere in the UK had topped 28°C or above for the 16th consecutive day.

June one of the warmest on record

Globally, June was the second warmest on record, according to the European Centre for Medium Range Weather Forecasts Copernicus Climate Change Service. The year to date is the hottest La Niña year on record.

Temperatures were exceptionally high over large parts of northern Siberia in June 2018.  They were also well above average over much of the USA, central Canada and North Africa, and over the Middle East and northern China.

The contiguous USA had 3rd hottest June on record. But many parts of the country had well above average minimum overnight temperatures.

Relationship with Climate Change

Episodes of extreme heat and precipitation are increasing because of climate change. Although it is not possible to attribute the individual extreme events of June and July to climate change, they are compatible with the general long-term trend due to rising concentrations of greenhouse gases.

Many recent studies have found that the probability of the extreme event has been influenced by human activity, either directly or indirectly. Of a set of 131 studies published between 2011 and 2016 in the Bulletin of the American Meteorological Society, 65% found that the event’s probability was significantly affected by anthropogenic activities.

It has been more difficult to identify anthropogenic influence in the attribution of precipitation extremes. Whilst some studies have found that the probability of some extreme precipitation events was increased, most often indirectly, by climate change, for many other studies the results have been inconclusive. This is because the underlying long-term climate signal in extreme precipitation is less clear than it is for temperature and, because extreme precipitation events typically occur on shorter spatial scales than extreme temperature events. At present, attribution studies are mostly carried out in research mode in peer-reviewed literature.

The full agenda for the Latin America and Caribbean Climate Week 2018 (LACCW2018) was released on Tuesday, July 10, 2018. It is being convened from August 20 to 23 in Montevideo, Uruguay.

The event – which lands three weeks ahead of both the Global Climate Action Summit in California and New York Climate Week – will be instrumental in demonstrating that there is genuine international support for stepping-up climate action by mobilising actors across the Latin America & Caribbean region.

UN Climate Change Executive Secretary, Patricia Espinosa, will participate in the event, alongside the High-Level Climate Champions, H.E. Minister Inia Seruiratu from Fiji and Mr. Tomasz Chruszczow, Special Envoy for Climate Change from Poland, as well as city and business leaders.

“Now more than ever we need action on climate change – here in the Latin America & Caribbean region and throughout the world. Let us then take advantage of this opportunity to make real and meaningful progress towards completing the rules of the Paris Agreement,” Espinosa said.

The theme of LACCW2018 is “Climate Action for Sustainable Development: Driving Change in Latin America and the Caribbean”. The high-level segment that takes place on Wednesday, August 22 will bring together the business community and focus on areas, such as: visions for NDC enhancement and implementation; challenges and opportunities for cities in the Latin America & Caribbean region; the role of transport for sustainable development and climate action; and climate finance.

Other highlights at the event include the Latin America Carbon Forum and a technical session on the cross-linkages between markets and the Sustainable Development Goals.

Owing to the political significance of the upcoming Talanoa Dialogue this year, LACCW2018 will host its very own “regional Talanoa” and explore strategies for accelerating global climate action, including by realigning finance flows in the Asia Pacific region consistent with a pathway towards low greenhouse gas emission and climate-resilient development for the implementation of the Paris Agreement.

LACCW2018 follows-on from the success of Africa Climate Week (ACW2018) hosted in Nairobi earlier this year and also the Asia Pacific Climate Week, which is currently underway in Singapore.

The goal of these Climate Weeks is to support the implementation of countries’ Nationally Determined Contributions (NDCs) under the Paris Agreement and climate action to deliver on the Sustainable Development Goals. In so doing, they will bring together diverse array of international stakeholders in the public and private sectors around the common goal of enhancing climate action.