The Heat Wave Phenomenon

If you saw the heat wave, would you wave back? - Stephen Wright

During this year we have seen some unprecedented high temperatures around the world. To some they come as a welcome chance to relax in a local park, while enjoying a refreshingly cool beverage or ice lolly. To others, they bring a host of unprecedented economic, social and health risks and challenges.

Countries around the world have experienced record breaking temperatures. For the first time, the UK exceeded 40C with a recorded temperature of 40.3C on the 19th July, exceeding the previous record by 1.6C. This was not just a one-off, a total of 46 weather stations across the country exceeded the previous UK record. In Nawabshah, Pakistan temperatures reached a sweltering 49.5C, likely the highest temperature on record for the Northern Hemisphere so far in 2022. Sichuan province in China has experienced the most severe heat wave ever recorded, the combination of low rainfall and high temperatures has caused rivers and reservoirs to run dry, and factories stop their operations due to lack of energy.

Causes of Heat Waves

Heat waves are caused by high atmospheric pressure at ground level, most common in summer months. When the atmospheric pressure increases over an area, it causes air to sink through the atmosphere, as it falls the air is compressed, and the temperature increases by 1C for every 100m it falls. On occasion a heat dome will form - this is where an area of high pressure remains over an area for an extended period, trapping the warm air underneath. As the ground heats, moisture is lost causing even greater temperatures. The heat dome will stay stationary until the weather patterns change.

In European latitudes, the jet stream normally steers areas of low pressure, however this flow can often be blocked when the jet stream weakens. The phenomenon of an Omega block can occur when two low pressure areas surround a high pressure area. The high pressure area causes the flow of weather fronts to either bypass the high pressure area, or simply just stop, creating extended periods of hotter than average temperatures. 

Cities are estimated to experience temperatures of 1 to 3C greater than countryside areas during the day time, and up to 12C greater in the evening. Natural surfaces such as grass have the effect of reflecting radiation back into the atmosphere, whereas surfaces such as concrete tend to absorb the solar radiation, releasing it during the evening periods.

Impacts

Economic impacts of heat waves are estimated to be caused by a number of factors, including the loss of working hours caused by temperatures that are simply too hot to work under, or because workers have to work at a slower pace. This is most acutely felt in agriculture and construction, as well as in developing countries, causing increased economic inequality. These short term weather effects create volatility in the price of food, increasing food insecurity. A World Bank report estimates that by 2050, approximately 600million Indians will be affected by short term heat increases. 

The impact in agriculture and the resultant food price can also prompt migration. As the competition for water and food increases, the population in the affected areas become unstable. A 2015 Columbia University study showed a link between drought induced by climate change and mass migration out of Syria from 2007 to 2010. It is also thought that when temperatures deviate from the optimal 20C, there is a higher likelihood of migration towards EU countries.

Although it is very difficult to quantify as the effect of social, economic and political factors also play an important part in the decision to migrate. 

Social divisions can also be exacerbated by the prohibitive cost of installing, maintaining and running air conditioning in poorer areas. In extreme temperatures, air conditioning can be seen as more than simply a luxury, but providing possibly life saving environments for those at risk.

The increase in air conditioning units in cities also has the effect of increasing the urban heat island effect, where the hot exhaust from the units add to the already increasing urban temperatures.

Short-term temperature rises also place stress on energy production, with increased power needed by air-conditioning, especially in cities. Heat waves are normally accompanied by lower wind speeds, reducing the energy produced by wind turbines. High temperatures also have an adverse effect on solar cells, increasing the need for them to be cooled to operate at their optimal temperatures. 

Heat waves can have an especially high impact on those with underlying health conditions, as well as the elderly and young children. According to the World Health Organisation, heat waves between 2000 and 2016 affected an additional 125 million people worldwide.

How Technology can Help

There have been many creative ideas to help cool down urban environments during times of extreme weather. 

For cities such as Stuttgart, that sits in a natural basin that has the added effect of trapping heat and smog, planners as far back as the 1930s have created natural ventilation corridors. These are green pathways that are carefully situated to catch the natural wind that blows through the valley, removing the smog and pollution from the city.

In Japan, the practice of uchimizu dates back to the Edo period. This involves sprinkling water droplets on pathways and in parks. The evaporation has the natural effect of lowering temperatures. In more recent times, uchimizu has become the regular event of sprinkling water by the public in communal areas, and has been used to highlight the effects of global warming. Cities around Japan have also installed mist machines that can reduce temperatures in certain areas such as Tokyo station by several degrees.

America is not without its own innovations. Chicago is famous for having over 1,900 miles of narrow alleys, used as service streets. The city is in the process of replacing the traditional black, heat-absorbing tar with a special reflective, and water permeable concrete. This not only has the effect of reducing city temperatures, but also the water run-off experienced during heavy rainfall. Louisville is in the process of planting 450,000 new trees that not only create a pleasant atmosphere, also have the effect of reducing temperatures and giving the population natural shade.

The newly planned city of Masdar City in Abu Dhabi faces more challenges than most urban areas. Situated in a desert, it has become a testing base for new, environmentally friendly cooling techniques.  These include angling the roofs to reflect the heat away from the city, optimizing the distance between buildings, and building an almost 50m high wind tower in the University campus. This structure funnels the cooler air from its top through to the city streets, creating a constant cool breeze in the desert city.

Architects are also adopting some ancient techniques to keep buildings naturally  cool without the need for energy-hungry air conditioning units. The traditional Indian and Islamic use of elaborate lattice screens, known as jali, reduce sunlight in a space, though allow a cooling breeze to flow. 

Understanding the Weather

Having a nuanced understanding of when heat waves will occur, their intensity and how long they will last gives valuable advanced warning to both individuals and organizations to prepare, create plans, and order in those ice lollies! 

OpenWeather supplies a number of products that can be used for both short and long term forecasting, including our Climate Forecast for 30 days - an API that allows you to request daily weather forecast information for the next 30 days.  

The OpenWeather Global Weather Alerts can be a valuable tool in providing a warning of impending extreme weather conditions, including high temperatures and heat waves. The product collates weather alerts distributed by government agencies around the world, and presents this information in a uniform and useful way. 

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