Weather watching

Posted: 11 April 2011 | Doug Johnson, Head of Transport at the UK Met Office | No comments yet

The coldest December in 100 years brought into sharp focus the impact that weather can have on the UK’s airports. Across Europe and North America heavy snowfalls and ice brought airports more used to severe winter weather to a standstill. But in a warming world, changing weather patterns are potentially a further complication for the world’s airports.

It is said that we have a fascination with the weather, from what is happening outside now to what conditions are likely to be weeks ahead. For airport and airline operators disruption due to weather, especially in winter, can put strain on schedules through misplaced aircraft, passengers and staff.

The coldest December in 100 years brought into sharp focus the impact that weather can have on the UK’s airports. Across Europe and North America heavy snowfalls and ice brought airports more used to severe winter weather to a standstill. But in a warming world, changing weather patterns are potentially a further complication for the world’s airports. It is said that we have a fascination with the weather, from what is happening outside now to what conditions are likely to be weeks ahead. For airport and airline operators disruption due to weather, especially in winter, can put strain on schedules through misplaced aircraft, passengers and staff.
The weather can, of course, affect operations all year round with fog, thunderstorms and strong winds all having the potential to cause disruption, both on the ground and in the air. But its impact is always at its greatest during the winter months.

Winter weather impacts

 Across the UK, December 2010 rewrote the record books with some exceptionally cold and snowy weather and temperatures regularly falling to between -10 and -20 °C at night. It turned out to be the coldest December across the UK since 1910 and the coldest month since February 1986. The number of days with air frost was the highest for December for over 50 years. All this presented challenging conditions to the airline industry for the second winter running. Snow and ice are the most obvious disruptive weather factors for operators to consider, which means the accurate forecasting of the timing of rain or snow and any drop in temperature are critical to ensure that clearing and de-icing teams and equipment are in place when the worst of the weather arrives. The UK Met Office has been forecasting the weather for over 150 years. We are one of just two World Area Forecast Centres (WAFC) and the only provider of low-level UK weather forecasts for the UK Civil Aviation Authority. Over the last couple of years we have worked closely with some of the UK’s leading airports and airlines to help understand the challenges they face and tailor our specialist winter weather services such as OpenRunway and Aircraft De-icing to their needs.

Met Office forecasters helped to keep the majority of the country’s airports and some of the main airlines running through the worst of this winters weather. Round the clock, our aviation forecasters monitored the developing weather situations and used the guidance from one of the worlds best weather forecasting computer models to provide critical forecasts to operators. These forecasts helped them make confident weather-sensitive decisions to plan ahead and reduce disruption by activating plans to mitigate against the worst effects of the weather. However, even the best forecasts cannot prevent some disruption, especially when temperatures remain below freezing for days on end. Snow and ice are not the only weather factors that can disrupt operations. It was only a few years ago that fog severely disrupted flights at Heathrow and other UK airports in the run up to Christmas. Hundreds of domestic and some international flights were grounded, with services out of Heathrow seeing a reduction of 40% on one day because the visibility was too poor for ground movements, take off and landing to continue safely. As part of our regulated service provision on behalf of the Civil Aviation Authority, Met Office forecasters provided regular updates on forecast changes to visibility at airports around the country, giving National Air Traffic Control at Heathrow as much notice as possible of improving conditions so they could get services back to normal as soon as possible.

Expert help all year round

Another issue faced by many airfields and aircraft are cross winds on the descent into an airport, these can make landing conditions difficult. The Met Office provides accurate forecasts of wind speed and direction to airline and air traffic control agencies through TAFs, warnings and specific hourly updates for each runway at an airport, to ensure the safety of aircraft and passengers. We also provide this advice for many airports around the world, particularly in locations where the local terrain and wind flows can cause particular problems, such as at Innsbruck and Funchal, Maderia. Thunderstorms can occur at any time of the year in the UK, but typically our period of the highest frequency of thunderstorm activity is the summer months, when large Cumulonimbus clouds can be seen to dominate the skyline. These pose a real threat to aircraft both on the ground and in the air. En-route icing and turbulence are significant risks to aircraft, but the risks are particularly high when on take off or landing from an airport; the rapid changes in wind speed and direction can have a dramatic impact on the air-speed and lift of an aircraft, resulting in a potentially catastrophic situation. On the ground, thunderstorms pose a threat to refuelling. The UK Met Office provides forecast advice of thunderstorm activity, including ICAO Annex 3 compliant warnings and specific tailored advice to airlines, airports and air traffic services. Using detailed satellite and high resolution model data, we have developed increasingly advanced ways of forecasting the extent and timing of thunderstorms, which are sometimes a phenomena which affect a relatively small area and for a limited period of time. As one of only two World Area Forecast Centres (WAFC) the UK Met Office (together with WAFC Washington) have, since 1984, provided international forecasting services to meet Annex 3 to the ICAO Convention on Civil Aviation. This means providing twice daily global forecasts of upper winds and temperatures for all flights around the world, and significant weather charts every six hours for 25,000 feet and above. This specialised information enables operators to optimise safety and fuel consumption for their aircraft, with a strong tail wind across the Atlantic often resulting in a time saving of an hour or more on a flight from North America to Europe.

The climate is changing

 When it comes to the changing climate, the debate up to now from aviation’s perspective has very much been about the industry’s impact on the environment. The industry has long been at the forefront of recognising and understanding the impact its operations have on the climate, and the resulting importance of mitigation measures. However, there is a real and, in some areas urgent need for the industry to formulate adaptation measures, to deal with the impacts climate change could have on aviation worldwide. Rachel McCarthy, climate impacts scientist at the Met Office, explains: “We all know that it’s essential to stay abreast of changes in the weather to keep airports and flights running smoothly. Indeed, planning for future challenges is how the industry stays one step ahead. However, we are no longer thinking just about tomorrow. We are now looking at the long-term impact of climate change and the potential effects of this on the kind of weather that affects airport operations.” One effect of climate change is the potential impact on tourism. As temperatures in Europe change and popular holiday destinations in the Mediterranean grow ever hotter, the aviation industry could see shifts in demand across the seasons or to different types of holiday. If these places become just too hot in summer, we may see tourists considering other options from the traditional beach holiday. The aviation and tourism industries may need to respond to changes in the holiday market. McCarthy continues: “Whether it’s studying rising temperatures in today’s holiday hot spots, or even studying rising sea levels near coastal airports, it is wise to be prepared for changing weather patterns.” In Europe, the UK Met Office has been working together with Omega and Eurocontrol to help the industry plan for an everchanging future. In 2008, Eurocontrol commissioned the Met Office and the aviation sustainability partnership, Omega, to study how weather conditions could change in the long-term and, crucially, how these need to be taken into account in strategic planning by the aviation industry. The end result was a review of climate impacts on aviation operations in Europe — from shifts in snowfall to potential changes in severe convection.

Wide-ranging impacts

 The study suggested that increasing global temperatures throughout the 21st century could result in a number of challenges for airports. The distribution of snow and frost across Europe is expected to change. While in the longterm average conditions are expected to be generally milder, this does not mean that cold winters or severe cold snaps will never happen. Some airports may experience more marginal conditions and consequently more disruption caused by snow and ice when it does occur, much as we see in the UK now. Decisions on maintaining snow-clearing equipment will need to take a careful risk-assessment approach. As the atmosphere warms up it has the potential to hold more water. This, and an increase in surface temperatures, is projected to result in increased convective activity at some times of the year, and there could be more days per year when flight paths need to account for this. Drought could prove an increasing stress in the Mediterranean. If reduced rainfall and higher temperatures cause water shortages or rationing, airport operators would need to keep a close eye on their water supplies, and plan their water supplies in order to meet the demands of their operations. Conversely, it is possible that we could increases in heavy rainfall events which may lead to an increase in the number of flash floods affecting airport operations and possibly even energy supply. However, it is not only flooding from rainfall that may be an issue.

Rising seas

Globally the sea level has risen throughout the 20th century, and is confidently expected to continue rising. Importantly, the study highlighted almost 40 major international airports at potential risk from projected sea level rise, due to their positions on coasts, artificial or reclaimed land stretching out to sea, or on floodplains. This number is thought to be an underestimate of those at risk as many smaller, but logistically or regionally important airports, are situated in similar locations and are likely to have fewer resources and strategies in place to deal with sea level rise. Due to the time taken for global temperatures to fully respond to greenhouse emissions, and the further time taken for glaciers, ice sheets and ocean waters to react fully to warming, sea levels will continue to rise to some extent even if emissions are cut back. This makes it imperative that airports and airport planners adapt to, and mitigate, rising water levels.

Planning for the future

To help airports prepare, the Met Office is developing tools to translate climate projections into information useful for planning. One such tool uses a series of climate model runs, alongside information on vertical land movement and digital terrain data from NASA to show the hazard posed by potential sea level rise for any airport of interest in the world. As part of the sustainable development work commissioned by Eurocontrol, an early version of this tool was used to further define the potential sea level rise hazard faced by three of the 40 major international airports in Europe readily identified as being at significant risk level. Two of these are privately owned and listed on international stock markets and the other is currently state-owned and operated. A team of researchers visited each airport and discussed existing adaptation measures with representatives of the airport authority. In all three cases the results identified not only the need for substantial preventative measures by the end of the century, but that it is also possible that impacts of sea level rise may be felt much earlier than that. With progressive sea level rise, the potential for significant coastal flooding around Europe by the middle of the century shows the need for action to be considered within more immediate planning horizons. The study shows that there is a clear need for all coastal airports to assess the potential hazard that sea level rise could pose to their operations and consider appropriate adaptation strategies to ensure future operational capacity. The aviation industry is benefiting from expert, impartial advice and in-depth understanding of the science behind weather and climate from Met Office scientists. It’s this understanding that really helps the aviation industry explore what to expect from weather conditions now and in the future — and how best to face them.

About the Author

Doug Johnson is Head of Transport for the Met Office. For more information about the range of services provided by the Met Office please contact [email protected] The Met Office is acknowledged as a global leader in Aviation Meteorology, one of only two WAFC centres and the sole provider of low level aviation meteorology in the UK. It also has the internationally renowned Met Office Hadley Centre, which researches and advises on climate change.

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