Climate Over Time
The Climate Today
Abu Dhabi's climate behaviour is largely the result of variations in surface pressure and the movement of air, both vertically and horizontally. In general, annual air circulation over the UAE can be grouped into two main periods, winter and summer. Volatile atmospheric conditions characterise the two transitional periods, autumn and spring, that separate the two main seasons.
Nocturnal Inversion Layer
At night, as the Earth's surface cools, the air next to it also cools. This cool moist air (sometimes laden with dust) becomes trapped beneath a layer of warmer air overhead, resulting in fog in the early morning, when maximum cooling takes place. This surface inversion will start to break down soon after sunrise, allowing the fog to dissipate.
The highest rainfall occurs during the winter, the result of cyclonic cloud bands that pass over the UAE driven by the westerly troughs. The average rainfall in Abu Dhabi is less than 100 mm annually, although this varies across the Emirate geographically and from year to year; e.g. one day's precipitation could exceed the total rainfall of two or three years.
Palaeoclimate and Climate Change
The Gulf region has experienced climatic changes throughout both geological and human history. The overall trend or cycle of climatic change basically comprises warmer and wetter interglacial periods alternating with much cooler and drier glacial episodes, often spanning many thousands of years. Historical evidence indicates conclusively that such environmental transitions are sometimes quite rapid and sudden.
Little Ice Age
Two hundred years ago, the last climate disruption occurred, known as the ‘Little Ice Age' and, although there have been warmer periods prior to this disruption, the world has since been experiencing a persistent and accelerating warming phase.
Temperature and CO2
During the past 400,000 years, studies show that global temperatures have risen when CO2 levels increase. Sudden increases in global CO2 concentrations, coinciding with the Industrial Revolution, have led scientists to believe with greater than 90% probability that most of the global warming witnessed in the last 50 years is the result of human activities.
The Emirate's landscape holds evidence of climatic changes including ancient pluvial (wet) episodes. These resulted in the formation of lakes and deposition of lacustrine (lake) sediments, alluvial fans and gravels, palaeosols (fossil), soils and speleothems (cave formations) created by secondary mineral deposits, typically in limestone. There are also many indicators of extreme dry periods that resulted in the development of extensive dune and sand seas such as the Rub' al-Khali, or ‘Empty Quarter', which extends into the UAE south of the Liwa Oasis. The climate cycle, especially rainfall, is partly affected by the intensity of the south-west Indian Ocean monsoon system.
Abu Dhabi Responds
Abu Dhabi has taken several steps to reduce greenhouse gas (GHG) emissions and is working to enhance its understanding and to respond to its own vulnerability to climate change. These include:
- The MASDAR initiative, which targets clean energy technology investments
- The Estidama programme, which aims to ensure green building design
- The Ecological Footprint initi-ative, which seeks to measure and better understand the country's GHG emissions
- The Renewable Portfolio Standard, which commits Abu Dhabi to deploying renewable energy equi-valent to 7% of Abu Dhabi's electric generation capacity by 2020
- Vision 2030, an urban planning strategy that emphasises sustainable transport and land use planning
- The greater use of Compressed Natural Gas (CNG) in municipal vehicle fleets
- Takreer, which aims to produce Sulphur-Free Gas Oil (SFGO) to decrease diesel emissions and is expected to be completed in 2010
The Air Masses Affecting the UAE
Modified Maritime Polar
From cold ocean currents or high latitude ocean water, this air mass is known for producing drizzle, cloudy weather and long-lasting, light rain.
Coming from the desert of South-West Sudan, this air mass builds moisture over the Red Sea and can lead to thunderstorms over the Arabian Peninsula.
Air masses in the highlands, such as the UAE's Hajar Mountains, can lead to thunderous conditions, especially in the summer.
The result of warm waters from the Arabian Sea and flowing from south-east of the UAE, this air mass is responsible for the majority of thunderstorms in the UAE.
Characterised by low dew points, cold temperatures and high stability, this air mass is mostly blocked by the Zagros Mountains before reaching the UAE.
Characterised as being colder than polar air masses, this mass spreads cold air to the southern UAE and leads to a significant drop in temperature.
Summer (June to September)
The Emirate's surface air temperature may exceed 50°C in some areas, especially the southern regions. This intense daytime heating causes a thermal low over the Arabian Peninsula, which usually causes a hot, dry south-easterly wind.
Furthermore, the Indian Monsoon Low provides the region with hot, humid air masses coming from the south-east. The eastern mountains often catch these air masses, causing a dynamic uplift and convective cloud formation. In fact, the huge amount of moisture driven by the monsoon is responsible for most of the precipitation that falls over the eastern area of the UAE, which is very high in the summer compared to other parts of the country.
Autumn (October to November)
As the sun appears to move towards the south, the surface air temperature gradually decreases and weakens the thermal lows as they move away from the region. The Siberian High Pressure System moves towards its winter position, which can lead to high winds during the autumn.
Throughout the autumn, a cool area (an area located between two lows and two highs opposite each other) affects the region. When the water temperature of the Arabian Gulf reaches its highest point, atmospheric moisture increases and causes frequent fogs throughout the UAE.
Winter (December to March)
The Siberian High Pressure System is dominant in the winter season, its effect diminishing towards the end of the season. The system causes north-westerly shamal swinds, leading to noticeable temperature fluctuations and rough seas. The system, combined with westerly upper ridge winds and clear nights, can cause heavy fog late at night or in the early morning.
Clear skies can also lead to rapid night-time cooling. In fact, it may reach zero Celsius, or slightly below, on high mountains and in some interior regions.
Spring (April to May)
As the sun appears to move towards the north, the temperature begins to rise. The Siberian High Pressure System moves northward, leaving the UAE's weather at the whims of various other synoptic pressure systems. Most notably, the extension of a tropical cyclone from the Indian Ocean to the Arabian Sea usually results in rain and thunderstorms. Fog is also quite common during the spring.
Inter-tropical Convergence Zone (ITCZ)
The shifting of the ITCZ significantly affects air circulation patterns in the UAE and, therefore, its climate conditions. During the UAE's summer, the Earth's northern hemisphere faces the sun, while the southern hemisphere faces the sun during the country's winter. As the transition between hemispheres takes place, its surface heating patterns shift along with it; due to this effect, major pressure systems, wind belts and the ITCZ follow the same route as the sun from hemisphere to hemisphere. The ITCZ leads to intense thunderstorm rains wherever it goes. Additionally, continental distribution affects heating patterns and, thus, the location of the ITCZ.