New weapon in the UAE’s war on dust

From left: Dr Imen Gherboudj, Luis Calisto and Dr Naseema Beegum watch real-time forecasts of dust movement on a system developed at Abu Dhabi’s Masdar Institute. Christopher Pike / The National

Masdar Institute scientists and researchers have developed a system to track the region's dust with forecasts that will become more accurate over time.

ABU DHABI // Anyone who keeps an eye on UAE weather forecasts will have heard or read warnings of dusty conditions.

It is no wonder that meteorologists include this information in their forecasts, because dust has widespread effects.

Aside from disruption to transport through flight delays and road accidents, solar panels can become less efficient because sunlight is blocked, people can suffer respiratory illnesses and agriculture is affected.

The ability to predict dust levels can be useful, giving time for the transport and energy sectors to plan, and allowing vulnerable people such as asthmatics room to take precautions.

At the Masdar Institute of Science and Technology in Abu Dhabi, scientists have developed such a system.

Available online, the system provides real-time forecasts into the following day on aerosol optical depth (AOD). This measures the extent to which airborne particles prevent sunlight from reaching the ground.

It is measured from zero upwards, with clearer air having a lower figure. A figure of 0.01 represents extremely clean air, while 0.4 represents quite hazy conditions when measured on a worldwide average.

To most of us aerosol means a spray can, but to scientists it represents extremely small particles suspended in the air.

They can include volcanic ash, sea salt, particles from factory pollution and – of particular relevance to the Arabian Gulf region – windblown dust.

Much of the dust blown over this country does not come from the UAE. It is mainly from the Empty Quarter, Iran and North Africa.

Taking that into account, the system, which can be viewed at atlas.masdar.ac.ae/forecast, covers most of the Arabian Peninsula and parts of Iran and north-west Africa.

As the forecast travels forward hour by hour, areas with significant AOD levels shift gradually on the map.

The work to produce the model took three years and was led by Dr Hosni Ghedira, a professor at Masdar Institute and director of the Research Centre for Renewable Energy Mapping and Assessment (Recrema).

The institute cooperated on the project with the King Abdullah City for Atomic and Renewable Energy in Saudi Arabia, with both keen to advance understanding of a variable that affects the solar energy industry.

The model uses an open-source air-quality prediction system called Chimere, which researchers use to generate forecasts and run simulations of levels of aerosols, ozone and other variables when they enter data.

Researchers say a dust storm in April forecast by Chimere proves its reliability.

Given how many factors affect the amount of particles in the air, it is easy to understand why the system took years to produce.

Dr Imen Gherboudj, a Masdar scientist who is part of Dr Ghedira’s team, explains that dust forecasts comprise of three key modules: dust emission, transport and deposition.

Of them, dust emission is the key variable, and it depends on a host of influences. Among them are meteorological factors such as wind speed, temperature and soil characteristics, including its texture, composition and moisture, and vegetation cover.

“Dust uplift into the atmosphere results from the interaction between moving airflows and soil particles on the ground, also called wind erosion,” says Dr Gherboudj, whose colleagues on the project are postdoctoral researcher Dr Naseema Beegum, research scientist Dr Naira Chaouch and Luis Calisto.

Depending on the diameter of the soil particles, this uplift occurs only when the wind speed exceeds a minimum value known as the “threshold friction velocity”.

Vegetation cuts the amount of wind that reaches the soil surface, thus inhibiting wind erosion. Higher surface roughness also reduces wind erosion, while higher moisture content does the same because it binds soil particles together.

“To put it simply, wind speed, degree of dryness of the soil and soil composition are the prime factors for producing dust,” says Dr Gherboudj.

Wind is important because it lifts dust particles from the surface and carries them through the air, but it is not the only factor.

Higher humidity is associated with more moist soil, so the amount of dust transported is reduced, whereas higher temperatures dry out the soil and increase the quantity picked up.

“The susceptibility to wind erosion varies with the soil composition,” says Dr Gherboudj. “If soil is claylike, it is likely to hold moisture and stick better and thus produce less dust.”

The nature of the factors that affect AOD helps to explain why its average figure tends to increase.

In a paper published last year in the journal Atmospheric Chemistry and Physics, scientists in Saudi Arabia, Germany and Cyprus analysed AOD figures for the Middle East since 2000.

They concluded that rising temperatures and lower relative humidity have made soils drier, leading to greater dust emissions and AOD increases.

"Consequently an AOD increase is expected due to climate change," says a paper titled Aerosol Optical Depth Trend Over the Middle East. Overall, between 2000 and last year, the paper names the Middle East and China as the world's two "hot spots" for AOD increases.

So, with AOD in the region tending to rise, it seems that having accurate forecasts will only become more important over time.

The model by the Masdar scientists is a work in progress, with the researchers looking to improve its performance at its geographical boundaries, such as the northern parts of Iran, Iraq and parts of North Africa that include Egypt and Sudan.

“We are planning to increase the spatial extent of the domain and [allow] finer spatial resolution,” said Dr Gherboudj.