Surprise pattern in Masdar’s rain model

Besides its predicting ability, the study, which was recently published in the Journal of Hydrology, is the first time that scientists have investigated how climate variability, a natural phenomenon different from human-induced climate change, is affecting the UAE.

Although records seem to show rain in the UAE to be decreasing, Masdar Institute scientists say that it is actually increasing. Fatima Al Marzooqi / The National
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ABU DHABI // Masdar Institute scientists have developed a model to predict the amount of rainfall for a given year.

Their study, published in the Journal of Hydrology, is the first time scientists have investigated how climate variability – a natural phenomenon different to human-induced climate change – is affecting the UAE.

“You have years with more rain than others, you have years that are hotter than others, and that variability we have to model and understand its causes,” said Prof Taha Ouarda, who led the research.

UAE records, which have only been kept since 1975, show that overall, rainfall appears to be decreasing, which many scientists attributed to human-induced climate change.

But when more advanced methods were applied to data from four weather stations in Abu Dhabi, Dubai, Sharjah and Ras Al Khaimah, a different picture emerged.

“A lot of people were looking at the signal in rainfall, the fact that it is decreasing and thinking it is climate change – that rain is decreasing in this part of the world,” said Prof Ouarda.

The team looked at three variables – events bringing maximum amounts of rain, the total amount of rain in a year, and the number of rainy days – with the data collected from 1975 or 1980 to the present day.

“Although statistically the whole sequence is decreasing, when we look in detail we see that, actually, there is a first period that seems to be increasing [in rainfall], then there is a sharp drop, then there is a second period that seems to be increasing,” said Prof Ouarda, who is also the head of iWater, a research centre within Masdar.

The year when all three variables registered a drop was 1999.

“Overall, the characteristics are going down but if you decompose it into two, we see that there is an increase, then a sharp decrease and an increase again, and we see this in every single variable,” said Prof Ouarda.

“The key point here is that rainfall in the UAE is actually increasing, if it were not for that sharp drop that we observed in 1999, and we tried to understand what that sharp drop is caused by.”

The team analysed data about climate oscillations. They are repetitive, natural variations in the Earth’s ocean and atmosphere that affect ocean currents, carrying warm or cool water across vast distances, thus affecting global weather.

“What we have demonstrated in the past is that the climate of the Earth is modulated by currents, which when strong affect climate in one way, and when they are not strong affect it in another way,” Prof Ouarda said.

The drop in rainfall in the UAE in 1999 corresponded to recorded changes in six climate oscillations.

“There are a number of oscillation indices that seem to influence our climate and all these indices went through change in 1999,” he said. “And that is what explains this change in the characteristics of rainfall that occurred in 1999 when we had increasing rain, then a sharp decrease and then we started observing an increase again.”

Prof Ouarda said this proved that the UAE rainfall trends investigated by the team were associated with natural variations in climate rather than permanent, man-made climate change.

The research also allows scientists to predict what kind of weather the UAE can expect.

“We can predict how much rain we are going to be getting in a given year in the UAE, in advance, the year before, just based on the state of these indices,” Prof Ouarda said.

“There are scientific impacts because we are understanding climate, but there are also practical, economic and engineering impacts because this kind of information is very important for the management of engineering systems.”

Prof Ouarda is involved in research into whether the Abu Dhabi’s urban drainage systems has enough capacity to remove water during times of peak rain.

He is also directing an effort to model wind speeds throughout the year, which could better inform decisions to invest in wind power, as well as public health concerns related to dust in the air.

vtodorova@thenational.ae