Over the last two days, much of Spain has been coated with dust (灰尘) , and the skies have turned bright orange. A huge cloud of dust from the Sahara Desert is causing the strange weather. The dust cloud is expected to spread to other parts of Europe.

Across much of Spain on Tuesday morning, a thin layer (层) of red dust coated everything outside. From streets to sidewalks to balconies, everything was covered with a layer of dust. As the sun rose, the dust in the air turned the skies in some cities a strange orange. The cause of the dust and unusual sky colour wasn’t a forest fire, but dust from the Sahara Desert.

Every year, a large cloud of dust rises from the Sahara Desert. It’s called the Saharan Air Layer. Usually, it crosses the Atlantic Ocean as part of a natural cycle that helps develop farmland and beaches in Central and South America.

But sometimes, depending on the weather, the layer of dust gets forced to the north. Large sandstorms in northern Africa lift sand and dust into the air, where it gets blown towards Spain. Though the particles (微粒) in the air come from sand, they’re much more like dust than sand at a beach.

These kinds of storms aren’t unknown in Spain. In fact, it has a special name. It’s called a “calima”. This calima is so large that it can be seen from space. A NASA scientist who studies weather in the atmosphere says it’s like a river of dust in the air. That river of dust has met with a river of wet air driven by strong winds.

Spain’s weather service described the dust storm as being “very intense (强烈) ”. At one point on Tuesday, the air quality in Madrid was the worst in the world. Government health experts warned people not to go outside without a mask, and to keep their windows and doors closed at home.

Floodwaters may not look all that dangerous on TV, especially if you’re a skilled swimmer.【小题1】Because they can happen with little to no warning.

【小题2】 So sign up for local weather alerts (警报), and be sure to check local forecasts if the weather starts to look a little questionable. It also helps to know what places are most likely to flood in your area.

As soon as you receive word of a flash flood, immediately head for higher ground and stay put until help arrives. If you see floodwaters, follow the advice “turn around, don’t drown.”【小题3】Just six inches of moving water can trip you up and knock you over. Anything deeper than your ankles is bad news, especially at night when it’s much harder to see. As you make your way to higher ground, avoid touching or getting near any electrical equipment since you’re probably wet or standing in water. 【小题4】

If you get swept away by floodwaters, hold or climb onto something as soon as you are able. Once you’ve climbed onto something, shout loudly for help and wave an arm if possible. It’s hard for rescue teams to find people in the water, so anything you can do to make yourself more noticeable is a big help.【小题5】 Keep shouting and waving until you’re rescued.

The sky turned orange and the hospitals were in chaos. Thousands of Iraqis came to emergency rooms complaining that they could not breathe. Some had to be put on respirators. Schools closed and airports cancelled flights. Life came to a stop amid a cloud of dust.

Such scenes have occurred almost weekly in Iraq since April. In decades past, two or three big sandstorms were expected every year. This spring, Iraq has already recorded at least eight. Sandstorms have always been a fact of life in the Middle East, and are now growing more frequently and intensely.

Scientists say dust storms are complex and poorly understood, but their main causes are natural. In 2015, some people blamed a fierce summer storm in the Levant on Syria’s civil war thinking that military vehicles travelling through fields kicked up enough dust to blanket the region. Researchers at Princeton University later cited a more ordinary mix of unusual heat and strong winds as its reason, not gunners.

Still, people plainly contribute to the problem. Demand for water is making a dry region even drier. A World Bank study in 2019 found that human actions, such as over-exploiting rivers and lakes, produce a quarter of the Middle East’s dust. Iran has drained wetlands for farming. Turkish dams on the Tigris and Euphrates mean drier riverbeds downstream. All of this means more dust needs to be swept up by the wind. The decrease of the region’s forests because of fires and cutting down trees means there is less vegetation to hold it back. Syria, for example, has lost an estimated 25% of its woodland and since 2001, most of it to summer fires. Climate change will make the problem worse.

For those who work outside, sandstorms make life unbearable. Sandstorms bring tiny particles that travel deep into the lungs. The World Bank estimates that air pollution causes 30,000 premature deaths a year in the Middle East — and rising.

Economic costs will mount, too. Workers stay at home. Crops are buried under dust. The UN puts the direct economic cost in the Middle East at $13 bn a year, with indirect costs many times bigger.