A big sandstorm hit northern China several months ago. It covered many cities with thick clouds of yellow dust (尘土).

The storm, which came from Mongolia, was the largest sandstorm in China in the past 10 years. Many flights and classes were canceled (取消) because the visibility (能见度) was lower than 500 meters.

The storm was the result of warm and dry weather in the area, together with the strong winds from Mongolia. “There has been little rainfall so far this spring and the temperature is rising. So now it is a worrying time for sandstorms,” said an expert from Beijing.

In recent years, sandstorms haven’t been as common in northern China as before. The land with desertification (沙漠化) has been falling by 7, 585 km per year in China, and the area of sandy land has been decreasing by 1, 284 km a year. This is thanks to China’s Three-North Shelter Forest Program (TNSFP, 三北防护林工程) which started in the 1970s. Millions of trees have been planted in northern China to prevent sandstorms and protect the environment.

Besides, China has a color-graded weather warning system (预警系统) for sandstorms, with red meaning the most serious, followed by orange and yellow. Therefore, people would have time to get prepared for the sandstorm.

At 5:13 on the morning of April 18th 1906, the city of San Francisco was shaken by a terrible earthquake. A great part of the city was destroyed and a large number of buildings were burnt. The number of people who lost homes reached as many as 250, 000. About 700 people died in the earthquake and the fires.

Another earthquake shook San Francisco on October 17th, 1989. It was America’s second strongest earthquake and about 100 people were killed. It happened in the evening as people were travelling home. A wide and busy road which was built like a bridge over another road fell onto the one below. Many people were killed in their cars, but a few lucky ones were not hurt.

Luckily the 1989 earthquake did not happen in the centre of town but about 50 kilometres away. In one part of the town a great many buildings were destroyed. These buildings were over 50 years old, so they were not strong enough. There were a lot of fires all over the city. The electricity was cut off for several days too.

Why do earthquakes happen? Scientists explain that the outside of the earth is made of a number of different plates. At San Francisco the Pacific plate which is moving towards the northwest meets the North American plate. The Pacific plate is moving very slowly—at 5.3 centimetres a year. Sometimes these two plates stop and do not move for years. Then suddenly, they jump and an earthquake is felt. As a result of the movement of these plates, west America near the sea has always been a bad place for earthquakes. When the 1906 earthquake happened, the Pacific plate jumped 5-6 metres to the north.

Scientists are afraid that one day an even bigger earthquake will hit the area around San Francisco. They call it “The Big One”. However, people today are still building more houses. The population in and around San Francisco is now ten times more than it was in 1906. This means that if there is another big earthquake, a great many houses and buildings will be destroyed.

A heatwave has hit many countries in Europe, pushing temperatures over 40℃. A heatwave is along period of unusually hot weather. The heat is expected to continue until the end of July.

The Italian Island of Sardinia reached 46℃ on 18 July. The Italy government has asked people to dress in linen (a thin, light material) and to stay indoors between 10 am and 6 pm. The government has asked people to drink plenty of water but avoid alcohol, fizzy drinks and coffee, which can make you feel thirstier. In Rome, the country’s capital, people aged over 70 can go to swimming pools for free to help them keep cool.

Wildfires have broken out in many places. In Greece, which recorded 41℃ on 18 July, fires near the capital, Athens, have destroyed huge areas of forest and thousands of people have been moved to safety. Heatwaves can make fires worse because hot weather dries plants, which fuel the fires.

In the US, temperatures in Death Valley, California, hit 53’℃ on 18 July, close to the hottest ever recorded on Earth. On 16 July, the US National Weather Service issued warnings in parts of the country, affecting more than 80 million people.

Despite the high temperatures in many European countries, the UK is not experiencing a heatwave. This is because a different weather pattern has brought rain and lower temperatures to the UK.

The heatwave in Europe is being caused by a weather pattern that has stopped the air from moving very much. That means the hot, dry weather has got stuck and temperatures have kept rising. Earth is also experiencing a natural climate pattern called El Nino (厄尔尼诺), which causes the water in the eastern Pacific Ocean to warm up more than usual. This can lead to hot weather around the world. Temperatures in some parts of Europe were expected to fall on 20 July.