Drought is one weather extreme which is not due to too much of something, but because there is too little rain. A drought can be defined as a continuous and long period in which rainfall is significantly below the average expected for a region at that time of year. In the UK a drought is when there is no more than 0.25mm (0.01in) of rain each day, for 15 days in a row. Minor droughts may happen during dry, hot summers and not last for very long. However, in some parts of the world droughts can last months, years and even decades.
Around the world, the impact of drought is usually seen by a series of pictures. Drooping, shrivelled crops, dry river channels, reservoirs and starvation amongst people are all possible impacts of drought. Under long drought conditions most vegetation is unable to survive, and the roots cannot help stop the erosion of soil. The soil and dirt can be blown into the air by winds to create dust storms. These can turn the sky very dark, block out the sun and can be called black blizzards.