Sandstorms are one of the hazards that occur during droughts

Where it occurs: All over the world, to varying degrees

Occurences per year: Variable

Casualties: In the mid-1980s, around 1m people died in Ethiopia due to drought-induced famine

The basic cause of drought is an insufficient amount of rainfall over a prolonged period of time. Lack of rain can be caused by global patterns of air circulation or through man-made intervention. Dams and irrigation systems can disturb the natural flow of rivers and lakes which means insufficient water vapour rises into the air to form rain clouds. Other factors that contribute to drought are high temperatures, low humidity and high winds.

During a drought, vegetation will die and crops will fail, affecting the surrounding animal and human populations. Even when the rain does finally come, the soil may already have been damaged by excess mineral salts or starved of nutrients, so crops can still fail. Soil erosion can also lead to long-term problems and it is important that areas prone to drought have good irrigation systems. Severe droughts can cause widespread famine which can lead to the deaths of thousands, even millions, of people. Other hazards which occur in times of drought include sandstorms and bushfires.