Least Developed Countries (LDCs) are the poorest countries in the world. A number of criteria determine this status. As of May 2009, LDCs number 50. Roughly 65 per cent are in Africa; a number of others are known as Small Island Developing States (SIDS). Many SIDS are low-lying and located in parts of the world already prone to extreme weather events, factors that make them highly vulnerable to climate change impacts such as sea level rise and fiercer and more frequent tropical storms.