== How they occur == 

   This section contains no references and some of the ideas seem contradictory or suspicious. For example, the lack of high level clouds and low humidity in deserts can hardly constitute a cause of heat waves in such regions. Also, in the South-western Cape of South Africa, where I stay, heat waves are usually associated with low (not high) pressure systems, responsible for off-shore flow, a mechanism I suspect may also at work during heat wave episodes along the eastern and southern coasts of Australia.