ABSTRACT
The term drylands is one which is easy to understand in a general sense, but is difficult to define in precise terms. The same is also true for concepts such as aridity and drought. With all of these terms it is water shortage which is the critical variable, though other factors are also important. In this study the term ‘drylands’ will be used to distinguish all those areas which experience regular water shortage on a seasonal or longer-term basis. This obviously includes all the arid lands of the world, defined by their extremely low precipitation totals, but will also encompass regions which may record significant rainfall for at least part of the year. In this context, the term ‘drylands’ involves a much broader interpretation than is the case with the more commonly used term, ‘arid lands’.
