Where rainfall is less than 40 inches, the forests gradually open into scrubland.
Farther east, where rainfall is higher, the Corn Belt of Illinois and Iowa also is centred on mollisols.
Durisols are found in the southwestern United States, Chile, South Africa, and especially Australia, where rainfall is low.
Even in the southwest, where rainfall is heaviest, the water supply is not constant enough for the generation of power.
Irrigation is not practiced in England, where rainfall during the growing season is usually sufficient to raise the plants.
Deserts cover about one fifth of the Earth's surface and occur where rainfall is less than 50 cm/year.
There was a sharp gradient between high rainfall totals in western Scotland and Snowdonia, where rainfall was above average, and dry conditions across parts of southern England.
A programme to rehabilitate small tank systems in the south Indian state of Tamil Nadu, where rainfall is low and is erratic, is a good example.
Argan trees also play a crucial role in the battle against desertification in this arid region where rainfall has become more erratic due to climate change.
A warm coastal desert extends from northeastern Colombia to Venezuela, covering a zone where rainfall is scarce and droughts are prolonged.
In Cumbria, where rainfall has smashed records, residents were bracing for more rain as Met Office experts said the weather band would continue to move northwards.
