Title: Desert | The Canadian Encyclopedia
Headings: Desert
Desert
Desert
Why Deserts Are So Dry
Temperature
Landforms
Influence of Climate
Canadian Examples

Content: At the centre of the basin an ephemeral water body (playa) may be present which occasionally receives runoff carrying fine silts and clays. Rarely, a playa lake may form rapidly following intense rain storms but lasting only a few days or weeks. In the more extensive deserts, low-lying areas may sustain a generally shallow, more or less permanent saline lake. Relatively small portions of desert regions (20% or less) are occupied by sand dunes, which may be transverse, barchane, elongate (also called longitudinal or seif), star or dome shaped ( see AEOLIAN LANDFORMS) depending on the local aeolian environmental parameters. Influence of Climate
The geological record from Earth's desert regions indicates that climate has not always been as rigorous as it is today. Most desert regions have undergone cyclic climatic changes ranging from humid and sub-humid to semi-arid, arid and even hyperarid. During the Quaternary Ice Age, global climate cooling reduced evaporation rates, which, coupled with higher amounts of precipitation, resulted in excess water accumulation, flooding many of the enclosed drainage basins. Present-day climate fluctuations are such that desertlike conditions are expanding in most places in the world. If GLOBAL WARMING continues then deserts will invade the less arid marginal regions, which would have catastrophic consequences for any life forms there. Desertification is a term that describes humans' contribution to the formation or expansion of desert regions through careless destruction of the fragile physical and biological environments and by the thoughtless exploitation of natural resources, principally groundwater.