Deserts are defined as areas that receive extremely low amounts of precipitation, less than 250 millimeters per year. Deserts make up about 20% of the Earth's land surface and are characterized by sparse vegetation and large daily temperature fluctuations. Many deserts form in rain shadows on the lee side of mountains that block incoming precipitation. Desert landscapes typically feature sand dunes, rocky surfaces with little soil development, and salt-covered flats in low-lying areas, and are shaped by eolian or wind-related erosion processes. Polar deserts, though receiving snow rather than rain, have similar arid features.

1. DESERT

2.  A desert is a landscape or region that receives
an extremely low amount of precipitation, less
than enough to support growth of most plants.
Deserts are defined as areas with an average
annual precipitation of less than 250 millimetres
(10 in) per year, or as areas where more water
is lost by evapotranspiration than falls as
precipitation. In the Köppen climate
classification system, deserts are classed as
BWh (hot desert) or BWk (temperate desert). In
the Thornthwaite climate classification system,
deserts would be classified as arid megathermal
climates

3. GEOGRAPHY
 Deserts are part of a wide classification of regions that, on an average
annual basis, have a moisture deficit (i.e. they can potentially lose more
than is received). Deserts are located where vegetation cover is sparse
to almost nonexistent. Deserts take up about one fifth (20%) of the
Earth's land surface. Hot deserts usually have a large diurnal and
seasonal temperature range, with high daytime temperatures, and low
nighttime temperatures (due to extremely low humidity). In hot deserts
the temperature in the daytime can reach 45 °C/113 °F or higher in the
summer, and dip to 0 °C/32 °F or lower at nighttime in the winter. Water
vapor in the atmosphere acts to trap long wave infrared radiation from
the ground, and dry desert air is incapable of blocking sunlight during
the day (due to absence of clouds) or trapping heat during the night.
Thus, during daylight most of the sun's heat reaches the ground, and as
soon as the sun sets the desert cools quickly by radiating its heat into
space. Urban areas in deserts lack large (more than 14 °C/25 °F) daily
temperature variations, partially due to the urban heat island effect

4.  Many deserts are formed by rain shadows; mountains blocking the
path of precipitation to the desert (on the lee side of the mountain).
Deserts are often composed of sand and rocky surfaces. Sand
dunes called ergs and stony surfaces called hamada surfaces
compose a minority of desert surfaces. Exposures of rocky terrain
are typical, and reflect minimal soil development and sparseness of
vegetation. The soil is rocky because of the low chemical
weathering, and the relative absence of a humus fraction.
 Bottomlands may be salt-covered flats. Eolian processes are major
factors in shaping desert landscapes. Polar deserts (also seen as
"cold deserts") have similar features, except the main form of
precipitation is snow rather than rain. Antarctica is the world's largest
cold desert (composed of about 98% thick continental ice sheet and
2% barren rock). Some of the barren rock is to be found in the so-
called Dry Valleys of Antarctica that almost never get snow, which
can have ice-encrusted saline lakes that suggest evaporation far
greater than the rare snowfall due to the strong katabatic winds that
evaporate even ice

5. SUBMITTED TO
SANJAY SIR