why is humidity low, skies clear and rainfall scanty in the sahara desert
Answers
Answer:
because there are not enough trees so that it could support a good amount of transpiration
Deserts cover 20 percent of the earth's surface yet are the driest regions in the world. Their lack of humidity is particularly striking because hot areas can hold so much moisture. Rainforests, for instance, combine warm air and high precipitation to produce some of the highest areas of humidity in the world. Deserts, on the other hand, are very dry, so they're antithetical to most life.
Humidity
Humidity is defined as the amount of moisture content or water vapor occupying the air at any one time. High humidity occurs in areas where the high moisture content evaporates into the atmosphere. Air expands as it gets warmer, so it can hold much more humidity than cold or frigid air.
Precipitation
According to the University of California Museum of Paleontology, deserts receive less than 20 inches of precipitation per year. Semiarid deserts receive between 3/4 to 1 1/2 inches annually. Cold deserts fare a little better at 6 to 10 inches a year. The Atacama Desert in Chile and some parts of inland Sahara average approximately a half inch per year, and some years they even go rainless.
Evaporation
Deserts are prone to having long periods of little to no rain before receiving short bursts of precipitation, but the amount of humidity that does enter the air is rare. The desert air is so dry that the rate of evaporation regularly exceeds the rainfall rate, and the rainfall may even evaporate before it hits the ground.
Solar Radiation
The scant desert humidity that exists in the air is unable to block the sun's rays, so the amount of solar radiation that deserts receive can reach twice the amount of humid regions. The daily temperature swings that follow can be extreme. On one end of the spectrum temperatures can reach up to 49 degrees Celsius (120 degrees Fahrenheit), and it's not unusual that it can occasionally drop below freezing.
Adaptations
Desert conditions are also exacerbated by the fact that desert organisms respond to the low humidity by preserving as much water as they can without losing it to evaporation. Many desert plants have evolved a waxy structure called a cuticle that can keep water inside. Small leaves and white hairs that reflect heat may also be strategies for dealing
Precipitation
Low and unpredictable precipitation is the primary characteristic of a dry climate. The lowest rainfall occurs in arid, or desert, areas where precipitation averages less than 35 cm (14 inches) per year, and some deserts have years with no rainfall at all. Semiarid, or steppe, regions are comprised of grasslands characterized by short grasses and scattered small bushes or sagebrush. They receive slightly more rainfall than deserts and can receive up to 70 cm (28 inches) per year. However, most semiarid regions have less than 50 cm (20 inches) of average annual precipitation.
Evaporation
Another characteristic of a dry climate is that evaporation is often greater than precipitation. This results in a climate that lacks ground moisture due to the low average rainfall and rapid evaporation of the precipitation that does fall. For example, arid regions in the Middle East average less than 20 cm of rainfall per year, but annual evaporation rates of more than 200 cm can be ten times that of precipitation. The extreme evaporation contributes to dry, coarse soils that support little plant life. Semi-arid regions with slightly more precipitation will support some grass and small bushes.
Temperature
A third common characteristic of dry climates are wide variances in seasonal and daily temperatures. Deserts are usually found in the rain shadows of mountain ranges and have hot summers, cool nights and moderate winters. However, in cold deserts, winters can be extremely frigid. In dry climates, the sun's rays are more direct, due to the lack of humidity, and this results in extreme daily temperature swings. Desert highs can approach 40 degrees Celsius (104 Fahrenheit) or more, and in some areas, winter lows can drop well below