(UNDERLINED WORDS ARE DEFINED AT THE END. SOME KEY TERMS AREN’T UNDERLINED AS THEY’RE EXPLAINED IN THE NEXT SENTENCE)
There are large seasonal temperature variations, though the average temperature is still very high at about 20-30°C. In the summer, the temperatures can teach up to 40°C in the Kuwaiti desert as shown by the graph the coldest winter months give a drop down to only about 15°C. Despite this example, a lot of deserts can experience below-freezing temperatures in the winter. There is a lot more precipitation during the winter too as the air is cooler and there is less evaporation of water meaning a larger quantity of water is in the system. Although there is more precipitation in the winter, the annual rainfall in a desert is very low in comparison to other climates (some parts of the Sahara get under 2cm of rain a year).
Diurnal temperature variations are large as well, because of the lack of clouds meaning the warm air is not trapped in at night and during the day there is nothing to block the sun’s rays from heating the desert. Clouds are accumulations of water vapour and since there is little to no precipitation in deserts for the majority of the year, there are no clouds. In many deserts you can see clouds from them because neighbouring mountain ranges act as a barrier to the moist air coming in towards the desert, though the cooling effect from the rising of the air means the air falls down in the direction of the desert dry. High air pressure also leads to there being a lack of clouds because of subsidence. This is when the air in the high pressure zone cools and becomes denser so travels towards the ground. As there is now more air in the same space the pressure is high. What water there is in the atmosphere is now evaporated so there is no vapour to coagulate around dust and become a cloud. Finally, the feature of no clouds allows there to be a lot of sunshine hours (this, and the angle of the sun hitting the Earth in the tropics, adds to the high daytime heat in deserts). The graph to the right shows the average daily sunshine hours in the Sahara desert in northern Africa. At the height of summer over 10 hours of sunshine a day are observed, comparatively, Bournemouth is among the sunniest places in the UK and it averages only 8 sunshine hours a day in midsummer; a feat accomplished by the Sahara in March.
Desert margins experience temperatures much lower than those of hot deserts in yearly average figures, around 10-20°C. In addition, the temperature variations between seasons and diurnally are smaller as a result of there being more clouds to both block the sun’s heat in the day and maintain the temperature at night – 10-35°C.
Sandstorms happen in the desert because of the mass of …