In this lesson we are going to discuss the definitions and causes of Aridity and Desertification
Aridity and DesertificationAridity - state of land beingdeficient of moisture leadingto little or no vegetation.Desertification - process inwhich desert like conditionsslowly and steadily encroachon formerly productiveagricultural land.Causes of Aridity andDesertification1. Low and unreliable rainfallbelow 250mm per annumcausing little or no vegetationand absence of animal andbiological life causing soilforming processes to beincomplete.2. High temperatures whichcause high rates ofevaporation which exceedsprecipitation or lowtemperatures which reducesair capacity to hold moisturecausing a place to receivelittle or no rain.3. Where a place is washed bycold ocean currents causingmoist onshore winds to cooland then drop moisture overthe sea and reach the land asdry winds e.g. Kalahari whenonshore westerlies cross thecold Benguela Current.4. Where relief barriers suchas hills or mountains causesome areas to lie on the rainshadow hence rain winds dropmost of their moisture on thewindward side and when theyreach the leeward side, theyare dry hence causing dryconditions e.g. Kalahari andNamib on the rain shadow ofDrakensberg mountains.5. Location of some placesvery far from the sea causingthem not to be washed fromwet onshore winds e.g. GobiDesert.6. Where hot dry winds blowover a region causing dryingeffect on land e.g. Harmattanover West Africa.7. Where cool air descendscausing no rain because coolair has to rise beforecondensation takes place.Human Activities8. When people clear forestswhich causes runoff to exceedinfiltration which interfereswith the water cycle.9. Keeping large number ofanimals which exceed thecarrying capacity of land.They eat vegetation leavingthe land bear exposing theland to soil erosion.10. Poor agricultural practicessuch as over cultivation,monoculture and slashing andburning which leads to soilerosion.11. Industrialization whichreleases greenhouse gasessuch as co2 to the atmospherewhich absorb more heatmaking the earth’stemperature to rise.12. Reclamation of waterlogged areas which lowers thewater table causing aridconditions to set in whenplants can’t access groundwater.13. Poor irrigation methods,when evaporation takes placeand salt from below arebrought to the surface and aredeposited on the top soilmaking the soil salty andhence unable to supportplants.