humidity It is the amount of water vapour held in a given volume of air at a given time.
Atmospheric water vapour is as a result of evaporation and transpiration.
Humidity varies from place to place usually ranging between 48% to 80%.
Water vapour is significant in the atmosphere because:
- It influences the formation of rainfall through condensation
- It regulates the temperature of the atmosphere through absorbing radiation i.e solar and terrestrial radiation
- It stores energy in the atmosphere
Factors which influence the Humidity of a place:
Temperature controls or determines the rate of evaporation and transpiration.
Hot temperatures lead to high rates of evaporation hence increasing the amount of water vapour in the atmosphere while cool temperatures reduce evaporation rates resulting into minimum condensation hence lowering the humidity of a place
Since temperatures decrease with increase in altitude, high altitude areas like mountain tops experience low humidity as water vapour condenses while areas of low altitude like the coastal areas of E.Africa and the rift valley region experience hot temperatures which encourage high evaporation rates leading to
Water bodies such as lakes and oceans act as sources of water vapour through evaporation.
Areas near water bodies therefore experience high amounts
of water vapour and hence high humidity e.g around the lake Victoria basin and the coastal areas compared to areas far away from water bodies e.g North eastern Uganda (Karamoja region) and North western Kenya (Turkana land)
Areas with thick vegetation cover such as forests experience high rates of evapotranspiration leading to high humidity than areas with scattered vegetation
such as scrub, thickets and steppe savannah which experience minimum evapotranspiration and therefore low humidity
Inter Tropical Convergence Zone (I.T.C.Z)
The apparent movement of the sun leads to variations in humidity between the northern and southern hemispheres.
When the sun is overhead in the north, hot temperatures are experienced leading to high humidity in the north and low
humidity over the south while the south experiences high humidity than the north when the sun is overhead in the south.
The equatorial region however experiences uniformly hot temperatures throughout the year thereby leading to
Continentality or Distance from the sea
Areas near the coast experience high humidity because of the effect of the land and sea breezes while the areas far away from the coast experience low humidity due to the absence of land and sea breezes.
Coastal areas also experience low humidity due to the effect of warm ocean currents which transfer warm temperatures towards the land masses leading to high evaporation
Influence of ocean currents
Warm ocean currents raise the temperature of the winds blowing over them hence resulting into high humidity while cold ocean currents have a cooling effect on the winds blowing over them leading to low humidity.
The high humidity experienced along the E.African coast is therefore as a result of the influence of the warm Mozambique currents
Moist winds such as the South east trade winds cause high humidity in the areas over which they blow e.g the E.African coastal areas and the Lake Victoria basin.
However, dry winds with less moisture cause low humidity in the areas over which they blow e.g the North east trade winds are responsible for the low humidity in Karamoja in North eastern Uganda and in the Turkana land in Northwestern Kenya
Highland areas tend to have high humidity on the wind ward side because of the ascending moist winds e.g on the wind ward side of Mt Rwenzori, there’s high humidity than on the lee ward side
Human activities such afforestation, re-afforestation and agroforestry
human activities encourage high rates of evapotranspiration resulting into high amounts of water vapour in the atmosphere hence high humidity while activities like bush burning, overgrazing, deforestation and swamp reclamation lead to reduced evapotranspiration and hence low humidity