Tropical Wet and Dry Seasons lo To know
- Slides: 10
Tropical Wet and Dry Seasons l/o: To know how to answer an exam question on tropical wet and dry seasons
What do we know? Ø ITCZ Ø Trade winds Ø Wet season Ø Dry season
Ø Wet and dry season changes between hot deserts and equatorial rainforests Ø Variations take place at different latitudes Ø All areas have a wet season (where up to 90% of the rainfalls) and a dry season (no or minimal rain)
Ø Rainforest Margins l l l Precipitation over 1000 mm per year 1 -2 dry months Temp range from 22 o. C (wet season) to 28 o. C (dry season
Ø Desert / semi arid regions l l l Precipitation under 500 mm 9/10 dry months a year Temp range from 18 o. C (wet season) to 34 o. C (dry season
DRY SEASON Ø Sub tropical anticyclone moves over desert margins Ø ITCZ is on the equatorial side Ø Trade winds blow over land to the coast, therefore are very dry
WET SEASON Ø ITCZ moves towards the pole Ø Trade winds now move from sea to land, therefore bringing moist air
Response to atmospheric change Ø Peak discharge of rivers in late summer (Aug to Oct) Ø Corresponds with heavy rainfall Ø Also corresponds with surplus water in the soil moisture budget (next lesson) Ø BASICALLY l When rain first starts falling there has been a deficit of water in the soil
l l During this period, the soil is recharging (June and July) Once soil is saturated, water can no longer sink in to the soil, therefore there becomes soil moisture surplus – river flow increases Ø Dry season, discharge decreases rapidly (with low flow Nov – May) Ø Minimum discharge comes soon after highest temperatures (peak time for evapotranspiration )
Today… Ø Ensure that the following are complete l l l Map of Africa Pictures of the overhead sun / ICTZ Hadley Cells / atmospheric circulation etc Ø What are the hydrological responses to the different seasons on the appropriate places.
