1. Tropical Wet and Dry Seasons
l/o: To know how to answer an exam question on tropical wet and dry seasons

2. What do we know?
ITCZ
Trade winds
Wet season
Dry season

3. Wet and dry season changes between hot deserts and equatorial rainforests
Variations take place at different latitudes
All areas have a wet season (where up to 90% of the rainfall falls) and a dry season (no or minimal rain)

4. Rainforest Margins Precipitation over 1000mm per year 1-2 dry months
Temp range from 22oC (wet season) to 28oC (dry season

5. Desert / semi arid regions
Precipitation under 500mm
9/10 dry months a year
Temp range from 18oC (wet season) to 34oC (dry season

6. DRY SEASON Sub tropical anticyclone moves over desert margins
ITCZ is on the equatorial side
Trade winds blow over land to the coast, therefore are very dry

7. WET SEASON ITCZ moves towards the pole
Trade winds now move from sea to land, therefore bringing moist air

8. Response to atmospheric change
Peak discharge of rivers in late summer (Aug to Oct)
Corresponds with heavy rainfall
Also corresponds with surplus water in the soil moisture budget (next lesson)
BASICALLY
When rain first starts falling there has been a deficit of water in the soil

9. Dry season, discharge decreases rapidly (with low flow Nov – May)
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
Dry season, discharge decreases rapidly (with low flow Nov – May)
Minimum discharge comes soon after highest temperatures (peak time for evapotranspiration )

10. Today… Ensure that the following are complete
Map of Africa
Pictures of the overhead sun / ICTZ
Hadley Cells / atmospheric circulation etc
What are the the hydrological responses to the different seasons on the appropriate places.