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Tropical Wet and Dry Seasons

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?. ITCZ Trade winds Wet season Dry season. Wet and dry season changes between hot deserts and equatorial rainforests Variations take place at different latitudes

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Tropical Wet and Dry Seasons

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  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. 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.

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