s:1299:"%T Influence of aridity on vegetation 
%A Trabucco, A. 
%A Zomer, J.R. 
%X The aridity index measures the adequacy of the precipita - tion to satisfy vegetation water requirements � Large areas of  northern and southern Africa are dry with an aridity index  of less than 0�65� In contrast central Africa is more humid  with an aridity index that exceeds 0�65� Variations in dry - ness reflect Africa’s geography and topography � For example  hyperarid zones such as the Sahara and Namibia deserts  which receive less than 100 mm of precipitation annually  correspond to prevailing high pressure systems preventing  cloud formation over the western edges of subtropical areas �  Equatorial areas are more humid than other parts of Africa  because low pressure systems and strong air convection con - dense the moisture into clouds which lead to high precipi - tation � Dry northeast monsoon winds blowing in from the  Arabian Desert make eastern Africa less humid than other  equatorial regions such as central Africa and the Gulf of  Guinea to the west � Mountains such as Mt � Kenya and Mt �  Kilimanjaro block the passage of rain-producing weather  systems creating more humid conditions in highland areas  and drier conditions on the shielded side of these highlands 
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