Friday, March 20, 2009

world climate Zone:

A Semi-arid climate or steppe climate generally describes climatic regions that receive low annual rainfall (250-500 mm or 10-20 in). A more precise definition is given by the Köppen climate classification that treats steppe climates (BS) as intermediates between the desert climates (BW) and humid climates in ecological characteristics and agricultural potential. The Köppen climate classification allows adjustments for temperature and for excluding forested regions (such as those in most of Canada and Siberia).
• To find the precipitation threshold (in millimeters), multiply the average annual temperature in °C by 20, then add 280 if 70% or more of the total precipitation is in the high-sun half of the year (April through September in the Northern Hemisphere, or October through March in the Southern), or 140 if 30%-70% of the total precipitation is received during the applicable period, or 0 if less than 30% of the total precipitation is so received.
• If the annual precipitation is less than half the threshold for Group B, it is classified as BW (desert climate); if it is less than the threshold but more than half the threshold, it is classified as BS (steppe climate).
• A third letter can be included to indicate temperature. Originally, h signified low latitude climate (average annual temperature above 18 °C) while k signified middle latitude climate (average annual temperature below 18 °C [64.4 °F]), but the more common practice today (especially in the United States) is to use h to mean that the coldest month has an average temperature that is above 0 °C (32 °F), with k denoting that at least one month averages below 0 °C.

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