How frequently do droughts occur?
Farming is clearly a risky business, as seasons vary between excellent and drought. In effect we take risks and gamble on outcomes each year. Since this is the case we need to know what the risks are we face, ie what are the odds for each year’s decisions? The way to do that is to examine the monthly rainfall data for as long as records exist, then classify each year as being Excellent, Above Average, Average, Dry or Drought. Al and Sally Nino attend a drought?planning workshop at which they receive local rainfall data dating back to 1896. They calculate the growing season rainfall for each year and use the following method for classifying seasons. Excellent season Good season Average season Below Average Drought season > 295 mm 24-295 mm 195-245 mm 120-195 mm By counting how many seasons fall into each category they calculate the following historic probabilities: Season Excellent Above Average Average Below Average (Dry) Drought Total Probability 0.16 0.17 0.30 0.28 0.09 1.00 Percenta
