 Estimation of Areal Precipitation from point measurements

Yüklə 494 b.
 tarix 30.04.2018 ölçüsü 494 b. • Method OK if gages distributed uniformly over watershed and rainfall does not vary much in space. • To determine ( ): • most accurate method if have a sufficiently dense gage network to construct an accurate isohyetal map. Can account for systematic trends, i.e., orography, distance from coast. • Frequency analysis of historic data relates the magnitude of events to their frequency of occurrence using theory of probability and statistics (mean, standard deviation, coefficient of variation, coefficient of skewness, return period) • For example, 25 year return period storm occurs on average once every 25 years and has a probability of 1/25 of occurring in any one year. • Rank annual maximum/minimum from largest to smallest (or smallest to largest if interested in drought) • What is probability T-year return period will occur once in N years?

• Probability does not occur
• P(x < xT)=(1-P)N
• Probability occurs at least once in N years
• = 1 - (1-P)N = 1 - (1-1/T)N • For example, 10 year return period storm has prob. of occurrence 0.1 in any 1 year. How probable once in 10 years?

• T = average recurrence interval for event =10 years
• Probability of occurrence in any one year = 1/T=0.1
• Probability = 1 - (1-1/10)10 = ______ at least once in ten years
• What is the probability that a 20 year return period storm occurs at least once in 10 years? Dostları ilə paylaş:

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