Frequency Analysis of Rainfall Data of Shimla and Dharamshala Region

Abstract

The present study aims to evaluate the rainfall magnitude for different return periods and also to ascertain the type of probability distribution that best fits the rainfall data of Shimla & Dharamshala (H.P.), India. Probability and frequency analysis of rainfall data enables us to determine the expected rainfall at various chances. Such information can also be used to prevent floods and droughts, and applied to planning and designing of water resources related to engineering such as reservoir design, flood control work, soil and water conservation planning. The present study involves the 20 years of annual rainfall data are useful for the prediction of annual one day maximum rainfall and two to seven days consecutive days maximum rainfall corresponding to return period varying from 2 to 20 years are to be used for the economic planning, by design engineers and hydrologists, design of small and medium hydrologic structures and determination of drainage coefficient for agricultural fields. Various probability distributions (viz: Normal, Log Normal and Gamma distribution) and transformations are applied to estimate one day and two to seven consecutive days annual maximum rainfall of various return periods at Shimla and Dharamshala (H.P.) region. A maximum of 121mm in 1 day, 178.15 mm in 2 days, 203.6 mm in 3 days, 219.4 mm in 4 days, 230.23 mm in 5 days, 240.6 mm in 6 days and 257.5mm in 7 days is expected to occur at Shimla, Himachal Pradesh every 2 years. For a recurrence interval of 20 years, the maximum rainfall expected in 1 day, 2, 3, 4, 5, 6 and 7 days is 160.5 mm, 239.11 mm, 265.36 mm, 285.9 mm, 297.42 mm, 309.5 mm and 330.38 mm respectively. A maximum of 191.1 mm in 1 day, 262.7 mm in 2 days, 314.27 mm in 3 days, 370.24 mm in 4 days, 419.7 mm in 5 days, 477.4 mm in 6 days and 522.32 mm in 7 days is expected to occur at Dharamshala, Himachal Pradesh every 2 years. For a recurrence interval of 20 years, the maximum rainfall expected in 1 day, 2, 3, 4, 5, 6 and 7 days is 277.7 mm, 373.6 mm, 445.11 mm, 518.62 mm, 589 mm, 680.3 mm and 753.79 mm respectively. Various probability distributions and transformations are applied to estimate one day and two to seven consecutive days annual maximum rainfall of various return periods. Three commonly used probability distributions (viz: Normal, Log Normal and Gamma distribution) were tested by comparing the Chi-square, Kolmogorov-Smirnov and Anderson Darling values