Frequency Analysis of Five Days Antecedent Rainfall for Different Seasons for Kohima (Nagaland)
DOI:
https://doi.org/10.53550/ijsc.v54.i1.214Keywords:
Antecedent Moisture Condition (AMC), Continuous probability distribution function, Kohima (Nagaland), 5-day antecedent rainfallAbstract
In the present study, daily rainfall data recorded at Kohima for 26 years (1997-2022) were collected. Data were grouped by seasonal rainfall: monsoon, pre–monsoon, and post-monsoon. The 5-day total antecedent rainfall prior to the storm was calculated for three seasons and fitted to various probability distribution functions. The distribution with the lowest χ2 value was declared the best fit function. Using the best fit probability distribution function, 05 days antecedent rainfall(mm) under different antecedent moisture conditions (AMCs) and seasons were calculated for different return periods. Only 15.56 % of the total number of 5 days of antecedent rainfall fall under AMC-II conditions. Therefore, of all recorded events, 60.05 per cent fall under AMC-I and 24.39 per cent under AMC-III, necessitating adjustment of the curve number from AMC-II to AMC-I or AMC-III, respectively, to reflect these proportions of cases. Results of the turning point test statistics fall within the 5% significance level for all seasons and AMC conditions, indicating that the data set could be considered random. Log normal and Normal probability distribution functions were found to be the best-fit probability distribution functions for AMC-I and AMC-III rainfall for the post-monsoon season, respectively. Extreme value-I probability distribution function was found to be the best fit for the pre-monsoon season rainfall of AMC-II and AMC-III, and the monsoon season rainfall of AMC-II. The log Pearson Type III probability distribution function was found to be the best fit for monsoon-season rainfall of AMC-I and for premonsoon- season rainfall of AMC-I. The gamma probability distribution function was found to be the best fit for post-monsoon season rainfall in AMC-II. Across all three seasons and AMCs, 5-day incident rainfall increased with increasing recurrence interval. The estimated values of 5-day antecedent rainfall (mm) under different AMCs and seasons at different recurrence intervals can be used to predict runoff in Kohima (Nagaland).
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