Investigation Analysis of the Agronomical Characteristics of the Daily Rainfall in Rain-Fed Agriculture (Case study: Tehran)

ABSTRACT:

In scientific agricultural planning, it is necessary to know how the precipitation occurs. This is especially important in rain-fed agriculture, because of its complete dependence on the precipitation. The occurrence of rainfall in Tehran, Iran has been analyzed, based on daily rainfall data of 45 years (1961-2005). Some important agronomical parameters, such as start and end of rains, rainy periods, probability of the occurrence of wet and dry spells following a rainy and/or a dry day, maximum daily rainfall with different probabilities, cumulative ratio of the start and their cumulative ratios, estimation of the average number of rainy days during the end of rains based on agronomical assumptions, estimation of annual and monthly rainfall each month, estimation of the amount of daily rainfall in different return periods (2 to 200 years), probability of the occurrence of the number of rainy days in different months, and prediction of different dry spells, have been analyzed, using SMADA and EXCEL software. All of the above characteristics have been estimated for this station based on their agronomical importance in rainfed agriculture.