Analysis of Rainfall in order to Determine of Sowing Date of Wheat in Karaj Region

Access to the daily records enables users to conduct many analyses that are not possible with just the use of 10 days totals or monthly totals. In this study dates of start of the rain are extracted by taking daily rainfall data as the basic unit at Karaj Agrometeorological Station during the period of 1970-1996 and summarize the records in ways that have direct applications in agricultural planning. Three alternative definitions for this date are considered in this paper which gain three statistical series. With application one, definition for date of end of the rain, we also got three series for length of the rains. Mean dates of start of the rain are calculated on 19 Nov, 7 Dec and 14 Dec respectively. With regard to sowing date of wheat in Karaj region and comparison the coefficients of variation in the series, the first definition was accepted. Fitting normal distribution to the climatologically series, provided us statistical forecasting.