Dry Days Analysis for Planning Supplemental Irrigation Schemes

ABSTRACT An estimate of the number of dry days in any month during the growing season is an important design parameter in planning supplemental irrigation schemes. Distributions like Gumbel and Log-Pearson Type III and transformations such as power, SMEMAX and Log-log were tested on data of dry days of the rainy months in Iraq. Of these, power transformation was the best in nor-malizing the series. A procedure is suggested to estimate the return periods for the months of total drought. Although all the transformations and distributions give identical estimates of dry days for a five year return period, power and SMEMAX transformations are the most reliable transformations for estimating number of dry days in planning supplemental irrigation schemes for longer return periods.