Assessing of vulnerable areas from precipitation reduction with regional analysis of no precipitation periods data of synoptic stations of Iran

Regional analysis is used as one of the low flow estimation methods for the study of drought in areas without sufficient data. In this study, drought analysis is done based on no rainfall periods data from 67 synoptic stations with an appropriate data time and uniform distribution in the country of Iran. After sorting out the daily precipitation, periods without precipitation is assessed in each station. First the homogeneous regions identified and then the most suitable criteria statistical distribution function was determined in those areas. In order to analyze the frequency the FREQ program in MATLAB saftware was used. The minimum and maximum daily rainfall was 17 years for Semnan station and 56 years for Tabriz station and several other stations respectively. Based on regional analysis, the whole country of Iran classified in 8 Classification homogeneous regions. Spatial maps of maximum periods without rain during dry periods showed that from north to south and from West to East in the country were longer and in general in the country there are three separate locations in the distribution of dry periods. In northern Iran, periods without rain spells reduction and increased wet periods, this indicates that low sensitivity of this area to dry condition. Southern regions (particularly the provinces of the Persian Gulf and Sea of Oman) and central regions as the most sensitive areas in terms of reduction of days of rain and increase in precipitation at different return periods were found.