Dr Hamid Ghorbani, Dr Abbas Ali Vali, Mr Hadi Zarepour,
Volume 6, Issue 2 (9-2019)
Abstract
Drought is one of the most complex and unknown natural phenomena that causes a periodic water crisis in the affected areas. Increasing water demand on the one hand and the experience of droughts in the province in recent years have led to the water crisis. Knowing the drought is one of the requirements for water crisis management. The purpose of this study was to analyze the trend of the SPI drought index in Isfahan province using nonparametric Sen’s slope test, Pettitt’s change point test and Man-Kendall test. From the monthly climatic data of 10 synoptic stations with a length of 27 years (1990-2017) for time series The results of applying Mann–Kendall and Sen’s slope tests based on SPI Index for 9, 12, 18, 24 and 48 month time periods, shows drought trend is significantly increasing for all stations out of Ardestan, Esfahan and Shahreza stations. In Ardestan station, the drought trend is significantly decreasing for 9, 12, 18, 24 and 48 month time periods and in Isahan station, the drought trend is significantly decreasing for only 48 month time period, and in Shahreza statition, the drought trend is significantly increasingonly for only 18 month time period.
Despite all stations, the drought trend for one month time period, is significantly increasing just for Naein station.
In addition, applying Mann–Kendall test on monthly rainfall for all station shows downward but not significant trend.
Finally, applying Pettitt’s change point test based on SPI Index for 9, 12, 18, 24 and 48 month time periods indicates the existence of a significant change point. For same periods we observe no change point for the monthly rainfall in all stations.
In summation, considering the SPI drought index, about 59% of all stations show significant downward trend bases on Mann-Kendall test and 60% of all stations show significant slope based on Sen's slope test and 75% of all stations show significant change point based on Pettitt's test. In general, for drought analysis using different time periods for the SPI index, in a short time period. (such as 6 months) drought is more frequent but shorter, and as the period increases the duration of drought also increases but frequency decreases. All together, we are facing a water crisis in Isfahan province and we must manage water demand very urgently.
Roya Poorkarim, Hossein Asakereh, Abdollah Faraji, Mahmood Khosravi,
Volume 9, Issue 4 (3-2023)
Abstract
In the present study, the data of the ECMWF for a period of 1979 to 2018 was adopted to analyze the long term changes (trends) of the number of cyclones centers of the Mediterranean Sea.There are many methods (e.g. parametric and non- parametric) for examining changes and trends in a given dataset. The linear regression method is of parametric category and the most common nonparametric method is Mann-Kendall test. By fitting the Mann-kendall model and the linear regression model, the frequency of the cyclone centers of the Mediterranean basin was evaluated in seasonal and annual time scales. Analyzing the trend of changes of the number of cyclone centers on a seasonal scale showed that the five-day duration have had a significant trend in spring, autumn and summer. Whilest on an annual scale, there was no significant trend in any of the duration. By fitting the regression model on seasonal and annual scale, one- and two-day duration have a positive regression line slop.
