Drought is universal phenomenon that can occur everywhere and can cause harmful impacts on human beings and natural ecosystems. Thus it is very important to study drought. In this study, the Standardized Precipitation Index is used for regional drought analysis in Isfahan Province. In this study, after collecting the Precipitation data in all Isfahan stations and removing those stations with incomplete data, (SPI) time series were calculated in different time scales of 3, 6, 9, 12 and 24 months. Then, frequency of drought extension's maps (in 12 months time scales) was prepared and analyzed using Geostatistics methods (Kriging). These schemes show moderate and severe drought mainly in the West regions of the province, I in the areas neighboring to Fereidoonshahr, Daran and Fereidan cities. They also show extreme droughts in the East and North East regions of the province with high drought risk and necessity for better future it planning and management strategies in these regions.

(SPI) is based on fitting a gamma distribution to Precipitation amounts in selected periods. Based on current research, the gamma distribution may not be fitted to annual Precipitation of some regions. In order to evaluate this subject, annual Precipitation have been used during 1958- 2007 at 11 Synoptic Stations in Iran. In first step, values of (SPI) and frequency of different classes of drought severity were calculated. The Kolmogorov–Smirnov test is used to assess the goodness of fitting most appropriate distribution function to annual Precipitation. Then, according to equi-probability transformation the values of (SPI) were modified. The impact of applying most appropriate distribution function was evaluated to change the frequency of different classes of drought severity in Modified Standardized Precipitation Index (M(SPI)). The results showed that annual Precipitation in all stations do not fallow Gamma distribution as appropriate distribution function except for Rasht station. Using appropriate distribution function in a M(SPI) leads to changing the frequency and/or displacement of different classes in (SPI). So displacements occurred in all classes of drought severity at Tehran and Gorgan synoptic stations. The Gorgan station with 15 events has the most changes in frequency classes.

Drought is defined as the continuous and abnormal moisture deficit. The term of continuous means continuation of deficit and the term of abnormal means deviation of favorite Index of natural condition from the mean. In every drought study four main characteristics are considered: severity, duration, frequency or return period and areal extent. The objective of this investigation is mapping drought severity in Golestan province. For this purpose, Standardized Precipitation Index ((SPI)) was used for drought monitoring in some meteorological stations located in Golestan province. This Index was computed in a period of 25 years Precipitation data (1975-2000) at four different time scales including 6, 9, 12 and 24 months. Consequently, the most sever drought in 6 month time scale was observed in Saliantapeh station while the highest severity in 9, 12 and 24 time scales was observed in Polejadeh station. The aerial extent (SPI) values for the most severe drought condition in different time scales were classified in Golestan province using geostatical techniques. The results showed that the area affected by drought decreased with increasing drought duration and the condition of drought in the province had west-east direction.

Drought is one of the natural disasters and it is very much frequent in dry and semidry areas of Iran. Lack of rainfall has different effects on underground waters, soil moisture and river currents. Examining and analyzing of drought severity duration curves and evaluation curves are essential to water resources and agricultural management planning. So, the drought indices should be used. Standardized Precipitation Index ((SPI)) is one of the most important indices that aims to assign numeric values to the most important climate factor (rainfall). It is used to determine Precipitation deficit in different time scales. Time scales show the drought effects on water resource abilities. In present study, the drought severities were determined in a 30 year statistical period for 20 stations across Fars province of Iran in three 6, 12 and 24 months’ scales. Then based on drought severities in different months, the change process curves of (SPI) Index were provided at different scales. Considering the short-time, mid-time and long-time scales, and the drought was examined from different viewpoints and its severest events and their alternation periods were compared and analyzed. The results showed that Fars province has been encountered with droughts for many years and it has deteriorated in recent years. Other results showed that the short-time droughts had very much fluctuation and were much sensitive to the moisture changes. But in long-term time scale, the sever droughts had long standing and reflected the drought in better fashion. Thus, since drought severity and its frequency are all directly or indirectly time scale depended functions, they may be regarded as the initial warning for drought and help to evaluate it. Result was also revealed the changes process from low severity to high one from northwest to the southeast of the province. The alternation period of drought occurrence with a mild severity varied 3-10 years in average at the studied stations. These quantities for moderate and severe droughts were obtained 5-15 and 10-15 years, respectively.

Drought monitoring is one of the key factors in drought risk management and the use of drought indices such as the Standardized Precipitation Index ((SPI)) is a useful tool in this regard. The aim of this study is to evaluate and zone drought risk in different years and return periods in Karkheh basin. For this purpose, Standardized Precipitation Index ((SPI)) as a selected Index was used to assess drought in 33 stations inside and outside the basin in five timescales. The results showed that the lowest values of (SPI), the most severe drought continuity of the large and the longest continuity were related to Govar stations of Kermanshah province, Biderood station of Khoozestan province and Jokar station in Hamadan province, respectively. Extensive drought risk maps for different return periods showed that in return period of 5 years, northern (Bavane station of Kurdistan province), northeast (Hamadan station) and northwest (Kermanshah) areas were more at risk of drought. This condition for a return period of 10 years was mostly related to northern (Bavane station of Kurdistan province), northwest (Kermanshah) and central areas. Drought risk for 20-year return period affected the northern (Bavane station of Kurdistan province) and Northwest (Kermanshah) areas more, while for 50-year return period, in addition to northern (Bavane station of Kurdistan province) and northwest (Kermanshah), it also affected the northeast (Hamadan station). The overall result showed that the periphery areas, especially areas of northwest, north, northeast and some parts of eastern and southeastern areas are the most susceptible areas affected by drought and with increase in the return period, the severity of drought risk can be reduced.

Drought is a natural and global phenomenon typically defined as a period of water scarcity relative to normal levels and is considered one of the most significant meteorological hazards. In many regions worldwide, both the frequency and intensity of droughts have dramatically increased. Drought refers to the reduction in water availability over a specific period and area. This study analyzes drought fluctuations during the period 1971 to 2019 and forecasts its status for 2019 to 2044 across various cities in Iran. The (SPI) was calculated at different time scales (1, 3, 6, 12 months). The (SPI) is an Index based on the probability of Precipitation deficits over a given period. (SPI) values are calculated using long-term Precipitation records (30 years or more) for a specific region. Positive (SPI) values indicate above-average Precipitation, while negative (SPI) values indicate below-average Precipitation. The results reveal severe fluctuations in (SPI) in cities like Aliabad and Gorgan, which have experienced alternating periods of drought and wet conditions. In contrast, regions such as Hashemabad and Incheh-Borun showed predominantly positive (SPI) values, indicating consistently wet conditions and regular rainfall. However, cities like Kalaleh and Maraveh Tappeh faced severe droughts. Forecasts for 2019 to 2044 suggest increased severe fluctuations and recurrent droughts in cities like Bandar-e-Turkmen and Gonbad-e-Kavus, while Gorgan and Hashemabad are expected to maintain relative stability. These findings underscore the urgent need for effective water resource management and climate planning to address potential droughts and climate change impacts. Overall, this study highlights the necessity of adopting preventive measures and establishing early warning systems to optimize water resource management and tackle future challenges associated with climate variability.

Drought which is one of the most injurious and chronic natural disasters, is defined as the continuous and abnormal moisture deficit. The term of continuos means continuation of deficit and the term abnormal means deviation of favorite Index of natural condition from the mean. In every drought study four main characteristics are considered: Severity, Duration, Frequency or Return period and Areal Extent The objective of this study was to analyze these characteristics of droughts and to use them in plotting drought maps over Karoon basin. For this purpose, the Standardized Precipitation Index ((SPI)) as a selected Index, was used for an evaluation of drought inside and outside the basin. Records from 29 stations within the same period of 28 years (1972-1999) in 3 time scales of 3, 6 and 12 months were used. After computing drought and wet period time series using the (SPI), several characteristics of droughts were considered and areal extent maps of droughts plotted using Arcview software. The result of stationary analysis, while with considering above characteristics show that the least observed (SPI) and the severest duration due to drought Magnitude has happened in Menj station while Darshahi station has experienced the longest duration as well as the highest frequency during the record period. Drought maps show that southeast of the basin, near Darshahi, Batari, Pataveh, Yasooj, Shahmokhtar and Menj stations has experienced severer drought as compared with the other areas. It seems that this area is potentially more prone to droughts than other sites.

Drought is one of the most chronic environmental instabilities that has extensive environmental effects. In this research, the evaluation of Standardized Precipitation Index ((SPI)) based on Precipitation and temperature data in Kashan synoptic station for the statistical period of 2019-1970 has been done. In order to check the trend, Mann-Kendall and Pettie tests were used. According to the results in Kashan station, from 1992 to the first quarter of 1994, with 27 months, it had the longest drought period and from 2015 to 2018, it had the longest drought period. The results of the Mann-Kendall test for the parameter of total monthly and annual Precipitation showed a significant downward trend of Precipitation in December. For the parameters of maximum temperature, minimum temperature and average temperature, the average temperature showed a significant downward trend in the months of April, August and November. The time series of minimum temperature and maximum temperature parameters showed similar results, so that these parameters had a homogeneous trend in most months. Of course, this trend for the maximum temperature time series in March was heterogeneous and significant at the 5% confidence level. The Pettie test for the average temperature parameter showed different results, and the time series for this parameter in the months of April, June, July, August, September, November and on an annual scale had a heterogeneous trend. In general, it can be acknowledged that the awareness of the process and characteristics of drought plays an important role in the management of dry areas.

The Standardized Precipitation Index ((SPI)) is a widely used drought Index to provide good estimations of the intensity, magnitude and spatial extent of droughts. The objective of this study was to analyze the spatial pattern of drought by (SPI) Index. In this paper, patterns of drought hazard in Khuzestan are evaluated according to the data of 17 weather stations during data recording. The influenced zone of each station was specified by the Thiessen method. Then, it was attempted to make a new model of drought hazard using GIS. Three criteria for drought were studied and considered to define areas of vulnerability. Drought hazard criteria used in the present model included: maximum severity of drought in the period, trend of drought, and the maximum number of sequential arid years. Each of the vulnerability indicators was mapped. These maps along with a final hazard map were classified into 5 hazard classes of drought included none, slight, moderate, severe and very severe classes. The final drought vulnerability map was prepared by overlaying three criteria maps in GIS, and the final hazard classes were defined on the basis of hazard scores, which were determined according to the means of the main indicators. The final vulnerability map showed that severe hazard areas (29% of the province) which were observed in the northern and central parts of study area are much more widespread than areas under the slight hazard class. Nevertheless, approximately more than half (64%) of the province area was determined to be moderate hazard class for drought.