The aim of the study is to evaluate the return period and risk of drought duration in five ancient and unique stations of Iran, having more than one-hundred annual precipitation data. For determining the return period and risk of drought in the stationsof interest (including Jask, Bushehr, Isfahan, Mashhad and Tehran) the following stages were performed: a) Applying a homogeneity test (i.e., Run test) on annual precipitation series was indicated the Jask station unlike other stations which were homogenous, is non-homogenous, b) Using a goodness-of-fit test (), the most suitable distribution function for annual precipitation data was selected from among fourteen functions, c) Based on the best-fit function obtained for each station, the amount of precipitation for seven probability levels (Thresholds) from 0.1 to 0.7 (with step 0.1) were determined, d) With respect to the precipitation of each probability level and subtracting it from annual precipitation data during record period, dry periods were indicated and drought duration for each dry period was computed, and e) The two statistical characteristics of drought including return period and risk were calculated with different mathematical equations. The results based on the annual precipitation series of four aforesaid stations showed: a) For a given drought duration, as the probability of occurrence of precipitation increases the return period decreases, or with a certain probability of occurrence of precipitation, as increasing drought duration the return period also increases, b) For the probability of occurrence of drought 30 %, the longest drought in Isfahan (i.e., six-year duration) and other stations (i.e., three-year duration) occur once each 2000 and 51 years, respectively, and d) for a certain probability of drought occurrence, as increasing the basic period, the risk of drought increases. For instance, for the probability of occurrence of drought 50 %, it was identified that the drought risk in Bushehr and Tehran station is more than Isfahan and Mashhad.

Drought is one of the natural hazards that occur in most parts of the world but its manifestation in the arid and semiarid regions of the world is more. First purpose of this study is the identification of synoptic patterns affecting in drought occurrence and second is its comparison with wet periods. For this purpose, daily and monthly precipitation data over a period of 20 years (2008-1989), were gathered and analyzed using statistical methods such as Z score for 20 meteorological stations in southwestern of Iran. Preliminary results showed that the frequency of drought events in the study area is more than wet occurrences. Trend of droughts, particularly in recent years is increasing, although January and December show a maximum frequency of occurrence of drought, but the phenomenon is declining in both. However, in March and February with a lower frequency of occurrence of drought, the drought is increasing. From synoptic view point the annual shift of sub-tropical high pressure belt, particularly meridional extension the STHP cell in southeast of Saudi Arabia plays an important role in the winter precipitation variation. So, often dry periods with the movement toward the West, taking place on peninsula and the increasing in heights, and wet periods with the movement toward the East, taking place on sea and the decreasing in geopotential heights. Also the location of the Mediterranean trough axis plays an important role in precipitation variations in southwest of Iran. Whatever the trough be closer to the east part of Mediterranean Sea and its axis forms a NW-SE orientation, rainfall in study area will be increased but with increase the trough distance from east part of Sea and with NE-SW orientation, it is usually associated with periods of reduced precipitation and drought events.

Sistan and Baluchestan provinces and especially Sib and Soran cities have been affected by drought for many years. Most of the effects of this crisis have affected the agricultural sector, especially in rural areas. The occurrence of drought in this city has many direct and indirect effects on the lives of villagers and, certainly, it is not possible to prevent the occurrence of this phenomenon in terms of natural factors and the occurrence of droughts; Therefore, the first step to deal with and reduce the economic and social effects of the phenomenon will be to know and accurately understand the management factors on the occurrence and intensification of this phenomenon. With this knowledge, the study investigated this issue in rural areas of Sib and Soran cities. Quantitative research is practical in terms of purpose. Because the goal of the research is to achieve rules that are used in real and practical situations and help to improve executive methods. 19 villages and based on Cochran's formula, 300 families were selected as a sample. Data collection on two questionnaires; First questionnaire was to identify the consequences and spatial effects of drought and the second questionnaire was in the form of the Delphi technique to determine the effective management factors and strategies for drought. The risk of drought in rural areas has had negative social, environmental, and economic consequences. The spread of false and illegal businesses, the depletion of springs, wells, and surface water resources, as well as the instability of residents' livelihoods have been among the most important negative consequences of drought. On the other hand, lack of job diversity and lack of government investment is the most important management factors in aggravating the effects of drought, in which changing the pattern of water consumption and its storage as effective solutions were obtained.

One of the main tasks of applied Geomorphology is study of position and of vulnerable human environment confronting to variety of geomorphologic hazards. In fact the area and its suburb is one of the area with frequent occurrence of climatic drought. these area turns to one of the most susceptible arid regions to sands migration hazards. then owing to the main target of research in first step, we calculate the main existing factors of climatic drought such as RAI, PNPI, RIA, z score and SPI in the study area. in the next step, using statistical analysis (Kendal and spear man correlation coefficient), to evaluate the effect and correlation between occurrence of drought and increase of hazard due to the migration sands was studied. Finally, results show field worked help us to make a comprehensive overview hazard in the study area and migration of sand dunes, in this study area. Furthermore, with periodic increasing degree of climatic Drought, also percent of frequency of sands occurrence, represent a relative increase, as the result we can predict and reduce occurrence of these kind of hazard and have more readiness in environmental management by appropriate planning to condition of the zone and exact calculation.

Drought is one of the most complex natural hazards that affect natural and human systems (Wilhite et al., 2005, Wilhite et al., 2007). Greenhouse gas emission has contributed to climate change in the last century (Van Pelt and Swart, 2011). Climate change has a significant impact on the hydrological cycle and consequently on water resources, and the frequency and severity of droughts and floods. The most reliable tool available for future climate simulation is the output of coupled atmosphere-ocean patterns of atmospheric general circulation (Shakarami and Massahbavani, 2007). The reports of the Intergovernmental Panel on Climate Change show that if the current trend of greenhouse gas production due to the consumption of fossil fuels continues, the concentration of these gases can reach more than 600 ppm before the end of the 21st century (IPCC, 2007). The downscale model, which is a downscale statistical method, uses semi-empirical distributions for simulation and downscale and can generate future climate parameters at the station level. A major application of these data is to monitor and evaluate future droughts (Hosseinabadi et al, 2020). In the occurrence of drought, there are many factors such as changing the course of rivers and draining reservoirs, climate change and warming of the earth. Nowadays, the increasing occurrence of drought has caused the attention of many meteorologists and climatologists around the world. Drought indicators are used to diagnose and classify drought conditions. These indicators include the possibility of evaluating the standardized precipitation evaporation and transpiration index SPEI, the Palmer drought intensity index PDSI, the standard runoff index SRI and the identification drought index RDI. SPI and SPEI are the most common drought indicators.

Drought is a recurrent feature in different climates, occurrence of drought do not limited to specific regions on times it should be possible in the region with high – rain in each seasons of the year. One of the most important stages of drought monitoring is to identify the indices to analysis severity – duration and frequency of drought events. This paper evaluates the Standardized Precipitation Index (SPI) on 3, 6, 12, 24 and 48- month scales using monthly precipitation totals for 10 stations in south-west basins of Iran from January 1960 to December 2000. Severity-Duration curves, as well as return periods were extracted for each station. Severity maps showed that in the east and the south of the region, drought intensity is more than other areas. The results show that when SPI index have negative sequences, drought will occur and when SPI values are -1 or less, drought occurrence is severe. These time scales explain the impact of drought to availability of water resources. Thus the reaction of soil moisture to precipitation occurs in short time while the response of underground water and stream flows are a long term processes.

In order to evaluate the impacts of climatic factors during the periods of the occurrence of wet and dry years, using a model is one of the best solutions. In this paper, drought severity was determined by using Scalogram model based on 3 climatic factors (annual precipitation, number of rainy days and amount of potential evapotranspiration) for Zabol region over 16-years period (1991-2006). The results showed that the most severe drought had not always occured in a year with the least precipitation. This is due to the role of other climatic factors. It is concluded that the occurrence of the most severe drought and the wettest year has been in 2001 and 1992, respectively. In addition, potential evapotranspiration is the most important factor affecting on occurrence of drought in the study area.

Because of the presence of special properties in semi arid catchment، these areas are suitable for drought events. The responses of these areas to drought events are in the form of the disappearance of plant cover on surfaces slopes، intensive erosion or landslide occurrence on side of rivers’ course. Azarshahr catchment (situated in 37˚ 36′ to 37˚ 49′ N and 44˚ 20′ to 45˚ 49′ E) as one catchment of Sahand mountains (located at west slopes of Sahand mountain) has experienced major changes at behaviors of geomorphological processes. The result of assessment of changes of surface and subsurface water، chemical characteristics of water، rivers’ sediment data show that these properties and characteristics influence drought events. To determine drought’s geomorphological effects resultant of these events all data were analyzed applying neutral networks and the final map was obtained by use of Arc/View. The results show that the major effects of drought are present in southern، west and east of Azarshahr catchment. These parts of catchment are very suitable for the occurrence of drought. Gulling، landslides and rill erosion are outcomes of drought.

Drought management and planning are based on recognizing drought characteristics and its spatial and ‎temporal extent. In the present research, SPEI12 was calculated using 4 kernels including rectangular, ‎triangular, circular and Gaussian at the 12 Zayandeh Roud watershed’s climatological stations. Four ‎important characteristics of drought including the time of occurrence, duration, magnitude and severity ‎were evaluated by applying the highest weight to the 5th month. It was revealed that kernels other than ‎rectangular were more sensitive in recognizing the four drought characteristics. While the rectangular ‎kernel showed the highest coefficient of variation (CV) in drought duration, the Gaussian kernel has the ‎least CV in duration and magnitude and the circular kernel has the least CV in severity. Moreover, it was ‎found that the Gaussian kernel was more successful in detecting the occurrence of drought in comparison ‎with others. Finally, the results of this research indicated that rectangular kernel i.e. using equal weights ‎for all months in deriving SPEI, may lead to overestimate or underestimate drought characteristics.‎

Drought is one of the most widespread and devastating phenomenon which has been more frequent due to climate change consequences in recent decades. The aim of this study is to project the agricultural drought in Birjand station, Iran using outputs of five GCM models approved in IPPC fifth assessment report, AR5, namely MIROC-ESM, GFDL-ESM2M, HADGEM2-ES, CSIRO-MK3.6 and IPSL-CM5A-LR under RCP4.5 and RCP8.5 scenarios. The retrieved outputs were downscaled using LARS-WG statistical model for the future period (2055-2025). For monitoring the drought the Self Calibrating Palmer Drought Severity index (SC-PDSI) during the baseline (1975- 2005) and future period was used. The results indicated that occurrence of droughts during future period will increase comparing to baseline, which might be caused by climate change in the study region. Models projections under both scenario revealed that the (2026-2035) period would experience more severe drought comparing to remaining years. According to results, the highest number of drought events in future period was projected by MIROC-ESM and CSIROMK 3.6, models under RCP8.5 scenario.