In arid and semi-arid areas, drought damages are more than other regions due to the fragility of environment. Parts of central, eastern and southern Iran with arid and semi- arid climate are include these regions. The object of this study was to investigate the relationship between hydrological and climatological drought in Sabzevar Plain. In this study, SPI and SWI indices were used for the zonation of hydrological and climatological droughts in Sabzevar plain. Precipitation and groundwater data were collected from 1999 to 2007 and from 2001 to 2007, respectively and then were analyzed by the mentioned indices. After calculating SPI and SWI, drought zonation was performed for each year using Kriging method in ArcGIS. Results showed that climatological and hydrological droughts did not follow a certain order and the highest intensity and frequency of droughts were west Sabzevar plain. In other hand, the east region has enjoyed normal and wet condition. According to the results, a significant relationship was found between climatological and hydrological drought in the study area as hydrological drought occurred one year later compared to climatological drought.

In this research, impact of drought on groundwater quality investigated on irrigation usage in Hashtgerd plain aquifer. First, using Thiessen-polygon method and precipitation values of 6 weather stations in Hashtgerd plain, total average monthly rainfall for a period of 30 years (1985-2015) was calculated. Average monthly of groundwater levels for a period of 23 years (1991-2014) were calculated using 8 observation wells data and Thiessen-polygon method. Climatological drought calculated by SPI and groundwater drought calculated by GRI. Based on results, the longest climatological drought with durability of 2 years, severity -2.73 (SPIsum), density -1.365 (SPIavg) and total average monthly rainfall 157.70 mm were in the water years 1998-1999. The most severe groundwater drought was in the water years 2010-2014 (4 years durability) with severity -6.10 (GRIsum), density -1.53 (GRIavg) and groundwater average monthly level 1180.26m. On 12 months period, correlation between groundwater levels and rainfall amounts were significant with time-lag of 11 months. In June of water year 2013-2014 with extreme drought condition, water quality of 16% aquifer area was appropriate to use plants irrigating but 84% was inappropriate while in December, 100% aquifer area was inappropriate as irrigation water quality. Based on LSI, in June and December of all studied years, water quality of 100% Hashtgerd plain aquifer area, it was possible to formation of calcium carbonate sediments.

Drought means scarcity of water, which various sectors of human society, agriculture, water supply, industry and environment can adversely affect due to its occurrence. Drought is best characterized by multiple climatological parameters as a natural hazard. An understanding of the spatio-temporal dependence relationships between effective variables on drought is necessary to its description and analysis. The main purpose of this study is investigation of climatological drought in synoptic station of the Kurdistan Province, Iran, by using Triple Diagram Model (TDM). The data consists of monthly average temperature, precipitation, and also relative humidity from seven synoptic stations. The standardized precipitation index (SPI) was calculated for each station. The semivariogram of different used models have been analysed and were been chosen using the cross validation method. According to coefficient of determination and residual sum of squares indices appropriate method was selected for drawing triple diagram models. The triple diagram models have been prepared based on geostatistic principles by SPI, Temperature, and relative humidity variables. The results indicate that SPI classification is characterized by the scattering in two input variables can provide the analysis framework of the characteristics and variations of climatological factors. The spatial relationship between stations/regions can be carried out by comparison of the humidity conditions. Application of the triple diagram models can be recommended for drought analysis in other climatological stations. The triple diagram plots help to make interpretations in spite of extreme scatter points facilitate the explanations of the influencing trend among variables.

Long meteorological drought can lead to the onset of hydrological drought. In this research, the lag time between the two types of drought was investigated for determining the hydrologic drought onset after realizing the climatological drought. This is a matter to provide managers with enough time for decision making before the occurrence of water shortage in the watershed. The SWAT water balance model was used to determine and predict the lag time between the two types of drought for Foomanat (Anzali wetland) watershed in Gilan province Due to the ability to simulate the long-term flow of representative rivers in the basin. The OAT method was employed for the sensitivity analysis of the water balance model. Among the parameters used in SWAT, three parameters including curve number, available water, and the evaporation compensation factor in the soil were recognized as the most effective parameters for the results of the model. Calibration and validation of SWAT were performed using SCH model. The calculated Nash-Sutcliff and correlation coefficient in estimating runoff as well as determining and predicting the lag time between the two types of drought by SWAT were acceptable. The Nash coefficient was obtained as 0.68 and 0.8 for calibration, and 0.65 and 0.79 for validation periods, respectively. Using the calibrated model, one can predict the water balance situation and the lag time between the onset of meteorological drought and the emerging hydrological drought in the watershed for any interested meteorological drought scenarios. Based on the results, the chance of having a one -month lag time, is more than 70 percent, while the chance of a 2-month lag time in the Foomanat watershed Anzali wetland) is more than 23 percent.

Most parts of the Isfahan province are located in central arid land of Iran and are sensitive to drought occurrences. So it is required to study drought for prediction. There are many ways to define drought using different indicators. Climatology drought was evaluated using annual precipitation time series and different truncation levels including 30% 40, 50, 60, 70, 80, 90 and 95%. In this study 85 precipitation stations were selected in Isfahan province and around of it, in period of 1966-1998.Interpolation methods such as, kriging, Co-kriging, inverse distance weighted and TPSS were evaluated for interpolation of truncation levels and the error of each method was calculated. In the selected methods, Co-kriging method had minimum error and TPSS method had maximum error. Drought extension maps were drawn for each truncation levels using ILWIS software. Also water volume of probable precipitation is calculated for each truncation levels. Results showed about half of rainfall events occurred in 30 percent truncation level, whereas about 80 percent of the events are in 30 percent truncation level. Thus intense droughts occurred in the study area. Maximum frequency of drought occurrences in basis of truncation levels in study area are 30, 80, 60, 50, 40, 90, 70, 95%, respectively. Results indicated that truncation levels are suitable method for climatological drought evaluation in the studied area.

In most regions of Iran the requisite water for populations and industry are supplied by groundwater resources. Drought is an important factor, which effects groundwater quality. Demand for groundwater resources is increasing in Qurveh - Dehgolan plain due to its position and limited access to surface water resources. In this research, the effects of drought on water quality of wells in Qurveh – Dehgolan studied. Water quality data in 38 wells for 21 years (1992 to 2013) used to define dry and wet period the Standardized Precipitation Index (SPI) for 3, 6, 12 and 24 months’ time scales calculated. Using Mann-Kendall tests, the trend of ground water quality parameters investigated and the relation between climatological drought and groundwater quality parameters calculated using correlation coefficients. Study of correlation coefficients between quality parameters and SPI showed in 22.2% of cases, drought effected on groundwater quality (at 95% level). Correlation coefficients were positive in some wells and were negative in other wells. Also in most quality parameters, with increasing of SPI time scale, the rate of correlation was increased. The results of Mann-Kendall test showed the most parameters of water quality had increasing trend and Cl-, HCO3- and Mg2 had negative trend in 60.53%, 60.53%, and 52.63% of wells respectively. In addition, CO32- had not trend in any wells. Zoning map of water quality showed that most reduction of ground water quality was happened in eastern part of plain, because the ground water level downfall in mentioned part was higher than other parts.

IntroductionDrought, with its gradual, tranquil, and crawling occurrence, is one of the most important natural disasters that affects various aspects of human life. This phenomenon, as a disastrous climatic phenomenon, directly affects communities through changes in their access to water resources. One of the most important effects of drought on water resources is the reduction and drop in groundwater aquifers and the decrease in river flow rates. The hydrological drought, with the effects of periods of atmospheric drops, affects the sources of groundwater or surface water supplies such as river flows, reservoirs, lakes, and groundwater. Therefore, the effect of the rainfall shortage on the components of the hydrological system such as soil moisture, river flow, surface of reservoirs, and groundwater is seen after a long time. Climatological drought with a time lag in one place leads to a hydrological drought which, consequently, leads to water stress. Determining the starting and ending dates of droughts, their severity, continuity, spatial distribution, assessment, and quantification is one of the most important issues in the study area. Accordingly, the main objective of this research was to determine the extent of the continuity of meteorological and hydrological droughts and the relationship between them.
MethodologyThe Gorganroud River watershed forms 48% of Golestan Province with an area of ​​11393.1 km2. It is located in the geographical range of '36 ° 36 'to 37 ° 37' the northern latitude and '00 ° 54 'to '29 ° 56 the eastern altitude. It is located in the national scale of the Gorgan River basin in the north of the country. From the south east to the eastern Alborz, from the east to mount Aladagh and mount Glydiyah, from the north to the Atrak basin, and from the west to the Caspian Sea and the Gharasso basin. The Gorganroud River has 17 main branches that are connected in different parts and, ultimately, flood the Caspian Sea. The basin is used as a forest in the south and east, but in the north and west, alluvial plains are exploited in agriculture and pasture. In order to study droughts, the standardized precipitation index (SPI) and standardized water-level index (SWI) were used. The data used in this study was extracted from 16 meteorological stations and 31 piezometric wells, with a common statistical period of 30 years (1362-1392). To analyze the drought's trend, seven scales of 1, 3, 6, 12, 24, and 48 were used in a monthly and annual scales. In this study, to reconstruct the statistical errors and homogenize the data, acorrelation and normal ratio methods were used. Then, the SPI and SWI indices and the quantitative analysis of droughts of basin were used to evaluate the trend of rainfall and underground water in different spatial and temporal scales.
ResultAccording to the calculations and checking the map of the annual extent of meteorological drought, the western and eastern regions of the basin were affected by drought more than other regions. In addition, according to the map of the annual extent of the groundwater droughts, the southwestern, western, and northern parts were affected by drought more than other regions. Considering the duration of the meteorological drought, the northeastern, western, and southwestern parts had longer durations than other regions. Considering the duration of the groundwater drought, the northern, southwestern, and central parts of the basin had the longest duration.

In various researches, implementation of meteorological parameters in drought prediction is studied. In the current work, meteorological drought classes based on Standardized Precipitation Index (SPI) for six seasonal scenarios (autumn, winter, spring, autumn + winter, winter +spring, and autumn + winter + spring) and meteorological predictors contained ground and sea surface temperature, weather temperature (at 300, 500, 700 and 850 mi bar) and geopotential height (at 300, 500, 700 and 850 mi bar) wide of North (0, 60) and East (0, 90) was applied in prediction models based on data from 1975 to 2005. In these models, temporal range of meteorological predictors is between October to April month on the same predicted SPI. SPI was calculated based on mean precipitation at seasonal time scale in the main watershed of Tehran (Taleghan, Mamloo) by Inverse Weighted Distance method. The well known statistical supervised machine learning method, support vector machine (SVM), is applied to predict SPI. Regarding to selected data points, the effective regions on Tehran precipitation are southern, southwestern and northwestern of Iran in spring, northern and northwestern in autumn and northwestern and western in winter. SVM depicted accurate results in prediction of SPI, spatially prediction of SPI in all scenarios, and it can be proposed as a very suitable statistical learning method in investigating of nonlinear behavior of meteorological phenomena with a short samples. The predicted SPI in spring and autumn are more accurate than the other scenarios.

Soil erosion in the watersheds is a function of some factors such as climatology, topography, soil type and land use. Within these factors, the importance of precipitation because of its high variation and land use because of the role of humans on community development is very clear. In this research, the precipitation, discharge and sediment data in a statistical period from 1967 to 2009 were used. Drought situation was calculated by standard precipitation index with 3 months’ time scale. Land use maps were prepared in three periods based on satellite images, and the changes of land use between these periods were compared. Results showed that the area of rangelands and farms from initial to final section of study period varied from 14% and 21% to 41% and 11%, respectively. Significant difference in sedimentation rate is visible between initial and final sections of study period. Percentage of drought occurrence increased to triple from initial to final period. The result of Mann-Kendall test showed a negative trend for watershed discharge at 95% significant confidence level. Therefore, it seems that increasing drought occurrences and therefore decreasing runoff and change of farms to rangeland, caused to the decreasing suspended sediment load in Senobar watershed.

Of the many Climatic events that influence earth’s environmental fabric‚ drought is perhaps the one that is most linked with desertification(WMO‚1997).This Investigation is an effort for assessment of acceptability about many of Climatic current Drought Indices in reagent and sample stations of Salt Lake Basin of Iran. These drought indices which are used in world active systems, are Percent of normal precipitation Index PNI, Deciles of precipitation Index DPI, Standardized precipitation Index SPI, and Z Score Index ZSI.The above mentioned indices were calculated first by average of monthly precipitation data for a 44 years period from 1957 to 2000 relate to 34 synoptic and climatological stations in their common time scales. Based on obtained results from one hypotheses, DPI and SPI indices in the contemporary with minimum occurrence, showed, extremely drought in the studied stations. These acceptability of indices in more than of other indices and according of this investigation,DPI index sit on the first place, SPI sit on the second place, ZSI index sit on the third place, and finally PNI Index, sit on the forth place. In next stage the Standardized Precipitation Index SPI, based on precipitation values from 34 monitoring stations around the Salt Lake Basin of Iran, is computed monthly and was performanced for climatic interpret and characteristic include assess drought relative frequency, intensity, expand and duration and calculated return period of the most intense drought and according to the point stations data, drew intense map. This investigation indicate the most intense drought in Salt Lake Basin of Iran belong to Hamadan(Nozheh) and the longest drought duration in Avaj ‚Dooshantappeh‚ and Kashan Stations with the highest relative frequency digit of drought (38/6%) and the lowest relative frequency digit of drought (18/1%) belong to Golpayegan. The most of severe year has occurred in 1973 and 1967 in 44 years period.