DROUGHT is a consequence of fluctuations of climatic conditions. Scientific investigation of DROUGHT is essential for water resources planning and management and to mitigate water shortages. DROUGHT analyses were done just by some quality factors during the last few decades, but currently there are several mathematical DROUGHT indices. In this research the Standardized Precipitation Index (SPI) was used for analysing and MONITORING climatological DROUGHT in Golestan Province. For this purpose, monthly rainfall statistical data of 24 gagging stations for 29 years periods were used. The DROUGHT status maps were then prepared by using Surfer 8.0 software, for all years. The results showed very high DROUGHT fluctuations. Despite finding any clear cycle for DROUGHT occurrence, it can be obviously showed that the major DROUGHT or wet conditions can occur roughly every 11 years. There can some DROUGHT and wet years be observed even during those 11 years. DROUGHT occurrence and frequency was found very high in the border parts of the province and also near the Caspian see beach. These regions are located in dry and semi-dry climate. Moreover, the exact time in which DROUGHT begins and ends are not the same in all the regions. Furthermore, there can be at least 3 humidity conditions every year.

DROUGHT is one of the major natural disasters which affect human society more than all other calamities. In order to monitor the DROUGHT conditions in Nahavand City, the province of Hamedan, the monthly and annual rainfall data of the Varayeneh and Vasaj Stations were collected for 41 years (1969-2009). The DROUGHT condition were analyzed using Rainfall Anomaly Index (RAI), Standard Index of Annual Precipitation (SLAP), Percentage of Normal Index (PNI), Deciles Index (DI), Standardized Precipitation Index (SPI), Chinese Z Index (CZI), Modified CZI (MCZI) and Z Score Index (ZSI). The results indicate that the most severe DROUGHT recorded at both the Varayeneh and Vasaj stations based on the PNI, SPI, CZI, DI and ZSI indices in the water year of 1998-1999. According to the MCZI index, a severe DROUGHT, was observed at both the Vasaj and Varayeneh stations in the water year of 1970-1971. Based on SLAP index, five severe DROUGHT cases were observed at the Varayeneh station, and seven severe DROUGHT cases were observed at the Vasaj station. Based on the RAI index, five severe DROUGHTs were observed at the Varayeneh station and seven severe DROUGHTs were observed at the Vasaj station. Moreover, based on the majority of these indices, the most severe DROUGHT of this 40-year period in Nahavand City occurred in the water year of 1998-1999.

The aim of this study is to link DROUGHT MONITORING systems to management actions in surface water systems. For this purpose DROUGHT early warning system is applied. In order to assess the proposed approach, water resources system of Zarine-rud River and Reservoir was used. Management actions includes utilizing coefficients that decrease the release from the reservoir. In each DROUGHT warning level, a reduction coefficient is computed by a Multi-Objective Genetic Algorithm. Utilizing the model during the entire historic period, the number of alerts is decreased on levels two to four by 18, 80, and 10%, respectively. Also, by applying reduction coefficients during index DROUGHT period, deficits above 80% decreased to less than 50% over six months. The effect of model in condition of supplying the environment water right of Urmia Lake is also evaluated. Applying reduction coefficients during index DROUGHT, the deficits above 50% is decreased to less than 30% over 14 months. This research showed that model had an appropriate function in warning declaration in long term periods. The assessments indicated the achieved results from the model are accurate and acceptable and therefore the application of this method is recommended.

DROUGHT is a climatological hazard and is a part of the climate of a region. This climatological phenomenon has some properties that distinguish it from other natural disasters. DROUGHT is a gradual phenomenon and when the amount of moisture and precipitation become less than normal value in a certain period, its damages are non- structural in this condition and it is said that DROUGHT has occurred. Researches show that DROUGHT damages are the highest among natural disasters. Therefore the extensive MONITORING or creating an early warning system in the DROUGHT prone area is inevitable. One of the basic instruments of DROUGHT MONITORING is the application of its index. In this paper Palmer DROUGHT Severity Index (PDSI) has been assessed as a valid and applicable model. The PDSI uses temperature (T), precipitation (P) and available water holding capacity (AWC) of the soil. Using these data for each period, potential amount of evapotranspiration is calculated based on two layer model for soil moisture computations. Then, other parameters such as potential of recharge and potential of runoff are being calculated. Finally the model output results which are monthly deviation moisture (Z) and DROUGHT severity index (X3i) have been determined to use designed software for mashed synoptic station for the statistical period (1971-2003).

Introduction MONITORING of hydrological DROUGHTs is one of the basic needs of water resources management in watersheds, especially in the field of water agriculture. DROUGHT is divided into three major groups: meteorology, agriculture and hydrology. Hydrologic DROUGHT can be studied in different ways. One of the common methods is the use of low flow indexes and threshold level approach. Materials and methods In this research, the minimum flow indices (Q75, Q90 and Q95) extracted from the flow continuity curve and minimum flow series (10 and 30 days) as well as the amount of flow deficit for hydrological DROUGHT MONITORING in the Caspian Sea Basin were investigated and evaluated. For this purpose, 40 hydrometric stations with 41-year statistics (1970-2011) were selected. In the next step, the data of the studied stations were evaluated in terms of homogeneity, independence and randomness. Then, with the help of hierarchical cluster analysis and step-by-step regression, hydrological homogenous areas were determined and regional analysis of these indicators was done. Results and discussion In order to investigate the characteristics of the minimum current in the Caspian Sea Basin, first, the continuous flow curve was drawn for each of the stations, and then, three indices Q75, Q90 and Q95 were calculated for each of the stations. For the spatial comparison of the minimum flow, the specific minimum discharge or qs (minimum discharge value divided by the area) was used. qs75 index varies between 0.0006 and 13 m3s-1per km2. The value of qs75 is less (drier) in the eastern parts and in the western parts of the region, the amount of dryness of the stream is less than other places. Examining the spatial distribution maps of these three indicators shows that the trend of their spatial changes is almost similar and they all indicate that the western regions of the Caspian Sea Basin are more humid than the eastern and central regions. In the next step, to examine the minimum flow indicators, a series of minimum flows of 10 and 30 days was prepared. By comparing distribution parameters with the help of scoring method, Log-Pearson type 3 distribution was selected as the best distribution in most stations. After choosing the most appropriate distribution, the values of the 10-day and 30-day minimum indices with different return periods were calculated. Examining the average indicators shows that the minimum discharge value of 10 days with a value equal to 0.01 m3s-1 in Vatana Station (12-035) located in the east of the basin and the highest with a value of 19.2 m3s-1, it is at Rudbar Station (17-034) in the western region of the basin. Regarding the average minimum discharge of 30 days, the lowest value is equal to 0.20 m3s-1 and the highest value is equal to 8.52 m3s-1in these two stations. In order to investigate the temporal changes of hydrological DROUGHT intensity, the annual time series of 10-day and 30-day low flow at each station were plotted in relation to the year of their occurrence, in order to determine the trend of changes in the DROUGHT situation in different years. Examining the time trend of the minimum flow indicators on the graphs, shows a decrease in the value of the indicators in recent years and a negative trend of the indicators. In other words, the graphs in almost all stations show hydrological DROUGHTs (reduction of minimum flow indicators) during recent years. In order to determine the length of minimum flow periods, 10 and 30 day moving averages of discharge were compared with Q90 index value in different stations. The results show that the persistence of DROUGHT in the central parts of the Caspian Sea Basin (Pulor, Razan, Karsang, Tange Lavij, Pol Zoghal and Zowat sub-basins) is more than the rest of the regions, these sub-basins are located in Mazandaran Province. The lowest duration of DROUGHT (between 22 and 25 days) is related to the sub-basins of Shalman, Pol-e-Sazman, Pashaki, Astana and Tutkabon in the eastern part of the Caspian Sea Basin and in Gilan Province. The eastern parts of the basin have also experienced a DROUGHT period between 28 and 30 days. Conclusion Results indicate that the years 1990 to 2010 have undergone severe and long DROUGHTs in most of the stations. The review of the spatial distribution of indexes shows better conditions in the western parts of the study area compared to the eastern sections in terms of dryness. However, the duration of hydrological DROUGHTs in the central study area is longer than in other parts of the basin. Investigating the time trend of the indexes also shows the increase in the frequency and duration of hydrological DROUGHTs in recent years. A comparison of different indexes shows that all of them have similar results in the region. The results of cluster analysis divided the area into three distinct homogenous units (in 0.01 significant level). The result of the regional analysis showed that in the eastern homogeneous region, the influencing factor on low flow indexes is elevation, while in the central and western regions, the drainage area and density have a greater impact.

The aim of this research is to investigate DROUGHT stress in rangeland rangelands in Ardabil province. According to the monthly rainfall data, 4 synoptic stations of Ardebil province (Ardebil, Khalkhal, Meshgin Shahr and Parsabad Moghan) during the statistical period of 2016-1996 were used to calculate DROUGHT index (SEPI) index for 4 periods of 1, 3, 6 and 9 months. Landsat TM and OLI satellite imagery was also used to prepare landslide classification maps based on the maximum probability model and calculation of vegetation indices NDVI, EVI, SAVI and LAI. In order to investigate the relationship between the studied indices, Pearson correlation coefficient (R) and root mean square error (RMSE) have been used. The results of the classification showed that the extent of the rangelands of Ardebil province in 1394 in the year 1377, both in the rangeland and in the rangelands, is a significant decrease. According to the results of SPI, the DROUGHT condition during 2011-2015 is more than the other periods studied. Vegetation dispersal maps were based on decision tree tree classification algorithm and according to NDVI index for the studied months. Also, according to the results of the evaluation, the highest correlation was observed between the NDVI index and the 6-month SEPI index, and the lowest mean squared error was found between the SAVI index and the 6-month SEPI index, but in general, the most suitable indicator for DROUGHT MONITORING in Ardebil province pastures is a 6-month NDVI and SEPI indicator.