Introduction: Hydrologic Drought in the sense of deficient river flow is defined as the periods that river flow does not meet the needs of planned programs for system management. Drought is generally considered as periods with insignificant precipitation, soil moisture and water resources for sustaining and supplying the socioeconomic activities of a region. Thus, it is difficult to give a universal definition of Drought. The most well-known classification of Droughts is based on the nature of the water deficit: (a) the meteorological Drought, (b) the Hydrological Drought, (c) the agricultural Drought, (d) the socio-economic Drought. Perhaps the most widely used model is the ARIMA model for predicting Drought. The two general forms of ARIMA models are non-seasonal ARIMA (p, d, q) and multiplicative seasonal ARIMA (p, d, q)×(P, D, Q) in which p and q are non-seasonal autoregressive and moving average, P and Q are seasonal autoregressive and moving average parameters, respectively. The other two parameters, d and D, are required differencing used to make the series stationary. The differencing operator that is usually used in the case of non-stationary time series. The aim of the study is to predict Hydrological Drought using time series analysis in the small forest watershed. . . .

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.

Increased or decreased rainfall compared to long-term average conditions, caused two phenomena such as floods and Droughts. Drought is one of the climatic events that exhibit different forms in the vast expanse of Iran and influence natural life of habitants. Drought, rising temperatures and evapotranspiration, increased consumption patterns and poor management are the fundamental elements of a water crisis.ZayandeRood river because of these reasons is faced with severe economic challenges, social and management of water resources. In this paper, the surface water supply index (SWSI) was investigated catchment Hydrological Drought. The results showed that the years 1377 and 1378 are the most arid years in the basin that the amounts of SWSI are -2.52 and -2.55. The most humid year is 1371 and the amount of SWSI is 2.88 the frequency of the SWSI was demonstrated that during the period, with 43% of the basin has the highest frequency in normal conditions and after it been poor Drought which has a frequency of 22%. Calculations have shown that in 31% of cases, the severity of Drought conditions in the area have been different.The findings indicate that the climatic Drought is the vital effective factor in the Zayande Rood Basin’s water crisis with high intensity and stability in relation to its past.According to SWSI, in a period of 23 years there exists Drought state for 7 years (31%). Normal state for 10 years (43%) and humid state (26%) for 6 years. The lowest SWSI volume was in the year 1999 at -2.55 indicating the most intense hydrologic Drought and 1992 with 2.88 as the most humid year in the study region.Despite other factors like water-consumption pattern, population growth, industrial use and water transfer to other regions the causation of Drought is due to the climate and hydrologic Droughts, the natural phenomenon. Drawing policies based on appropriate scientific water management knowledge accompanied with risk management indexes the damage level on this Basin can be reduced.

Extended Abstract Introduction: The occurrence of Droughts in a region is closely related to water supply. Since water supply in each region is related to the climatic regime of that area, so the definition of Droughts varies according to the conditions of each region. Drought can be attributed to a period of abnormally dry conditions that is sufficiently long to produce an imbalance in the hydrologic state of an area. Monitoring systems play an important role in the management of Drought plans. The beginning of Droughts is due to the occurrence of the meteorological Drought caused by the precipitation shortages. The Hydrological Droughts are usually more delayed than the meteorological or agricultural Droughts. ...

Water crisis and Drought are among the most important issues to which the human has been faced particularly in the recent years; hence, investigation of Drought is so important in optimal water management. Drought has been known as an environmental phenomenon which is inseparable from climate changes which can occur in any geographical region. Various definitions have been presented since yet. By a general definition, Drought includes abnormal shortage of precipitation in a long-term period so that, it causes soil moisture shortage and reduced current waters; therefore, human activities and natural life of plants are disturbed. Qarehsou watershed is among the places which are affected by Drought issue. Considering the major role of this watershed on water supply of Kermanshah Province as well as recreational value of Qarehsou River; the occurred Droughts can cause economic challenges and ultimately, social crisis in the region. The objective of the present study is to determine meteorological and Hydrological wet and Drought periods and investigating the relationship between them of which the results can be used for more appropriate water resources management in Qarehsou watershed. In the present study, the statistics of five rain-gauge stations, five hydrometric and 20 piezometric wells existing in the watershed were used for Drought analysis. Drought indices RAI and SIAP were used to extract meteorological Drought periods and also the indices SDI and SWI were used to analyze Hydrological Drought. According to the obtained amounts by each Drought indices, the severest Drought has occurred in 2007; hence, the Hydrological and meteorological Drought zoning maps of the year 2007-2008 were drawn. The results showed that, the Drought severity has been increased gradually since 1999 and the severest Drought was in 2007 and the most durable one has occurred during 2007 to 2012.The results indicated that, Hydrological Drought has been occurred since the cropping season 2007-2008 with one-year delay relative to meteorological Drought. Also during the recent years, one or two years of delay has been observed between the occurrence of Hydrological Drought of underground waters and meteorological Drought. The results demonstrated that, based on the index RAI, the maximum frequency was related to the stations Mahidasht, Pol Kohneh and Ravansar by 27% at a very severe Drought class. Also based on the index SIAP, the maximum frequency was related to the station Doabmerk by 23% at a moderate Drought class. Based on the index SDI, the maximum frequency was in the station Sarasiab by 45% at a moderate Drought class and finally, based on the index SWI, the maximum frequency was related to the piezometric wells of Hashilan, QarehTapeh and Kahriz by 45% at a moderate Drought class. Zoning maps of meteorological Drought showed that, meteorological Drought has occurred in all the region. According to the zoning map of Hydrological Drought, Hydrological Drought of the surface flows is at a moderate class throughout the watershed while, Hydrological Drought of the underground water resources at the north east and south west and somewhat central parts of the watershed is at a very severe class. Generally, results of the present study indicated that, duration and severity of the Droughts and particularly Hydrological Drought are considerable during the recent years in QarehSou watershed. Hence, results of the present study can be useful for optimal management of water resources and water demand and supply planning, as well as the managers, lanners and experts who can be enabled to provide required strategies and practical solutions.

The aim followed in this research work was a study of effects the of temporal climatic Drought on the Hydrological Drought, the study being carried out in Hashtgerd plain, karaj. Throughout the study the SPI (Standardized precipitation Index) for climatic Drought and GRI for the Hydrological Drought were assessed. Mann-Kendall trend test was applied to assess data (rainfall and water level). Pearson correlation was determined through cross-correlation between SPI and GRI. For a detailed study of the correlation, the SPI time scales were calculated from 0 to 200 months and the monthly lag time from 0 to 150. The results indicated a high correlation related to interaction between SPI and the lag time with the GRI. Also, the behavior patterns of piezometers led to three groups of time actions within the study area.

Drought as a natural hazard has always affected some parts of the country. Nowadays, it is possible to study Drought using remote sensing techniques through its effects on the plants and achieve more accurate and efficient results for Drought modelling. This study aims to investigate the relationship between meteorological, Hydrological and agricultural Drought using Drought indices and remote sensing method in Gharehsou watershed. For this purpose, MODIS images (satellite Terra, product MODO9Q1) and rainfall and discharge data of five meteorological and hydrometric stations for 2000 to 2015 time period were used. The results of the comparison of meteorological, Hydrological and agricultural Drought represent conformity of the three types of Drought in the years 2000, 2001, 2004, 2005, 2007, 2009, 2010, 2011, 2012, 2013, 2014 and 2015. Although the SPI and NDVI values were positive in the years 2002, 2003 and 2008, SDI index showed the occurrence of Hydrological Drought (negative values). In the year 2006 despite the rainfall increase, but this year has been facing the agricultural and Hydrological Drought. So the results simultaneity of Drought there does not exist in all the years. The results of Pearson correlation showed there is a high correlation between mean NDVI and SPI and SDI indices equal to 0.706 and 0.788 respectively at the significance level of 0.01. Generally, the results of SDI and SPI indices largely confirm the results of the NDVI index.

Introduction: Climate change has been a very important issue in recent decades. Recently, frequent climatic events such as storms, floods, and Droughts have been reported around the world (Habeeb et al., 2015). These extreme events will have devastating effects on ecosystems, society, and the economy (Hallegatte et al., 2013). Among these extreme events, Drought plays a more prominent role due to its direct impact on socio-economic development and environmental degradation. Therefore, understanding Drought phenomena is important for proper planning and management of water resources (Yilmaz, 2019). So far, various indicators have been proposed to monitor the Drought. Undoubtedly the most well-known Drought monitoring index is SPI proposed by McKee et al. The World Meteorological Organization has recommended this index as the main indicator of meteorological Drought. It is also important to analyze the SPI trend, which provides scientific information for better modeling as well as the prediction of the phenomenon (Golian et al., 2015). A review of research conducted worldwide and in Iran shows that Drought trend analysis has been mainly done using parametric tests such as linear regression and non-parametric tests like Mann-Kendall, Spearman, Sen’ s estimator, and modified Mann-Kendall. These methods require a set of assumption validity such as serial correlation structure, probability distribution functions, and seasonal trends. For this reason, Ş en (2012) proposed the Innovative Trend Analysis (ITA) method, which does not require any assumptions and analyzes the trend of time series based on a comparison of two ascendingly ordered halves. This method has found wide applications in hydro-climatic research and has been considered and used by many researchers. This study aimed to identify Drought-prone areas in the Lake Urmia basin using SPI time series and the innovative trend analysis (ITA). For this purpose, SPI values in 12 and 24-month time scales were calculated based on 32-year-long precipitation data (1986-2017) in 8 synoptic stations in the Lake Urmia basin. Then the trend of the SPI. series was investigated using the ITA method. Finally, the results of this method were compared with the results of the Mann-Kendall test. Methodology: 2. 1. Standardized precipitation index (SPI) Among the quantitative indicators in Drought analysis, SPI is acceptable as a suitable index for Drought analysis due to the simplicity of calculations, the use of available rainfall data, and the ability to calculate for different time scales as well as different spatial scales. SPI can show the impact of Drought on water resources. In a general classification, it is possible to use the 1 to 3-month SPI for meteorological Drought, 3 to 6-month SPI for agricultural Drought, and 12 to 24-month SPI for Hydrological Drought analyses and applications (Bonaccorso et al., 2003). 2. 2. Innovative Trend Analysis (ITA) This method has been proposed by Ş en (2012). In this index, time series are divided into two equal parts, which are separately sorted in ascending order. Then, the first and the second half of the time series are located on the x-axis and y-axis, respectively, of a Cartesian coordinate system. If the data are collected on the 1: 1 straight line (45° ), there is no trend in the time series (Fig. 1). If data are located on the upper triangular area of the ideal line, an increasing trend in the time series exists. If the data pile up in the lower (upper) triangular area of the 1: 1 line, there is a decreasing (increasing) trend in the time series (Ş en, 2014). Method: The statistical significance test of the ITA method has been also proposed by Ş en (2017). This test is performed based on the construction of confidence intervals and considering the difference between the two population means. If the slope value (s) isbetween the upper and lower confidence limits, the null hypothesis (H0) is confirmed; otherwise, the alternative hypothesis (H1) is accepted. The type of trend depends on the slope sign. The slope value can be positive or negative; this means that there is an increasing (+) or decreasing (-) trend in the time series (Ş en, 2017). 2. 3. Mann-Kendall test (MK) The non-parametric Mann-Kendall test is one of the most widely used methods for trend detection in time series. One of the main advantages of nonparametric methods is that the presence of outgoing data affects the result of the data process less than parametric methods. Besides, it is more suitable for data series having a short length and not normal statistical distribution or having missed data (Partal and Kahya, 2006). The positive and negative Z values indicate the increasing and decreasing trend in the series, respectively. Results and Discussion: To detect the Drought trend in the stations of the Lake Urmia basin, the ITA method was used for the 12 and 24-month SPI series. All SPI series were divided into two 16-year sub-series: from 1986 to 2001, and from 2002 to 2017. To identify the possible trend of the Drought as well as normal and wet conditions easily and better, two vertical lines have been added to the diagrams. The red line indicated the Drought limit and the green line indicated the limitations of the wet conditions and the area between the two lines representing the normal conditions. According to the figures, the 1: 1 line shows the neutral line (no trend) and in the case of no trend, the center point falls on the 1: 1 line. The results of the trend analysis of 12-month SPI values showed that the Drought and normal periods in Urmia, Saghez, and Mahabad had an increasing trend, but the wet conditions followed a decreasing trend. In Tabriz, an increasing trend was seen in normal and moderately Drought periods, and a mild decreasing trend was seen in wet periods. In Takab, wet periods showed a sharp decreasing trend, and a slightly increasing trend could be seen in Sarab. In Sahand and Maragheh, there has been a declining trend in all SPI values, leading to more severe Drought and weaker wet periods. The significance analysis of ITA and the Mann-Kendall test showed that in the 12-month SPI time series and based on the ITA method, all stations showed a significant trend, which was increasing in Tabriz and Sarab, and in other stations, it was decreasing. While the Man-Kendall method did not have a significant trend in Urmia, Tabriz, and Sarab, it showed a significant decreasing trend in other stations. In the trend analysis of 24-month SPI values by the ITA method, almost the same results were obtained. However, it should be noted that there was an increase in the slope of the trend for all stations. Another important point is that there were no significant increases in wet conditions. Similar to the results of 12-month SPI and based on two methods, the significance analysis of the ITA and Mann-Kendall test showed that Takab, Saqez, Sahand, Maragheh, and Mahabad had a significant decreasing trend and the difference was only observed in the higher ITA slope as well as the higher Z values in these stations. While in Urmia, Tabriz, and Sarab, there was no correspondence between the two methods. Conclusions: In this study, the ITA and Mann-Kendall trend tests were used for the 12 and 24-month SPI time series, determined for the 1970-2017 period, in order to demonstrate the Hydrological Drought trends in the Urmia Lake`s basin. The results of ITA and Mann-Kendall tests showed that Maragheh, Sahand, Saqez, Takab, and Mahabad had a significant decreasing trend in the 12 and 24-month SPI series. In Urmia, Tabriz, and Sarab, the Mann-Kendall test did not show any significant trends; while the ITA method showed significant decreasing and increasing trends in these stations. The results of this study can be used to manage water resources and understand the characteristics of climate change in the studied area.

Introduction: Drought is a natural phenomenon that may occur in all areas of land under any climate conditions. Scientific study of Drought is essential for water resource planning and management and for mitigating water shortages. Low rainfall is the main cause of the occurrence of Drought. Precipitation reduction in a period of time than long term average of an area is defined as meteorological Drought. Hydrological Drought is defined as a significant reduction in available water of all forms in a landscape. Meteorological Droughts lead to Hydrological Droughts with decreasing flow rates and aquifer discharge. Methodology: In order to quantify Drought phenomenon, some indicators on the basis of Drought definitions or computational methods were provided. These indicators are calculated for a single point, but the extent of the Drought and its severity vary in different parts of the basin and it is the key point of water resource management and planning for mitigation of Drought crisis. The purpose of this study was to investigate the spatial and temporal variations of climatic and hydrologic Drought in the North Karun Basin. In this study, some of the meteorological and Hydrological indicators such as Deciles (DI), Z score, Standardized Runoff Index(SRI), Stream flow Drought (SDI), Standardized Water Index (SWI) and Groundwater Resource Index (GRI) were calculated to assess the status of the study area. In order to expand point information and convert it to spatial information, after calculating different indices, the meteorological and Hydrological Drought severity mapping was done using Kriging and IDW(with power 1, 2, 3 and 4) methods. Result and Discussion: The results of the meteorological Drought indices showed that during the 30-year period (1974-2014), the studied area had experienced a severe Drought only once between the years 2007 and 2008. The SDI index showed that the river flows had declined at the same time as the meteorological Drought between the years 2007 and 2008. In addition, the river flow Drought (2007-2008) is clearly obvious in the next water year. In recent years, the SDI has fluctuated from moderate to severe Drought, and in general, all stations experienced a moderate Drought. SWI indicator analysis showed that groundwater level drop in the North Karun Basin occurred in 2007 and 2008, that has been delayed by one year to the meteorological Drought. The results of the GRI in the North Karun Basin showed that the Hydrological Drought began between 2007 and 2008. Due to the sharp drop in groundwater level, the severity of the groundwater Drought in recent years has been dramatically increased in the plains of the study area. The analysis of the Z index map indicated that while the Drought is more intense in the eastern parts of the basin, it is less severe and intense in its northern and southern parts. Groundwater Drought zoning showed that the severity of groundwater Drought in the northeast and southeast of the plains is high. The Shahrekord plain is one of the most important plains in the North Karun Basin, because it has the main concentration of agricultural and animal husbandry activities and has undergone a sharp decline in groundwater over recent years. The groundwater level of this plain reached its lowest level between the years 2013 and 2014. Conclusion: In general, the findings indicated that sever meteorological Droughts in the time period of thirty years (1986-2015) occurred in two years (2000-2001 and 2007-2008). But its impact on surface flow and groundwater recharge is significant due to anomalies in the rainfall – runoff process and excessive withdrawals from the groundwater resources. The meteorological and surface water Droughts periods in this basin often take one to two years. The duration and severity of Droughts, especially in groundwater resources, have been significant in recent years. The results also showed that geostatistical method of kriging with exponential and gaussian model has a high ability for Drought zoning. Also, it can be understood that the eastern part of the area has received fewer precipitation than the other parts. This result is also derived from the zoning of groundwater Droughts that the eastern parts of the plains are more severely affected by Drought. In general, Hydrological Droughts in the north Karun Basin are more intensive in the southern and southeastern regions. Simultaneous use of the meteorological and Hydrological indicators can be a useful tool for the separation of the meteorological and Hydrological Droughts as well as the assessment of Drought in the region.

Extended Abstract Introduction Drought is a weather phenomenon that causes much damage every year. Kohgilouyeh and Boyer Ahmad province is located in the Southwest of Iran. Since it provides a substantial portion of the water of Karoun, Maroon, and Zohreh, which are three important rivers in this province, and evaluation and prediction of Drought in this province seems necessary. This study aims to evaluate the compliance of meteorological and Hydrological Drought of the Zohreh river basin is in this province. Materials and methods: Using SPI (Standardized Precipitation Index) and SWI index (Standardized Water level Indicator), the relationship between meteorological and Hydrological Drought was evaluated, and the comparison between the occurrence of meteorological and Hydrological Droughts was performed. The SPI was calculated for 10 meteorological stations with 30 years of data, and SWI for 11 piezometric wells for the whole statistical data available. The trend of the river streamflow and piezometric wells' groundwater levels was assessed using the Mann-Kendall test for 5 hydrometric stations and the piezometric wells. The Pearson correlation coefficient was used to assess the relationship between rainfall, discharge, and groundwater level in different time lags. Results and Discussion: Results showed that in negative SPI durations, the groundwater level decreased with some delay. The delay increased when the Drought scale increased. In recent years, the duration and intensity of Drought have increased. Maximum volume of 3, 6, 9, and 12 months precipitation Drought of Nazmakan station occurred in 1378-78, the maximum intensity of 3, 6, and 9 months in 1383, and 12 months occurred in 1388. When the Drought scale increased, Drought duration and intensity increased, and the Drought frequency decreased. Results for the other stations were nearly similar. SWI of Basht well showed that 6, 12, 24, and 48 months Droughts continued nearly 48 months, from the end of 2006 to the middle of 2010. The intensity of 48 months Drought was maximum and 12, 24, and 6 months were in the next level of intensity. This trend shows the long time accumulating effect of meteorological trends on the decreasing level of groundwater, although pumping withdrawal of groundwater is also effective. The trend for other wells was nearly similar. The Mann-Kendall test did not confirm the trend of stations discharge, but the decreasing level of groundwater in all wells was statistically confirmed. The Pearson’s coefficient of precipitation-discharge showed the maximum correlation with the same month data. It could be from the surface water's direct relation with groundwater, and the decreasing amount of snow precipitation in recent years, which lead to a delay between them. The maximum Pearson’s correlation of the groundwater level-precipitation, and groundwater level-discharge was observed with two months delay. It could verify the groundwater recharge with surface water, and the time needed for infiltration and movement of water in the aquifer. Conclusions: The results could be used for predicting the effects of meteorological Drought on Hydrological Drought. The properties of meteorological and Hydrological Droughts could be used to manage Drought and water resources, supply water for agriculture, industry, and livestock, and supply drinking water for humans in the province.