جستجوی مقالات مرتبط با کلیدواژه « drought indices » در نشریات گروه « آب و خاک »

This study identified and described drought using multiple MODIS-based indicators, so the temporal-spatial characteristics of the intensity and frequency of drought in the entire country in the period from 2001 to 2021 using the standardized precipitation index in the form of one month SPI-1. Three-month SPI-3 and one-year SPI-12, based on CHIRPS precipitation data set with spatial resolution of 5 km, vegetation condition index (VCI), temperature condition index (TCI) and vegetation health index (VHI) were investigated. the distribution of rainfall in the southeastern and central regions of the country is less than 200 mm per year. Examining the ratio of drought classes based on the TCI index shows that the area ratio of the areas that are in the severe drought class in 2020 and 2021 is 36.7% and 43.2%, respectively, which has increased by about 7%. The comparison of the area of the drought class of the TCI and VCI indices also shows that the VCI index has overestimated the areas in the severe drought class by 3.7% and 5.1% in 2020 and 2021. Also, the VHI index shows that 6 provinces in the southern region of the country have experienced long-term drought between 2009 and 2021.

Studying the effects of drought in mountainous areas is facing problems due to the inappropriate distribution of stations, the lack of long-term data, and areas lacking statistics. Therefore, the main objective of this research was to investigate the drought indices of Kurdistan province using TRMM satellite data and ECMWF dataset, as well as to evaluate their accuracy against the data of land stations in Kurdistan province. First, ECMWF precipitation data for the 2000-2020 period and TRMM precipitation data for the 2000-2019 period were obtained and evaluated using RMSE, MBE, and correlation coefficient statistics. Spearman's correlation coefficient showed a significant relationship between the TRMM satellite precipitation data and the ECMWF dataset with ground stations at the 5% level, and the value of this coefficient was between 0.95-0.85. According to the results, it can be acknowledged that the TRMM satellite rainfall and ECMWF dataset in the monthly time scale had proper accuracy at the Kurdistan province level. Therefore, these two sources were used to examine the drought indices. SPI, SPEI, and ZSI drought indices were calculated in different monthly periods (1-48), PNI in different monthly, seasonal, and annual periods in Kurdistan province (Saqqez, Qorveh, Bijar, Sanandaj stations). Spearman's correlation coefficient indicated a significant relationship at the 5% level between the SPI, ZSI, PNI, and SPEI index of the ECMWF dataset with ground stations. The results of the SPI index showed that the lowest RMSE value for the TRMM satellite at the Saqqez station and the three months was equal to 0.45, and for the ECMWF dataset at the Sanandaj station and the 24 months was equal to 0.35.

Although Iran has 1.1% of the world's land area, it has only 0.34% of the available water resources. On the other hand, in most parts of Iran, precipitation is not evenly distributed. The average annual rainfall in Iran is about 250 mm and is one of the arid and semi-arid regions of the world and drought is one of its main climatic characteristics. Drought can be defined as a period of time with abnormally dry climatic conditions that cause serious hydrological imbalances due to prolonged lack of sufficient rainfall. Drought is a natural, temporary and reversible phenomenon in any climate, which is more pronounced in arid and semi-arid regions. According to different definitions, the drought phenomenon is divided into four different categories based on the damages that drought causes to different sources such as river flow, groundwater level, soil moisture, agricultural products and people's living conditions. These four categories are named meteorological, hydrological, agricultural and socio-economic drought, respectively. Recognizing the drought phenomenon and quantifying it by using drought indicators, suitable for the conditions of each region, is one of the main ways to adapt and control this phenomenon and is also a suitable tool for managers and policy makers in different sectors to be able to reduce drought damages as much as possible with coherent planning. One of the main sources of fresh water needed by human societies is groundwater resources, which are the largest reserves of fresh water on earth after glaciers. Groundwater resources are used for different purposes. For example, more than 90% of cities and about 70% of the needs of the agricultural sector worldwide are supplied from these sources. Droughts and precipitation occurrance are the most important factors that affect groundwater resources in the long run. In arid and semi-arid regions, groundwater depletion and quality play a key role. As a result of the drought phenomenon, the amount of groundwater consumption also increases. Severe droughts have occurred in different provinces of Iran in recent years. This shows that it is important to study the drought in this country to prevent the environmental crisis and the damages caused by it. Occurrence of drought in Damghan city, located in Semnan province, has caused the development of deserts, especially in its southern regions, and in the crisis of groundwater and surface water shortages, agricultural lands, gardens and livestock are in danger in this regard and the damages caused through this has economically reduced the quantity and quality of products. Investigation and monitoring of drought are important tools for drought management, which could determine its beginning and end, areal extent and severity by using climatic and hydrologic parameters. Knowledge of the occurrence of drought is essential to design environmental and executive planning to raise awareness of this issue and mitigate its negative and harmful effects as much as possible and make the right decisions for the study area.

The objectives of the present study are summarized as follows:A) Understanding the general situation of Damghan city in terms of long-term rainfall characteristicsB) Examining the trend and characteristics of drought and determining the various indicators of meteorological drought in the regionC) Investigating the correlation between drought indicesD) Finding the most suitable drought index in the regionE) Analysis of the relationship between drought and rainfall changes with groundwater level in the region.In the current research, meteorological drought of Damghan region is studied by using drought indices. For this purpose, monthly precipitation data of Damghan, Hossein Abad, Khourzan, Ghousheh, Mabad, and Astaneh stations were obtained for a common statistical period (1997-2019). After studying annual precipitation trend for each station, duration and maximum drought were determined using SPI, DI, PN, CZI, MCZI and ZSI indices. To investigate the performance of these indices and select the best-fitted index for Damghan region, the minimal theorem of precipitation was used.

Based on the results, the best-fitted index for Damghan township was DI, which showed proper performance in both prediction of severe drought and wet years. In the next step, using Spearman correlation between precipitation and drought indices, the PN index had acceptable performance in prediction of severe droughts, but could not predict wet years. To compare the indices for prediction of fluctuations of groundwater level, the 3, 6, 9, 12, 18 24 an 48-month moving averages were used. Finally, the SPI index was selected as the best-fitted index for predicting groundwater level in Damghan region.

One of the most important natural hazards that is affecting a large number of people, due to extensive damage, is drought. Drought is also a phenomenon directly related to the issue of water scarcity and because of its reversibility, it can affect the various aspects of human life and the environment. The drought affects almost all the determinants of the hydrological cycle from the onset of precipitation and then the surface water flow and eventually storage in groundwater. Therefore, in this research, due to the results of the stable process of precipitation and temperature in the Ardabil DareRood basin, SPI Index which relies on precipitation, with the RDI index which combines the parameters of potential evapotranspiration and precipitation, were compared and evaluated in different time intervals.

In this study, in order to identify drought and wet periods, it was used from monthly precipitation data, Minimum and maximum monthly temperature for seven synoptic stations, for a 30 years (1985-2014) in the Ardabil DareRood basin in the northwest of Iran. In order to identify the trend in the precipitation and temperature series in this research was used Man-Kendall (MK) and Sen's slope (Sen) models. Also, to assess the long-term stability of the trend in the time series was used the LOWESS curve (at a significant level of 5%). Also using Aridity index, four stations in the arid area and three stations in the semi-arid region were established. In order to calculate the RDI index, the values of potential evapotranspiration were use. The amount of PET in the RDI index using monthly temperature values, and was obtained by the Hargreaves method. Finally, SPI and RDI indices were compared in 3, 6, 9, and 12-month scales.

The results of the LOWESS curve showed that the annual temperature at all stations follows an incremental scenario. While the precipitation behaves differently and often is decreasing. The results also showed that SPI and RDI indices are very similar in different time scales, and R2 is in most cases greater than 0.90. The extreme drought the observed in SPI and RDI models is related to the Ardabil station in 2010-2011 on a 3-month scale, whose values were respectively -3/11 and -3/09. Also, the results showed that the RDI index that Extreme and severe wet values it’s larger than SPI. Eventually, both indices are many similarities with each other but because of RDI's use of PET, It can be used more widely for arid and semi-arid regions of Iran

this research, two SPI and RDI indices were used to compare the drought events in the DarehRood Ardabil basin of the northwest of Iran.Due to the dry and semi-arid climate of most regions of Iran, It is very probable that the amount of precipitation is zero in some seasons. Therefore precipitation-based indices such as SPI may have less efficiency than RDI index, which, in addition to rainfall, uses potential evapotranspiration (PET) in their formulation. Considering the importance of PET parameter in agriculture and water resources management in Iran, It is necessary to examine the RDI index in other regions of Iran, such as the northwest and mountainous regions of Iran and its results can be compared with other indicators such as the important and highly applicable SPI indicator.

Continual drought affected on the earth surface and has changed appearance of it. Therefore accurate assessment of changes in the climate parameters and effect of them on the environmental factors and water resources is very important and necessary. In this paper¡ precipitation and temperature changes in Shiraz synoptic station since 1983 to 2013 were evaluated. In this study various drought indexes such as SPI¡ RAI¡ PNPI¡ DI and SIAP evaluated in the annual scale and based of them¡ the different rainfall regimes in Shiraz were categorized. According to the monitoring of drought and wet years condition¡ maximum similarity is between SIAP index and DI¡ RAI indexes¡ SPI and RAI indexes have minimum similarity. According to the Results of this paper in the recent decade changes trend of annual precipitation¡ maximum intensity of rainfall and minimum absolute of temperature have been decreased. So that annual precipitation decreased about 50 millimeters in the last decade¡ maximum intensity of daily precipitation decreased 20 percent and average of minimum annual temperature decreased 2 degrees centigrade. Also the trend changes of maximum absolute temperature and number of frost days have been increased. According to results difference between maximum and minimum annual temperature have been increased¡ average of maximum absolute temperature in the ten years periods have been increased about 0.6 degrees centigrade.

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.

In this study reservoir inflow volume is used to investigate drought conditions by various methods so that by comparison with drought conditions at meteorological and hydrometric stations, the used drought indices could be evaluated. Also, relationships between cumulative reservoir inflow volumes at critical dates and those of the previous months were investigated, in order to identify effective variables for future utilization of stored water and implementation of optimal management decisions for reservoir operation. At first, the SPI was used in two different manners, by applying the method by Mckee and also by applying the method by Nalbantis and Tsakiris, in order to investigate meteorological droughts in four rainfall stations at Kor watershed (upstream of Doroodzan Dam). Also, hydrological drought conditions were investigated based on data on inflow into the Doroodzan reservoir and Chamriz hydrometric station, which were modeled utilizing the SDI, which according to the results the SPI and the SDI from the hydrometric station data, would not be sufficient for drought monitoring and utilization of the SDI on inflow into the reservoir as a good representative of the entire watershed would be more appropriate. In order to establish relationships between cumulative reservoir inflows at critical dates with cumulative reservoir inflow of previous months, the first days of Farvardin, Ordibehesht, Khordad and Tir were considered as critical dates. According to final equations, inflow into the reservoir on the first days of Ordibehesht, Khordad and Tir are directly related to cumulative inflows of the previous month. This would indicate that as the non-rainy season approaches, inflow volume stabilizes and is less effected by rainfalls or in other words by climatological factors. Whereby, for the first day of Farvardin, month of Mehr along with Dey and Bahman as effective variables indicates that inflow volume on the first day of Farvardin is dependent on the rainy season, which would highlight the importance of drought indices and also climatological factors on reservoir inflow during the rainy season.

Drought is a natural phenomenon that periodically, every region and every climate, occurs in different sectors of human life can be affected by many negative effects. So far, the drought has many definitions. The lack of a comprehensive definition of drought and the different means, from a different perspective, the drought has hampered. For this purpose the quantitative expression of drought This phenomenon is used. This research proposes four characteristics of drought intensity, duration, and extent of occurrence of drought has been studied. To determine the extent of drought and its effects on different parts of the study area, indicators PNPI, MPNPI, DI and RAI in different parts of the draft Zoning calculated using ARC GIS software have been conducted. To achieve this goal, the statistics for 32 meteorological stations and synoptic polls that are doing good distribution in the region, 30-year period (from 1981 to 2010) were collected. Spatial distribution of drought indices using ground ordinary kriging (OK) and the spherical model, exponential, linear and Gaussian and inverse distance method (IDW) Batvan 1 to 5 were calculated, and the area classified drought done were. Then the method ground by using various criteria to evaluate and compare the RMSE and MAE. The results show that the ordinary kriging (OK) Gaussian model is more appropriate than the inverse distance method (IDW) and has a higher accuracy. It is recommended that this method be used for mapping regional drought.

Prediction of precise forage production and proper management strategies requires identifying key climatic factors in different regions. The objective of this research is to compare forage production in different region based on climatic factors and drought indices. The study sites include Arak، Roudshore، Baghic، and Gharahso in Central and Qom provinces. Climatic factors and drought indices include precipitation، temperature، evapotranspiration، standardized precipitation index (SPI)، and Reconnaissance Drought Index (RDI). For each climatic variable/or indices، 33 time periods of 1، 2، 3، 4، 6، and 9-month were specified. We have used Principle Component Analysis to decline the number of variables and then، the appropriate time periods were selected. By using stepwise and best subset، the relationship between forage production and each of the climate factors and indices was modeled. To select model، assessment statistics of R، MBE، RMSE، MARE، and IPE were used. Finally، to predict forage production in Roudshore، Baghic، and Gharahso sites، models based on evapotranspiration (RMSE=7. 7، r=0. 99)، RDI (RMSE=3. 1، r=0. 99) and precipitation (RMSE=4. 0، r=0. 99) were selected respectively. The best model was based on the combinations of climatic factors and drought indices (RMSE=0. 2، r=0. 99) for Arak. In general، the relation between forage production and drought condition based on RDI is stronger than its relationship with precipitation and temperature. As we have used precipitation and evapotranspiration simultaneously in RDI، so this index is more precise than SPI.

The mean annual precipitation (MAP) is the most important criterion used in drought classification. Different indices have been developed based on the MAP for drought classification، of which four most commonly used are: the percentage indices of normal (PN)، the standardized precipitation index (SPI)، deciles (DPI) and the rainfall anomaly index (RAI). Each of these indices is classified into classes for drought description. Each class is represented as a state of severe drought. This study compares these indices benefiting from the rainfall data collected during 30 years (1980-2010) at seven stations in the Province of Sistan andBaluchestan. After calculating the indices during the desired time scale، the results were classified and evaluated based on sequence similarity factors of dry، normal and wet years، and by using the cluster analysis and developing statistical correlation between them. The analysis indicated that the PN index and RAI were statistically similar and lead to identical results in the dry and hot climate of Sistan and Baluchestan. It was further revealed that، the paired PN-RAI، PN-SPI and SPI-RAI were highly correlated at most of the stations. Moreover، the PN index and the RAI were placed in one class in the cluster analysis. Calculations indicated that the results of PN and RAI criteria were close to each other in terms of describing drought. Therefore، these indices are recommended for determining the drought severity in the province of Sistan and Baluchestan. Despite the widespread use of the SPI، this index is not suitable for determining the severity of drought in this province.

Regional vegetation plays an important role in modeling ecosystem changes and conservation. Meteorological drought indices which are directly obtained from such meteorological data as precipitation cant be useful in drought monitoring if those data are absence. Therefore, remote sensing techniques may provide an efficient technique for drought monitoring. In this study, the values of Normalized Difference Vegetation Index (NDVI) changes was investigated in the pasture and rainfed lands of Neishabour watershed during November to May, 2001 to 2010 using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images. In order to practice a more precise drought monitoring, standardized precipitation (SPI) and vegetation indexes (VCI) were also computed and drought class determined based on both values. The results showed that the highest correlation coefficients between NDVI and precipitation were obtained for 6-months time step; however the highest increment in correlation coefficients were as transition from one to two month(s) precipitation (increment from 0.068 to 0.547). The lowest and highest mentioned correlation coefficients during 2001 to 2010 were achieved as zero and 0.73 for pastures, zero and 0.71 for rainfeds, respectively. Comparison of SPI and VCI results as for drought classing showed that SPI index cannot exactly describe agricultural drought conditions perfectly. The lowest and highest correlation coefficients between VCI and SPI with time series of 1, 3, 6, 9 and 12 months were obtained as (0-0.23), (0.04-0.8), (0.001-0.66), (0-0.57) and (0.15-0.83), respectively. Analysis of the correlation coefficients between SPI and VCI showed that its lowest value (0.001) was happened for monthly SPI.

Drought is a phenomenon that occurs frequently in all over the world. It is clear that cannot basically campaign with drought. However, one is able to adapt with planning and preventing actions. Southern Alborz area selected for drought studies. This area is limited to Alborz chain in northern way and central salt desert of Iran in southern way. Researching stations are located in different elevations from 900 to 2500 meters above sea surface elevation. By using of different indices of drought, calculated and analyzed different precipitation states. In all of stations, often years and in most of drought indices, all precipitation categories existed. By two ways, it proved that precipitation states, especially droughts, become independence from elevation. These two ways are, 1. Amount of drought indices regress and analyze with elevation, 2. Amount of drought indices classified and these classes regress and analyze with elevations.

Drought is caused decrease by of rainfall، runoff and soil moisture and also increase of air temperature and water table compared to long time average condition. Drought can be divided into four major groups of Meteorological، Hydrological، Agricultural and Social- economical which meteorological drought will be evaluated by rainfall values comparing with its average. In this study، by use of monthly rainfall data of Babolsar، Noushahr and Ramsar synoptic Stations which are related to Mazandaran Meteorological Organization، Drought events was quantified by Standardized Precipitation Index (SPI)، Percentage of Normal Index (PNI)، Deciles Index (DI)، Chinese Z Index (CZI)، Modified Chinese Z Index (MCZI) and Z- Score Index and Mohan & Rangacharia method. Results shows that PNI and DI in all stations have similar trends and the Curves of SPI، ZSI and CZI in all stations are well coincide with each other and have a very good fitness but MCZI. In Mohan & Rangacharia method، drought events characteristics consists of commencement، termination، duration and intensity were determined for all stations. Applying this method for preparing iso-duration and iso- intensity maps of drought (Drought zoning) for determination of the drought susceptible area and also forecasting the future condition are recommended.