جستجوی مقالات مرتبط با کلیدواژه "شاخص های خشک سالی" در نشریات گروه "کشاورزی"

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.

Drought and grazing rangelands play an important role in changing the structure of vegetation and losing the biodiversity of natural ecosystems. In this research, in order to determine the effects of drought and livestock grazing on the vegetation structure of rangelands located in the Nakhab Forest of South Khorasan Province, species abundance, biodiversity, and range condition and trend were evaluated. For this purpose, sampling was done in 80 plots (2×2 m) located on four transects of 150 m using conventional methods in a two-year period (between the water years of 2019-2020 and 2020-2021). According to the standard precipitation index (SPI) and the normal percentage index (PN), 2019-2020 was very wet and 2020-2021was a mild drought. According to the physiognomy method, the plant type of the study area is Hammada salicornica and the important species include Aeluropus littoralis, Haloxylon persicum, and Zygophyllum atriplicoides. In terms of the percentage of vegetation, litter, bare soil, and stones and gravel, there is no significant difference between the grazed rangeland and enclosure in two years. The results show that in the two sampling years, the grazed rangeland has a higher species density than the enclosure. Enclosure rangeland has benefited class I and III species and livestock grazing has caused a significant decrease in class I and III plants and an increase in class II plants. Livestock grazing caused a significant decrease in the density of grass, forb, and shrub plants and did not affect the density of shrubs. The results showed that in the very wet year, there is no difference in species richness between the grazed range and the enclosure. Nevertheless, the enclosure has more species diversity than the grazed range. However, in the mild drought year, all biodiversity indices were not different between the grazed range and the enclosure. This indicates that in drought conditions, the enclosure does not help to improve species diversity.

Drought is one of the major problems facing countries in subtropical offerings such as Iran. Fars province, which is one of the southern provinces in the field of tourism and agriculture, has long been facing the problem of drought and water shortage, so the study of drought in this province to better manage the problem of drought and improve the situation of agriculture and agricultural tourism is necessary. The purpose of this study is to investigate the drought trend in this province using drought index and drought identification index. The parameters used in these indicators are potential rainfall and evapotranspiration. In this regard, rainfall and maximum temperature data of 10 stations in the statistical years 1999-2020 were used and the evapotranspiration of each station was calculated using Larry-Johnson method. Necessary indicators and diagrams were drawn by MATLAB software (a2020) and based on the obtained results, the average maximum and minimum drought intensity occurred in 2008 and 2004, respectively, also in 2020 showed a dry and normal situation. Finally, according to the zoning maps obtained from ArcMap software (10.8), an increase in drought intensity was observed in the southern and central parts of the province.

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.

The temporal and spatial variability of rainfall within and between years is a characteristic of Iran's climate. The aim of this study was to investigate the PCI, SPI, RDI and MFI indices and map their spatial variations. These data were obtained from the Meteorological Organization of Iran. The results idicated that the PCI index had an upward trend in 50% of the stations and a downward trend in the remaining stations. The lowest value of the PCI index was observes for the northern regions in 1992 at the Rasht Station (9.22), and the highest value for southeastern regions in 2008 at the Bandar Abbas Station (76.36). The MFI index had a downward trend of 28 stations with the lowest value of the MFI index in 2010 at the Yazd Station (4.42) and the highest value in 2001 at the Yasuj Station (451.65). According to the PCI index, the rainfall pattern at most of Iran's synoptic stations is seasonal and completely seasonal. The results of drought indices indicated that the SPI and RDI indices were higher in the western regions than the other regions. The severest drought based on both indices was observed at the Bushehr Synoptic Station in 2010. The values of these indices were (-3.4) and (-3.3), respectively. The results also indicated that the RDI index revealed a more severe drought conditions. As the RDI index includes air temperature as a direct factor affecting drought, it is recommended to replace the SPI index with this one. The Fornieh Rain Erosion Map maybe of great help to watershed managers and natural resource experts in planning soil conservation, erosion control, and land use schemes.

Drought is a phenomenon which is not preventable, but its outcomes could be mitigated by a holistic and scientific managerial vision. In order to approach to this goal, some practical frameworks is needed for different parts of the country, in respect to their climates. This paper is introducing development of the first agricultural drought risk management plan by experts of Agricultural Drought Management (ADM) for a pilot area. This project lasted for three years from 2009 to 2011. In this project some educational workshops and specialized meetings were held and have helped the plan to be more succeeded. At first, all needed climatic and agricultural information were collected and then a program for agricultural risk assessment in the region were selected. The drought plan was developed with a nine steps proposed method, in respect to advice of experts. Considering the average income of 41 billion Riyals from agricultural and animal husbandry activities, damages costs of poor to very severe drought varied from 3.450 to 10.350 billion Rials. Agricultural drought risk management plan can reduce drought damages from 30 to 47 percent, depended on drought intensity.

Water is one of the most basic human needs and other living creatures. Drought is a natural phenomenon and repeatable, which could be caused serious crisis. This phenomenon may be seen in any climate regime, even in humid regions, but the effects and its frequency are more observed in arid and semi-arid areas. The most important cause of drought is precipitation, but the increase or decrease in evapotranspiration can partly intensify or modify drought conditions. In order to drought monitoring are used different indices that generally can be based on precipitation or precipitation and evapotranspiration. On the other hand drought monitoring based on different indices maybe cause different results. Therefore, in this study, meteorological drought monitoring and evaluation of the effect of evapotranspiration on it were examined during a 50 years period from 1961 to 2010. Drought conditions are compared based on three drought indices of SPI, RDI and SPEI for Ramsar, Hamedan, Shiraz, Sabzevar, Bandar Abbas and Yazd synoptic stations, which respectively are located in Coastal Wet, Mountain, Semi Mountain, Semi Desert, Coastal Desert and Desert climates.
In this study, were used monthly statistics of meteorological parameters such as precipitation, mean temperature, minimum temperature, maximum temperature, relative humidity, sunshine hours and wind speed in six synoptic stations. Firstly, fulfilled initial statistical tests on monthly meteorological parameters. For this purpose, is used three known tests as Mann-Kendall test for the identification of Trend, Mann-Whitney test for detecting of Homogeneity and Grubbs-Beck test for detecting of Outlier. After verifying these data in terms of Homogeneity and Outlier, values of each of SPI, RDI and SPEI indices calculated in annual and seasonal scales.
Comparing results represented that in humid regions, there are not any significant differences between SPI index with RDI and SPEI indices which consider evapotranspiration. However; the difference between the indices is clear in arid regions. The least difference in terms of drought condition monitoring is between SPI and RDI in spring in Hamadan and the greatest difference between SPI and RDI indices is in the summer and the city of Yazd (desert climate). This shows the role of evapotranspiration and its impact on the drought, in the hot and dry season, especially in arid and desert regions. In autumn and winter seasons in every six studied stations, the least difference has happened between SPI with SPEI and SPI with RDI indices, so in this seasons, which evapotranspiration is lower, it has less important role in humidity condition (drought or wet).
According to the results of this study, can be concluded that in most cases the indices performance are not the same in different regions and at different time intervals. On the other side, can be concluded that the fluctuations of humidity condition (wet and drought) is very high in studied stations and based on any of the examined indices. While drought severity and its frequency of occurrence are different according to different indices. It is recommended for drought monitoring in arid regions, which the precipitation is negligible and the other side the evapotranspiration is manifold of annual precipitation, are used indices which are based on precipitation and evapotranspiration. Whereas in humid regions (such as Ramsar) evapotranspiration phenomena does not make significant role in the drought and in order to simplification, meteorological drought can be monitored only by precipitation.

Drought is a creeping natural phenomenon, which can occur in any region. Such phenomenon not only affects the region subjected to drought, but its adverse effects can also be extended to other adjacent regions. This phenomenon mainly starts with water deficiency (say less than long- term mean of variable under study such as rainfall, streamflow, groundwater level or soil moisture) and progress in time. This period can be ended by increasing the rainfall and reaching the mean level. Even after the ending of a drought period, its adverse effects can be continued for several months. Although, it is not possible (at least at this time) to prevent the occurrence of drought in a given region, it is not impossible to alleviate the drought consequences by scientific water management. Such a management should be employed before drought initiation as well as during it and continue on even after the end of the drought period. The frequency of the main drought characteristics is a major concern of this study. The Northwest of Iran recently encountered severe and prolonged droughts, such that a major portion of the Urmia Lake surface disappeared during the last drought in recent years. In order to study drought characteristics, we used the Reconnaissance Drought Index (RDI). This index is based on annual rainfall and potential reference crop evapotranspiration (abbreviated by PET here). This study employed the Monte Carlo simulation technique for synthetic data generation for analysis. The information from the 17 synoptic weather stations located in the North-west of Iran was used for drought analysis. Data was gathered from the Islamic Republic of Iran’s Meteorological Organization (IRIMO). In the first stage of research, the ratio of long term mean annual precipitation to evapotranspiration was calculated for each of the stations. For this purpose, the Penman-Montheis (FAO 56) method was selected for PET estimation. In the second stage, the 64 candidate statistical distributions were fitted for the mentioned RDI’s of each station. The best statistical distribution was selected among the 64 candidate distributions. The best fitted distribution was identified by the chi-square criterion. The parameters of the distribution were estimated by the Maximum Likelihood Estimation (MLE) scheme. Then 500 synthetic time series (each of them have the same number of observed data) were generated employing the parent population parameters. The three main drought characteristics (namely duration, severity and magnitude) were obtained for each of the mentioned artificial time series. The maximum values for each of the mentioned drought characteristic were selected for each year. Then, a new time series having the 500 elements were obtained by collecting the chosen values for each station. Once again the best distribution was selected for each series. Drought characteristics for different return periods (2, 10, 25, 50, 100 and 200 years) were estimated for each station. Preliminary results indicated that a negative trend existed in annual rainfall time series for almost all of the stations. On the other hand, the pattern of monthly PET histograms were more or less similar for all of the selected stations. The peak of the PET was mainly observed in the hottest month of year, whereas the lowest value of the monthly PET belonged to the coldest month of year. The results showed that the amount of annual rainfall time series decreases sharply, after the year 1991. However, PET values significantly increase for all of the selected stations. After calculation of RDI values, the histogram of annual RDI’s was plotted against the year. This is repeated for all of the selected stations. Figure. 6 shows the mentioned diagram for Tabriz station as an example. In the mentioned Figure, negative values of RDI (shown by red bars) indicated the drought years. A critical prolonged drought with a sixteen years duration period (neglecting the 2001 in which RDI value was a small positive value) was experienced in Tabriz. The maximum drought severity in Tabriz was estimated to be about -7 in RDI units. Urmia station experienced the longest drought period, starting from 1995 and ending in 2005. It can be concluded that although few sparse wet years were observed in some of the selected stations in the studied period, they cannot compensate the water deficiency accumulated during several consecutive years. The results showed that the lowest value of the ratio of drought severity in a 100 year return period to the corresponding value for 2 year return period was about 2.13 (belonged to the Tabriz station), whereas the highest value was 3.17 (belonged to the Tekab station). On the other hand, the lowest value for the ratio of drought duration in 100 year return period to its corresponding value for 2 year return period was 1.95 (experienced in the Makoo station). The highest mentioned ratio was 9.18 (observed in the Sardasht station). The lowest and highest value of the ratio of drought magnitude in 100 year return period to its corresponding value for 2 year return period were 1.17 and 2.74, respectively. The mentioned drought magnitude ratios were observed in the Urmia and the Khalkhal stations, respectively. The isoplethes of the three main drought characteristics (severity, magnitude, duration) for a 10 year return period was illustrated for the study area (Northwest of Iran). In the present study RDI values were used to analyze drought characteristics of Northwest of Iran. The Penman-Montheis method was used to estimate PET (needed for RDI) values of the stations. The main three drought characteristics were calculated for each of the 500 synthetic time series. The results showed that nearly all of the areas under study experienced severe and prolonged droughts. It can be concluded that a sharp decrease in annual precipitation as well as the increase in PET (due to greenhouse effects of consuming fossil fuels as the main source of energy in the region) from 1995 to 2005 was observed in the study area. Scientific management of available water in the study area is extremely vital to alleviate the adverse consequences of drought. Several economic and social problems were anticipated in these arid and semi-arid regions of Iran.

In this research, 5 percent of normal Precipitation Index (PNPI),Deciles of Precipitation(DPI),Rainfall Anomaly Index (RAI), Bahlme & Mooley Drought Index (BMDI) and standardized Precipitation Index (SPI) were used in order to investigate drought in Yazd synoptic station and 31 non synoptic stations all around this province. For this purpose, the present statistical errors were reconstructed via correlation between the stations, after raining data collection from the considered stations. Then, calculation of PNPI, DPI, RAI, BMDI and SPI indexes were calculated on monthly and annual scales. Situation of drought was determined based on the obtained values from calculation of each index according to tables related to the considered indexes in different classes of drought during the statistical period. Then indexes were compared to each other, considering drought given situation for each station. The difference and similarity of each index with other 4 indexes were calculated and investigated. Also after determination of drought situation in each station, given percentage of drought different situations via each Index was determined on annual scales, in 33 study stations. After passing the above mentioned stages, it was found that there was the highest percentage value of similarity between the two indexes RAI & DPI, as both indexes indicated similar situation of hard drought in the stations. These two indexes are considered most efficient to investigate aerology drought. But considering that static indexes are faced with problem on monthly scales and in stations located in drought regions, it is recommended to use‌ SPI & BMDI dynamic indexes whose similarity percentages are acceptable.

The growing season climatic parameters, especially rainfall, play the main role to predict the yield production. Therefore, the main objective of this research was to find out some possible relations among meteorology parameters and drought indexes with the yield using classical statistical methods. To achieve the objective, ten meteorological parameters and twelve drought indexes were evaluated in terms of normality and their mutual influences. Then the correlation analysis between the barley yield and the climatic parameters and drought indexes was performed. The results of this study showed that among the drought indexes, Nguyen Index, Transeau Index, Rainfall Anomaly Index and Standardized Precipitation Index (SPI24) are more effective for prediction of barely yield. It was also found that the multivariate regression is better than the univariate regression models. Finally, all the obtained regression models were ranked based on statistical indexes(R,RMSE and MBE). This study showed that the multivariate regression model including wind speed, sunshine, temperature summation more than 10, precipitation and Nguyen index is the best model for prediction yield production in Miane. Average wind speed and Nguyen index were recognized to be the most effective parameters for yield production in the model.