جستجوی مقالات مرتبط با کلیدواژه « خشک سالی » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

As the first social system, nomadic life has faced many challenges, including the need for drinking water, livestock, agriculture, and horticulture, despite their significant role in the country's economic, social, and cultural development. Low rainfall with inappropriate time and place distribution and increasing demand are the main problems in nomadic areas. On the other hand, water extraction is a method; which has been used for more than several thousand years to concentrate, collect and distribute water for various purposes. The purpose of this research is to introduce new and traditional methods of water extraction, suitable for summer and winter areas. The research method is descriptive-review and the tool for collecting information, documents and documents related to the subject. The collection of information continued until we reached the saturation stage in extracting the main research keywords and new and traditional methods of water extraction. The success of water extraction systems depends a lot on their environmental criteria and technical design. Therefore, each of the mentioned methods should be selected according to the climatic conditions of summer and winter areas and the technical design of the construction of each of the structures.

The use of simulations combined with the drought index enhances forecast accuracy. The exploratory approach provides the scope for drought warning and the opportunity for financial support and insurance mechanisms for local communities. The most important part related to the reduction of the effects of drought is the improvement of the precision of forecasting systems.

In this research, the precision of the new Anfis Simulation combined with the meta-heuristics of ant colonies in drought prediction is compared to the normal ANFIS Simulation. Simulation performance is estimated using the Mean Squared Error, Mean Absolute Error and Coefficient of Determination.

Validation of the simulation in the three month profile shows that the Absolute Error Value and the Root Mean Square Error in the Zabol Station are lower by Anfis Simulation. This article examines the Compatible Adaptive Neuro Fuzzy Inference System (ANFIS) and ANFIS models with Ant Colony Optimization Algorithm (ANFIS-ACOR) for drought forecasting. Drought forecasting was done using monthly precipitation data from synoptic stations Zabol (1983-2020) and Zahak (1994-2020). The results showed (ANFIS-ACOR) improved the performance of the Adaptive Neuro Fuzzy Inference System. The model predictive correlation test (ANFIS-ACOR) values in the 3, 6, 9 and 12-month intervals are equal to 0.738, 0.854, 0.801 and 0.898 at the Zabol Station. As well 0.792, 0.804, 0.759 and 0.887 at Zahak Station, respectively. In addition, Anfis Simulation-ant colony has a higher coefficient of determination. Validation of the simulation related to the three-month profile of Anfis-ant Colony Simulation showed that the absolute error and the Root Mean Square Error are lower and the coefficient of determination is higher. In the Zahak Station, the Anfis Simulation is more accurate in the 3-month formation, but in the validation section, the Anfis-ant Colony Simulation is superior. Overall, in the three-month SPI profile, Aanfis Simulation training is more accurate, but Anfis Colony Simulation is superior in validation.

Conclusion and Suggestions :

Ant colony optimization as a function of the data population progressively brings the proposed solutions closer to the overall optimal solution. This problem increased the efficiency of the numerical calculation of the ant colony compared with the Anfis in predicting drought. Anfis Simulation in combination with ant colony provides efficiency for large-scale problems in a short time by auto-tuning. These features reduce the cost of calculating natural data with irregular geometric pattern or data recorded in high volume. Simulations which optimize will fail at the local optimum level. Anfis-Ant Colony Simulation evaluates simulation space for predicting droughts on a global scale. This research proposes to compare the Anfis Simulation with other numerical calculations and to choose the best simulation for the Zabol Watershed.

Resilience and vulnerability of Society plays an important role in facing natural hazards. Due to the dependence of the rural economy on agricultural activities, the impact radius of the drought phenomenon is higher in rural areas. The purpose of this research was to assess the resilience and vulnerability of rural households in Kavar city located in Fars province, against the effects of drought with the capital analysis approach including economic, social, environmental, human, physical and political capital.

In order to conduct this research, samples were collected in 44 villages of Kavar city that were directly affected by drought. The statistical population includes 198 people from the local elite, including villagers, the Islamic Council and local trustees. Using Cochran's method, 131 people were selected as a statistical sample. The tools used were questionnaires and interviews. The variables used in this research included 62 samples which were divided into six groups of social, economic, environmental, physical, human and political capital. The validity of the questionnaire was confirmed by a group of experts in natural resources and sociology. The reliability of the research questions was also obtained using Cronbach's alpha. In order to prioritize capitals in terms of importance in the process of resilience and vulnerability of rural settlements against drought, the data obtained from the questionnaires were weighted and prioritized using the AHP method.

According to the research results in the case study, the highest vulnerability and resilience were related to human capital and environmental capital, respectively. Also, the least vulnerability and resilience are related to economic capital and political capital, respectively. The vulnerability of all investigated funds was more than the statistical median of the sample, which shows that the target society has high vulnerability. The capacity of resilience in economic, physical and political capitals was lower than the statistical median of the sample and for social, environmental and human capitals it was more than the statistical median of the sample. The average of the total funds in the region shows that vulnerability is high and resilience is low in this region.

Conclusion and Suggestions :

The results of capital prioritization in terms of importance in the process of resilience and vulnerability of rural settlements against drought using the AHP method showed that environmental, social, human, physical, economic and political capitals in resilience and human, Political, environmental, physical, social and economic capital’s, have the highest to lowest priority in vulnerability. In addition, the results showed that the level of community preparedness is at a low level when drought occurs. The vulnerability index was 3.74 and the resilience index was 2.81, which show that vulnerability is high and resilience is low in this area. It is suggested that the prevailing approach be changed from a weak focus on reducing vulnerability to drought crisis to increasing resilience against this crisis. In this connection, planning should be done in order to strengthen resilience characteristics in societies exposed to drought crisis.

Watershed health provides an integrated view of the factors influencing the watershed conditions. In the current study, the data length effect on changes in SPI-based watershed health index was evaluated using the RelResVul framework for the period of 1961-2021 in Sahneh, Kermanshah, and Harsin stations in Kermanshah Province, Iran. For this purpose, reliability (Rel), resilience (Res), vulnerability (Vul) indicators, and mean watershed health (RelResVul) were calculated in different periods. According to the results, watershed health indicators were different in 1961-1980, 1981-2000, and 2001-2021. In addition, with the increase in the length of the statistical period, health indicators had different changes, so that in short-term data, the changes of the indicators mentioned above were more than the whole period. The maximum changes in the first 30 years of the statistical period, and with the increase in the length of the statistical period until the end of the period, changes decreased. Accordingly, the last 30 years of the statistical period have reliable results in calculating health indicators. Considering massive calculations, climatic data deficits, and limited stations while increasing the length of the statistical period, it is suggested to use the climatic data of the last 30 years to estimate watershed health.

In recent decades, following the exploitation of groundwater, especially in areas with limited surface water and in which groundwater is the greatest resource in meeting the needs of water demands, the trend of reducing the volume of aquifers has increased. Meighan watershed, which includes Meighan wetland, is one of the most important plains of Iran that supplies a significant part of Arak city's drinking water and many agricultural wells. Since the drought causes a rapid reduction in surface flows, declines the ground water level, intensifies the wind and water erosion, changes the quality of water resources, causes ground settlement and especially, leads to the problem of salinization of drinking and irrigation water, it is necessary to evaluate the effects of drought and manage its risk.

The study area of Meighan is located in Central Iran with 2854.63 km2 area. To investigate the possible drinking water crisis in the region, water level decline of agricultural wells, and the risk of ground settlement in the groundwater measurement network, the observed groundwater level and absolute height of groundwater level data were collected in 46 piezometric wells in the statistical period of 1986-2006 and 2006-2020. For each year, an average isopieze map was drawn. Then by deducting the maximum and minimum values in each well, the amount of loss in each year was determined. These data were used to draw maps of annual decline. The reason can be the lack of proper feeding of the aquifer due to the decrease of precipitations and drought and as a result of the reduction of the aquifer storage due to the excessive exploitation.

From 1971 (the first data collection) to 2004, with the increase in the number of deep and semi-deep wells, the discharge rate of the wells has increased by a total of 531.5 mm3. In 2009, despite the increase in the number of wells, the discharge rate of wells has decreased by 153.9 mm3 in 6 years. In the last data collection in 2020, the number of wells and their discharge rate have decreased which indicates drying up of the wells due to the decline in the groundwater level in many areas of the plain which has led to the disuse of wells.Reviewing the decline maps of 1986-2006 and 2006-2020 indicate that the northern and eastern areas of the plain do not show significant changes and have a relatively constant trend. However, as it is shown in isopieze maps, in the western regions and in the south of the plain, groundwater level has had the highest decline. From 2006 to 2020, in the north and northeast, as well as in the south, west and southwest of the basin, there are areas with the highest rate of decline.

According to the analysis of rainfall data and the absolute height of groundwater level of Arak Plain, it can be concluded that the amount of rainfall does not directly affect the decline of the groundwater level. Research results indicate that before 1986, the hydraulic slope of the Arak plain aquifer conforms to the level of the plain and the Meighan playa has been a natural drainage of the plain. However, during the period of 1986-2006 with the increase and concentration of exploitation wells in the western and southwestern parts of the plain, the hydraulic slope of the aquifer has inclined towards the western regions. From 1986 to 2006, it can be concluded that the maximum groundwater level decline of 20 meters occurred in the western and southwestern areas of the basin and extended to the eastern areas of the basin. However, from 2006 to 2020, the decline classes have increased significantly, such that in the west, southwest, north and northeast of the basin, an increase in the groundwater level decline up to 70 meters has been observed.

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.

Shortage of rainfall and drought are among the factors affecting the water shortage crisis in arid regions due to the high rate of evaporation in these areas, while reducing the amount of water productivity, it reduces soil moisture. Therefore, the application of conservation methods by reducing the rate of evaporation and maintaining soil moisture in addition to improving plant growth and yield increases water productivity. The aim of this study was investigation of the effect of sand mulch and nano-clay in buried clay pot irrigation on temperature and humidity changes in one of the wind erosion centers of Sistan region. For this purpose, wind sediments accumulated in Sistan plain as well as flood sediments of Helmand riverbed (sediments transported during floods entering from Afghanistan) were sampled. By determining the particle size of sediment samples, the largest particle size of wind sediments was separated to prepare a sandy cover using a sieve. To prepare clay nanoparticles, Flood sediments were also pulverized using ball mill by examining the particle size and determining the main elements (using the XRF method). By preparing treatments including sand cover, nano-clay and control by installing thermometers and probes at depths of 10, 30 and 50 cm Soil temperature and humidity were measured (using TDR) for a period of 186 days. Also, at the end of the test period to evaluate soil stability indices by sampling from different depths, the mean weight diameter (MWD) and geometric mean index (GMD) of aggregate diameter were measured based on dry sieving method. The results showed that there was significant different at 5% level on soil moisture and temperature distribution between treatments. In depth 10 cm, the highest amount of retained moisture were measured in sand mulch treatment (1.2 and 1.4 times retains moisture compared to nano-clay and witness treatments, respectively). The highest amount of retained moisture in depth 30 and 50 cm is related to nano-clay treatments (45 and 68% more maintain compared to sand mulch and witness treatments, respectively). The results also show that the highest and the lowest amount of soil temperature at different depths related to witness and sand mulch treatment respectively. Mulch cover by shaping temperature equilibrium in soil profiles, caused 17.2 and 33 % reduction of temperature compared to nano-clay and witness treatments. The results also showed that, there were significant differences between treatments in mean weight diameter (MWD) and geometric mean diameter (GMD) and the highest amounts of this index related to nano-clay treatment (p<0.05). Based on the results of this study, the use of sand mulch and nano-clay by reduces the temperature and improving the stability of aggregates, increases the volume of soil moisture in the subsurface layers by 30 to 45% and also increases the retention time in soil moisture and reduces irrigation frequency compared to the state without protective action in the soil. Therefore, the application of the methods used in this study, provides the required moisture to the plants to establish vegetation in the wind erosion centers of the study area.

This research has done to study the relationship between dust storms frequency and climatic factors included monthly rainfall data, monthly average temperature, monthly maximum temperature, maximum wind speed, frequency of dust occurrence from internal Sources and SPI in northern, Central and coastal part of Jarrahi watershed (cities of Ramhormoz, Omidieh and Mahshahr port) in Khouzestan province were investigated. First of all linear trend in time series using Mann-Kendall test was assessed. Then, using Pearson correlation, the dependence of the dust storm and climatic factors was studied and with path analysis beta weight or participation of each factor in explaining the variance of dependent factor. The results showed that, except in the occurrence of dust phenomena, linear trend is not observed with a gradient (Sen's Slope) of 2 days in 10 years and Pearson correlation confirmed the significance of the dependence of the occurrence of dust on climatic factors at 1% level. The results of the path analysis indicate that two factors of mean temperature and monthly maximum temperature, directly and indirectly, affect the maximum wind speed by more than 50% of explaining the variance of dust storms. The result of a partial correlation matrix showed with temperature effects control none of the climatic factors in storm dust except maximum wind velocity is significant. Thus, the average monthly temperature and maximum temperatures not only directly but indirectly cause changes in other climate factors. Totally climatic factors explain 15% of the variance in the frequency of storm dust.

The aim of current study was to study the trend of linear and non-linear changes in vegetation cover under the influences of climatic factors (rainfall, temperature and drought) and human activity (biological watershed management measures) using satellite images over a period of 20 years (2000-2019) on the Khor-Sefidarak Watershed, the Province of Alborz. Vegetation index (NDVI), drought index (SPI) and PolyTrend algorithm were used by extracting the monthly time series. Then, using climatic and implemented watershed management measures data for the basin, the impact of natural (temperature, precipitation and drought) and human factors on vegetation changes was assessed. The results indicated that 35% of the area had significant changes (92.6% increasing and 7.4% decreasing) in vegetation, and 65% of the area had insignificant changes during the last 20 years. The results also indicated that 87.71% of the vegetation changes in the region had experienced a linear type change and the remaining 6.62 and 5.68% haddemonstrated second and third degree nonlinear changes, respectively. Considering the effects of the two climatic variables on vegetation, precipitation did not show a significant trend over the two decades; however the temperature indicated a significant decreasing trend. Assessing the impact of drought on vegetation change, the largest decline in vegetative cover occurred in 2008, which was strongly influenced by severe climatic drought. Although the vegetation changes have not been affected by climatic factors in the long term, short-term changes in extreme events, including drought, strongly justify changes in the region's vegetation. On the other hand, the results indicated that the watershed management measures have caused changes with a linear pattern; however, the changes and expansion of the residential areas (as human factors) have caused a nonlinear pattern in vegetation. Thus the biological watershed management measures have increased and strengthened the vegetation of the region linearly; however, sudden and rapid changes in the rural areas have caused a non-linear decrease in vegetation.

Studying climate change and its effect on the intensity and frequency of drought can help the proper use of water resources and adaptation to the destructive effects of the drought phenomenon in the future decades. In recent decades, rising global temperatures have disturbed the planetchr('39')s climate balance and caused widespread climate change in most parts of the world. This research tries to assess climate change in 2021-2050 and its impact on drought in the Latian dam. For this purpose, after assessing the efficiency of the SDSM model in simulation of the base period (1992-2019), the downscaling output of the HadGEM model under RCP4.5, and RCP8.5 scenarios was performed to estimate maximum and minimum temperature and precipitation based on Standardized Precipitation Evapotranspiration Index. The outcomes show an increase of 0.85 to 1.54°C in the average monthly temperature under the RCP8.5 scenario and an increase of 0.25 to 1.45°C under the RCP4.5 scenario. Furthermore, the results show a decrease of 31 to 100 mm in average annual precipitation. The highest decrease in precipitation is in February. Also, the annual analysis of the SPEI showed that 65% of the years are normal, therefore, the Latian dam will not face an increase in the frequency of drought in the period 2021-2050, but it is expected that precipitation events mostly will occur in the warm season.

Understanding the behavior of phenomena requires attention to all its dimensions, and one way to understand their complexities is modeling. Soil surface moisture is a key variable for describing drought, water, and energy exchanges between Korea and the air, as well as assessing crop conditions. Soil moisture is affected by both environmental variables and many environmental variables such as runoff, soil erosion, and crop production, but is highly variable due to unstable spatial and temporal conditions. The purpose of this paper is to investigate, extract and evaluate the spatial model of soil moisture dispersal after more than normal rainfall in 1979-98 in Kurdistan province. In this regard, after analyzing soil moisture dispersion as dependent variable and precipitation variables, snow water equivalent, topographic moisture index and vegetation index were selected as independent variables. Then, using a general regression model (OLS) and geographically weighted regression (GWR), spatial modeling was performed. Based on the evaluation criteria, the results showed that the GWR model with R2 = 0.74 has better explanatory power and better estimation than the general regression model with R2 = 0.68. According to the results of the GWR model, snow water equivalent variable in the northern mountainous regions had the highest effect on evapotranspiration and the least effect on soil moisture. The obtained spatial model can identify low or moist soil areas in order to identify environmental potentials and improve decision making, allocation and spatial distribution of agricultural services.

The Hashtgerd Plain of the Savojbolagh Watershed with an arid and semi-arid climate is one of the plains that have experienced a significant increase in groundwater exploitation in recent years. Over the past five years, the water table has dropped more than 5 meters. Therefore, the role of management factors in this plain is important. To find the effects of rainfall and climatic conditions on the groundwater level fluctuations, rainfall data from 6 rain gauge stations and 21 piezometric wells during the 1991 –2011 period were used. Meteorological and hydrological drought sequences were prepared by using the standard precipitation index (SPI) and the standard groundwater index (SWI) for six cumulative periods of these indices of 6, 9, 12, 18, 24 and 48 months. As the rainfall data series and groundwater level did not have a normal distribution, the Mann-Kendall nonparametric test was used to determine the trend of meteorological data and the water level, which showed that the slope of the groundwater level has been decreasing in all months of the period. Correlation analysis between the two indices indicates a 24-month lag between meteorological and hydrological droughts. According to the SPI6 index, the highest drought occurred during the dry season in the last quarter of of 1995 and fisrt qurter of 1996. In addition, drought zoning maps were prepared using the IDW method on a 24-months time scale, indicating severe droughts in the south of the basin. The results in some parts of the region show that there was a two-year lag between meteoroiogical and hydrological droughts. The perception of this phenomenon may help planners to manage the water resources efficiently.

Drought is one of the most destructive environmental phenomena that causes extreme damages to the natural resources and human lives. As the Province of Kurdistan supplies many agricultural products in the country, the occurrence of drought is very important and that is the main reason behind the execution of this study. The data of twenty-three hydrometric and seven synoptic stations were used in a 29-year common statistical period (1985-2013). To calculate the meteorological drought, the SPI and PNI indices, and for the hydrological drought, the SDI index were used at the annual time scale. Results of the Mann-Kendall and Thilson tests indicated the existence of a trend for the meteorological drought at Sanandaj, Marivan, Ghorveh, Zarrineh and Saqez Stations. Also, the running of this test on the SDI index indicated a downward trend in all of the hydrometric stations, except for the Sentin Khorokhoreh, Ghashlagh, Qeblv and Meyar stations. Results also showed that the root mean square error for SPI, PNI, and SDI were 0.41, 0.49 and 0.47, and the coefficient of determination (R2) were 0.65, 0.51 and 0.59, respectively. Therefore, the SPI index is the best function among these three.

Abstract: Optimal management of natural resources requires an understanding about the effect of land use/ land cover change on hydrological circle of the water in the area. The location of this study is Chaghalvandi, Lorestan province. In this research, to investigate the relationship between land use changes and drought with groundwater-level decline maps of land use were extracted from ETM satellite images of the Landsat satellite during 2004, 2009 and 2014. Next, the images were processed and analyzed, and then land use was classified into six levels including forest, pasture, shrubbery, agriculture field, residential area, and miscellaneous. The Kappa coefficient for the 2004, 2009, and 2014 classifications was 0.89, 0.9 and 0.92, respectively. Quantitative data of 18 piezometric wells during 2004, 2009 and 2014 were used to assess the relationship between land use change and groundwater level dropping in the area. The moving averages of 3, 5 and 7 year periods were used to determine precipitation level changes and drought and wet periods. The results showed that deterioration of the natural resources, destruction of forest lands and turning them into agriculture fields and residential areas, and groundwater level dropping in the time of long term drought. In 2104 the level of groundwater has dropped about 6 meters in comparison to 2004.

Drought monitoring is one of the key factors in drought risk management and the use of drought indices such as the standardized precipitation index (SPI) is a useful tool in this regard. The aim of this study is to evaluate and zone drought risk in different years and return periods in Karkheh basin. For this purpose, Standardized Precipitation Index (SPI) as a selected index was used to assess drought in 33 stations inside and outside the basin in five timescales. The results showed that the lowest values of SPI, the most severe drought continuity of the large and the longest continuity were related to Govar stations of Kermanshah province, Biderood station of Khoozestan province and Jokar station in Hamadan province, respectively. Extensive drought risk maps for different return periods showed that in return period of 5 years, northern (Bavane station of Kurdistan province), northeast (Hamadan station) and northwest (Kermanshah) areas were more at risk of drought. This condition for a return period of 10 years was mostly related to northern (Bavane station of Kurdistan province), northwest (Kermanshah) and central areas. Drought risk for 20-year return period affected the northern (Bavane station of Kurdistan province) and Northwest (Kermanshah) areas more, while for 50-year return period, in addition to northern (Bavane station of Kurdistan province) and northwest (Kermanshah), it also affected the northeast (Hamadan station). The overall result showed that the periphery areas, especially areas of northwest, north, northeast and some parts of eastern and southeastern areas are the most susceptible areas affected by drought and with increase in the return period, the severity of drought risk can be reduced.

The impact of drought can be water supplies decrement¡ agricultural production reduction¡ changes in vegetation and rangeland area or desertification accelerating. Quantify the effects of drought indices are necessary for drought episodes monitoring. Based on accessible data type into two general these indices were divided in two categories: terrestrial and satellite.The aim of this study was to compare the diagnosis and classification ability of vegetation changes which have occurred as a result of drought. The SPI used as earth index and WSVI¡ TCI¡ VCI and VDI used as satellite indices for monitoring vegetation change in the southern part of Hamadan Province. For this purpose¡ the indices were extracted from Landsat TM and images and the correlation between them done based on Pearson correlation. The results showed that the highest and lowest correlations with the drought variables at the studied years were achieved with VDI and TCI indices respectively. Compared to meteorological methods¡ the satellite images have advantages such as wider coverage¡ higher temporal resolution and lower cost. So¡ the use of remote sensing is recommended.

Consecutive droughts in Sistan and Baloochestan province cause water resources restriction and this is a very significant problem for this region. In this study, in order to forecast the drought cycle in 9 climatological stations in the province, we used Artificial Neural Networks. The input data were average of annual rainfall data in all stations and also deciles precipitation index, which the first 30 years from 1971 to 2000 used for training the network and the last 8 years from 2001 to 2008 for simulating it. The network consists of Multilayer Perceptron (MLP) and Back Propagation Algorithm (BP) and also sigmoid transfer function. Number of Neurons in hidden layer was 10 with 1 10-1 structure and was calculated based on the lowest RMSE. Then drought prediction was done in neural network with the trained algorithm and without using actual and observed data in 2009 to 2012. Results showed that, the network was able to simulate and forecast DPI index with 97% regression and average RMSE error less than 5%. According to drought indices, results showed that the drought will have an increasing trend in all stations in this region in 2009 to 2011. Therefore, by using this method, drought can be predicted in later years without any need to have actual meteorological data and also can be used in water resources management, drought management and climate changes.

A better understanding of rangeland vegetation cover and its variation in different years based on wetness and droughtiness fluctuations is a great importance. Economical priority setting of rangelands is based on variations in rainfall and drought patterns، because it yields to better characterization of vegetative cover. Yet a comprehensive and continuous monitoring of vegetative cover of rangelands has not been established. To study the influence of droughtiness and wetness on vegetation cover and production forage، 11 sampling areas and 3 reference areas were selected in Herat. Three 100-m transects were located 25-m apart within each sampling area. Production and cover were estimated within 10 located 2- plots along each transect. Data were analyzed using Duncan›s test Design a completely random with a factorial GLM procedure at 99% and 95% confidence levels. Results showed that the vegetation cover and production in wetness were significantly different from those in droughtiness (P<0. 01). The vegetation production and cover increased by 36. 3% and 34% respectively in the wetness compared to the droughtiness. The influence on production and cover was positive and efficient in the wetness with the average rainfall higher than the 30-yr average. Finally، the results of flood spreading increased vegetation cover and production forage in dams.

Rangeland ecosystems in semi-arid regions are vulnerable systems to climatic changes specially precipitation. In such conditions droughts are predictable. In this study the relationship between rangeland production and spatial and temporal changes of precipitation was investigated. Therefore، rangeland production through 10 years data set (1377-1387) in steppic bioclimatic of Esfahan province (Alavije، Muteh، Kalahrood and Gardaneshadian) using Standard Precipitation Index (SPI)، the relationship between SPI series of 3، 5 and 8 month time scales، and rangeland production of 10 years. Thus Anova and correlation matrix between production and SPI factors were formed. Results indicated that the most severe drought has occurred in 1387 simultaneously، with the least production. A harmony between change trend of production and SPI in the sites showed that in most cases maximum and minimum production have occurred simultaneously with maximum and minimum of SPI series. Also، the production correlated with SPI series of three، five and eight months'' time scales with correlation coefficients more than 63 percent which were significant in 1% and 5% level. Due to efficacy of production from spring precipitation and soil depth less than 30 cm in the sites، it is proposed to use SPI series of three months scale to evaluate drought in similar rangelands.

Annual rainfall data related to a 26 year period from a number of Mazandaran climatologicalstations were employed to analyze and model the precipitation toward a determination ofdrought as well as wet years. Results indicate the occurrence of different intensity drought phenomenon in all stations. As regards the classification of the annual wet and dry years, normal precipitation among various alternate dry and wet years can be observed with the normal years having more stability and continuity as compared to wet and dry years. The Standardized precipitation Index (SPI) was recognized better and more accurate model compared to the other models because of more potential such as high sensitivity to precipitation variation and more punctual separating of drought and wet year classes in every events.