جستجوی مقالات مرتبط با کلیدواژه "خشکسالی" در نشریات گروه "اکولوژی"

Drought is one of the natural disasters that can occur in any climate. In recent decades, Iran has been continuously affected by severe and widespread droughts and has imposed harmful effects on various economic sectors, including the country's water resources. One of the needs for the growth and development of every country is water. On the other hand, due to the lack of permanent or even seasonal surface water flows in many plains of the country, one of the most important sources of water harvesting is the use of underground water reserves. Therefore, it is very important to investigate the status of these resources and determine the influencing factors on them. In this research, it has been tried to identify the areas that are exposed to severe groundwater drought and the impact of the factors affecting groundwater drought using the maximum entropy model and using MaxEnt software in the basin. The Jiroft plain watershed should be identified. To implement the maximum entropy model, 70% of the data were used for model training and 30% for model testing. The results of this study, based on the jackknife test, showed that the most important factors affecting groundwater drought are altitude, distance from the river, and soil moisture, and the model shows the most sensitivity to these parameters. gave Also, the results showed that the model has an acceptable accuracy in identifying groundwater drought, so that the accuracy of the model was estimated at 0.76.

This research assesses and investigates the impact of automating the Abshar irrigation network's main canal using a decentralized control system on the adequacy and stability of surface water distribution. To achieve this, the study analyzes 30 years of historical discharge data at the Abshar diversion dam and selects seven representative operational scenarios. It then employs the Integral-Delay (ID) hydraulic simulation model to simulate surface water distribution in the main canal under each scenario (a total of 540 simulations). These simulations are compared with results obtained using a simplified Integral-Delay (ID) mathematical model. Additionally, the research develops a decentralized PI automatic control system model for the network. This control system model is then integrated with the Integral-Delay (ID) hydraulic simulation model within the MATLAB environment. By utilizing system identification techniques, the study determines the proportional and integral gains for each controller in the control system. Finally, the performance of the automated control system is evaluated by analyzing the simulated surface water distribution results for the chosen scenarios using performance indices related to water distribution adequacy and stability. This allows for a comparison of the automated control system's effectiveness with the pre-automation scenario.

One of the effects of droughts on the catchment area is the impact on sediment production. The purpose of this study was to investigate the effect of drought on the amount of sediment production estimated by the sediment gauge curve located at the Chamriz hydrometric station. In this study, using the long-term data of the Chamriz hydrometric station located upstream of the Darudzen dam, the rate of changes in the produced sediment discharge in each year was calculated using different methods of the sediment curve. Then, by evaluating the applied methods, the best method for performing the subsequent analyses was selected (the non-parametric method (CF2)). Then, using the station's meteorological data, two SPI and RDI drought indicators were calculated, and finally, they were compared with the average annual sediment discharge rate. The results showed that by increasing the amount of drought index (SPI) and RDI (toward tiredness), the amount of sediment discharge increased, indicating the positive effect of climate conditions on the sediment yield of a basin. Finally, by examining the state of sediment production in many years of drought, it can be concluded that during the year of the drought, due to the effect of drought on vegetation status, soil moisture, and other factors, in the years after the occurrence Drought has caused a significant increase in sediment deposition compared to years when the drought was normal on the floor, and since then it has been terrible.

The present research aimed to investigate the crown dieback of Persian oak trees in relation to their individual and site characteristics, evaluated the changes in crown health of trees during the years 2019 to 2022 in Meleh-Siah forest in the northern half of Ilam province. Two sites were identified in the northern and southern aspects and 100 oak trees were marked in each site. The characteristics of each tree, including the diameter at breast height, tree height, max and min crown diameter and tree origin were measured and recorded. The dieback condition of tree crowns was evaluated and divided into four classes of crown dieback. The evaluation of crown dieback of trees was done during four years and in September. The results showed that the highest abundance of trees in the northern site is in the classes of declining and crown dieback up to 50%, and in the southern site is in the class of crown dieback more than 50%. The number of trees leaving the healthy and declining classes was higher, respectively, which were transferred to the higher crown dieback classes. The healthy and declining classes were associated with decreasing changes and the crown dieback less than 50% class was associated with increasing changes. dbh, height and crown area of ​​healthy trees were lower than those of other crown dieback classes. The frequency of crown dieback was higher in denser stand. The rate of crown dieback was higher in coppice trees than in standard trees; in addition, the temporal changes of crown dieback were more in coppice trees. It was concluded that individual and social traits and environmental conditions had a considerable impact on the crown health of oak trees and how they reacted to recently happened droughts.

Salehiyeh Wetland, located in Alborz and Qazvin provinces, is one of the wetlands that has dried up in recent years and has become a center for dust production. The aim of this study is to evaluate the trend of changes in moisture in Salehiyeh Wetland and investigate the role of drainage channels in the drying of the wetland bed. To achieve this goal, the MNDWI index was calculated using Landsat 5, 7, 8, and 9 satellite images from 1990 to 2023. The construction of drainage channels has caused some changes in the wetland catchment area. Therefore, the non-parametric Mann-Kendall test was performed before and after the construction of drainage channels in two previous and current catchment areas. Also, the wind data from synoptic stations around the wetland were analyzed by drawing the storm rose diagram. The results of the study show that the overall trend of changes in moisture in Salehiyeh Wetland during the study period has been decreasing, and the MNDWI index has been negative in most years due to the drought prevailing in the region. Due to this, the phenomenon of dust and the problems resulting from it have spread to the surrounding cities. Therefore, measures need to be taken to preserve and manage the water resources of Salehiyeh Wetland and prevent its drying, such as optimizing water consumption, preventing the construction of inappropriate drainage channels, and using various solutions such as implementation of mechanical windbreak to reduce the sand and dust storm.

Spatiotemporal changes of net primary production (NPP) is one of the essential indicators in determining rangeland ecosystem condition. Therefore, the aim of current research was to map and monitor the actual and potential NPP of rangeland ecosystems in Kohgiluyeh and Boyer-Ahmad province, using CASA and Miami models, MODIS and field data from 2009 to 2018. The accuracy of the produced NPP maps was assessed in 253 sampling sites located in different vegetation types with good, fair and poor rangeland conditions, using linear regression. Results showed that the difference between actual and potential NPP was greater than 56 gr C/m2/month, which can be a sign of human impacts and interferences in the rangeland ecosystems of the region. The highest and lowest relationships between modeled and field productions were observed in the Astragalus spp. - Bromus tomentellus vegetation type with good rangeland condition (R2=0.84) and Astragalus sieberi- Stipa capensis vegetation type with poor rangeland condition (R2=28), respectively. The present research findings indicated the importance of drought conditions, vegetation type and rangeland condition in estimating the actual and potential NPP and the difference of these productions can be used as an index to determine and monitor the condition of rangeland ecosystems.

Groundwater is the most valuable water resources in any region and in many arid and semi-arid regions of the world, such as Iran, is the main source for drinking and agricultural needs. In recent years, with the increase in population and as a result of increasing withdrawals from aquifers and climate change, many of aquifers are in poor condition, and these conditions continue or are deteriorating. In this study, in order to determine the effect of climate change on groundwater drought on the aquifer of Shahrekord plain, the output of CMIP6 models and SPI and GRI drought indices have been used. Simulations of GFDL-ESM4 model show that the average rainfall by 2050 in Shahrekord plain, under scenario SSP1-2.6 will increase by 4.85 mm and under scenario SSP5-8.5 will decrease by 21.34 mm. In order to determine the effect of climate change on the aquifer of Shahrekord plain, a regression relationship between the two indices of SPI and GRI in six selected piezometers has been used. The results show that droughts with higher intensity and duration will occur in the region and more than 60 percent of the future period of Shahrekord plain aquifer will be in drought conditions and the most severe drought under SSP1-2.6 scenario will last 52 months and its severity will be 59.32 and under the SSP5-8.5 scenario the most severe drought will last 70 months and its severity will be 86.59.

Drought monitoring using appropriate drought indices is of importance in water resources management, especially in arid and semi-arid regions. Therefore, choosing the suitable drought index and calculating the desired drought index appropriately is of considerable importance in the study of drought. This study is aimed to determine the appropriate statistical distribution to calculate RDI drought index in arid and semi-arid regions of Central Iran. For this purpose, 16 synoptic stations in Central Iran were selected. To calculate RDI, precipitation and potential evapotranspiration values are required. The FAO-Penman-Monteith method was used to calculate potential evapotranspiration. To select the most appropriate statistical distribution, 17 statistical distributions were used. RDI for each synoptic station was calculated annually by fitting to each of the 17 distributions, separately. Then, based on the AIC and BIC criteria, the best statistical distribution was selected to calculate RDI for each station. While based on the literature, it is recommended to calculate RDI by fitting the data to one of the Gamma or log Normal distributions, the results showed that in most of the studied stations, the log Normal and Gamma distributions are not the most appropriate distribution. However, according to the results, Gamma distribution was one of the top 6 distributions in all the studied stations. The results also showed that the difference of RDI values ​​calculated based on different distributions in dry and wet years are relatively significant, which shows the importance of choosing the appropriate statistical distribution. The fit of the studied distributions to the precipitation data at different stations showed that the Nakagami distribution presents the best performance. In case of potential evapotranspiration, different distributions provided the best fit at different stations.

The negative balance of water reserves and reduce the size of static storage aquifers including the effects of the drought phenomenon is repeated on the status of surface and groundwater resources in Iran including Khuzestan province has had an impact. In this study, using fuzzy and ArcGIS version also better understand the effects created in the statistical period on the aquifer Gotvand – Agile plains try to influence the result of the drought on groundwater modern manne and visible as much as possible he predicted.Gotvand Plains - Aghili (with an area of approximately 370 km north Khvzstan province is the the agricultural poles) separated by Karun River is dumped. To determine the patients in the study area input and output data network with the same time step with the corresponding number, wells data was introduced as the basis of monthly data, from 1996 until the end of 2002  considered. Studies showed that groundwater levels in the aquifer is heavily dependent on rainfall and water inputs (irrigation and drainage networks and Karun River) is the also well as the behavior of aquifers in drought fuzzy logic high accuracy And the results of the model with current realities in the region and results of studies and maps in ArcGIS environment is consistent.

Sistan has recently confronted to periodic drought and water scarcity that destroyed vital resources especially vegetation. Information about reaction of the vegetation species to drought is necessary for protecting and biological restoring this ecosystem, so density of Tamarix aphylla, Salix babylonica and Eucalyptus were investigated using quadrates 50m × 50 m during wet (1366-1376) and drought years (1377-1387) in Sistan plain. MANOVA showed that vegetation species and drought significantly affected on species density. Although drought declined density of three species, tree species destroyed more than Tamarix as a shrub species. Salix that it has favorite condition in normal years and its root depth is lower than Eucalyptus lost its density sooner in drought years

Drought risk management requires a strategy. Choosing a spatial scale is one of the strategic aspects. In the present study, drought monitoring was carried out at sub-basin scale and for dry lands products. For this purpose, using the SWAT simulator, the Khorramabad basin with a total area of 2480 km2 was divided into 31 sub-basins based on homogeneity of soil texture, land use and elevation. The RDI Drought Detection Index was calculated on a 9-month time scale for assessing agricultural drought during the period of 1348-1396, in accordance with the crop year. Using Thiessen method and the use of meteorological stations in the studied area, rainfall and temperature of each sub-basin, the estimation and relative reduction of yield of dryland products were calculated for each of the different drought intensities. The present study was able to compare the different areas of the basin with respect to the drought risk in different products. So that the risk of product production varies from 14 to 30 percent in each sub-basin. The average risk of producing dryland products including wheat, barley, peas and lentils was 21.2%, 18.8%, 17.4% and 18%, respectively. The results also showed that the effect of drought severity on the yield of each product is different. So, in the middle drought, 54-60, 47-55, 46-54, 47-57%, severe drought, 63-70, 58-64, 49-60, 51-62% and very severe drought, 75-82, 69-74, 59-68, 67-74%, reduced potential yield of each product, respectively, wheat, barley, peas and lentils respectively.

Sustainability is considered as an effective framework for managing rural areas against a variety of environmental hazards, including droughts, which require the use of sustainable sustainability techniques. The purpose of this study was to assess the stability of the villages of Qaleh Chaie watershed in Ajabshir city against the drying of Lake Urmia. The research was applied and the information gathering method was library and field research. The statistical population of the study is 21185 people living in 21 villages in this area. The sample size was 380 using Cochran formula and was selected by simple random sampling method. The findings of the study, using the Barometric Model of Sustainability, showed that the environmental sustainability of the villages in the years 2005 to 2017 was exposed with a sustained reduction of -0.146. From the viewpoint of social sustainability and economic sustainability, they experienced a relative increase of 0.132 and 0.055 respectively. Finally, the Javan Qaleh village with a sustainability level of 0.742 has been the most stable village over the past 15 years and then the villages of Qajuldeh (0.666) and Yengeje (0.657) are located. Also, the villages of Chenar, Mahmoudabad and Gonbad have been the most volatile villages in the last 15 years. Also, Kendall's findings showed that there is a positive and significant correlation between the location of villages in Lake Urmia in terms of distance and proximity to their sustainability level at the level of r = 0.577.