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

Over the past decade, the Zagros region, specifically its Zagros oak trees, has experienced significant impacts from droughts and climate change. Climate change has resulted in heightened desertification and oak forest decline. This study examines and analyzes meteorological droughts and their correlation with climate change. This is a prominent contributing factor to oak tree decline in Ilam Province. The focus is on study sites in the northern and southern Serabaleh regions, where oak decline has been observed.

For this study, comprehensive data on daily precipitation and minimum and maximum temperature were obtained from the synoptic station in Ilam, covering the period from its establishment until 2019. The Standardized Precipitation Evapotranspiration Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) were developed to assess meteorological drought and identify wetter and drier years. The SPI measures the deviation of precipitation from the mean value and normalizes it by the standard deviation. In contrast, the SPEI considers the discrepancy between precipitation and evapotranspiration. These indices were calculated on various time scales, including 3, 6, 12-month, and annual periods, and drought status was analyzed based on their respective classifications. To examine the role of climate change and identify influential precipitation and temperature patterns in drought occurrence, a set of four precipitation indices and eight temperature indices were calculated using ClimPACT software. These indices, developed by climate change experts, capture changes in mean or extreme weather conditions. The analysis also included wind speed. The relationship between drought indices and climate change was assessed through regression analysis and the Pearson correlation coefficient. Moreover, the study employed the Mann-Kendall and Pettitt Test to identify change points or significant abrupt changes in the time series. These tests were conducted at 5% significance and 95% confidence levels.

The study findings indicate a decreasing trend in the highest consecutive 5-day rainfall since 1995. In addition, there are insignificant reductions in the annual sum of wet days and the highest rainfall events of one or two days since 1998. This decrease in rainfall has been accompanied by increased maximum air temperatures since 1998, with a significant intensification observed from 2007 to 2015. Additionally, there has been a slight increase in minimum temperatures since 2002 and a significant wind speed since 1996. These factors have contributed to increased evaporation since 1998 and the occurrence of droughts on different time scales, ranging from six and twelve months since 1998 to three months since 2003. Global warming has influenced droughts. Three-month droughts have resulted in milder six- and twelve-month droughts, but more severe three-month droughts in oak decline, primarily due to significant changes in maximum temperatures since 2007. The occurrence of these droughts has been associated with an increase in the percentage of days with temperatures above the average since 2007, leading to more severe droughts from 2007 to 2015, with the peak in 2008 coinciding with the highest level of oak decline during the study period and under the influence of climate change phenomena.

The SPEI drought index indicates a higher frequency and longer duration of droughts during the study periods, albeit with less severity than the SPI index. This suggests that the rising temperatures during cold months, in addition to dry months, have played a role in influencing the drought conditions. The results demonstrate that drought and climate change are the primary influential factors contributing to oak tree dryness in the forests of Ilam Province. Considering the decreasing precipitation trend and increasing temperature trend observed in the studied region, the occurrence of climate and environmental hazards, such as heatwaves, droughts, and floods, may further increase.

Land use change is an important global and local ecological trend and is one of the major challenges in the 21st century. The purpose of this study was to model land use changes in the Gahvareh region, Kermanshah province using the LCM model. This model has the ability to simulate several land use changes by utilizing and integrating Markov chain models, multi-layer perceptron neural network, logistic regression, and MLOP. In this research, Landsat 4, Landsat 5, and Landsat 8 satellite images were used to prepare land cover maps. After initial corrections, the images were classified using the Maximum likelihood method, and land use maps for the years 1986, 2000, and 2018 were prepared. After monitoring the changes of different land uses during two periods (1986-2000) and (2000-2018) and assessing the validation of the model, finally, the land use map of 2028 was predicted using the LCM model. The results showed that during the first and second calibration periods, 30% and 42% of forest land were reduced, 26 and 37 ha were added to agricultural land and 80% and 32% were added to residential land respectively. The most changes during the study period were the conversion of forest lands to pasture and thin forest (80%). Forecasts for the year 2028 showed that the dense forest would be destroyed and would be decreased in half in comparison to 2018. Evaluation of the accuracy of transmission potential modeling using artificial neural networks showed high accuracy in most of the scenarios.

Fire affects quantitative and qualitative indicators by changing stable plant communities, changing genetic diversity and reducing plant and animal species and the succession and steps are effective. The severe effects of fires on the reduction of soil protection, production and changes in plants palatability, animal breeding conditions, challenges in the livelihoods of farmers, disturbance in ecosystem cycles, and on a large scale the impact on climate change, add to the sensitivity of the issue. Therefore, wildfire in natural areas is an ecological and economic risk and has profound effects on vegetation and soil and economic production of the country. So, it seems necessary to know the effects of fire, which is the purpose of writing this article.

To conduct this study, Veysian site with an average height of 1580 meters above sea level and an average annual rainfall of 470 mm was selected. Then, 200-meter transects with four numbers and a distance of 100 meters from each other and 10 squares of one square meter fixed on each of them formed the sample units in each field. This sample unit was executed exactly in a similar and homogeneous arena in its immediate area, which is protected from fire and is called the control area, with the same quality. This site was burned for the second time in 2011 and 2016, and it was surveyed in 2018 and 2019. In this site, 80 plots of one square meter each year and finally 160 plots were studied in two years and in two areas of control and treatment. After sampling, the data were normalized and analyzed using T-TEST and ANOVA in the SPSS version 22 software environment and comparing the average data using the DUNCAN method.

In this research, the general comparison of the control and treatment areas in all sites shows that there is a significant difference between the control and fire treatments at the level of 1%. In other words, the fire has been able to create major changes in terms of quantitative and qualitative indicators in the sites. The fire has obviously increased the forbs relatively compared to the grasses due to the overall decrease in canopy cover and production. The dominant species in this vegetative form is the annual species Coronilla scorpoioides (L.) Koch, which prevailed over other species after the fire. Also, the fire caused the reduction of the condition rangeland from average to poor and the trend of the status from +22 points in the control to +1 in the fire treatment. According to the annual increase of rainfall from 356 mm in the first year to 778 mm in the second year, data shows that the amount control area of production has increased from 1276 to 1454 kg per hectare (178 kg), while the burned area has decreased by 2 kg.

Covering the soil surface and its quality is one of the most important factors for soil health protection and reducing erosion and preventing of splash erosion. Fire resistance is different in different species in a vegetative form. Plant species whose seeds are more easily moved by the wind are more successful in reestablishing in the burned zone and this point is independent of their vegetative form. In this research, fire is like preparing the field for planting plants, so reviving fire fields with high-quality species is a necessity. Considering that the fire destroyed the positive aspects of the soil and vegetation and the management of burnt areas is very specialized and sensitive. Therefore, according to the existing conditions, it is not recommended to create a fire either intentionally or accidentally in this vegetation area of Iran.

As a complex phenomenon occurring due to a long period of poor precipitation, drought causes water scarcity in the soil and the hydrological system via hydrological, bringing about long-term consequences which may lead to severe economic, environmental, and social problems worldwide. Droughts are classified into four types: meteorological (rainfall), agricultural (soil’s moisture), hydrological (flow and groundwater), and socio-economic droughts. It should be noted that all types of droughts originate from meteorological ones, bringing about social and economic damages. on the other hand, Iran has long been known as a dry country with a low annual precipitation rate. Moreover, the development of spatial and satellite sciences, the application of remote sensing techniques, and GIS together with previous methods have led to more accurate results. Therefore, investigating the relationships between satellite-derived indicators and meteorological droughts could improve our understanding of the response of such indicators to climate change.

This study sought to investigate the relationship between remote sensing indices and the drought index (SPI). To this end, first, the daily precipitation statistics of 103 meteorological stations located in the study area were collected from the Iranian Meteorological Organization’s website for the 2000- 2019 period and their quality was controlled. Then, the SPI drought index was measured for all such data on monthly and annual scales using the McKay method, according to which the total annual precipitation was compared to the fit of different distributions. Then the probability of the observations’ experimental occurrence was calculated based on the relationship between the aforementioned equations. Moreover, after measuring the SPI index in the stations located in the study area, the MOD021KM outputs of the Terra sensor for the 2000-2019 period were obtained from the USGS website, to which necessary geometric, radiometric, and atmospheric corrections were applied. Finally, the NDVI, VCI, TCI, VHI, DDI, NDDI, EVI, NDWI, and SAVI indices were used to assess the drought conditions, and a monthly time series database was created for each of the indices over the past 20 years.

The study’s findings indicated the acceptable efficiency of remote sensing indices in extracting the data required for analyzing the drought in Central and South Zagros via the SPI index. The drought-related data and indicators of the study area were obtained and identified using the KMO and Bartlett index, whose range varies from zero to one. Accordingly, in cases where the index value is close to one, the collected data are suitable for factor analysis; otherwise, the results of factor analysis would be not appropriate for the intended data. In this regard, the results of Bartlett's statistics also suggested that the remote sensing indices affecting the drought in the study area were suitable for factor analysis, indicating that the confirmation of the opposite hypothesis, according to which there was a significant correlation between the variables.

This study sought to investigate nine remote sensing indices affecting the analysis of drought in Central and South Zagros. The results of factor analysis revealed that the drought in the study area was affected by three factors. In the first factor, SAVI, NDVI, VCI, and EVI indices showed the highest correlation. In the second factor, NDVI, DDI, TCI, and VHI were of great significance, and in the third factor, the NDDI index played the most important role. In the next phase, the relationship between the spatial pattern of remote sensing indices and drought’s spatial clusters was examined. Spatial relations analysis is a method to spatially analyze the randomness and non-randomness of the distribution of spatial variables. Furthermore, spatial autocorrelation is one of the most practical and important analytical tools for researching spatial relationships. In this regard, it was found that remote sensing indices and SPI drought index possessed a positive spatial autocorrelation in terms of spatial relationship in eastern, southern, and some parts of the central regions of the study area. Therefore, it could be argued that the areas were more affected by drought in terms of spatial autocorrelation index G *. On the other hand, out of the indices investigated in this study, SAVI and NDVI had the most similarity in terms of regions with positive cluster patterns, possessing the most positive spatial patterns. The results of the impact factor analysis performed on the correlation between the SPI and remote sensing coefficient confirmed that the spatial distribution of drought was of cluster type.

Appropriate use of rangelands, creates vegetation stability, prevents degradation and improves their suitability  conditio. Determination of allowable level of vegetation utilization of the species could lead to plan for the proper distribution of livestock on rangeland. To measure the level of use, a 0.5 ha exclosure was established in Karsanak site before the start of the growing season in 2007 and 40 individual Plants of Bromus tomentellus were selected randomly inside of the exclosure in order to determine the effect of different harvesting intensities (simulated grazing) on forage and seed production. Clipped treatments included 0, 25, 50 and 75 percent of annual growth. There were 10 replications in the plan. Clipping continued for 4 years in three months of grazing season. Vigor and freshness, mortality, plant maximum height, forage and seed production were observed and measured during the 4 years. Data were analyzed in a split plot design in time with SAS software. The results of forage production of Bromus tomentellus showed that the effect of years is statistically significant at 1%. And the interaction of the year and different intensities of harvest, is not significant at the 5%. Lowest forage production has happened in 2007 harvesting at 25% and its highest in 2009 in control treatment. The results of seed production showed that the And the interaction of the year and different intensities of harvest is statistically significant at 1% But their interaction was not significant at the 5% error level. Due to environmental changes affecting of this species, it can be concluded that about 50 percent of annual yield removal is safe for persistence and health of Bromus tomentellus in Karsanak and other areas with similar climate and soil conditions in drought years but the harvest of up to 75 percent in normal years apparently does not harm the plant.