نشریه مهندسی اکوسیستم بیابان
پیاپی 30 (بهار 1400)

As serious problems especially in Iranian border provinces, wind erosion and dust storm exert harmful effects on human health and the environments, including reducing soil fertility, increasing desertification, etc. So far, a variety of efforts such as using polymers and mulch, vegetation, oil emulsions, microorganisms have been done to reduce wind erosion and stablize the soil. However, none of tham have proved effective due to special circumstances that exist in Iran. Therefore, using modern thechnologies for controlling wind erosion and reducing wind speed in Iran seems necessary. In this research which sought create a bio-soil windbreak to control wind erosion and reduce wind velocity, a new device called “Ridging device” was used to build a ridge or windbreak. 

The ridging device comprises of three main parts, including the digginh of soil part, mixing soil- polymer part, and the ridge maker part. This machine digs the soil from within 30 cm depth, transfer it to the conveyor where polymer (polymer suspension) is added, and finally pours the mixture of soil- polymer into the ridge maker part. As a result of the pressure exerted by two plates embedded in the ridgid maker part, a ridge with a penetration resistance of 1.5 kg per square centimeter and an aggregate stability of 80% is created. Moreover, The penetration resistance of the ridge also increases with increasing polymer concentration. Through the settings placed at the end of the ridge maker part, the height and width of the ridge could be adjusted based on soil conditions, the region’s climatic conditions, initial soil moisture, and other conditions. To investigate the effect of the ridges on reducing wind velocity, the latter was recorded at heights (Z) of 0.05 m, 0.1 m, 0.2 m, 0.4, and 0.6 m above the surface, and at distances (x) of -2.5H, -1.25H, -0.62H, 0.62H. 1.25H, 2.5H. 3.75H, 5H, 6.25H, 7.5H, 10H, and 12.5H from the ridge. It should be noted that for simulateing wind erosion reduction with the ridge, a wind erosion measuring device with a speed of 15.6 m/s was used under laboratory conditions. The wind speed was measured with an AN-4330 Anonometer.

The results of the wind velocity profile showed that the wind velocity increased with increasing distance from the soil surface and reached its initial constant value (15.6 m/s) at a distance of 20 cm from the soil surface. The study also found that the ridge effectively reduced wind speed in such a way that by increasing the distance from the ridge, the wind speed also increased and reached a constant trend at 10 to 12 times the height of the ridge. Moreover, it was found that the region’s wind erosion threshold speed was 6.52 ms-1 and the distance between the ridges was 20 m. Therefore, to control erosion with this method, 500 meters of the ridge per hectare is requires.One of the advantages of this device is that constructing a ridger and controlling wind erosion is less costly compared to other techniques. Another important advantage of this ridger device over other living and non-living windbreaks is the accessible regional raw materials used in its construction. Generally, this ridge device is durable for four to five years, and it is constructed with low costs and no damages to the environmnt. This technique has no adverse effects on the environment and is very environmentally friendly. Given that the device is first of its kind, further studies are required for upgrading its design and function. Moreover, considering the special circumstances of Iran, effective policies and studies are needed for reducing air pollution and dust concentration in line with Iran’s sustainable development. 

Existence of nearly 30 million hectares of areas affected by wind erosion in Iran and various environmental stresses such as water shortage, soil salinity, erosive winds, etc., makes it necessary to use efficient methods such as mechanical windbreaks to control these areas. On the other hand, soil ridge is a very cheap thoough efficient mechanical windbreak that can be accessed and implemented in any area.The application of the windbreak device introduced in this study would be an effective step in using cheaper and faster windbreaks. This device ican create a ridge of desired size up to a maximum height of 70 cm in a short time, and thus greatly help control wind erosion. Finally, it is suggested that the performance of the device be evaluated in areas with different soil texture, climatic conditions, and topography.

As one of the most significant environmental problems in recent decades, wind erosion has caused environmental pollution throughout the world (Shojaei et al., 2019; Aliabad et al., 2019; Alipour et al., 2016).), inflicting damages to nearly 500 million hectares of land worldwide per year (equivalent to 46.4% of the world's degraded lands) (Rand et al., 2015). On the other hand, the presence of large areas of running sands, wind erosion-inflicted damages, and problems regarding the use of oil-based mulches, highlights the necessity of using nature- friendly mulches. This study, therefore, sought to investigate the effects of lignocellulosic nanomaterials and lignocellulosic micromaterials on shear strength of soft sands and to the positive and negative effects of such mulchs in that regard so that the most appropriate composition and extent of those mulchs could be identified in terms of increased shear strength of sand particles.   

To conduct this study, a sample of sandy soil with 89% sand particles was collected from the Isfahan’s sand dunes (Rig Boland of Kashan) in the central Iran. Bagasse paste is used to make lignocellulose materials. Using blade mills and super disk mills, bagasse paste is transformed into lignocellulosic micromaterials and nanomaterials. Moreover, the Black liqueur is a paper industry’s waste that is used as an adhesive element. To investigate the effect of lignocellulose nanomaterials and lignocellulose micromaterials on soft sands’ shear strength, nano and microparticles each with 0.3% concentration at three levels (2.5, 5 and 10 g/L in 0.3 m2 soil), Black liqueur with 1% concentration at the level of 10 g/L in 0.3 m2 soil, a combination of Nano lignocellulose (NL) and Black liqueur (BL) in three levels (2.5, 5 and 10 g/L at 0.3 m2  of soil), composition of Micro-lignocellulose (ML) and black liqueur at three levels (2.5, 5 and 10 g / L in 0.3 m2 soil), the control sample and all treatments in one-later and two-layer thickness were sprayed on the surface of the sand. Furthermore, shear blades were used to measure the adhesion of the mulches under saturated and dry conditions.   

In saturated mode, the maximum shear strength of the double-layer microlignocellulose was found to be 10 g/0.3m2, with the shear strength increased to 13.6 kN/m2 compared to the control sample (zero), followed by double layer- microlignocellulose at 5 g/0.3m2 (8 kN/m2) level, double layer- nanolignocellulose at 10 g/0.3m2 (7 kN/m2) level, and the combination of single-layer microlignocellulose plus Black liqueur at 10 g/0.3m2 level (7 kN/m2). It was also found that the lowest shear strengths belonged to single-layer treatments of NL (at all levels), ML (2.5 and 5 g/0.3m2), and the combination ML + BL (2.5 g/0.3m2), as well as double-layer treatments of the combination of NL + BL (at all levels), and 2.5 g/0.3m2 ML + BL. In the dry mode, the maximum shear strength belonged to double- layer NL + BL mulch at 10 g/0.3m2 level, with its shear strength increased by 39 kN/m2 compared to the control sample (zero), followed by double-layer ML at 10 g/0.3m2 (36.33 kN/m2), and a combination of double- layer ML + BL (33.33 kN/m2), respectively. The study’s findings indicated that there was no significant difference between these three types of mulches in terms of shear strength at 5% confidence level, while the results of the mean comparison between these three types of mulches and the control sample showed a significant difference in terms of shear strength (P <0.05).   Table (7): Shear strength of different mulches in both saturated and dry conditions One Layer Double Layer   Black Liqueur control (water)  lignocellulose lignocellulose + Black Liqueur lignocellulose lignocellulose + Black Liqueur  Saturation level 2.5 5 10 2.5 5 10 2.5 5 10 2.5 5 10 One Layer Double Layer   Nano 0 0 0 1 4 3 1 6 7 0 0 0   3.3   0.3   0 Micro 0 0 0.66 0 3 7 1.33 8 13.6 0 3.6 6 Dry Nano 0 5 26 1 4 22 1 16 26 0 7 39   1   0   0 Micro 0 0 5 0 1 13 1 14 36 2 15 33.

As mentioned above, the amount of shear strength increased in the dry mode compared to the saturation one. Therefore, it seems that the passage of time and dryness of the sandy bed have increased the efficiency and strength of the mulch. While the findings of some studies have indicated a significant correlation between the soil’s shear strength and time, other studies have proven the opposite. Moreover, this study found that the paper layer created by the spray of NL on the sand’s surface increased the resistance to sand retardation as well as surface resistance to sinking. Therefore, it appears that the morphologic structure of NL which is comprised of long hole-less nano strings increased both abrasion and strengths. According to the study’s findings, the minimum amounts of shear strength belonged to the treatments of 2.5 gr/0.3m2 NL, ML, ML+BL, 5 gr/0.3m2 of single-layer ML, the combination of NL+BL, and double-layer BL, with the results of the mean comparison between these treatments (minimum shear strength) and the control sample proving no significant difference between them in terms of shear strength (P <0.05). The results of the study also showed that while a seemingly integrated layer had been created on the sand surface via the addition of those mulchs, limited suspensions may have prevented proper adhesion of the sand particles, leading to the easy disintegration of the particles. Therefore, it is recommended that these types of mulches be tested in the natural field first, and should they produced favorable results, be used for the stabilization of the running sands.

The complex relationship between soil and vegetation is difficult to be simulated by mathematic and statistical models. Since soil, vegetation, and atmosphere are interrelated, they cannot be separately compared. As an important basic factor with regard to soil, vegetation greatly affects ecosystems, especially in arid and semi-arid areas. Therefore, the restoration and recreation of this complex phenomenon is much more difficult in arid and desert regions. On the hand, considering the fact that plants generally affect the soil both physically and chemically, it is necessary to know how these parameters interact, the knowledge of which could significantly help restore the vegetation. As a natural, resistant and desert-friendly plant, Capparis spinosa has been known as a multipurpose species in recent years. Because of its deep roots, this species is resistant to wing and its wide canopy can cover a wide range of the soil’s surface and stabilize sand hills. Therefore, it could be an appropriate choice for preserving soil and water, and anti-desertification programs. It could also help control dust storms in different regions. This study, therefore, sought to investigate the effects Capparis spinose on soil characteristics of the Eyne-Khosh desert area in Dehloran, southern Ilam province, offering it to the relevant officials and decision makers as an effective plant for anti-desertification programs. 

As a part of desert areas in southwest Iran, the study area is located in Dehloran city, Ilam province. To investigate the effects of Capparis spinosa on soil characteristics, this field study used satellite images, GIS, laboratory analysis, and the date obtained from a statistical software. To this end, first the species’ distribution map was prepared, using field observation and liner transect for calculation of coverage percentage in the growing season. Then, other characteristics including canopy percentage, soil preservation percentage, and other factors were measures, using sixty-nine species randomly selected for the study. As for investigating the effects of Capparis spinosa on soil’s physical and chemical characteristics, a soil profile was dug, and the intended samples were collected from two layers (surface and subsurface) of fifteen points including the surface soil of the existing bushes (near the stem) and control areas (bush-less), which were then moved to the laboratory (totally 30 samples) where chemical factors including N, K, P, OC, ESP, CEC, Ca, Mg, Caso4, Caco3, Cl, HCO3, pH, EC, and SAR were measured.

The study’s findings showed that the highest values of all chemical factors (N, C, P, K, Na, Ca, C/N) belonged to the bushes’ subsurface soil. On the other hand, there were statistical differences between land use (control areas, Nebka bushes, and natural bushes) and land depth for other seven parameters (OC, ESP, Ca, Na, EC, pH, SAR). There were 5% difference between EC and PH in terms of land use, and 5% difference between CA, OC, and CI in terms of land depth. For physical soil factors, actual soil moisture and saturated soil moisture show a strong relationship to depth and they are more in both depth, comparing to control part, although for the other parameters (clay, silt, sand, field capacity and wilting point) there were not statistical different. It was also found that the presence of the study bushes decreased salinity and increased alkalinity of the soil. Moreover, the highest number of variations of the organic matters of the control points’ deep layers occurred in subsurface layer of under-bushes, indicating that this species had increased the organic carbon of its sub-soil compare to the surrounding areas. The findings also showed an increase of OC, Na, Cl, and HCO3 in under-bushes soil. 

According to the study’s results, Capparis spinosa has significant effects on soil characteristics and may change soil texture, increase the soil’s organic matter, maintain the soil’s moisture, and in general, preserve the soil and control its erosion. It could also positively affect chemical parameters such as decreasing the salinity, increasing the alkalinity, and increasing OC, Na, Cl, HCO3, and nutrients of the soil. Therefore, this species could be an appropriate choice for anti-desertification programs in this region and similar areas.

The complex and dynamic nature of watershed problems requires flexible and transparent decision-making that embraces a diversity of sciences and values. However, while the significance and effective role of stakeholder participation in natural decision-making and its benefits have been emphasized and discussed by different scholars and it has been considered in national and international planning, it has not been put into practice in desirably, leading to the discontent of some watershed stakeholders and operators. As watershed projects play an increasingly important role in managing soil and water resources throughout the world, knowing the factors involved in encouraging residents of watershed areas to participate in watershed activities is considered a significant principle in realizing the effective participation of stakeholders in integrated watershed management and achieving the intended goals in this regard. Therefore, the identification of such factors can help relevant authorities benefit from the effective participation of the stakeholders in conservation activities. This study sough to identify, classify, and prioritize the factors involved in discouraging people from participating in watershed projects, using the viewpoints of the experts and residents of Bozijan watershed in Markazi Province. 

Different factors which may be involved in discouraging people from sustained participation in watershed plans were classified in terms of economic, social, human (educational and propagational), and planning indices. To this end, these factors were identified and categorized based on the review of related literature, and in-person interviews with experts and residents of the watershed area. Then, pairwise and Likert questionnaires were prepared as a measuring tool whose validity were confirmed by expert opinions. Finally, after determining the sample size via Cochran formula, 101 questionnaires were administered and the indicators and sub-indicators involved in discouraging people from sustained participation in watershed plans were prioritized, using Fuzzy Analytical Hierarchy Process and Friedman Test.

After identifying various factors involved in non-participation in watershed projects, they were classified in terms of are educational-propagational, social, design-executive, and economic indices and sub-indices for the Bozijan watershed.
In this study, eight questionnaires which had been completed by experts and one hundred and one questionnaires which had been completed by residents of the watershed area were analyzed via T test, Analytical Hierarchy Process, and Friedman nonparametric test. The results showed that while from the experts’ viewpoints, the educational-propagational, design-executive, economic, and social indices were, respectively, the most influential factors involved in order of propriety in the non-participation of the Bozijan watershed’s residents in watershed management projects, it was educational-propagational, economic, design-executive, and social indicators that contributed the most to such non-participation from the resident’s perspective.Moreover, experts argued that “Concentration of decision-making power regarding planning and implementation in the Directorate General”, “The elderliness of the residents”, and “Offering no training for the watershed area’s residents by executive officials" were the most effective sub-indices in discouraging people from sustained participation of rural communities in watershed projects, and "The residents’ ethnic and local disagreements” was the least effective sub-index in this regard. The range of average ratings varied from 3.79 to 11.6 in this group. In addition, based on the viewpoints of watershed area’ residents, sub-indices such as "The residents’ discontent concerning the projects’ outcomes”, “Disregarding the residents’ benefits as direct economic incentives, and “Lack of sense of belonging in areas of project implementation by the residents” were the most important factors in their non-participation in watershed activities in order of propriety. The range of average ratings varied from 3.096 to 10.86 in this group.

As mentioned before, from the viewpoints of experts and the watershed area’s residents, the educational-propagational index was the most important factor involved in non-participation of people in watershed projects, followed by the design-executive and economic factors. In other words, both experts and the residents believe that prior to any planning and executive activity, people should well be informed and trained; a fact also confirmed by Rahimzadeh and Charrmchian (2019), and Mahmoudi and et al (2018).
The order of sub-categories mentioned by the watershed area’s residents indicated that any decision made concerning the watershed-related issues could somehow affect their lives. Therefore, they expect to be involved in decision-making structure, and economic approaches are of second importance for them. The experts have also affirmed the non-presence of people in decision-making and planning of executive tasks. In other words, both people and experts argue that mutual communication and participation are necessary for deciding over watershed issues.

As proven by some researches, the atmosphere’s general circulation models (GCMs) well predict the temporal and special variations in climatic variables such as temperature and precipitation at a global scale. However, although these models can simulate the global climate in a three-dimensional grid for the whole world, the resolution of their images cannot display the details of the climate changes at regional scale. Therefore, to predict climate changes at regional and regional scales, downscaling tools are needed to be developed. This study, thus, sought to investigate the variations of temperature and precipitation in future periods in a semi-arid region in Iran. 

To conduct this study, the Kermanshah province with average annual precipitation of 402.27 mm and mean temperature of 15.9° C was selected. To investigate the future climate change, we need a base period as an evidence or reference (1961-2005). The data used in this study were collected from station observations based on the required output and large-scale data NCEP and GCM gained from the nearest global network to the study area. To estimate the future periods’ temperature and precipitation data, the GCM model of the CanESM2 was applied under three scenarios including RCP 2.6, RCP 4.5 and RCP 8.5, and SDSM 4.2.9 model was used in this regard for downscaling the output data. The SDSM is a multivariate regression model for the production of climatic data via statistical downscaling techniques, seeking to generate high-resolution climatic data from GCM’s large- scale simulations data. This model is used when rapid and low-cost estimation of the climate is required.

This study evaluated the model’s performance in predicting climatic parameters based on R2, RMSE, and NS. As confirmed by the results of RCP2.6, RCP4.5 and, RCP8.5, the values regarding the climatic parameters were modeled with acceptable accuracy. However, precipitation prediction was less accurate than temperature which could be attributed to the inaccuracy of the precipitation data and their unconditional nature.The study’s results showed that the annual mean temperature values in the period 2020-2049 under RCP2.6, RCP4.5 and RCP8.5 increased by 0.6, 0.7, and 0.9°C, respectively, compared to the base period. Moreover, the investigation of the prospective temperature changes in 2050-2069 period under the above-mentioned scenarios suggested that the temperature would increase throughout the year except in September, October, November, and December. The highest increase would occur in June by 6.6°C under RCP8.5, and the lowest increase would happen in October by 4°C under RCP2.6 scenario. Furthermore, the annual mean temperature values would increase by 0.8, 1.4 and 2.4°C in 2050-2069 under RCP2.6, RCP4.5 and RCP8.5 scenarios compared to the base period, respectively. It was also found that the temperature would increase in all season but autumn throughout 2070-2099, with the annual mean temperature values getting increased by 4, 1.9 and 4°C, respectively, under RCP2.6, RCP4.5, and, RCP8.5 scenarios.Precipitation values and its variations in 2020-2049 period indicated that the highest decrease in precipitation value would occur in March by 38.2 mm under RCP2.6 scenario and the highest increase in this parameter would occur in October by 127.5 mm. Moreover, the annual mean precipitation rata would be 6.4 mm lower in 2020–2049 period than the observed value based on RCP2.6 scenario, and it would increase by 2.6 mm in the same period under the RCP4.5 scenario compared to the baseline period, and it would decrease by 2.6 mm under RCP8.5 scenario. Precipitation values for the period 2050-2069 show that the highest decrease in precipitation in March was 38.3 mm under RCP2.6 and the highest increase in October to 127.5 mm under RCP4.5. Furthermore, according to the annual mean precipitation values for 2050-2069 period, it was found that the highest decrease in precipitation rate would occur in March by 38.3 mm under the RCP2.6 scenario, and its highest increase would occur in October by 127.5 mm under RCP4.5 scenario.Also, the annual precipitation rate in 2050-2069 period would increase by 2.6 mm and 4.2 mm under RCP8.5 and RCP4.5 scenarios, respectively, compared to the observation period, and it would decrease by 4.9 mm under the RCP2.6 scenario compared to the baseline period.The results of the precipitation rate for 2070-2099 period showed that the highest decrease would occur in March by 48.1 mm under the RCP2.6 scenario, and the highest increase would occur in September by 129.5 mm under the RCP8.5 scenario. Moreover, in 2070-2099 period, the average annual precipitation values would decrease by 0.6 and 7.4 mm under RCP2.6 and RCP4.5 scenarios, respectively, and it would increase by 7.8 mm under the RCP8.5 scenario compared to the base period. 

The climate changes observed in the 20th and 21st centuries are incompatible with those of the past millennium. Arid and semi-arid regions are extremely vulnerable to climate changes. Therefore, identifying and comprehending the relationship between climate variables, and knowing their future changes are important for sustainable and efficient management of resources in such areas. According to studies conducted in this regard, climate change will inevitably occur in Iran. On the other hand, one of the most important issues in dealing with climate change in recent decades has been susceptibility to the climate changes. The investigation of the trends of the climatic data recorded in last decades, and the outputs of all climate models that predict future climates indicate that undeniable changes would occur in global climate.To conduct this study, the daily temperature and precipitation data of Kermanshah province’s synoptic station were used. However, non-conditional data presented more acceptable results. The study’s findings showed that in 2020-2049 period, the precipitation rate increased under RCP4.5 scenario compared to the observation period (1961-2005), and it increased in the same period under the RCP2.6 and RCP8.5 scenarios. It was also found that in 2050–2069 period, the precipitation rate decreased under RCP2.6 scenario compared to the observation period (1961–2005), and increased under RCP4.5 and RCP8.5 scenarios. Generally, it could be argued that the precipitation rate would increase in this period. Moreover, it could be said that the precipitation rate would be decreasing throughout the 2070-2099 period compared to the observation period, and temperature would experience an increasing trend during 2020 -2049, 2050-2069, and 2070- 2099 periods compared to the observed period.
As indicated by the results, the Kermanshah province’s climatic conditions in the prediction period would considerably differ from the current situation, suggesting serious changes in the region’s climate status. Therefore, getting aware of the direct and indirect negative effects of the climate on different parts of the region and developing long–term strategic plans are necessary for dealing with such conditions.

Various problems regarding watershed issues that have occurred because of human activities and economic development, are attracting increasing attention. Subsequently, many researchers are concerned about the effect of land use change on runoff which depends on the size, average slope, and the watershed’s baseline land cover characteristics. Moreover, the extent of the land-use change effect on simulated runoff depends on the hydrological model used and the processes considered in this regard. Any change in Land Cover and Land Use (LCLU) would affect the runoff characteristics of a drainage basin to a great extent, which, in turn, influences the region’s surface water and groundwater availability, leading to further changes in LCLU. Therefore, it is necessary to evaluate the effect LCLU changes on a region’s runoff characteristics in general and on small watershed levels (sub-basin levels) in particular.Land use changes in developing countries usually affect forests and national reserves. This is due to human activities such as creating settlements, developing agriculture, and encroaching on forestlands. Poor hydrological measuring infrastructure and lack of expertise are amongst the main factors which prevents a comprehensive analyses of catchment scenarios and their impact on the environment. Changes in climate and land use/cover (LUC) play an important role in altering the runoff trend. Climate change influences the runoff and the regional water balance by affecting precipitation and temperature rates. While precipitation is particularly crucial in determining the amount of water for runoff, temperature mainly affects evapotranspiration, which is regarded as a kind of loss for runoff formation. Moreover, changes in LUC influence the runoff routing trend.For instance, the destruction of a forest may affect soil permeability and further alter the runoff generation trend. On the other hand, an increase in impermeability of the surface areas’ soil because of urbanization can decrease the infiltration rate and concentration time, leading in turn to an increased in surface runoff. As changes in runoff considerably affect water resources, investigation of the runoff responses to climate and LUC changes is essential for the preservation pf local ecology and sustainable utilization of water resources. Furthermore, environmental scientists and local planners need a model for estimating the impacts of land-use change on groundwater recharge, water supply, and wetland hydrology.There are several evidences indicating that changes in land cover have influenced the hydrological regime of various river basins. Furthermore, the effects of climate change on hydrological cycle and the runoff behavior of river catchments have largely been discussed in recent years. However, it is currently not clear how, to what extent, and at which spatial scale such environmental changes are likely to affect storm runoff generation, and consequently on the rivers’ flood discharges. Changes in Land Cover and Land Use (LCLU) affect to a great extent the runoff characteristics of a drainage basin, which in turn, influence the surface and groundwater availability of the area, leading to further change in LCLU.Land use/land cover (LULC) change is a dynamic and complex process that can be exacerbated by a number of human activities, including an increase in human population and population response to economic opportunities. While in the past, the rivers’ corrective operations were focused on building constructs for controlling the rivers’ flow and implementing construct operations, hydrological consequences of climate change and land use changes, flood plains’ economic and ecological developments, and the alteration of social views regarding rivers’ safety and ecological functions have directed the attentions to the more sustainable use of rivers. Unfortunately, river systems have not been monitored with sufficient spatiotemporal resolution over long periods to deal with the above-mentioned issues through field observations alone. Therefore, to make appropriate management decisions for watershed basins, the effect of land use change on runoff should be evaluated based on hydrological models.

To assess the impact of land use changes on the Khorramabad watershed’s hydrological behavior, land use map, CN and the runoff coefficient maps was prepared for 1985, 2000, and 2016, using Landsat satellite imagery. Moreover, HEC HMS computer model was used for modeling rainfall-runoff. 

The study’s results showed that the change in the region’s land use, especially the reduction of forest lands and increase of urban areas, has led to an increase in peak-flow discharge, an increase of runoff volume, the reduction of concentration time and lag time, the reduction of the time required for reaching the hydrograph time, and decrease of the watershed’s runoff, with the watershed’s peak discharge changed by 54.195 to 150 percent in 1985-2000 period, 82.867 to 210.714 percent in 1985-2016 percent, and 18.594 to 24.285 in 2000-2016, period, and the concentration time and the flood’s peak discharge time changed by -6.99 and -5.02 percent in 1985-2016 period, respectively. Furthermore, the results of implementing the model on precipitations with return periods indicated that with an increase in return time, the amount of discharge changes decreased. For instance, in 1985- 2016 period, the increase in the discharge rate in return times of 2 and 100 years was 22.55 and 16.87, respectively.

Land use changes vary in different parts of a land, including the conversion of forest lands to agricultural ones, ranch and agricultural lands to residential and urban areas, and agricultural lands into abandoned ones. In the north and northwestern part of the basin, severe destruction of forests and their conversion to agricultural lands, and in the south and southwestern part of the basin, the conversion of agricultural and rangeland lands into residential and urban areas was observed. Moreover, CN has particularly increased in these areas under the influence of land-use changes.

In recent years, dust storms have turned into a serious problem in Khuzestan province during the cold season. Therefore, this study sought to investigate and analyze the sweeping dusts’ synoptic pattern in Khuzestan province during the cold season. 

In order to study and analyze the synoptic pattern of dust in Khuzestan province in the cold period of the year, two databases were used, and the dust codes were extracted, according to which an all-out dust was defined as a situation in which the dust covers at least 50 percent of the spatial area and lasts for two days. After identifying the all-out dust days, the corresponding pressure data of such days were extracted. These data included ground pressure data, geopolitical altitude, moisture depletion, and atmospheric precipitation for 100 to 500 hpa levels, obtained from NCEP / NCAR. The data’s spatial resolution was 2.5*2.5 arc degrees.
 According to the research topic and in order to fully display the effective systems involved in creating dusts within the study range, atmospheric systems were determined from -10 degrees west longitude to 100 degrees east longitude, and from 10 to 70 degrees north latitude. This stud attempted to identify and analyze the effective patterns involved in creating dusts in Khuzestan province by using a Perimeter Environmental approach. In the next step, the dust days’ pattern was identified, administering a cluster analysis on the corresponding pressure data of such days. Following the extraction of the corresponding pressure data regarding those days, cluster analysis was used for identifying Khuzestan province’s dust patterns.Then, to classify the ground surface pressure data and identify the representative days, cluster analysis was performed on the data. Cluster analysis is a method in which variables are classified into specific groups based on their characteristics so that real representative groups are identified and the data volume is reduced. In other words, cluster analysis seeks to reduce the number of identified groups, with similar cases being grouped in the same category where intra-group variance is minimum and inter-group variance is maximum. In this method, grouping is made based on group’s similarity or interval. There are different methods for measuring the distance among the data, a most commonly-used of which is the Euclidean Distance method.To select the representative days of the groups obtained from the classification of dust-related data, the Lund correlation method was used. The correlation coefficient in such cases typically varies between 0.5 and 0.7. Therefore, the representative days were extracted based on 0.5 threshold. So, the day with correlation coefficient of 0.5 with more days was selected as the representative day. 

After identifying the dusty days and performing cluster analysis on pressure data, four synoptic patterns were identified, including 1) Caspian Sea low pressure – Siberian high pressure, European high pressure pattern, 2) European-Mediterranean Integral high Pressure- Sudan low Pressure, North Caspian low Pressure pattern, 3) The Arabian Sea low pressure and North African high pressure pattern, and 4) Siberian high pressure - Sudan low pressure, and low Mediterranean pressure pattern, with the first pattern having the highest frequency. 

According to the study’s findings, in latitudes over 20 degrees, Iraq, northern Saudi Arabia, and eastern Syria are the main sources of dust formation in the region, that, together with western winds emanating from those areas of the Middle East which are prone to dust generation, including the Sahara Desert in northern Africa exacerbate the situation. Environmental conditions along with increasing temperature, low humidity, wind speed, soil particles’ lack of complete adhesion, and atmospheric factors that develops instability in these areas, are also fully involved in the occurrence of such a phenomenon. The Sudanchr('39')s low-temperature thermal tabs that are stretched to higher ranges, the dynamic change in their nature when the Mediterranean or Red Sea pressures land in the deserts of Saudi Arabia and Africa, and the deep pressure dust formed in the eastern Mediterranean within the troposphere’s middle layer are the main generators of dust in south-west Iran and Khuzestan province. Therefore, it could be argued that when a deep landing in the eastern Mediterranean is created, the flows of the east side coincide with the North African currents which will eventually merge with the high divergence in the southwestern part of Iran, provided that environmental conditions are provided. The ground level instability due to the low sea-level pressures on the great deserts of the Middle East will lead to the phenomenon of dust in Khuzestan province.

Sand and dust storms (SDS) are naturally occurring phenomena in arid and semi-arid areas that cause some critical challenges in such areas, whose intensity have increased by drought and water scarcity. Located in eastern Iran, the Sistan plain is affected intensively by the negative effects of such storms, which also affect Afghanistan and Pakistan. This study sought to investigate the extent and range of changes in the effects of dust storms, the variations of the wind velocity, and the changes in climatic factors in the Sistan plain so that managerial measures could be developed for fighting against such storms.  

In this study, annual mean temperature and precipitation were selected as climate variables to measure the change in the study area’s climate. These data were analyzed for 1977-2014 period, using the Mann-Kendall (M–K) test. The magnitude of slope in the MK test, is applied to determine the tendency of parameters. A positive slope magnitude indicates an increasing trend, while a negative slope magnitude suggests a decreasing trend. The changes in sand and dust storms intensity in Sistan plain was investigated through the Present weather data (WW). Also, the wind speed data during the study period were applied to investigate the changes in this parameter. The brightness temperature degree index was calculated to determine the affected sand and dust storms extend. This affected area was mapped for 2000, 2004, 2013, and 2018 to determine the changes made by sand and dust storms in the area.

The study’s findings showed that the intensity of sand and dust storms increased during the study period, and the area under their influence was expanded in recent years especially in years when the precipitation were low. Moreover, the results indicated that while the main hotspot in the Hamoun body was expanded to more distant areas out of Sistan plain especially in Afghanistan, the wind speed did not change significantly. On the other hand, MK test conducted on precipitation and mean annual temperature showed a decreasing trend in precipitation an increasing trend in annual mean temperature during the study period, indicating that the region’s climate had been getting drier and warmer. Furthermore, the intensity of dust storms had increased and the number of dusty days was doubled, and a wider area was affected by such storms. The findings clearly indicate that the extent and intensity of the sand and dust storms in Sistan plain have increased.

The study’s findings suggested an increase in the extent and intensity of sand and dust storms was in the Sistan Plain throughout the study period (1977-2014), which could be due to the changes in the wind speed or annual mean temperature and precipitation of the region. In this regard, it was found that while the changes in the wind speed was not significance, there were significant changes in the region’s annual mean temperature and precipitation. Moreover, the results of Man-Kendal test showed a decreasing trend in precipitation and an increasing trend in temperature during the study period, indicating that the region had become drier and warmer, which in turn had increased the potentials for the rise of dusts in each storm. Therefore, with the dryness of the region, the soil moisture would decrease, providing the grounds for the occurrence of a dusty day by any wind. Moreover, as the areas affected by sand and dust storms have been expanded, this study emphasizes on long-term planning for protecting local people against such storms.