مجله سامانه های سطوح آبگیر باران
سال یازدهم شماره 3 (پیاپی 38، پاییز 1402)

Considering the role and importance of environmental factors in the distribution and spread of vegetation, as well as the existence of wind of 120 days in the Sistan region, and the necessity and importance of vegetation and flood spreading in the region, this research was done to classification and ordination of plant communities in Niatak flood spreading area, Zabol. Vegetation types were determined by Braun-Blanquet's physiognomy-floristic method and cluster analysis based on species composition and soil characteristics were used to classify vegetation. In each plant type, soil and vegetation sampling was done. In the key area of each plant type, 3 transects of 30 m were established, and during each transect, all surface features were measured. In addition, in each transect, soil samples were taken and physical and chemical properties were determined. The results of the preliminary studies obtained from the initial typology by the physiognomy-floristic method in 17 investigated types led to the identification of five plant communities, such as Ta. stricta, Ta. aphylla, Ha. ammodendron, Ha. persicum and Pr. stephaniana. In addition, the classification of vegetation by cluster analysis method based on species composition and soil properties was identified as five and three plant communities, respectively. The ordination results showed that the first axis and the second axis together with 64% of the variance of the distribution of plant communities are the most important axes. Sand percentage has the most positive correlation and absorbable phosphorus (Pav) has the most negative correlation with axis 1. Sodium (Na) and exchange sodium percentage (ESP) have the most positive correlation with axis 2. Redundancy analysis (RDA) biplot shows that characteristics, such as sand and fine sand percentage have a positive correlation with Ta. aphylla and Ha.ammodendron communities, and factors such as Pav, absorbable potassium (Kav), and cation exchange capacity (CEC) cause the distribution of Ta. stricta community in the region. Electrical conductivity (EC) and sodium absorption ratio (SAR) cause the presence of Ta. aphylla and Ha. ammodendron communities. There was a special relationship between different plant communities and soil characteristics.

During the last few decades, the ecosystem of natural areas has suffered as a result of improper exploitation of water and soil resources. To revive and develop renewable natural resources, it seems important to analyze and optimize rainfall storage systems and provide integrated techniques. Rainwater harvesting, in conjunction with plant species cultivation, is critical in the restoration and improvement of rangeland, particularly in dry areas. The present research was conducted with the aim of investigating the effect of rainwater harvesting methods (contour furrow and microcatchment) on increasing the percentage of vegetation cover in the Khajeh research station in East Azerbaijan province. To accomplish this, two methods of rainwater harvesting system, contour furrow and microcatchment, were established in the form of a randomized complete block design with three repetitions, in a land with a slope of 2-6%. After preparing the plots, Agropyron elongtum was planted in the form of seeding. Vegetation cover percentage was measured from the second year of planting for three years. A linear transect was used to determine vegetation cover percentage. The results showed that the microcatchment treatment significantly increased vegetation cover compared to the control. So that with the construction of the microcatchment, the vegetation cover increased about 183% (three times) compared to the control. In the case of contour furrow treatment, an increase of about 53% was observed compared to the control treatment. The microcatchment method performed better than the contour furrow, so that it increased the vegetation cover by about 85%. Therefore it seems the microcatchment is the best rainwater harvesting system in terms of increasing vegetation cover in the study area.

The current research aimed to investigate the impact of a semi-circular bunds system on vegetation and soil moisture levels. This research was carried out in the plain rangeland of Ahangaran region, South Khorasan province. Rainwater harvesting projects with semi-circular bunds structure along with Haloxylon persicum planting have been done in the years 2018-2021 in four areas adjacent to each other. In this project, biological restoration including seed broadcasting in the inside and on the bund ridge have been carried out. In the four studied areas, the canopy cover area and plant height and production of Haloxylon persicum were estimated. To investigate the effect of the structure on the soil properties, in April 2022, soil samples were taken from inside and outside of the semi-circular bunds at a depth of 0-30 cm. Soil moisture levels, soil texture, Bulk density, and soil organic matter content were determined in the laboratory. Kruskal-Wallis test was used to investigate the effect of year on vegetation characteristics. Moreover, to compare the vegetation characteristics of the inside and on the bund ridge, as well as the soil characteristics of the inside and outside of the structure, the Student's t-test were used. The results showed that the location of seed broadcasting in semi-circular bunds systems has a significant effect on vegetation characteristics (p≤0.01), canopy cover area and plant height resulting from seeding on the ridge are higher than on the inside. The results showed that the effect of the semi-circular bunds on other soil moisture properties (except for saturation moisture), soil texture, bulk density, and soil organic matter was not significant (p≥0.05). Soil texture of both areas with sandy loamy has not changed after four years. In 2018 and 2019, as wet years, semi-circular bunds project in this region has increased the vegetation compared to the control region, but in 2020 and 2021, as drought years, this system did not play a role in the increase of quantitative of rangeland vegetation.

Vegetation as a natural component plays a significant role in increasing permeability, improving soil, reducing evaporation, and reducing the runoff and thus reducing the possibility of flooding. The use of new technologies such as remote sensing and geographic information system to study plant ecosystems and prepare land cover maps is necessary to know the effectiveness of these tools and to identify the best methods of their use. The purpose of this research is to investigate the vegetation cover using the NDVI and compare the performance of three supervised classification methods, the maximum likelihood method, the minimum distance from the mean, and the parallelepiped method in a part of the Great Karun watershed. To this end, TM and ETM images of Landsat satellite were used in one interval and NDVI in a 10-year interval (May 2008 to May 2018) with the help of supervised classification and maximum likelihood algorithm. The above data were prepared and analyzed using ENVI4.2 software, and the effectiveness of each method was evaluated with the overall accuracy index and Kappa coefficient. Based on the results in the maximum likelihood method, the overall accuracy rate is 90.35% and the Kappa coefficient is 0.878, in the minimum distance method, the distance from the mean is 74.32% and its Kappa coefficient is 0.675, and in the parallelepiped method, the overall accuracy is 67.09% and the Kappa coefficient was calculated as 0.593. Based on the results, the maximum likelihood method has the highest level of accuracy in satellite data group classification. Moreover, the results showed that in the 10-year period in Dez, Karun, and Karkheh watersheds, the spectral reflectance related to vegetation has decreased by 7.4%, 10.64%, and 13.83%, respectively. The results of this research can be effective for the practical use of the analysis that was done in relation to the studies of runoff and flood. According to the process of vegetation changes due to natural or human factors, the need for proper management in this area seems necessary.

Groundwater is the main source of fresh water in arid and semi-arid regions, which make them resilient against lack of rainfall. Considering the great impact of groundwater quality on water and soil health, its evaluation is important. In this study, the assessment of the quality of underground water resources of the Shamil plain aquifer was carried out in Hajiabad county of Hormozgan province using the groundwater quality index (GQI) in the GIS environment. In this study, the results of the analysis of ten chemical parameters of calcium, sodium, magnesium, potassium, sulfate, bicarbonate, chloride, electrical conductivity, total dissolved solids and total hardness were used in 9 wells between 2017 and 2023. Then, using the geographic information system (GIS), the concentration map of the variables was first drawn using the IDW (interpolation) method, and based on the WHO standard, a normal and rank map was prepared, and by extracting the weight of each component from the rank map, a qualitative index map was prepared. Also, the time analysis was analyzed by Mann-Kendall and Pettit trend analysis test in two wet and dry periods of the year. Based on the results of time analysis with Mann-Kendall, all the physicochemical variables of underground water have a decreasing trend in two periods and GQI has an increasing trend, and the time of change in most of them was reported by Petit method, 2013. Also, based on the results of spatial analysis, all the ten investigated variables, except for bicarbonate and potassium, have similar changes in the plain. The group of variables with similar spatial changes on the level of the plain has the lowest concentration in the southern parts of the plain, and its concentration gradually increases in the northern parts of the plain. During the studied period, the groundwater quality index (GQI) was between 96 and 97 and it is placed in the appropriate category based on the WHO standard.

Climate change affects extreme events such as floods and droughts. This research was conducted in the watershed of Kashmar City in Khorasan Razavi province and the output of general circulation models from the CMIP5 model series was used to check the performance and validity of these models in predicting the climatic parameters of precipitation, average temperature, maximum temperature, and minimum temperature during the period 1989-2005. The best model was selected using the evaluation indices of the determination coefficient, the root means squared error, the absolute mean error, the correlation coefficient, and the mean squared error. Finally, the BCSD method was employed to downscale the data for three time periods near future (2020-2038), middle future (2039-2069), and far future (2070-2100) under the IPSL-CM5A-MR model and future emission scenarios (RCP2.6, RCP4. 5, RCP6, RCP8.5). The Mann-Kendall statistic test was used in order to investigate the trend of changes in monthly, seasonal, and annual rainfall and temperature variables. The results of the model evaluation indices for four climate models indicated the highest performance of the IPSL-CM5A-MR model in simulating precipitation and temperature with a high correlation coefficient and relatively low error indices compared to other models. The results of the investigation of the rainfall trend showed that in the far future, the rainfall component will be completely decreasing and it will have the largest decrease under the RCP8.5 scenario with a value of -41.12 mm. The average temperature is also increasing in all months and the maximum increase in the average temperature in the far future under the RCP8.5 scenario is 7.58 °C. The amount of minimum temperature and maximum temperature increases in all months, and the maximum increase of minimum temperature in the far future interval under the RCP8.5 scenario is 8.35 °C. Furthermore, the maximum increase in the maximum temperature in the far future interval under the RCP8.5 scenario is 7.09 °C.