جستجوی مقالات مرتبط با کلیدواژه "sub basin" در نشریات گروه "کشاورزی"

Nowadays, prevention or reduction of undesirable consequences due to degradation and increased vulnerability of forest ecosystems has become one of the most important goals of natural resource managers around the world. The existence of incompatible land uses is considered one of the most important threats to forest ecosystems, especially their biodiversity. To discover and evaluate such threats, which pave the ground for changes at the ecosystem level, using techniques and tools such as remote sensing and geographic information systems with analytical capabilities can play a major role in producing spatial information. The aim of this research is to evaluate degradation in the Dadab forest ecosystem based on the degradation model of working sub-units and investigate the most important human activities paving the ground for degradation in the area.

To quantify landscape metrics, the land use/forest cover map of the Dadab region with 13 sub-basins was used. To prepare the land use/cover map, satellite imagery was first pre-processed and the image was classified into different land use classes. For this purpose, satellite images from the 30-year period (2018-1988) were used to analyze the structure using landscape metrics. One of the advantages of assessment using landscape metrics is timely awareness of the intensity of degradation in the landscape in the shortest possible time with quantitative data that can be compared with future re-studies. Then, based on the landscape degradation model, the ecological vulnerability degree was determined, the intensity of activities and the amount of degradation in the landscape were calculated. Subsequently, based on the degradation coefficients obtained, landscape analysis and mapping were carried out. Finally, the ANP method was used, based on expert opinions, to prioritize the most important human activities paving the ground for degradation in the area. The ANP is one of the multi-criteria decision-making methods used in this research to classify the human activities affecting degradation in the area; one of the most important reasons for using this method compared to other MCDM methods is considering the interdependence or relationship between factors as well as using nonlinear network structure analysis. To achieve this goal, first, the most important factors paving the ground for forest cover degradation in the Dadab region were extracted by reviewing the resources in this field. Calculations related to the ANP method with a multi-criteria decision-making model were performed in the Super Decision.

Sub-basins 3 and 5 had the highest numbers of landscape degradation in the Dadab region, and sub-basins 4, 8, 9, 12, and 13 had the least fragmentation. In total, 40.58% of the total area of Dadab was identified with low degradation and development potential that can be developed by considering ecological constraints. It is noteworthy that the reason for the low degradation rate in these areas was their mountainous and inaccessible nature, and therefore they were less affected by human activities. Also, 25.33% needed restoration and rehabilitation, and 37.8% needed protection measures.

Among the various factors, the three factors of converting national lands to agriculture, socio-economic issues, and widespread development activities (road construction) were the most important parameters for degradation in the area with final weights of 2.0, 182.0, and 18.0, respectively. The results of this study can play a significant role in the effectiveness and success of protection and management programs for Lorestan province's forests by prioritizing the most important factors of forest degradation.

It is impossible to manage water resources in basins without the accurate determination of the peak flood discharge. Therefore, this study was carried out to determine the peak flood discharge for the return period of 10, 25, 50, and 100 years using RSM model in Darrehrood sub-basins with 12900 km2 area in Ardebil Province. Flow data of 16 hydrometric stations were collected in a statistical period of 15 years (2001-2005) and statistical deficiencies in the joint period were eliminated by using regression methods between hydrometric stations. Floods were calculated with different return periods. Also, physiographic characteristics of sub-basins that affect flood rate including area, slope, shape factor, height average, concentration time, and curve number were achieved using ArcGIS10.2 and WMS7.1 (watershed modeling system). The Goodness of Fit (R2) in the return periods of 10, 25, 50, and 100 years was estimated to be 96, 97, 95, and 94%, respectively. This indicates the model's high accuracy to predict the peak discharge in the sub-basins using the basin physiographic parameters. Model performance indexes of the model evaluation for return period of 10, 25, 50 and 100 years were calculated respectively including root mean square error (RMSE)  of 20.99, 7.16, 29.05, 39.55, relative percentage error (ε) of 52.7, 37.7, 45.1, 49.13, mean absolute error (MAE) of 0.52, 0.45, 0.48, 0.55, coefficient of residual mass (CRM) of 0.28, 0.16, 0.56, 0.82, and model efficiency (EF) of 0.74, 0.85, 0.71, 0.75. Cross-validation diagrams showed that RSM model was very suitable for the whole return periods. Paired t-test showed that the difference between predicted and actual values in different return periods was not significant (P< 0.01). The results of this study showed that the RSM has good accuracy for estimating floods in sub-basins of Ardebil Province.

Talar watershed with various land use, hydrological and vegetation characteristics is located in Mazandaran province In recent years, numerous devastating floods have occurred in this basin.In this study, flooding prioritization of Talar sub-basins under different hydrological and physiographic conditions were compared with an area of 189613.6/ha in agricultural, residential, rangeland and forest land-uses.First, the basin is divided into six sub-basins, including Shirgah, Karmozd, Drasleh, Polusfid, Arjangrudbar and Chashem and for each sub-basin, geometric, climatic, permeability and physiographic parameters such as; area, perimeter, length of main channel, length and slope of basin, time of concentration, CN, discharge, etc.have been calculated using GIS software.Time of concentration with methods of Branci Bay Williams, Johnson, Pilgrim-McDremat, Kirpich, California, Chow, Spey, Ventura was evaluated based on the characteristics of the basin but the Bransi-Williams method with 19.2 hours TC, showed the most suitable method for the all basin. Based on SCS method, the share of each sub-basin was determined in the flood of output from the whole basin. The results of the maximum stannous flood peak also showed that Polsefid with a flow of 380 cubic meters per second had the highest flow during the statistical period (1986-2019). Sub-basins are divided into three groups with high, medium and low flood potential in terms of similarity of flood potential, erosion, vegetation, and effects of human impact. The results showed that the highest amount of flooding in each of the sub-basins includes the sub-basin of Chashm with 29.19%, in Draseleh with 23.25% and finally shirgah with 16.76%

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.

Runoff generated by rain in forest areas and its flow on the roads can cause road damage and disrupt the operation and transportation. This research aims at minimizing the runoff damage to the road due to the flood by determining the optimal culverts diameter on the path of Tuska Kalam - Lyre Sar, Tonekabon, basin 35 in 23 forest sub-basins. Using the Curve Number method with different return periods, the maximum runoff flow of each sub-basin was calculated in cubic meters per second. Then, the optimal culvert diameter of the sub-basins was determined by using the Nomograph for determination of the diameter of concrete pipes. The results showed that on the B3 sub-basin, the maximum runoff for the return periods of 5,10,25,50 and 100 years is 3.37, 4.48, 6.04, 7.29 and 8.63 cubic meter per second, respectively, in which the culverts diameter is not suitable for the maximum passage runoff above the 5-year return period. On the B23 sub-basin, the maximum runoff for the return periods of 5,10,25,50 and 100 years is 2.24, 2.98, 4.02, 4.86 and 5.75 cubic meters per second, respectively, in which the culverts diameter, for the maximum passage runoff different return periods, is more than optimal. On the B9 sub-basin, the maximum runoff for the return periods of 5,10,25,50 and 100 years is 2.8, 3.73, 5.02, 6.06 and 7.17 cubic meters per second, respectively, in which the culverts diameter, for the maximum passage runoff different return periods, is optimal.