Sahar Daraei; Abdolreza Bahremand; Hamid Karimi
Abstract
The land use changes cause changes in components of the hydrological cycle and increase or reduce the amount of runoff. Subsurface runoff is one of the most important parts of the runoff in wet areas, especially in steepy lands with higher vegetation. Given the advantages and capabilities of distributed ...
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The land use changes cause changes in components of the hydrological cycle and increase or reduce the amount of runoff. Subsurface runoff is one of the most important parts of the runoff in wet areas, especially in steepy lands with higher vegetation. Given the advantages and capabilities of distributed hydrological models, these models are appropriate to assess changes in land use and quantitative estimates of changes. In this study, evaluation of the effects of land use change scenarios on the subsurface flow rate was investigated using WetSpa model on daily basis in Horo-Dehno Watershed with an area of 263.43 Km2. Daily hydro-meteorology data including evapotranspiration, precipitation and temperature from 2006 to 2010 were used to run the model, . The model input maps included DEM, land use and soil texture maps. According to the watershed potentials, four scenarios of land use change were planned in ArcGIS and entered in the calibrated model for simulation. In order to use model to simulate the effects of land use change scenarios, sensitivity and uncertainty analysis and calibration were performed manually and afterwards with the PEST optimization program. In addition, to compare the output hydrograph of subsurface flow in current situation of four scenarios with simulated results, changes in hydrological processes and parameters were evaluated. This analysis showed that improving land use is the reason of increasing of subsurface flow, increasing of deep infiltration, reducing of surface runoff and increasing of watershed time of concentration . Whereas, land degradation reduces the amounts of subsurface flow, permeability to deep and surface aquifers and increases runoff volume. Therefore, maintaining and improving current land uses are one of the major alternatives for watershed surface runoff management.
Narges Ghasemiamin; Nasim Arman; Hossein Zeinivand
Abstract
Land use and its fluctuations is one of the most important factors that affects on the natural cycle in the ecosystem. Land use changes cause change in watershed hydrological cycles, water balance between precipitation, evaporation, infiltration and runoff response. Understanding the relationship between ...
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Land use and its fluctuations is one of the most important factors that affects on the natural cycle in the ecosystem. Land use changes cause change in watershed hydrological cycles, water balance between precipitation, evaporation, infiltration and runoff response. Understanding the relationship between land use changes and its factors and secondary effects on the hydrological regime provides the necessary information for planning of land use and sustainable management of natural resources. At first, land use maps related to years of 2000 and 2014 were prepared, then CLUE-s model was applied to simulate land use map of 2025. For simulating runoff, WetSpa model was employed to simulate daily runoff with land use maps related to years of 2000, 2014 and 2025. According to the results, the Nash-Sutcliffe evaluation criterion was calculated 68.26 % and 66.75 % for the calibration and validation periods, respectively. In addition, model Aggregate Measure (AM) was calculated 64 % and 54.15 % for the calibration and validation periods, respectively. Land use maps comparison showed, the main land use changes in Nojian Watershed was the conversion of forest and rangeland areas to agricultural lands .As a result of these changes the annual runoff volume, peak discharge, mean daily discharge increased to 16.20, 11.35 and 9.15 percent, respectively. Results of statistical analysis using paired t-test showed that land use change has effect on discharges in the study area at the level of 1%.