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• SWAT hydrological model has high potential in the assessment of watershed changes. • Land use changes caused by forest fires affect hydrological response of watershed. • Significant increase in surface runoff and sediment load in the post-fire scenario. • Sediment yield increased by 6.5 times with the highest fire spatial distribution. • Forest fire scenarios help to limit hydrological impacts of fire on sediment load. Forest fires profoundly affect the nature of watershed responses to precipitation, increases in runoff rate and volume, and post-fire sediment discharge. A post-fire watershed assessment to identify potential trouble spots for soil erosion and flooding can help land managers for decision-making on deploy mitigation, remediation measures, and restoration action plans. Predicting the potential impact of fires on runoff and soil erosion requires distributed hydrological modeling methods. This study used the Soil and Water Assessment Tool (SWAT), a rainfall-runoff model, to investigate the hydrological consequences of forest fires and their impact on sediment load under different burnt scenarios. For the pre-fire (baseline) scenario, the watershed is calibrated by using the measured discharge and suspended sediment concentration data from the weather station during the time step to estimate post-fire changes at the sub-catchment scale. The total water and sediment yield for the selected sub-catchment in the post-fire scenario with the highest spatial distribution of forest fire, due to the excessive surface runoff (an increase of 14.5%) increased significantly, resulted in 6.5 times increase in sediment yield. The results obtained from the study indicate a significant increase in sediment transport into the stream in the post-fire scenario. A large volume of soil losses occurred during the time step. In contrast, due to removing trees and vegetation from the ground, less evapotranspiration and infiltration occurred in selected sub-catchment areas after forest fires. In terms of watershed management, understanding the consequences of forest fires on hydrological services will be an effective method for sediment budget control. Therefore, applying the rainfall-runoff and erosion models for the watershed with developing plausible forest fire scenarios can be a productive method to deal with the threats and hydrological risks such as soil erosion and sediment transfer to the downstream environment. [ABSTRACT FROM AUTHOR]

Abstract: A new grid-based model of nutrient dynamics and transport process has been developed within a distributed hydrological modelling framework and integrated with river network module. The key aspect of this development is a process based description of nutrient generation process on the land surface and its related nutrient release with hydrologic runoff and soil erosion. Whereas the conventional modelling uses the event mean concentration method for nutrient dynamics modelling and estimates nutrient loads from catchments to the rivers this study has introduced an export function based release related with flow capacity. The river module solves the dynamic equation for transport and chemical reaction. The model output is available in high spatial and temporal resolution, which was tested and verified applying in two catchment areas from different hydro-climatic backgrounds. The model was able to simulate short term high intensity flood events as well as long term seasonal patterns. The simulated results for most of the nutrient parameters are within acceptable range as reflected by measures of statistical indices and visual interpretation. For example, the R 2 values for different nutrient levels in the Saru River, Japan are within the range of 0.83–0.99 and 0.66–0.87 for calibration and validation, respectively. Similarly, the relative root mean square error (RRMSE) values for different nutrient levels in the Saru River range between 0.06–0.22 and 0.06–0.26 for calibration and validations, respectively. The maximum load of nutrients in each grid was extracted from time series output, analyzed further and presented in two dimensional maps, which showcase the usefulness of the model in decision making process for management of land and maintenance of the in-stream water quality. [Copyright &y& Elsevier]