Spatially Distributed Hydrological Modeling considering Land-use changes using Remote sensing and GIS
Distributed hydrological modeling considering spatial variability using remote sensing, and GIS is developed to assess the changes in runoff value due to land use change in a hydrological basin. Kathmandu Valley basin, Nepal, is chosen as a basin of case study. In this paper, a spatially distributed model with SCS curve number is developed to assess the runoff changes due to land-use changes. It is found that the average daily monsoon flow is increased by 12% for 9% deforestation and 17% urbanization. Peak flow value in the basin during monsoon season is found increased by 14%. It is found that the percentage change in runoff due to land use change is almost constant for different land use irrespective of the rainfall pattern and time of occurrence. The percentage changes in peak runoff during particular season due to land-use change for the given time interval are found equal regardless of storm events. The relationship developed for the changes in runoff values with respect to change in curve numbers are useful in quantifying the effects due to land-use change. The sensitivity analysis showed that the runoff calculation with distributed is very close to that of approach on estimation of initial abstraction ratio could be taken as 0.25 for observed values. It is found that average value of forestland, 0.2 for agricultural land, 0.22 for urban and 0.12 for pastureland. In the study area, the peak runoff is found to be increased by 14 % during monsoon season due to deforestation and urbanization. Considering the subbasins, the runoff is found to be increased by 19 % for 13 % increase in curve number. The study clearly demonstrated that the integration of spatial data and application of a distributed model in GIS and Remote-sensing environment provide a powerful tool for assessment of effects due to land-use change.