Impact of climatic parameters on watershed management practices using gis techniques

Abstract

Water is one of the most important natural resources supporting all forms of life on earth and the sustainable use and conservation of this resource has to be planned on watershed basis. Watershed is a land area which drains water received through precipitation to a common outlet, usually a small drainage channel to a river. Changes in weather parameters will lead to cascading effects on watershed hydrology, biomass production and many other natural processes. The changes in precipitation pattern with changes in intensity and frequency will give rise to corresponding changes in the surface runoff, lateral flow, base flow, evapotranspiration and soil erosion. Quantifying these hydrological processes are very important from the point of view of sustainable use of land and water and their conservation planning and implementation. Since the various watershed processes are interdependent, highly variable with respect to time and space, measurement of these natural processes at different spatial location is not an easy task. Watershed models are a solution to meet the challenge of estimating watershed processes to reasonable level of accuracy. Among the watershed models, physically based watershed models will be yielding better results as they are designed to simulate the physical processes more close to reality by considering maximum number of parameters governing those processes. In the present study, Kurumali sub basin of Karuvannur river in Thrissur district, Kerala was selected for the estimation of surface runoff using the widely used SWAT model. The study envisaged to determine the impact of climate changes on various watershed processes using SWAT model. Secondary data on climate, river flow, DEM, soil map have been used and landuse map has been prepared from satellite imagery procured from NRSA. The river flow prediction efficiency of the calibrated watershed model has been tested by Nash Sutcliff efficiency (NSE) and Coefficient of Determination (COD). A very high Nash Sutcliffe Efficiency (NSE) of 0.88 and Coefficient of Determination (COD) 0.96 have been obtained for the calibration period. Corresponding NSE and COD of 138 the model simulation for the validation period were 0.90 and 0.99. The very high NSE and COD for both calibration and validations periods are the clear indication of the good model prediction of the river flow. The study revealed that average annual rainfall of the area was 2829 mm with a standard deviation of 748. For the existing climatic scenario (year 1993 to 2012), water balance components including the surface runoff, lateral flow, base flow and evapotranspiration of the basin were 306 mm, 339 mm, 1649 mm and 337 mm respectively. The predicted mean annual rainfall for the basin for the years 2021 to 2030 was 3655 mm and the water balance components including the surface runoff, lateral flow, base flow and evapotranspiration of the basin were 756.92 mm, 407.56 mm, 1802.78 mm and 456.02 mm respectively. Future rainfall was 29 percent greater than the existing rainfall and the river flow predicted for the basin for the changed climate was 46 per cent higher than the existing one. Similarly, surface runoff, lateral flow and base flow also showed considerable increase in the changed climatic scenario. Study highlights that soil and water conservation measures, presently being practiced in the area, will have to be modified and augmented as rainfall and surface runoff showed remarkable increase for the future time period.