TREND ANALYSIS OF CLIMATIC VARIABLES AND THEIR IMPACT ON STREAM FLOW USING NAM MODEL

Significant changes observed in the behaviour of climatic variables over a period of time, has triggered unexpected variations in the stream flow pattern in many catchments across the globe. In present study, 30 years (1975-2004) rainfall, potential evapotranspiration (PET), temperature and stream flow data are analyzed for Gopalkheda sub-catchment in upper Tapi basin, India. The sub-catchment spreads over an area of 7225 km(2), and incorporates nine raingauge stations, two weather stations and one stream gauging site. The change in the climatic variables of aforesaid sub-catchment is examined using non-parametric Mann-Kendall (MK) and Sen's slope estimator test. The available data were checked for effect of serial correlation and normality using Chi-square and Kolmogorov-Smirnov tests before applying MK test. The percentange increase in annual average PET and temperature have been found to be 32% and 1.11% respectively in the study period. On other hand, the rainfall and stream discharge patterns have shown a decreasing trend with magnitude 23% and 31% respectively over the period. Further, a lumped conceptual hydrological model, NAM (MIKE11), calibrated from 27 years data (1978-2004) is used for assessing the hydrologic processes in the sub-catchment. The calibrated model has been able to simulate the peak events satisfactorily. The NAM model parameters are also estimated for the three splitted time periods (1978-1986, 1987-1995, 1996-2004) vis-a-vis total period (1978-2004) to ascertain the possible changes in the parameters due to changes in the climate variables and land use/land cover in the study area.