Spatial Distribution of Rainfall in Indian Himalayas – A Case Study of Uttarakhand Region

Continuous rainfall data in grid format are required to run models for hydrological and agricultural research as well as water resources planning and management. The present work attempts to prepare a normal annual rainfall map in Himalayan region of India lying in Uttarakhand state at 1 km spatial resolution which currently is not available. In the region, India Meteorological Department maintains observatories/raingauge stations and data from 44 stations were used in this study. A comparative analysis of interpolation techniques like Inverse Distance Weighted, Polynomial, Splines, Ordinary Kriging and Universal Kriging shows that Universal Kriging with hole-effect model and natural logarithmic transformation with constant trend having Root Mean Square Error (RMSE) of 328.7 is the best choice. This is followed by Ordinary Kriging (RMSE 329.1), Splines (RMSE 392.4), Inverse Distance Weighted (RMSE 409.8) and Polynomial Interpolation (RMSE 418.5). Cross validation of the results shows the largest over prediction at Tehri rainfall station (62.5%) and largest under prediction at Nainital station (−36.5%). Physiographic zone wise, the least errors occur in the plains and the largest in the Great Himalayas. The spatial average rainfalls are 1,472 mm for Terai/Bhabar, 1,782 mm for the Shivalik ranges, 1,591 mm for the Lesser Himalayas and 1,635 mm for the Great Himalayan region. The mean areal rainfall in the region is 1,608 mm.