This book determines the trend and variability of a time series data, focused on traditional time series models forecast analysis and their volatility and also focuses on a comparative study of different existing individual and combination forecasts with a proposed Hybrid Stochastic Model (HSM) forecast procedure. For this considered a hydrological time series data of the Indian subcontinent to test the proposed forecast model, and also examined the model's dimension reduction approach to choose an optimum number of forecast techniques to be included in the model to yield the best forecasts.