Deriving dynamic reservoir operating policy under the changing precipitation and inflow patterns in snow-dominated Himalayan regions

The impacts of climate change and complex local weather in the Himalayan region tend to change the characteristics of the precipitation, leading to a high non-stationarity. While studies have been performed to analyse the change in the rainfall pattern due to climate change, no attempts were made for the quantifiable impacts linking with reservoir operating policy. The assumption of stationary while deriving the operating policy of reservoirs is prevalent due to less computational effort. Reservoirs built for hydropower generation is expected to meet the energy demands that largely varies. Thus, adopting the conventional stationary operating policy derived based on the historical data might lead to create a havoc leading to underutilized when the reservoir operation is mainly meant for hydropower generation. In this study, the influence of alterations in the meteorological and inflow pattern on the dynamics of operation policy is explored for the reservoirs located in the snow dominated Himalayan region (Tehri reservoir). To demonstrate the proposed simulation optimization framework, the daily gridded rainfall data (0.25^o x 0.25^o) for the period 1901 - 2021 collected from Indian Meteorological Department and monthly inflow of tehri reservoir for the period 1965 - 2021 was used.  Several statistical methods were employed to quantify the alterations in the precipitation data and inflow to the reservoirs. A stochastic optimization algorithm was applied to derive the dynamic reservoir rule curves for maximizing the hydropower generation including the weighted over-shifting and seasonality. The statistical analysis of both precipitation and inflow shows negative trend during the drawdown periods (January, March, October, and December) with a mean release of 170 MCM. Further, the alteration in precipitation and inflow is dynamically accounted in operating policy under two release scenarios (i.e. scenario 1 by increasing reservoir release (10%, 20%, 30%) in the negative trend period and decreasing release in the positive trend period and scenario 2 by only increasing release during negative trend period). It is found that the scenario 2 (only increase in release) have resulted in higher hydropower generation. In addition, the changing pattern of the precipitation and inflow is performed by superimposing principle the assessed similar performance in hydropower generation. The outcome of the study indicates the adaptivity of developed framework and applied in other reservoirs under changing environment.

Keywords: Reservoir Operation, Rule curve, Pumped storage, Hydropower.