The Nepalese theoretical hydropower potential in a changing climate

Abstract

With steep elevation gradients and an abundance of water, Nepal is one of the leading countries in hydropower capacity. This potential is largely unutilised; representing a significant untapped renewable energy resource that could help Nepal achieve its emissions target and improve its energy security. However, future climate projections suggest changes in discharge seasonality, which will impact the hydropower potential. Hence, we provide an estimate of current and future theoretical hydropower potential in the four large basins in Nepal, namely Mahakali, Karnali, Gandaki, and Koshi. We use current and future discharge simulated in the Spatial Processes in Hydrology (SPHY) model from a previous study to force the theoretical potential module in the Hydropower Potential Exploration (HyPE) model. The HyPE model set up for Nepal is run for 48 combinations of future climate scenarios, combining temperature change in the range of 3°C to 8°C and precipitation change in the range of -30% to 40%. Average monthly discharge components (baseflow, rainfall runoff, snowmelt, and glacier melt) are analysed separately for the reference period (1979-2018), mid-century (2036-2065), and end of century (2071-2100). For each time horizon, we evaluate the relative contribution of the discharge components to the theoretical hydropower potential and quantify the impact of future changes in discharge seasonality.   The Indian summer monsoon dominates the discharge patterns in Nepal. The historical water balance shows an overlap in the peak contributions from rainfall and glacier melt to discharge with both occurring in July and August. A shift in the peaks from these components is not apparent for the climate scenarios considered. However, the peak from snow melt contribution shifts one to two months earlier for most climate scenarios in all basins. Such shift in the seasonal discharge composition could prove promising for stabilizing year-round hydropower generation. At 5 km resolution, we estimate the total theoretical hydropower potential for the four Nepalese basins to be 1170 TWh/yr during the reference period. While challenges remain in accurately simulating discharge in mountainous and data-scarce basins in Nepal contexts using SPHY, the majority of the projections suggest a promising increase in the monthly average discharge and the subsequent monthly theoretical hydropower potential. We observe an increase in total Nepalese hydropower potential up to 22% for the mid-century and 36% by the end of the century. Variations across the basins occur and a decrease in hydropower potential is also observed for the dry future climate scenarios. However, it is important to note that theoretical potential may not be a realistic indicator for hydropower development. Only a small part of the theoretical potential may be technically and financially feasible and an even smaller part may be sustainable. Nonetheless, our research provides a first step to the identification of hydropower project sites considered within the context of a changing climate.