Evolution and future prospects of hydropower sector in Nepal: A review.

Nepal is one of the pioneers of hydropower development among Asian countries. The plethora of fast-flowing rivers provides immense potential for hydropower generation. However, Nepal still lacks a clear blueprint for the overall development and management of this sector. This paper aims to review the evolution of hydropower development, future prospects and roadblocks to hydropower development. With the growing energy demands projected to reach as high as 41,264.82 Gigawatt hours (GWh) in 2030 and 115,294.4 GWh in 2040 under different scenarios, this paper highlights the huge prospects the sector holds. It also proposes a focus on storage-type hydropower plants and concepts of energy banking to address the incipient condition of seasonal energy mismatch in the country, which has developed a condition of energy shortage during the winter and energy surplus during the monsoon. Moreover, projected changes in hydro-climatic extremes under the climate change scenarios is likely to affect water availability and subsequently the energy production in the majority of hydropower projects. Thus, this review can serve as a guideline to help understand the current scenario and make rational decisions and policies for the future management of the hydropower sector of the country.

Implementing conjunctive management of water resources for irrigation development: A framework applied to the Southern Plain of Western Nepal.

Climate variability and insufficient irrigation are primary constraints to stable and higher agricultural productivity and food security in Nepal. Agriculture is the largest global freshwater user, and integration of surface- and ground-water use is frequently presented as an strategy for increasing efficiency as well as climate change adaptation. However, conjunctive management (CM) planning often ignores demand-side requirements and a broader set of sustainable development considerations, including ecosystem health and economics of different development strategies. While there is generic understanding of conjunctive use, detailed technical knowhow to realize the CM is lacking in Nepal. This article presents a holistic framework through literature reviews, stakeholders consultations and expert interviews for assessing CM and implementation prospects from a systems-level perspective. We demonstrate the framework through a case study in Western Nepal, where climatic variability and a lack of irrigation are key impediments to increased agricultural productivity and sustainable development. Results show that knowledge of water resources availability is good and that of water demand low in the Western Terai. Additional and coordinated investments are required to improve knowledge gaps as well as access to irrigation. There is therefore a need to assess water resources availability, water access, use and productivity, to fill the knowledge gaps in order to pave pathways for CM. This paper also discusses some strategies to translate prospects of conjunctive management into implementation.

Climate change and river health of the Marshyangdi Watershed, Nepal: An assessment using integrated approach.

Climate change alters the river flow regimes causing significant changes in the structure and function of an aquatic ecosystem, ultimately affecting river health. This study applied a customized framework consisting of 1-index, 4-components, 6-indicators, and 43-metrics, to assess river health for two seasons and future periods, in the Marshyangdi Watershed, Nepal. Hydrological, water quality, biological and physical conditions were assessed using simulated results from a hydrological model, physiochemical analysis of water samples, macroinvertebrates assemblages analysis, and physical habitat condition assessment, respectively. Climate change impact on river health was assessed based on projected climate (precipitation and temperature) based on regional climate models under representative concentration pathways (RCP) 4.5 and 8.5 scenarios until the mid-century. Results showed moderate river health condition in both the seasons and it's deterioration for future scenarios and periods. It reveals the need to formulate appropriate measures for the conservation of the river health.

An assessment of climate change impacts on water sufficiency: The case of Extended East Rapti watershed, Nepal.

An understanding of water sufficiency provides a basis for informed-planning, development and management of water resources. This study assessed spatio-temporal distribution in water sufficiency in the Extended East Rapti watershed in Nepal. The "Palika" (local government unit) is considered as a spatial-scale and seasons and future periods as temporal-scale. The water sufficiency was evaluated based on water sufficiency ratio (WSR) and water stress index (WSI). A hydrological model was developed to simulate water availability. An ensemble of multiple Regional Climate Models was used for assessing climate change impacts. Results showed water sufficiency by mid-century is projected to decrease; WSR by 40% and WSI by 61%. Despite projected decrease in water sufficiency, annually available water resources are projected as sufficient for the demands until the mid-century, however, seasonal variability and scarcity in future is projected in most Palikas. Such results are useful for water security planning in the Palikas.

Hydrological response of Chamelia watershed in Mahakali Basin to climate change.

Chamelia (catchment area = 1603 km2), a tributary of Mahakali, is a snow-fed watershed in Western Nepal. The watershed has 14 hydropower projects at various stages of development. This study simulated the current and future hydrological system of Chamelia using the Soil and Water Assessment Tool (SWAT). The model was calibrated for 2001-2007; validated for 2008-2013; and then applied to assess streamflow response to projected future climate scenarios. Multi-site calibration ensures that the model is capable of reproducing hydrological heterogeneity within the watershed. Current water balance above the Q120 hydrological station in the forms of precipitation, actual evapotranspiration (AET), and net water yield are 2469 mm, 381 mm and 1946 mm, respectively. Outputs of five Regional Climate Models (RCMs) under two representative concentration pathways (RCPs) for three future periods were considered for assessing climate change impacts. An ensemble of bias-corrected RCM projections showed that maximum temperature under RCP4.5 (RCP8.5) scenario for near-, mid-, and far-futures is projected to increase from the baseline by 0.9 °C (1.1 °C), 1.4 °C (2.1 °C), and 1.6 °C (3.4 °C), respectively. Minimum temperature for the same scenarios and future periods are projected to increase by 0.9 °C (1.2 °C), 1.6 °C (2.5 °C), and 2.0 °C (3.9 °C), respectively. Average annual precipitation under RCP4.5 (RCP8.5) scenario for near-, mid-, and far-futures are projected to increase by 10% (11%), 10% (15%), and 13% (15%), respectively. Based on the five RCMs considered, there is a high consensus for increase in temperature but higher uncertainty with respect to precipitations. Under these projected changes, average annual streamflow was simulated to increase gradually from the near to far future under both RCPs; for instance, by 8.2% in near-, 12.2% in mid-, and 15.0% in far-future under RCP4.5 scenarios. The results are useful for planning water infrastructure projects, in Chamelia and throughout the Mahakali basin, to ensure long-term sustainability under climate change.

Groundwater vulnerability to climate change: A review of the assessment methodology.

Impacts of climate change on water resources, especially groundwater, can no longer be hidden. These impacts are further exacerbated under the integrated influence of climate variability, climate change and anthropogenic activities. The degree of impact varies according to geographical location and other factors leading systems and regions towards different levels of vulnerability. In the recent past, several attempts have been made in various regions across the globe to quantify the impacts and consequences of climate and non-climate factors in terms of vulnerability to groundwater resources. Firstly, this paper provides a structured review of the available literature, aiming to critically analyse and highlight the limitations and knowledge gaps involved in vulnerability (of groundwater to climate change) assessment methodologies. The effects of indicator choice and the importance of including composite indicators are then emphasised. A new integrated approach for the assessment of groundwater vulnerability to climate change is proposed to successfully address those limitations. This review concludes that the choice of indicator has a significant role in defining the reliability of computed results. The effect of an individual indicator is also apparent but the consideration of a combination (variety) of indicators may give more realistic results. Therefore, in future, depending upon the local conditions and scale of the study, indicators from various groups should be chosen. Furthermore, there are various assumptions involved in previous methodologies, which limit their scope by introducing uncertainty in the calculated results. These limitations can be overcome by implementing the proposed approach.

Evaluation of index-overlay methods for groundwater vulnerability and risk assessment in Kathmandu Valley, Nepal.

This study aimed at evaluating three index-overlay methods of vulnerability assessment (i.e., DRASTIC, GOD, and SI) for estimating risk to pollution of shallow groundwater aquifer in the Kathmandu Valley, Nepal. The Groundwater Risk Assessment Model (GRAM) model was used to compute the risk to groundwater pollution. Results showed that DRASTIC and SI methods are comparable for vulnerability assessment as both methods delineate around 80% of the groundwater basin area under high vulnerable zone. From the perspective of risk to pollution results, DRASTIC and GOD methods are comparable. Nevertheless, all the three methods estimate that at least 60% of the groundwater basin is under moderate risk to NO3-N pollution, which goes up to 75% if DRASTIC or GOD-based vulnerabilities are considered as exposure pathways. Finally, based on strength and significance of correlation between the estimated risk and observed NO3-N concentrations, it was found that SI method is a better-suited one to assess the vulnerability and risk to groundwater pollution in the study area. Findings from this study are useful to design strategies and actions aimed to prevent nitrate pollution in groundwater of Kathmandu Valley in Nepal.