Energy-balance modeling of heterogeneous glacio-hydrological regimes at upper Indus

Study region: The Upper Indus River Basin (UIB). Study focus: The UIB has experienced marked runoff change due to the accelerated glacier melting under climate warming. Nonetheless, the glacio-hydrological regime in the UIB remains unclear due to considerable uncertainties in precipitation data and glacio-hydrology modeling. Here, we used a state-of-the-art water and energy budget-based distributed glacio-hydrology model (WEB-DHM-S) that employed an energy-balance glacier module for both clean and debris-covered glaciers to analyze the hydrological regimes within the UIB during 2001–2020, particularly the spatial heterogeneity among the Himalaya-Karakoram-Hindu-Kush mountains. New hydrological insights for the region: Results indicated that the high-resolution ERA5-Land precipitation data showed the most reliable estimate (∼750 mm/yr) among available products, which was the model’s forcing data. Our results showed that the mean contributions of snow, glaciers, rainfall, and baseflow to total runoff in the UIB were 41.5%, 23.3%, 34.7%, and 0.5%, respectively. Glacial melting made the largest contribution to total runoff in the Karakoram (35.3%), while the smallest contribution was made in the Hindu Kush (15.9%). Further, we showed that glacial melting was highly sensitive to changes in air temperature and solar radiation inputs. In particular, fluctuating solar radiation could change the magnitude and timing of annual flood peaks in ice melting, which emphasized the crucial role of energy-related forcing data (besides the traditional precipitation and air temperature inputs) in glacio-hydrology modeling

A Model-Based Flood Hazard Mapping on the Southern Slope of Himalaya

Originating from the southern slope of Himalaya, the Karnali River poses a high flood risk at downstream regions during the monsoon season (June to September). This paper presents comprehensive hazard mapping and risk assessments in the downstream region of the Karnali River basin for different return-period floods, with the aid of the HEC-RAS (Hydrologic Engineering Center’s River Analysis System). The assessment was conducted on a ~38 km segment of the Karnali River from Chisapani to the Nepal–India border. To perform hydrodynamic simulations, a long-term time series of instantaneous peak discharge records from the Chisapani gauging station was collected. Flooding conditions representing 2-, 5-, 10-, 50-, 100-, 200-, and 1000-year return periods (YRPs) were determined using Gumbel’s distribution. With an estimated peak discharge of up to 29,910 m3/s and the flood depths up to 23 m in the 1000-YRP, the area vulnerable to flooding in the study domain extends into regions on both the east and west banks of the Karnali River. Such flooding in agricultural land poses a high risk to food security, which directly impacts on residents’ livelihoods. Furthermore, the simulated flood in 2014 (equivalent to a 100-YRP) showed a high level of impact on physical infrastructure, affecting 51 schools, 14 health facilities, 2 bus-stops, and an airport. A total of 132 km of rural–urban roads and 22 km of highways were inundated during the flood. In summary, this study can support in future planning and decision-making for improved water resources management and development of flood control plans on the southern slope of Himalaya

Planning in democratizing river basins:The case for a co-productive model of decision making

We reflect on methodologies to support integrated river basin planning for the Ayeyarwady Basin in Myanmar, and the Kamala Basin in Nepal, to which we contributed from 2017 to 2019. The principles of Integrated Water Resources Management have been promoted across states and regions with markedly different biophysical and political economic conditions. IWRM-based river basin planning is complex, resource intensive, and aspirational. It deserves scrutiny to improve process and outcome legitimacy. We focus on the value of co-production and deliberation in IWRM. Among our findings: (i) multi-stakeholder participation can be complicated by competition between actors for resources and legitimacy; (ii) despite such challenges, multi-stakeholder deliberative approaches can empower actors and can be an effective means for co-producing knowledge; (iii) tensions between (rational choice and co-productive) models of decision complicate participatory deliberative planning. Our experience suggests that a commitment to co-productive decision-making fosters socially legitimate IWRM outcomes

Development of a land surface model with coupled snow and frozen soil physics

Snow and frozen soil are important factors that influence terrestrial water and energy balances through snowpack accumulation and melt and soil freeze-thaw. In this study, a new land surface model (LSM) with coupled snow and frozen soil physics was developed based on a hydrologically improved LSM (HydroSiB2). First, an energy-balance-based three-layer snow model was incorporated into HydroSiB2 (hereafter HydroSiB2-S) to provide an improved description of the internal processes of the snow pack. Second, a universal and simplified soil model was coupled with HydroSiB2-S to depict soil water freezing and thawing (hereafter HydroSiB2-SF). In order to avoid the instability caused by the uncertainty in estimating water phase changes, enthalpy was adopted as a prognostic variable instead of snow/soil temperature in the energy balance equation of the snow/frozen soil module. The newly developed models were then carefully evaluated at two typical sites of the Tibetan Plateau (TP) (one snow covered and the other snow free, both with underlying frozen soil). At the snow-covered site in northeastern TP (DY), HydroSiB2-SF demonstrated significant improvements over HydroSiB2-F (same as HydroSiB2-SF but using the original single-layer snow module of HydroSiB2), showing the importance of snow internal processes in three-layer snow parameterization. At the snow-free site in southwestern TP (Ngari), HydroSiB2-SF reasonably simulated soil water phase changes while HydroSiB2-S did not, indicating the crucial role of frozen soil parameterization in depicting the soil thermal and water dynamics. Finally, HydroSiB2-SF proved to be capable of simulating upward moisture fluxes toward the freezing front from the underlying soil layers in winter.National Key Basic Research Program of China [2013CBA01805]; Chinese Academy of Sciences [XDB03030302, 131C11KYSB20160061]; National Natural Science Foundation of China [41322001, 41401080, 41571033]; Key Technologies R&D Program of China [2013BAB05B03]; Top-Notch Young Talents Program of ChinaSCI(E)ARTICLE65085-51035