How Important Is Meltwater to the Chamkhar Chhu Headwaters of the Brahmaputra River?

Abstract

As our global climate warms, people, and economies utilizing water resources sourced by snow and ice melt in mountain areas are disproportionately affected relative to locations that rely on rainfall. Worldwide, the vast majority of those impacted by snowfall changing to rainfall and earlier melt from a warming climate live in Asia. The Brahmaputra River originates in the declining glaciers and snowfields of the Chinese and Bhutanese Himalaya before flowing to the mega population centers of the Bangladesh delta. Bhutan's economy relies on water resource-dependent hydropower and agriculture imposing important questions about the impact of climate change on the long-term viability of water supplies in these important economic sectors. To clarify potential effects on water supplies in a warming world, and specifically to quantify the role of meltwater to river discharge in the headwaters of the Brahmaputra basin, we utilize a combined field observation-remote sensing approach to quantify river discharge source waters in a representative headwater basin, the Chamkhar Chhu. Using 4 years of water isotope and chemistry data together with a Bayesian Monte Carlo mixing model run seasonally in 2016, we find that the Chamkhar Chhu is mostly a rain-dominated basin at the lower elevation of our study domain (2591 m a.s.l.), with peak contributions from snowmelt in the early-monsoon and ice melt in the post-monsoon seasons. The radioactive tritium isotope shows glacier ice at the terminus was formed before the 1960s bomb spike while groundwater and river water samples taken in August (late monsoon) are sourced from mostly newer water inputs that show little tritium. The influence of the highly reacted Tsampa tributary, sourced by a debris covered glacier, and additional groundwater inputs generally increase major ion concentrations with distance from the glacier snout. An overall decreasing trend in the minimum snow and ice cover extent maps produced using MODIS Terra data from 2000 to 2017

Surface Water Isoscape Modeling in the Himalayan Region: An Alternative for Moisture Source Investigation, Hydrograph Separation, and Paleolatitude Estimation

“…The LMWL shows a substantial difference in slopes and intercepts (Figure 3a). However, their slopes and intercepts are close to the GMWL and LMWLs previously reported in the Himalayan region (Ali et al., 2020; Dar, Rai, & Kumar, 2022; Hill et al., 2020; Jeelani & Deshpande, 2017; Kumar et al., 2010, 2020; Pant et al., 2021), and the Tibetan Plateau (Tian et al., 2001). Based on the predicted GWRM isoscapes, we determined new basin‐wide meteoric water lines using least‐squares regression.…”

“…A portable hand‐held, multi‐parameter kit (HANA USA) that was calibrated before field sampling was used to measure the temperature, pH, EC, TDS, and ORP of the samples. In addition, we compiled a comprehensive δ 18 O, δ 2 H and d‐excess data set across the three HRB published in articles and/or online data repositories (Table S1 in Supporting Information ) during past decades (Ali et al., 2020; Bhat et al., 2022; Bhattacharya et al., 1985; Bershaw et al., 2012; Boral et al., 2019; Dar, Rai, & Kumar, 2022; Gajurel et al., 2006; Garzione et al., 2000; Hill et al., 2020; Hren et al., 2009; Karim & Veizer, 2002; B. Kumar et al., 2010; A. Kumar et al., 2018, 2019; N. Kumar et al., 2020; Lambs 2000; Lambs et al., 2005; Majumder et al., 2013; Maurya et al., 2011; Navada & Rao 1991; V. N. Nijampurkar & Rao 1992; V. Nijampurkar et al., 2002; Pande et al., 2000; Pant et al., 2021; Quade et al., 2011; Racoviteanu et al., 2013; Rai et al., 2009, 2016; Ramesh & Sarin 1992; Ren et al., 2016; Sharma et al., 2017; Yoshimura et al., 2021) to attain the best practicable regional broad spatial resolution that could be interpolated and modeled with reliability.…”

“…The river network is derived from the DEM. Dar, Rai, & Kumar, 2022;Gajurel et al, 2006;Garzione et al, 2000;Hill et al, 2020;Hren et al, 2009;Karim & Veizer, 2002;B. Kumar et al, 2010;A.…”

A data‐oriented strategy to support water resource managers and researchers

“…NASA, through its Water Applications program, supported three GEOGloWS projects that have developed tools to improve decision‐making for water resources in South Asia. One study explored the use of Earth observations to improve the management of irrigation water reservoirs in the upper Indus River Basin using methods reported in Hill et al (2020), while a second study used improved snowmelt estimates to provide more accurate predictions of flows into irrigation water reservoirs. In the Lower Mekong River Basin, a system for monitoring surface water storage using integrated multi‐satellite products is providing new tools for water management agencies in Viet Nam and Cambodia (Kim et al, 2019).…”

Contrasting changes of snow cover between different regions of the Tibetan Plateau during the latest 21 years

“…With an average altitude over 4,000 m, the Tibetan Plateau is the highest plateau in the world, which is covered by a large amount of seasonal and perennial snow. Rivers originating from the plateau provide domestic and production water for dozens of neighboring countries and regions, and snowmelt water is one of the important supplies for these rivers (Immerzeel et al, 2009;Smith et al, 2017;Hill et al, 2020). Climate warming causes rapid changes in snow cover on the Tibetan Plateau, which affects the annual distribution of runoff, local ecosystem, and disaster prevention.…”