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- Title
Streamflow Composition and Water "Imbalance" in the Northern Himalayas.
- Authors
Fan, Linfeng; Kuang, Xingxing; Or, Dani; Zheng, Chunmiao
- Abstract
The Yarlung Zangbo River (YZR) is the largest river in the northern Himalayas, providing crucial water resources for downstream. A full understanding of the streamflow dynamics and regional water budget is critical to secure water security of the Himalayan water tower. Here we establish a comprehensive hydrological model to simulate the precipitation‐runoff‐evapotranspiration‐groundwater‐streamflow complex in the YZR basin. We decipher contributions of different water sources (e.g., precipitation, meltwater, groundwater) to YZR's streamflow and estimate that groundwater sustains ∼36% of annual streamflow in the YZR, while precipitation and melt surface runoff contribute 40% and 24%, respectively. Combining modeling, observation and reanalysis data, our results reveal a water "imbalance" that ∼31% of annual precipitation and meltwater (∼333 mm yr−1 or ∼85 km3 yr−1) is unaccounted for in the YZR basin. We propose that the "excess water" discharges to deep fractured bedrock aquifers, which is promoted by widespread permeable active structures (e.g., faults, fractures). This hypothesis is supported by groundwater storage (GWS) estimates where inclusion of the deep groundwater bridges the discrepancy between baseflow‐derived (shallow) GWS and those derived from the Gravity Recovery and Climate Experiment satellite data. The deep groundwater most likely flows across basins, bypasses streams, and finally discharges to downstream aquifers in the Indo‐Gangetic Plain as mountain block recharge. This study not only provides a comprehensive analysis of the streamflow composition in the YZR, but also contributes to shaping a more complete picture of the functionality of the Himalayan water tower, highlighting the importance of groundwater in regional water transfers. Plain Language Summary: Understanding the streamflow dynamics and components feeding the Yarlung Zangbo River (YZR), the largest river in the northern Himalayas, is critical for quantifying regional water resources. Here we show that shallow groundwater sustains ∼36% of the annual streamflow in the YZR, while the contribution of precipitation and melt surface runoff is 40% and 24%, respectively. Regional water balance indicates that ∼31% of precipitation and meltwater, corresponding to ∼333 mm yr−1 and ∼85 km3 yr−1, is unaccounted for in the YZR basin. This component of water "imbalance" is hypothesized to recharge deep fractured bedrock aquifers (promoted by widespread faults and fractures) and flow out of the basin bypassing surface streams. This hypothesis is supported by satellite‐based groundwater estimates. The study yields new insights into streamflow components of the YZR and highlights the significant role of deep groundwater in the water budget of the Himalayan water tower. Key Points: Groundwater, precipitation and snow/glacier melt runoff contribute 36%, 40%, and 24% to annual streamflow in the Yarlung Zangbo River (YZR)∼31% annual meteoric water (∼333 mm yr−1) in YZR basin discharges to deep fractured bedrock and forms inter basin flow that bypasses streamsGRACE‐derived groundwater storage observations support the hypothesis of inter basin deep groundwater pathways
- Subjects
HIMALAYA Mountains; MELTWATER; STREAMFLOW; RUNOFF; WATER security; WATER transfer; WATERSHEDS; WATER supply; HYDROGEOLOGY
- Publication
Water Resources Research, 2023, Vol 59, Issue 10, p1
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2022WR034243