Flood Seasonality Over the Third Pole Region Modulated by Upper Level Moisture Transport. Issue 9 (15th September 2022)

• Record Type: Journal Article
• Authors: Yang, Long; Li, Kunbiao; Shen, Ye; Tian, Fuqiang
• Is Part Of: Earth's future. Volume 10:Issue 9(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-15
• Subjects: flood -- hydrology -- Tibetan Plateau -- hydrometeorology; Environmental sciences -- Periodicals; Environmental sciences; Periodicals; 550
• DOI: 10.1029/2022EF002828
• Languages: English
• ISSNs: 2328-4277

Abstract

Abstract: The nexus between atmospheric moisture transport and basin‐scale flood response is still lacking over the Third Pole (TP) region, despite projected increases in extreme rainfall under a changing climate. Based on long‐term daily streamflow observations, we show that peaks‐over‐threshold floods over the Yarlung Zangbo River (YZR) basin show two temporal clusters, that is, July and late August, with the flood magnitudes of the second cluster larger than the first by 20%. These floods are resultant from a mixture of flood‐producing storms with contrasting storm motion and moisture transport pathways. A suite of coupled atmospheric‐hydrological modeling experiments further quantify the impacts of different moisture transport pathways on the space‐time rainfall structure and flood response. A 50% reduction of upper level moisture transport (i.e., through the upslope of the Himalayas) leads to decreased flood peak magnitudes by 30% at the basin outlet for the August 1998 floods over the YZR basin. Upper‐level moisture transport is associated with the notable low pressure over the central‐east India and westward extension of West Pacific Subtropical High that enhances convergence of water vapor fluxes from Bay of Bengal toward TP. The magnitude of impact can potentially alter the seasonal clustering of high‐flow events over TP. Our analyses contribute to improved characterization of flood risk over TP, and advances in flood frequency hydrology. Plain Language Summary: Floods over the Third Pole (TP) region, mainly include the Tibetan Plateau and its adjacent mountain ranges, threatens sustainable socioeconomic development for the countries that inhabitate 1.4 billion population. Despite projected increases in extreme rainfall and thus flooding, there are limited understandings on the link between moisture transport and basin‐scale flood response in this region. Based on long‐term daily streamflow observations, we show floods over the Yarlung Zangbo River basin tend to cluster in July and late August, with the magnitudes of flood peak in late August larger than the July peak by 20%. These floods are produced by storms with contrasting storm motion and moisture transport pathways. We carry out atmospheric and hydrological modeling simulations to quantify the impacts of different moisture transport pathways on space‐time rainfall structure and flood response. We show a 50% reduction of moisture transport through the upslope of the Himalayas leads to decreased flood peak magnitudes by 30% at the basin outlet for the August 1998 floods. The upper level moisture transport plays an important role in the seasonal clustering of floods over Yarlung Zangbo, although it is not as efficient or frequent as the moisture transport pathways along the Yarlung Zangbo Grand Canyon. Key Points: Peaks‐over‐threshold floods over the Yarlung Zangbo River (YZR) basin are related to storms with contrasting storm motion and moisture transport pathways A 50% reduction of moisture transport through the upslope flow of the Himalayas leads to a 30% decrease in flood magnitudes at the outlet Upper level moisture transport (i.e., above 2, 500 m) plays an important role in characterizing the flood seasonality over the YZR basin