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Emergence of Heavy Tails in Streamflow Distributions: the Role of Spatial Rainfall Variability
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  • Hsing-Jui Wang,
  • Ralf Merz,
  • Soohyun Yang,
  • Larisa Tarasova,
  • Stefano Basso
Hsing-Jui Wang
Helmholtz-Centre for Environmental Research UFZ

Corresponding Author:hsing-jui.wang@ufz.de

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Ralf Merz
Helmholtz Centre for Environmental Research (UFZ)
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Soohyun Yang
Helmholtz Centre for Environmental Research-UFZ
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Larisa Tarasova
Helmholtz Centre for Environmental Research - UFZ
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Stefano Basso
Helmholtz Centre for Environmental Research
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Flow events with low frequency often cause severe damages, especially if their magnitudes are higher than suggested by historical observations. Heavier right tail of streamflow distribution indicates the increasing probability of high flows. In this paper, we investigate the role played by spatially variable rainfall for enhancing the tail heaviness of streamflow distributions. We synthetically generated a wide range of spatially variable rainfall inputs and fed them to a continuous probabilistic model of the catchment water transport to simulate streamflow in five catchments with distinct areas and geomorphological properties. Meanwhile, we used a comparable approach to analyze rainfall and runoff records from 175 German catchments. We identified the effects of spatially variable rainfall on tails of streamflow distributions from both simulation scenarios and data analyses. Our results show that the tail of streamflow distribution becomes heavier with increasing spatial rainfall variability only beyond a certain threshold. This finding indicates a capability of catchments to buffer growing heterogeneities of rainfall, which we term catchment resilience to increasing spatial rainfall variability. The analyses suggest that the runoff routing process controls this property. In fact, both small and elongated catchments are less resilient to increasing spatial rainfall variability due to their intrinsic runoff routing characteristics. We show the links between spatial rainfall characteristics and catchment geometry and the possible occurrence of high flows. The data analyses we performed on a large set of case studies confirm the simulation results and provide confidence for the transferability of these findings.