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Process oriented insights from interpretable machine learning - what influences flood generating processes?
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  • Lina Stein,
  • Martyn P. Clark,
  • Wouter Johannes Maria Knoben,
  • Francesca Pianosi,
  • Ross Woods
Lina Stein
University of Bristol

Corresponding Author:lina.stein@bristol.ac.uk

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Martyn P. Clark
University of Saskatchewan at Canmore
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Wouter Johannes Maria Knoben
University of Saskatchewan
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Francesca Pianosi
University of Bristol
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Ross Woods
University of Bristol
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Abstract

Hydroclimatic flood generating processes, such as excess rain, short rain, long rain, snowmelt and rain-on-snow, underpin our understanding of flood behaviour. Knowledge about flood generating processes helps to improve modelling decisions, flood frequency analysis, estimation of climate change impact on floods, etc. Yet, not much is known about how climate and catchment attributes influence the distribution of flood generating processes. With this study we aim to offer a comprehensive and structured approach to close this knowledge gap. We employ a large sample approach (671 catchment in the conterminous United States) and test attribute influence on flood processes with two complementary approaches: firstly, a data-based approach which compares attribute probability distributions of different flood processes, and secondly, a random forest model in combination with an interpretable machine learning approach (accumulated local effects). This machine learning technique is new to hydrology, and it overcomes a significant obstacle in many statistical methods, the confounding effect of correlated catchment attributes. As expected, we find climate attributes (fraction of snow, aridity, precipitation seasonality and mean precipitation) to be most influential on flood process distribution. However, attribute influence varies both with process and climate type. We also find that flood processes can be predicted for ungauged catchments with relatively high accuracy (R2 between 0.45 and 0.9). The implication of these findings is that flood processes should be taken into account for future climate change impact studies, as impact will vary between processes.