Non‐stationarity and flooding
Dr Gabriele Villarini, University of Iowa, USA
Flooding is one of the costliest natural hazards and it is often associated with a high toll in terms of fatalities. Over the past several decades, the frequency and magnitude of these events have been changing, complicating the capability to prepare to and respond against this hazard. Most of the literature has focused on the detection of changes in flooding, with much less emphasis on their attribution. Improving our understanding of the physical drivers that are responsible for the observed changes in this natural hazard can enhance our capability of predicting and projecting these changes, with large implications for water resources management and the design of hydraulic structures. This presentation will discuss some of the issues associated with the nonstationarity in the flood records, and provide an overview of some of the methodologies to deal with these changes.
A synthesis of hourly and daily precipitation extremes in different climatic regions
Dr Renaud Barbero, National Research Institute of Science and Technology for Environment and Agriculture, France
Climatological features of observed annual maximum hourly precipitation have not been documented systematically compared to those on daily timescales due to observational limitations. Drawing from a quality-controlled database of hourly records sampling different climatic regions including the United States, Australia, the British Isles, Japan, India and peninsular Malaysia available over multiple decades, we examined climatological features of annual maximum precipitation (AMP) across timescales ranging from 1-hr to 24-hr. Climatological features include seasonal and diurnal distribution of AMP, the storm duration triggering AMP, as well as the relation with the convective available potential energy. This study provides insights on climatological features of hourly precipitation extremes and how they contrast with the daily extremes examined in most studies.
The role of short-duration high-intensity precipitation in geohazards and information needs in a changing climate
Dr Nina S Oakley, Western Regional Climate Center, Desert Research Institute, USA
There is a well-established connection between short-duration, high-intensity rainfall and geohazards such as shallow landslides and post-wildfire debris flows. The applied meteorology and geomorphology research communities in the western United States are currently working together to improve early warning and forecasting of potential impacts of these geohazards. One of the questions these scientists often hear from floodplain managers and community planners is, “How will the frequency and impacts of geohazards change in a warming climate?” To address this question, sub-daily precipitation projections at spatial scales relevant to the geohazards in question are necessary. For application in the far western United States, there must be consideration of short-duration precipitation changes within cool season mid-latitude cyclones, as they produce the highest precipitation intensities in these regions. This poster demonstrates the common meteorological drivers of short-duration, high-intensity precipitation producing cool-season shallow landslides and post-wildfire debris flow events in the western United States. Additionally, it describes the temporal and spatial resolutions needed in precipitation projections such that they can be applied to these geohazards. Current research goals on climate change, precipitation intensification, and geohazards are also discussed to stimulate a conversation about data needs from the applied research communities to promote collaboration and progress.
What can the UK rain gauge network tell us about changes to intense rainfall?
Dr Stephen Blenkinsop, Newcastle University, UK
It is widely expected that anthropogenic warming will lead to an increase in the intensity of extreme rainfall. The Clausius-Clapeyron (CC) relationship indicates an increase of ~7% per degree of warming, but in some regions the scaling rate for hourly extremes has been observed to be higher, leading to concerns over increased risk of flash flooding in the future. The group has collected and quality-controlled data from ~2000 rain gauges across the UK, providing high resolution rainfall data to assess the climatology of extremes at timescales from 5 minutes through to 5 days, leading to improved understanding of when and where intense rainfall is more likely. They have also quantified changes in hourly extremes and find evidence of recent intensification in summer. However, although intense UK summer rainfall was found to scale in accordance with the CC relationship suggesting a possible thermodynamic cause, the group cannot rule out the influence of large-scale modes of variability as potential mechanisms, especially as they note the dependence of intense rainfall on weather patterns. These results highlight the difficulties of both quantifying, and understanding the processes behind, observed changes in intense rainfall, and confirm the need to combine knowledge derived from observational and modelling studies.