What can storm-scale models tell us about climate change impacts on extreme rainfall?
Dr Andreas Prein, National Center for Atmospheric Research, USA
Simulating storms that cause extreme rainfall accumulations has been a long-standing challenge in weather and climate modelling. Tremendous improvements have been made over recent decades due to advances in models and computational resources that nowadays allow us to explicitly simulate storm-scale dynamics within models. This results in a step-improvement in simulating extreme rainfall and allows unprecedented insights into climate change impacts on rainfall extremes. This talk will exemplify the added value of simulating extreme rainfall producing storms in storm-scale models compared to coarser-resolution models. It will be shown how the most important storm characteristics that are associated with flooding (eg, rainfall rates, storm movement speed, and storm spatial extent) are simulated in storm-scale models and how these characteristics are projected to change in future climates. Storm-scale model-based changes in future rainfall extremes will be summarized and areas of uncertainty and opportunities for research will be highlighted.
Using a convection permitting model ensemble for projecting future change in precipitation extremes
Dr Elizabeth Kendon, Met Office Hadley Centre, UK
For the first time internationally a model at a resolution on par with operational weather forecast models has been used for national climate scenarios. As part of the UK Climate Projections (UKCP) project, an ensemble of 12 projections at 2.2km resolution have been carried out over the UK. These were launched in September 2019, with the aim of providing an improved simulation of extreme precipitation and also other high-impact events at local scales for the coming decades. At such high (2.2km) resolution, convection can be represented explicitly (‘permitted’) without the need for a parameterisation scheme, leading to a much more realistic representation of hourly precipitation characteristics, including extremes. In this talk initial results from the UKCP local (2.2km) projections, including changes in hourly precipitation extremes, will be presented.
The role of stratification changes for the future European precipitation climate
Professor Christoph Schär, ETH Zurich, Switzerland
There is tremendous interest into future changes of the precipitation climate, as precipitation touches upon a large number of human activities. The scientific argumentation often invokes changes in large-scale circulation and absolute humidity. Here another important aspect is considered, namely the role of stratification (or lapse-rate) changes. These changes are closely linked to climate change, as global warming will imply substantial shifts in the moist-adiabatic lapse rate. Lapse-rate changes have already been identified to instigate important impacts in the tropics, but they are also important for European climate change. Here an overview on lapse-rate changes is provided, together with examples from two recent publications. It is demonstrated that lapse-rate changes are particularly important for the European summer climate and strongly influence the projected drying in the Mediterranean, as well as short-duration precipitation events and the associated Clausius-Clapeyron scaling. It is argued that lapse-rate changes can be considered more reliable than circulation changes, and thus may help adding more confidence to some specific aspects of European climate change projections.
Using high resolution modelling to understand the urban influence
Professor Jason Evans, University of New South Wales, Australia
With the ever growing population living in cities worldwide, it is increasingly important to understand how the expanding cities influence their own climate. The urban environments' effect on temperature, referred to as the urban heat island (UHI), generally means urban environments are several degrees warmer than the surrounding region. While there are many factors that influence the UHI intensity, these are reasonably well understood. The influence of urban environments on precipitation is more complicated and involves the various ways in which the city (including the UHI) can alter the local circulation of the atmosphere. Here Jason Evans discusses several mechanisms to alter the local circulation and impact precipitation over urban areas. He suggests that large cities within the tropics (on coasts) are ideal places to observe these effects and show some results of studies looking at Kuala Lumpur, Malaysia, and Jakarta, Indonesia. In order for climate models to capture the UHI and changes in local circulation, resolutions at the kilometre scale are required.