Climate-related hazards with potential high impacts on human and/or natural systems include extremes such as storms, storm surges, hail, heavy rains and drought. Such events are often of low probability and subsequently existing knowledge drawn from past instances of similar extremes may be scarce or lacking. Therefore, a better understanding of many of the fundamental processes driving the occurrence of high impact events (including the dynamic links with human activities) is critically needed. Only an improved understanding of fundamental processes (including better models) will allow more reliable predictions and projections.
Research tasks include:
Better estimates of historical occurrence frequencies. Two time horizons can be considered here: (i) The near past that is described by observations and reanalysis data (state analysis of the atmosphere and ocean) for the last 50 to 100 years allowing in-depth assessments of selected events (e.g. strong storms), and (ii) The faraway past that is described by carefully collected proxy data which in certain areas can provide a very long record of a particular high impact event (e.g. lake overturning).
Studying mechanisms: (i) Scale interactions in the atmosphere including dynamics/energetics and composition, for example in the context of mid-latitude blockings or tropical cyclones; (ii) Critical processes involved in high impact events, for example the factors that govern the structure and characteristics of extratropical and tropical cyclones, and how these factors are influenced by greenhouse gas and other climate forcings, including stratospheric composition.
How do the statistics of severe weather affect composition and vice versa? Heat waves and future air quality, severe (tropical) storms/convective events (tropical UT/LS composition) and the feedback of changing composition on climate.
