Richard Allan on the Consequences of Intense Rainfall

Emerging Research Fronts Commentary, December 2011

Richard P. Allan

Article: Atmospheric warming and the amplification of precipitation extreme

Authors: Allan, RP;Soden, BJ
Journal: SCIENCE, 321 (5895): 1481-1484, SEP 12 2008
Addresses: Univ Reading, Environm Syst Sci Ctr, Reading RG6 6AL, Berks, England.
Univ Reading, Environm Syst Sci Ctr, Reading RG6 6AL, Berks, England.
Univ Miami, Rosenstiel Sch Marine & Atmospher Sci, Miami, FL 33149 USA.

Richard P. Allan talks with and answers a few questions about this month's Emerging Research Front paper in the field of Geosciences.

SW: Why do you think your paper is highly cited? Does it describe a new discovery, methodology, or synthesis of knowledge? Would you summarize the significance of your paper in layman's terms?

Intense rainfall and its associated consequences are of great importance across a number of disciplines, including, for example, hydrology, ecology, health, and the insurance industry. Projections of future climate change simulated by complex physical models of the atmosphere, land surface, and ocean have long indicated an increase in rainfall extremes. It is therefore crucial that such expectations are fully backed up by physical understanding and observational confirmation.

Building upon a large volume of research, the work carried out in this paper for the first time combined more than a decade of satellite observations with model simulations or rainfall at the daily time-scale and across the entire tropical oceans. Using the natural fluctuations in ocean temperature and atmospheric moisture content, the frequency of the most intense rainfall was found to vary with atmospheric warming. Both simulations and observations indicated a robust increase in the frequency of the strongest downpours in warmer months, consistent with climate change projections into the future.

Richard P. Allan
Distribution of (a) total atmospheric water vapour (mm) and (b) precipitation rate (mm per hour) over the oceans estimated from the Special Sensor Microwave Imager and Sounder (SSMIS) onboard the NOAA F17 satellite for the local morning passes on the 19th November 2009. The most intense rainfall is associated with tropical convective storms (for example near to Indonesia) but sustained heavy rainfall is also associated with warm, moist flows of air often referred to as moisture conveyor belts or atmospheric rivers in the middle latitudes (for example the tongue of moist air extending up towards Ireland and the UK which resulted in intense rainfall and flooding in Cumbria in the North West of England).

SW: How did you become involved in this research, and how would you describe the particular challenges, setbacks, and successes that you've encountered along the way?

This research was made possible by the award of an Advanced Fellowship from the UK Natural Environment Research Council (NERC) in 2005 which allowed me to tackle the interesting and important question: how will the global water cycle change in a warming climate? The most exciting results were developed following a scientific visit to the University of Miami and the productive collaboration with co-author Brian Soden.

Challenges arose in efficiently sharing data and working to tight deadlines although the analysis was made possible by the availability of satellite data from Remote Sensing Systems and climate model data from the Program for Climate Model Diagnosis and Intercomparison model archive enabled by the World Climate Research Programme support.

SW: Where do you see your research leading in the future? Do you foresee any social or political implications for your research?

Satellite records are beginning to span time periods of relevance to climate change. It will be vital to demonstrate that the fluctuations in the current climate can be directly linked with future anticipated changes as a consequence of increasing heating of the climate through human-induced emissions of greenhouse gases. There are also challenges relating to the reliability of the observations themselves and continued comparisons between climate model simulations and observations are vital in building a consistent physical picture of changes in Earth's environment.

Continued refinement in understanding of the key physical processes through these evaluations are underway (for example the NERC projects, PREPARE, PAGODA, and HYDEF) and results from these and other projects will figure in the next Intergovernmental Panel on Climate Change report due for completion in 2014, which will inform policy, in particular relating to adapting to change and mitigating damage. A great challenge is to provide more accurate regional predictions of how Earth's water cycle will evolve over the coming decades.End

Dr. Richard P. Allan
Department of Meteorology
National Centre for Atmospheric Science
Walker Institute
University of Reading
Reading, UK



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