© University of Reading 2009 EUMETSAT Monitoring changes in precipitation and radiative energy using satellite data and climate models Richard P. Allan - University of Reading Thanks to Viju John and Brian Soden

© University of Reading 2009 EUMETSAT Increased Precipitation More Intense Rainfall More droughts Wet regions get wetter, dry regions get drier Precipitation Change (%) CLIMATE MODEL PROJECTIONS IPCC WGI Precipitation Intensity Dry Days

© University of Reading 2009 EUMETSAT Low-level water vapour rises with temperature at ~7%/K in models & observations John et al. (2009) GRL models Water Vapour (mm)

© University of Reading 2009 EUMETSAT For a given precipitation event, more moisture would suggest more intense rainfall Can realism of model projections be assessed?

© University of Reading 2009 EUMETSAT Frequency of rainfall intensities vary with SST in models and obs Frequency of intense rainfall increases with warming in models and satellite data Model scaling close to 7%/K expected from Clausius Clapeyron SSM/I satellite data suggest a greater response of intense rainfall to warming dP/dSST=7%/K Allan and Soden (2008) Science

© University of Reading 2009 EUMETSAT Trenberth et al. (2009) BAMS

© University of Reading 2009 EUMETSAT Models simulate robust response of clear-sky radiation to warming (~2-3 Wm -2 K -1 ) and a resulting increase in precipitation to balance (~3 %K -1 ) e.g. Allen and Ingram (2002) Nature, Lambert & Webb (2008) GRL Radiative cooling, clear (Wm -2 K -1 ) Allan (2009) J Clim

© University of Reading 2009 EUMETSAT Contrasting precipitation response expected Precipitation Heavy rain follows moisture (~7%/K) Mean Precipitation linked to radiation balance (~3%/K) Light Precipitation (-?%/K) Temperature e.g.Held & Soden (2006) J. Clim; Trenberth et al. (2003) BAMS; Allen & Ingram (2002) Nature

© University of Reading 2009 EUMETSAT Contrasting precipitation response in ascending and descending portions of the tropical circulation GPCP/NCEPModels ascent descent Allan and Soden (2007) GRL Precipitation change (mm/day) Allan and Soden (2007) GRL; John et al. (2009) GRL

© University of Reading 2009 EUMETSAT Contrasting precipitation response in ascending and descending portions of the tropical circulation GPCP/NCEPModels ascent descent Allan and Soden (2007) GRL Precipitation change (mm/day) Land descent Allan and Soden (2007) GRL; John et al. (2009) GRL Updated analysis

© University of Reading 2009 EUMETSAT Estimated variability in longwave radiative cooling of the atmosphere and precipitation John et al. (2009) GRL

© University of Reading 2009 EUMETSAT Allan et al. (2007) QJRMS 2008 Are the cloud feedback and water/energy cycles issues linked? Combining GERB, CALIPSO and SSM/I

© University of Reading 2009 EUMETSAT Conclusions Low level moisture responses robust –Around 7%/K in models & SSM/I Explains enhanced frequency of intense rainfall with warming in models and obs –Differences between individual models/obs Mean and regional precipitation response: a tug of war –Slow rises in radiative cooling (~2-3 Wm -2 K -1 ): robust in the models but difficult to monitor using satellite data (CERES, GERB, SRB) –Rises in low-level moisture (~7%/K) faster than precipitation (~3%/K) –Reduced frequency? Rich get richer? –Who cares about drought/flooding over the ocean? Precipitation Responses appear larger in observations than models. –Could aerosol be influencing decadal variability in the hydrological cycle? –Are observing systems up to monitoring changes in water/energy cycles? –New NERC project PREPARE with Met Office/ETH Zurich starting soon

© University of Reading 2009 EUMETSAT Daily Satellite Microwave Observations over tropical ocean appear to confirm warmer months are associated with more frequent intense rainfall Allan and Soden (2008) Science More frequentLess frequent