The uneven nature of daily precipitation and its change (Invited)

Thursday, December 14, 2017 - 08:00
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Our daily experience tells us that a few days with heavy rain (or snow) contribute disproportionately to the annual precipitation, while many days with light drizzle don’t add much. What is not generally appreciated is just how asymmetric this distribution is and the even more asymmetric nature of anthropogenic trends. I will present an analysis diagnosing the asymmetry of precipitation observed at stations in the GHCN-Daily network and changes in precipitation from CMIP5 simulations. On average, a quarter of the anthropogenic excess rain falls in the wettest 2 days, and half in the wettest 2 weeks. In contrast to temperature where climate change can be thought of as a simply shift of the daily temperature distribution, the distribution of precipitation shifts and its shape also changes so that the heaviest events make up a larger fraction of total precipitation. Rather than assuming more rain in general, society needs to take measures to deal with a handful of events with much more rain, and little change in between.

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