Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling
27 March 2019

The Uneven Nature of Daily Precipitation and Its Change






Rain falls unevenly in time, which can lead to floods and droughts. It is widely known that precipitation is uneven, but it is difficult to quantify. Here we develop a measure for the unevenness of precipitation: the number of the wettest days each year in which half of the annual rain falls. We apply this to rain observed by gauges around the world. At all gauges combined, it takes only 12 days each year for half of the rain to fall. We also apply the measure to climate model simulations, with projections for the rest of the century. In the climate model simulations, the change in future rainfall is even more uneven than rainfall today: in a scenario with high greenhouse-gas emissions, half of the increase in rainfall happens in the wettest 6 days each year. Rather than assuming more rain in general, society needs to take measures to deal with little change most of the time, and a handful of events with much more rain. 

Angeline Pendergrass
National Center for Atmospheric Research (NCAR)
Pendergrass, A, and R Knutti.  2018.  "The Uneven Nature of Daily Precipitation and Its Change."  Geophysical Research Letters 45(21): 11980-11988.