It is widely known that rain falls unevenly in time, which can lead to floods and droughts. A new study, published in the journal Geophysical Research Letters, has not only quantified the unevenness but also made projections for the rest of the century, taking into account climate change models.
The key finding is that half the world’s precipitation takes place in just 12 days each year, calculated from the combined rain observed by gauges around the world. In the climate model simulations, the change in future rainfall is even more uneven than rainfall today.
In a scenario with high greenhouse gas concentrations — called Representative Concentration Pathway 8.5 (RCP8.5) — 20% of the change occurs on the wettest 2 days each year, half on the wettest 8.6 days, and 70% in the wettest 2 weeks. Adjusting the modelled unevenness to match present-day unevenness at stations, half of the precipitation increase occurs in the wettest 6 days each year, the researchers found.
For station observations, the study used data from the Global Historical Climatology Network Daily (GHCN-D), a global database.
In the climate simulations that factored in RCP8.5, they estimated precipitation up to 2100.
The two study authors, from the National Center for Atmospheric Research (Colorado) and the Institute for Atmospheric and Climate Science (Zurich), suggest that rather than assuming more rain in general, society needs to take measures to deal with a handful of events with much more rain.