NGDIR News Section-- A new study shows that the most extreme rain events in most regions of the world will increase in intensity by 3 to 15 percent, depending on region, for every degree Celsius that the planet warms.
If global average temperatures rise by 4 degrees Celsius over the next hundred years, as many climate models predict given relatively high CO2 emissions, much of North America and Europe would experience increases in the intensity of extreme rainfall of roughly 25 percent. Some places such as parts of the Asian monsoon region would experience greater increases, while there will be smaller increases in the Mediterranean, South Africa and Australia.
There are a few regions that are projected to experience a decrease in extreme rainfall as the world warms, mostly located over subtropical oceans that lie just outside the tropical, equatorial belt.
As a region warms due to human-induced emissions of carbon dioxide, winds loft that warm, moisture-laden air up through the atmosphere, where it condenses and rains back down to the surface. But changes in strength of the local winds also influence the intensity of a region's most extreme rainstorms.
A global grid view
Since the 1990s, scientists have predicted based on climate models that the intensity of extreme rain events around the world should increase with rising global temperatures. Current observations have so far verified this trend on a broad, global scale. But knowing how extreme storms will change on a more specific, regional scale has been a trickier picture to resolve, as climate data is not equally available in all countries, or even continents, and the signal of climate change is masked by weather noise to a greater extent on the regional scale.
O'Gorman and his colleagues began their study by taking a global perspective. They first looked through a massive archive of global simulation runs, known as the Coupled Model Intercomparison Project Phase 5, which aggregates outputs, or predictions, made by different climate models, for everything from local air pressure to the thickness of sea ice in response to changing climate.
For this study, the researchers culled the CMIP5 archive for specific outputs, including daily accumulated surface precipitation and temperature, vertical wind velocity and pressure, and daily atmospheric humidity. These outputs were simulated by 22 climate models, for the years 1950 to 2100, under a scenario in which there are relatively high emissions of CO2.
The team looked at each of the 22 models' outputs on a regional, grid-by-grid basis. Each model simulates climate conditions by dividing the globe up into a grid, with each grid cell's side measuring 100 to 200 kilometers. For each cell in each model, the researchers identified the maximum daily rainfall per year and compared this to the average global temperature for that year.
All 22 models predicted that the highest increases in extreme rainfall will occur over parts of the Asian monsoon region such as India and over parts of the equatorial Pacific, with more moderate increases in North America, Central America, the Mediterranean, and Australia.
By MIT News