Atmospheric rivers are only going to get BIGGER: New study
Tuesday, June 5, 2018, 11:23 - Atmospheric Rivers (ARs) or 'Rivers in the Sky' as some call them, have become more popular around the world since the turn of the century. These prominent, intermittent circulation features account for over 90% of the poleward water vapor transport across middle latitudes, where they can cause heavy and prolonged downpours, especially when they traverse mountain ranges capable of enhancing their effects.
Atmospheric Rivers are responsible for some of the most extreme precipitation events, and while they can contribute with beneficial rain and snow, which can mitigate droughts, they also cause major flooding and hurricane force winds.
Now, a recently published study in Geophysical Research Letters shows that climate change is expected to intensify ARs across many areas of the earth by the end of the century, although the number of events could be slightly reduced. Computer model simulations indicate that under a scenario with current greenhouse gas increase rates, there will be a 10% reduction in the number of ARs by 2100. However, these systems will be on average 25% wider and longer, and heavy rain and wind conditions related to them around the globe will increase about 50%.
2017 WAS AN UNPRECEDENTED YEAR FOR U.S. ATMOSPHERIC RIVERS
On average, Atmospheric Rivers bring anywhere from 30 to 50% of U.S. West Coast precipitation, and in 2017, we saw one of the best examples of how much they can contribute to the precipitation season. A total of 45 Atmospheric Rivers made landfall somewhere along the U.S. West Coast between October 1st and March 31st 2017, making the overall season one of the most plentiful of this century. In 2018, the numbers have been far from those of 2017 and below what they should be on an average season.
WATCH BELOW: Satellite Animation of an Atmospheric River in 2017
HOW MODEL PREDICTIONS ARE USED TO UNDERSTAND THE FUTURE OF ATMOSPHERIC RIVERS
Most climate change modeling studies related to ARs have been conducted for two specific regions of the earth: Europe and the western United States. They have typically used different methodologies for identifying atmospheric rivers and different climate projection models, meaning results from one are not quantitatively comparable to another.
In this study, however, they used a set of common global climate model projections for the 21st century based on the Intergovernmental Panel on Climate Change latest assessment report. A global Atmospheric River detection algorithm, developed by the research team, was then applied to the climate model output. The algorithm identifies AR events from the model data, quantifying how much water vapor they transport as well as their length and width.
The main purpose of the study has been to better understand how ARs may behave in the future as global climate is reshaped. This should help meteorologists, hydrologists, water managers, stakeholders and citizens living in ARs affected regions like western America, South Africa, New Zealand or western Europe, to better plan when extreme precipitation events are forecast.
But despite the fact that all models appear to be consistent showing stronger ARs in a warmer world, co-author Dr. Marty Ralph of UC San Diego – Scripps, points out that there is still work to be done. In order to understand the details of why the model representations of ARs vary with different climate projections research must go on.