Summer Rainfall Forecasting More Accurate with New Model

Meteorologists can now make use of a new statistical framework to make more accurate forecasts of the intensity of summer rainfall.

The framework, developed by two Duke University scientists, is able to compensate for a variety of unknown variables in the summer precipitation forecasting process

"Using our new framework, we found that the characteristics of southeastern U.S. rainfall are influenced by multiple climate factors," said Laifang Li, a PhD student in climatology at Duke's Nicholas School of the Environment. "By identifying which of these climate factors or conditions is occurring, we can make more accurate rainfall intensity forecasts."

Intensity of rainfall depends on a number of factors including the combined effects of La Nina and something known as the tri-pole sea surface temperature anomaly (SSTA) pattern over the North Atlantic.

The model suggests that when the SSTA develops in a horse-shoe-like pattern over the North Atlantic, strong, heavy storms are more likely to occur. In contrast, moderate rainfall is suggested by the model to be caused more by internal dynamics within the atmosphere and less tied to SSTA.

"Traditionally, probability models treat rainfall samples with a single cluster. These models cannot capture the multi-mode feature of summer rainfall and associated factors that influence precipitation over the Southeast. Our new framework, by comparison, is based on a configuration of a three-cluster finite normal mixture model and is realized using Bayesian inference. Each cluster reflects the characteristics of light, moderate or heavy rainfall," Li said in a statement.

Li developed the statistical framework model with her doctoral advisor Wenhong Li, an assistant professor of climatology at Duke.

The new framework allows the researchers to better identify the characteristics of rainfall and its underlying physical processes, which in turn allows them to make more accurate seasonal forecasts.

The current model is only designed to specifically forecast rainfall in the Southeast during the summer, but the researchers say it can be adjusted and extended to other regions and other seasons.

"This could be a very useful tool to help us better understand the response of regional hydrology to climate variability and climate change in similar areas around the world," Wenhong Li said.

The research is published in the journal Environmental Research Letters.