Florida Tech’s Pallav Ray Seeks to Improve Accuracy of Rainfall Predictions During Monsoon Season

Growing up in Kolkata, India, Pallav Ray recalls hot spring days leading up to summer’s monsoon season. Temperatures sat above 35 degrees Celsius (95 degrees Fahrenheit), rarely falling below that. When it rained, however, that’s when he could find relief – often by walking barefoot on the cool ground.

Now an associate professor of ocean engineering and marine sciences at Florida Tech, Ray studies tropical climate dynamics and their variability using observations, models and theory. His paper, “Rain‐Induced Surface Sensible Heat Flux Reduces Monsoonal Rainfall Over India,” was published in Geophysical Research Letters and highlights research he said was inspired by his childhood in India’s hot climate.

His research, funded by the National Oceanic and Atmospheric Administration (NOAA), found that including a variable that is often neglected by climate models could improve the accuracy of rainfall predictions. In turn, that could help agriculture industries better prepare for regional irrigation and flooding during monsoon season. Ray’s climate modeling research spans across the globe, from India, to Chicago, Ill., and most recently the Indo-Pacific Maritime Continent archipelago, which includes countries such as Indonesia and New Guinea.

The variable, notated as “Qp,” represents precipitation-induced sensible heat flux, which is a component of surface energy that influences precipitation. It essentially accounts for how precipitation cools land surface temperatures. Qp is calculated using a formula accounting for the specific heat of rainwater, density of rainwater, the rate of rain, surface temperature and the temperature of raindrops when they hit the surface.

This variable is important, Ray explained, because the temperature of raindrops is typically cooler than the temperature of the surface, so when it rains, the surface cools down.

During monsoon season, land is warm and the ocean is cooler, which pushes moist air from the ocean to the land. The higher the temperature difference between the land and the ocean, the stronger the monsoon because it brings more moisture, Ray explained.

In testing Qp, Ray and his team of researchers ran simulations investigating the variable’s role on precipitation. They found that when incorporating it, not only is anticipated precipitation reduced by up to 5% – which he says is a significant reduction – but the models also reflect changes in the spatial distribution of precipitation.

“The moment we include that term, it cools down the surface, land surface. The temperature difference is smaller between the land and the ocean,” Ray said. “That reduces the overall precipitation overland because now less moisture is coming from the ocean.”

In India, Ray explained, most models, overestimate precipitation. His results generated predictions that were much closer to observed rainfall.

He says that inclusion of this variable in common climate models could influence India’s regional agriculture and irrigation strategies. According to Ray, rainfall is closely tied to the India’s industries, especially agriculture.

He said the variable may have the greatest impact on seasonal rainfall predictions, which happen months in advance and determine how the country approaches its agricultural practices. Policymakers rely on seasonal rainfall predictions to anticipate and plan for summer monsoons, and the money allocated to deal with excess rainfall is “tremendous,” he said.

“If you can do a seasonal prediction a few months in advance and your precipitation actually changed by 5%, it’ll change whether you’ll have an excess year versus you’ll have a deficit year,” Ray said. “I think that’s where the main, major impact is.”

In his future research, Ray would like to explore how Qp would impact climate models over urban areas here in Florida.

If you're interested in learning more about predicting monsoons and the other fascinating research  Pallav Ray is doing at Florida Tech   - simply contact  Adam Lowenstein, Director of Media Communications at Florida Institute of Technology at adam@fit.edu to arrange an interview today.