Research Shows Rain is Heaviest When Storms Slow

Dec. 6, 2019
According to UCSB researchers, when hurricanes are downgraded to tropical storms, rainfall is more intense

Flooding is a serious concern when a hurricane is barreling down on a community. The one-two punch of a storm surge and torrents of rain can damage properties and infrastructure or even cause loss of life. Ahead of a storm, communities do their best to anticipate and prepare for the additional water their stormwater infrastructure will need to handle, usually during gale-force winds. Once the winds die down, we can assess the damage and begin repairs...right? 

According to researchers from the University of California, Santa Barbara (UCSB), the highest intensities of rainfall during a severe storm event may actually occur after the hurricane has weakened. The study, "Variations in the Intensity and Spatial Extent of Tropical Cyclone Precipitation," appears in the journal Geophysical Research Letters.

The researches used measurements from weather stations, which have records dating back to 1900, in addition to satellite and radar data to calculate how much land experienced how much rain from a given weather system. The records showed that rainfall tended to be more severe after the wind speeds had slowed and hurricanes had been downgraded to tropical storms. 

Tropical cyclones, a category that includes both tropical storms and hurricanes, slow down once they hit land and spread out, dropping more rain in a single location. The effect is worse the larger the storm, as larger storms have the ability to hold and, consequently, dump more precipitation, causing more damage. 

As global temperatures rise, scientists predict the intensity of tropical cyclones will increase—storms will become faster and rainfall more intense. According to the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory, studies suggest that for a 2-degree Celsius global temperature increase, tropical cyclone windspeed will increase from 1–10% and precipitation rate will increase 10–15%. 

This new research will hopefully help stormwater managers and others responsible for preparing communities for heavy rainfall and flooding ahead of hurricanes better understand what to expect ahead of tropical cyclones and other severe weather events. 

For more information on this research, visit the UCSB website

Related

Photo 59441063 © Rawpixelimages | Dreamstime.com
Photo 91848825 © Leowolfert | Dreamstime.com
Photo 102975436 © Photovs | Dreamstime.com