It has been a summer of unprecedented rainfall throughout the globe, with extreme flooding events spanning from the United States to western Europe to China.
Western Germany and surrounding portions of the Netherlands, Belgium, and Switzerland were ground zero for the latest in a string of flooding disasters, inundated last week with up to two months’ worth of rainfall in under 48 hours, leaving at least 188 people dead and hundreds still missing as of Sunday, July 18. The flood waters left entire villages destroyed with tens of thousands of homes flooded and thousands more without power or running water in what is now regarded as Germany’s worst natural disaster in living memory.
The Northeast and Mid-Atlantic have also experienced frequent flash flooding from difficult to pinpoint thunderstorms. Earlier this month, parts of Pennsylvania and New Jersey saw more than 6 inches of rainfall in just a few hours, prompting water rescues on roadways that quickly became raging rivers. A week before that, New Yorkers watched as subway stations filled up with waist high water from thunderstorms that lasted several hours and dropped more than 5 inches of rain over parts of Manhattan.
Flooded Portion of the Major Deegan Expressway in New York City, July 2021
Source: NY Times
Another slow-moving frontal system delivered rain across the Northeast corridor this past weekend, dropping 2.28” of rain in one day at Newark Liberty International Airport. This drove July accumulation totals to nearly 8”, making this Newark's wettest July on record by over an inch, with two weeks still left on the calendar. Newark's previous record was set recently, in 2020.
Texas, another hotspot for recent flash floods, saw inundating heavy rainfall earlier this month as a stalled area of low pressure delivered rain for several days in the Southeastern part of the state. In less than 72 hours, 11 inches of rain fell at the Rockport Aransas County Airport, with rates exceeding 2 inches per hour. As a result, many streets and neighborhoods were deemed impassable.
Source: National Weather Service, Corpus Christi, TX
This excessive rain event came only a month after torrential rain from a slow-moving disturbance dropped double-digit rainfall in the same region in early June. These downpours fell on already saturated soil, after cities like Victoria, TX experienced the wettest May on record.
The peak of hurricane season is yet to come, and if 2021 is anything like years past –– see catastrophic rainfall and flooding from Hurricane Harvey in 2017 for example –– then Texans might be in for another record-shattering year. In fact, 2021 marks the 4th year in a row that Southeastern Texas has experienced over a foot of flooding.
Hurricane Harvey Rainfall Totals
Source: National Weather Service, Houston/Galveston, TX
This year follows a concerning trend of increased frequency and intensity of flooding. In March 2019, for example, the Mississippi River experienced some of the worst flood conditions on record as a sudden rise in temperatures abruptly melted previously fallen snow. The soil remained too frozen to absorb any of this snowmelt, which overwhelmed surrounding rivers and streams. To make matters worse, some tributaries experienced ice jams which delayed further drainage. Although only a few locations observed record-breaking river levels, the Great Flood of 2019 was historic for how long flood conditions persisted, with some sections above flood stage for a whopping 211 days.
These physical impacts expanded far beyond the streams and tributaries of the Mississippi River. Estimates from the U.S. Department of Agriculture found that the 2019 Midwest flood prevented farmers from planting over $20 million worth of crops, despite a longer growing season due to rising temperatures.
Missouri Neighborhood Inundated by Historic 2019 Flood
Source: The Scientific American
Why Flash-Flooding is Becoming More Frequent
Many climate scientists agree that a strong correlation exists between rising temperatures and severe floods, and climate change is to blame. Ice sheets and glaciers at the poles have been melting as a result of escalating global temperatures, which has left seaside communities much more susceptible to coastal flooding.
Warmer temperatures don’t just melt ice at the poles –– they also fuel stronger, longer-lasting, and more frequent precipitation events, since more latent heat is stored in higher temperatures in the form of water vapor. Since the turn of the 20th century, Earth’s average surface temperature has skyrocketed nearly 2°F, which has in turn left the atmosphere about 7% more saturated. More moisture in the air means more precipitation readily available to fall, amplifying the potential for flooding.
A prime example of this is the uptick in hurricane frequency and intensity within the last several years. The 2021 Atlantic Hurricane Season is off to an active start already with five named storms, following a record-breaking 2020 season that observed the most storms on record. Recent cyclones aren’t only shattering records for frequency –– they’re also dropping much more rain.
Hurricane Harvey delivered nearly 61” of rain to parts of Texas in 2017, ranking as the largest rainmaking hurricane in US History. Less than a year later, Hurricane Florence unleashed 36” of rain in North Carolina, joining Harvey on the top 10 list of wettest hurricanes in the United States. Regardless of whether the rain falls from hurricanes or thunderstorms, there has been an evident increase in heavy precipitation events within the last five decades, and meteorologists believe climate change is the impetus.
With global temperatures expected to escalate, trends suggest that unprecedented flooding may very likely be the new normal. In their third National Climate Assessment, the U.S. Global Change Research Program highlighted that several regions in the United States will experience disastrous flood conditions due to climate change:
“Flooding may intensify in many U.S. regions, even in areas where total precipitation is projected to decline… The risks from future floods are significant, given expanded development in coastal areas and floodplains, unabated urbanization, land-use changes, and human-induced climate change.”
Leveraging Weather Intelligence for Flood Risk
In this new world of extreme weather volatility, advanced knowledge and actionable intelligence is crucial to prevent these events from costing more lives and bringing businesses and supply chains to a halt.
Floods, while typically attributed to the amount of rain that has fallen, are highly dependent on geospatial and non-weather factors. Both the Federal Emergency Management Agency (FEMA) and NOAA have useful tools to determine a location’s flood risk and any necessary next-steps to help better protect properties against flood damage.
For those who need a more direct integration with real-time and predictive flood impacts, the WeatherOptics Flood Index boils risk down to a simple 1-10 scale and offers insights to help both business and people understand the ramifications of a potential flood up to 7 days in advance.
WeatherOptics’ meteorologists and engineers understand that 4 inches of rainfall in Chicago vs. Houston can have entirely different flooding outcomes, and we use ground-truth, geospatial data to better predict the likelihood and severity of flooding down to a 3km level.
During both the recent Texas floods and the flooding in the Northeast, the WeatherOptics Flood Index predicted ratings above 7 (out of 10) and signaled that water rescues and significant damage to infrastructure would occur.
You can learn more about our Flood Index and Impact API here.