There has been a lot of rain in Coastal Georgia and the Lowcountry of South Carolina the last week or so. How unusual is this? Is it climate change? Given the lack of rain and heat last month causing desperation among gardeners, maybe a voodoo ritual gone wrong? Let’s take a closer look …
No doubt that some areas have received a *lot* of rain lately, with roads under water and the streets and sidewalks lined with flooded out (and likely totaled) cars from drivers who didn’t take it seriously. Here at the Enki office in mid town Savannah, our calibrated gauge shows 16.62″ of rain this month, with Saturday the 20th recording a deluge of 6.1″, and two other events over 3″ this week including Friday evening at 3.21″. The Friday storm may have included a tornado, there were warnings based on radar indications, and at least two reports of funnel clouds, one of which was from Hunter Army Airfield looking south.
Convective rain events are an extremely spatially diverse phenomena. That’s a fancy way of saying you can get a lot of rain and right across the street can be dry, as any long time resident of the south can testify. Here is a map of Friday (26 July 2024) night’s rain event:
As noted above, near Daffin Park got 3.21″, and the radar derived rainfall showed over 4″ on the south-side and in to Bryan county (the bright greenish-blue blob south of Savannah). Notice the blank area just to the upper left of the “S” in Savannah? That’s about where the airport is. The official rain total for the day at Savannah International Airport was … nothing:
So this is the first thing to understand about extreme rain events, especially in tropical and subtropical environments where a lot of it is convective: the rain can vary a lot. Another thing to keep in mind as people report rain amounts is that all rain gauges are not made equally. The small garden gauges are often not that accurate in a heavy rain, and even some of the electronic gauges can over or underestimate the rain depending on the design. Placement is of course a big factor as well.
So how unusual is all this? Unfortunately my gauge has not been active long enough to develop a long historical record, when you really need 50 years or so to have a good baseline. The official reading at the airport is somewhat of a problem because it is in a different microclimate than downtown. Long time residents know that the weather is very different as you move from the island to downtown and especially as you approach and cross I-95. Often thunderstorms moving in from the west die out as they approach the coast, and likewise, as seen yesterday, sometimes systems enhanced by the coast don’t reach very far inland. But it’s our longest source of statistics, and while the details will be different the big picture should be ok, so let’s see how it looks.
How unusual is a 6″ rain event? It’s unusual but far from unheard of. Looking at the statistics, it seems to be about a 1 in five year event. The *rate* we had last Saturday (how fast the rain came down) was pretty unusual but again not unheard of – on the order of a 1 in 15 or so event. The other rain totals are far more regular – it’s not unusual at all to get 3″ rain events in Savannah. But getting multiple events in a month starts to add up.
So what about the total for the month? At least here in mid town, it’s getting up there. Depending on how much we get the next couple of days, we’re already in the top five, approaching August 1995’s 16.7″. But we’re a good bit short of 1973’s 20.3 inches (in February) or October 1994 of 21″. That said, the official records are not in any danger. The airport has only recorded 8.42″ of rain this month, which isn’t even in the top 30 (would have to top 10″ to make that cut).
The last question is if are we seeing trends. These days everybody is looking for signs of climate change. In this case, looking at the Savannah rainfall data, there just doesn’t seem to be one. We are seeing more damage from rain, but that’s not climate, but like other trends in increasing weather damage that is due to development, inflation, and poor infrastructure planning. A related factor is technology. Flood a 1970’s car and, with some work, it could likely be repaired. Flood a 2020’s car and it’s a jumbo sized paper weight: all that electronics and sensitive hardware likely means it is a total loss.
That’s not to say we aren’t seeing other indications of a changing climate. Humidity is trending higher, but the clearest trends are in average daily temperatures. While the high’s aren’t obviously higher in Savannah, the night time low temperatures are higher (in other words, it’s not cooling off at night as much as it used to). Here is a plot of of the July daily average temperature by day, with the long term average (blue dots), this year (red dots), and the averages for the 70’s, 80’s, 90’s, and 2000’s noted by other symbols.
Note to avoid the leap year problem, in climatology we typically use day of the year counting from January 1st rather than calendar days, so July is day 183 to day 213.
Twelve of the hottest average days in the last 50 years occurred in the first 20 days of July, before the rains cooled things off. That’s unusual to the point of saying “ok, something’s going on here.” Combined with data from around the world, taking in to account everything we can like urban heat islands, solar activity, natural climate cycles like ENSO, and so forth, it is pretty clear that temperatures are trending higher, and other variables like oceanic heat content, humidity, wind patterns, ocean currents, and so forth are also becoming anomalous.
So what to do about it? I’ve written some other blog posts on this subject such as this one on temperatures, and this on billion dollar disasters. I’m not trying to minimize the climate change debate, but to try to put it in to context that this is complicated, and simplistic, cookie-cutter, solutions driven by unrelated agendas not only won’t work but can actually make things worse. Economics, the environment, and human quality of life are all intimately tied together and all aspects have to be balanced if we are to make any kind of progress in solving our problems. Unfortunately our political system doesn’t seem to be able to do that.
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PS – with respect to voodoo and curses, for the record here is the curse on the city made by Dr. John M. Harney on the 25th of November, 1818 (as reported in the August 16th, 1876 Savannah Morning News).
I leave it to theologians to decide if that has anything to do with the local drainage system.
Excellent.
Thank you for
Thank you for this most informative data and commentary.
I love your explanations and logic. We all say we want the weather man job. They get paid and never right. You’re spot on! Funny and easy to understand. I appreciate your perspective and insight.
Is the Atlanta airport microclimate potentially able to affect rainfall such that the amount of rain there may not be representative of the whole Atlanta area? I’ve always wondered if that’s the best place to be taking the official measurements for Atlanta. Especially for temperature. I would think that the amount of pavement, plus the mixing of the air from the constant air traffic, would affect temperature readings. On the other hand, it’s the best place to collect data for aviation purposes.
That’s a great question, and points to a real problem. Most weather stations are at airports for the obvious reason: they have to have them, and the FAA funds them (and as I pilot I really want weather data at airports!). Likewise, most river flow stations are funded by USGS or state agencies. Yet the weather service depends on all these sensors they don’t control. So often things like weather stations aren’t representative of the conditions most people experience. There are cooperative reporting stations that contribute data, but they generally don’t have long enough or reliable enough histories to do climatology.
On a related note, I’ve also wondered whether the owners of these sensors look for consistently anomalous data that may indicate either a problem with the sensor or a less than ideal location. Specifically, here in the Atlanta area I’ve noticed that Peachtree City often reports temperatures that are significantly different than the surrounding area, especially in the winter. I’m not aware of any topo or hydro features of that area that might explain it. As a software developer (retired), pilot, amateur meteorologist, with a degree in Geography, makes me notice this type of thing and want to know why. Detection of such things might be a use case for AI.
I’ve lived on Goebel near President St. for almost 17 years now. We’ve had pretty bad flooding every so often which is exacerbated by the trench the golf course decided to dig across from my neighbor’s house to drain the water from the course. The water gushes out into the street like river rapids. My husband and I have both lost cars in the past. 3 floods in 6 days is INSANE! The first 2 caught us off guard, but the other day we implemented our little system to keep the waves from people driving through it out of our yard. We staple pond liners to our picket fence and weigh the bottoms down with cinder blocks and weights. It looks tacky but it works! I’ve spent too many years watching my mulch and other landscaping float away down the street. I’m worried about any upcoming hurricanes now more than ever because all the inconsiderate people driving through have washed out a good chunk of the embankment on the golf course side and tree roots are showing. This story is long winded but I had to tell an outsider to get it off my chest because I’m so frustrated and angry!!!
Common story in Savannah – “small” changes in the local hydrology can have outsized impacts downstream, and the City does a terrible job of managing this, not to mention the lack of preventive maintenance on the system. The interplay of engineering, hydrology, development, and budgets is complex but we know how to manage it. Unfortunately the political structures here can’t seem to handle it.
We’re constantly putting in 311 requests to have the drains cleared and the huge drainage ditch near President to be cleared out. Our neighbor has complained to the city and the golf course about their trench, but nothing comes of it. This morning, we were scraping mud from both sides of the street ourselves. It’s maddening!
Before retiring, I worked for the parent company of DTS Weather. One of the most vexing things about trending, they told me, is that the sites of long term monitoring stations are dramatic changes in their surroundings. That aside, there is abundant astrological evidence that suggests the Earth would be warming even if man didn’t exist. Makes me wonder why we aren’t planning more aggressively for the inevitable rather than trying to prevent it.
It seems the only effective change agent is dramatic increases in insurance premiums.
Great job and very exact predictions on our storms
Thank you the updates