Putting Harvey's rain into perspective

With Hurricane Harvey causing catastrophic flooding in parts of Houston and southeast Texas, it is a little hard to get a full grasp on how much water really fell.

Ryan Maue with WeatherBell Analytics calculated that around 20 trillion (20,000,000,000,000) gallons of water fell across east Texas during Harvey. To compare, around 6.5 trillion gallons fell during Hurricane Katrina in 2005.

Rain totals at the time of Maue's tweet was calculated around 15 trillion. That translates into filling every NFL and Division I football stadium more than 100 times.

Stadiums are different sizes, so the amount each can hold will vary. Let's try to make the conversions a little simpler.

Let’s start with Lake Travis. The LCRA states the lake has a volume of 1,134,956 acre-feet when full. An acre-foot is defined by Merriam-Webster as “the volume (as of irrigation water) that would cover one acre to a depth of one foot,” which is 325,851 gallons. Running the conversion calculation, Lake Travis holds 369,826,547,556 gallons when full.

20 trillion/Lake Travis' volume = 54.08, meaning the amount of rain that fell during Harvey could fill Lake Travis to capacity a little over 54 times!

While that is an incredible amount of water, let’s go for the Texas-sized comparison. If the rain from Harvey was spread out evenly across the entire state of Texas, how deep would the water be?

Admittedly, I solved this equation at one point while working on this article during the day and promptly forgot it while working on other stories. I then spent the next two hours trying to replicate the answer through a myriad of methods that included calculating the size of Texas in square inches (1.08 x 10^15). Here’s the method I used after an embarrassingly long amount of time:

First, convert the amount of rain to liters (1 gallon = 3.78541 L).

Second, multiply the amount of liters to cubic meters (1 L = 0.001 m3)

Then divide the number of cubic meters by the area of Texas (695.622 billion m2)

If you did everything right, the number will be represented in meters and should be smaller than one. Convert it into inches (1 meter = 39.3 inches) and you should get 4.28 inches.

This formula checks out with a Forbes article that estimated the state would be under roughly 5.4 inches of water, assuming 25 trillion gallons of water fell from Harvey.

To compare this further, during a very wet May 2015, the National Weather Service Office in Fort Worth calculated that more than 37 trillion gallons fell over the state during that month. 

Just remember that was from May 2015, a month with 31 days. Harvey dumped more than half of that on the Houston area in less than one week.

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