Picturing how many Great Salt Lakes Harvey dropped onto Texas | Science News for Students

Picturing how many Great Salt Lakes Harvey dropped onto Texas

Here are some ways to visualize Tropical Storm Harvey’s mega deluge
Sep 7, 2017 — 6:50 am EST
flood boating

Some people needed boats to deal with catastrophic flooding, seen here, due to Tropical Storm Harvey’s astounding downpours in Texas last week. Such mega-storms could become more common, scientists worry.

Karl Spencer/iStockPhoto

Hurricane Harvey will always be known as the deadly storm that dumped a dramatic amount of water across Texas in 2017. Rain totals varied greatly from one area to the next. But an average of 76 centimeters (30 inches) fell across a region home to some six million people, the National Weather Service reported.

At least one Houston neighborhood recorded 131.78 centimeters (51.88 inches) between Friday, August 24, and Tuesday, August 29. That toppled the previous rainfall record for the continental United States.

And that, of course, wasn’t the end of it. After stalling over Texas for days, the storm went back out to sea only to make landfall again. It now could dump even more water on Texas and Louisiana. The storm then weakened into a tropical depression over the Tennessee Valley. There, it sparked more urban flooding, and unleashed a barrage of tornadoes over Alabama and Mississippi.

But the Texas downpours were what proved truly astounding. Even more mindboggling is the total quantity of water that rained down — in liters or gallons — across the Southeast Gulf Coast of Texas and Louisiana over six long days. Picturing that total is challenging, but we’ve taken a stab at crunching the numbers.

Great Salt Lake
Utah’s Great Salt Lake, roughly 113 kilometers (70 miles) long and up to 47 kilometers wide, holds a bit more than one-third as much water as was dumped by Harvey’s rains on Texas and Louisiana, late last month.
USGS

To do so, we utilized the National Weather Service’s final rainfall map. Then, by contouring different amounts of rainfall, we took the area enclosed and tallied how many liters (which we also converted to gallons) would be needed to drop that many inches of rain.

By our calculations, that cumulative rainfall would fill 13.5 trillion 4-liter buckets (or 14.3 trillion gallon buckets)! Maybe you want to think in terms of bathtubs. Harvey’s downpours would fill 178 billion bathtubs. That’s enough to give every person in the world two dozen baths — and still have leftovers.

Pooled in one place, Harvey’s rains would be enough water to occupy the entire volume of Utah’s Great Salt Lake — 2.85 times. If the mouth of the Mississippi River were draining into Texas (although it doesn’t), it would take more than two weeks of its total flow to deliver all of Harvey’s water.

The Great Pyramid of Giza is huge. But Harvey’s downpours would fill this structure roughly 21,000 times. Or imagine this precipitation measured in giant “blocks” of water a kilometer (or mile) on each side. Harvey’s Gulf Coast downpour would equal 54 cubic kilometers (or 13 cubic miles). Now pour the water out of these blocks onto the streets of New York City and it would flood the city to a height of 68 meters (224 feet). That’s as high as a 20-floor high-rise office building, yet averaged across the entire length and breadth of the city.

Tipping the scales

How much does all of this water weigh? Plenty. Try an estimated 53.8 trillion kilograms (118.6 trillion pounds). That’s 184 times the weight of all of the food that is purchased in the United States each year. It’s also 8.1 million times the weight of the Eiffel Tower.

flood wading
Texas National Guard soldiers aided families in areas of Houston, Texas, that were heavily flooded by Hurricane Harvey.
Lt. Zachary West/Texas Military Dept./Flickr (CC BY-ND 2.0)

The average African elephant tips the scales at roughly 5,900 kilograms (13,000 pounds). So put Harvey’s rains on one side of a scale and you’d need more than 9.1 million elephants to sit on the other side to balance out the weight of this massive storm’s rainfall.

Even by hurricane standards, this was no average storm. Indeed, a storm that can drop this much rain is approaching a “once-in-a-million-year event.” That assessment comes from a 1978 report by the U.S. Army and the National Oceanic and Atmospheric Administration (NOAA).

Meteorologists and climatologists alike note that it’s impossible to say any one storm is caused by climate change. However, they have already been suggesting that Harvey shows the “fingerprint” of climate change. By that they mean that it is likely that Harvey was made worse due to environmental changes made by human activities.

A role for Arctic warming?

Charles Greene directs the Ocean Resources and Ecosystems Program at Cornell University in Ithaca, N.Y. “Houston would have suffered much less damage,” he says, if Harvey behaved like an ordinary hurricane. “But instead, the storm stalled in place and just continued to dump record amounts of rainfall from the Gulf on the city.” Harvey’s unusual four-day stall meant that it could unleash unprecedented amounts of rain. 

So what role could climate change have?

A swift river of west-to-east winds, known as the jet stream, flows in the upper atmosphere. It divides cold Arctic air in the north from warmer, subtropical air in the south. As the Arctic warms, these winds in the upper atmosphere weaken. Normally, the jet stream gently undulates up and down. But with Arctic warming, it becomes wavier. Climate scientists believe that North American storms will have a greater chance of stalling as this occurs. And that ups the threat of very heavy rain events where clouds are able to dump more of their precipitation in one place.

What’s more, as Earth has been warming, the ability of the air to hold moisture also has climbed. So far, there has been a worldwide average temperature increase of between 1 degree and 2 degrees Celsius (1.8 degrees and 3.6 degrees Fahrenheit) since the start of the Industrial Revolution.

Why the broad range? The total depends on how researchers have measured it. Some estimates take into account ocean temperatures. Others only average the observed rise in the atmosphere. The atmosphere’s growing fever has boosted the amount of water vapor available for a storm to store — and eventually release. Harvey tapped into this extra humidity. And then released it as super-heavy rains.

NOAA already has noticed a sharp uptick in the number of “extreme” precipitation events over the northeastern United States. In a report it issued four years ago, the agency described a ”recent elevated level in extreme precipitation.” Extreme events are not just becoming worse — they're becoming more common, too, the report concluded.

Another symptom of global warming is a planet-wide rise in sea levels. And that has increased the risk of damaging storm surges — storm-related tidal rises that send an influx of seawater into coastal communities. A century-long plot of the sea level at Galveston Island, Texas, for instance, shows that the ocean has risen nearly a half-meter (19.7 inches) in the past 150 years or so. (These data come from a study conducted by Texas A&M University at Corpus Christi.)

With higher sea levels, there is an increased risk of water being swept inland and causing destruction. This is especially true for hurricanes that come ashore. This is known as storm surge flooding.

The future of weather is directly related to Earth’s climate. As that climate changes, so will the weather. Signs now point to weather everywhere becoming more extreme. As Texas continues to pick up the pieces from catastrophic flooding, we have to ask ourselves: Could events such as Harvey become the new normal?

Power Words

(for more about Power Words, click here)

Arctic     A region that falls within the Arctic Circle. The edge of that circle is defined as the northernmost point at which the sun is visible on the northern winter solstice and the southernmost point at which the midnight sun can be seen on the northern summer solstice.

Atlantic     One of the world’s five oceans, it is second in size only to the Pacific. It separates Europe and Africa to the east from North and South America to the west.

atmosphere     The envelope of gases surrounding Earth or another planet.

average     (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

climate     The weather conditions that typically exist in one area, in general, or over a long period.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

cloud     A plume of molecules or particles, such as water droplets, that move under the action of an outside force, such as wind, radiation or water currents. (in atmospheric science) A mass of airborne water droplets and ice crystals that travel as a plume, usually high in Earth’s atmosphere. Its movement is driven by winds. 

ecosystem     A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.

global warming     The gradual increase in the overall temperature of Earth’s atmosphere due to the greenhouse effect. This effect is caused by increased levels of carbon dioxide, chlorofluorocarbons and other gases in the air, many of them released by human activity.

humidity     A measure of the amount of water vapor in the atmosphere. (Air with a lot of water vapor in it is known as humid.)

hurricane     A tropical cyclone that occurs in the Atlantic Ocean and has winds of 119 kilometers (74 miles) per hour or greater. When such a storm occurs in the Pacific Ocean, people refer to it as a typhoon.

Industrial Revolution     A period of time around 1750 that was marked by new manufacturing processes and a switch from wood to coal and other fossil fuels as a main source of energy.

jet stream     A fast-flowing, high-altitude air current. On Earth, the major jet streams flow from west to east in the mid-latitude regions of the Northern and Southern Hemispheres.

meteorologist     Someone who studies weather and climate events.

moisture     Small amounts of water present in the air, as vapor. It can also be present as a liquid, such as water droplets condensed on the inside of a window, or dampness present in clothing or soil.

National Oceanic and Atmospheric Administration     (or NOAA) A science agency of the U.S. Department of Commerce. Initially established in 1807 under another name (The Survey of the Coast), this agency focuses on understanding and preserving ocean resources, including fisheries, protecting marine mammals (from seals to whales), studying the seafloor and probing the upper atmosphere.

precipitation     (in chemistry) The creation of a solid from a solution. This can occur if there is too much of a chemical to dissolve completely into a solution. It also can be a sign that some chemical reaction is taking place. (in meteorology) A term for water falling from the sky. It can be in any form, from rain and sleet to snow or hail.

pyramid     A monumental structure with a square or triangular base and sloping sides that meet in a point at the top. The best known are those made from stone as royal tombs in ancient Egypt.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

sea level     The overall level of the ocean over the entire globe when all tides and other short-term changes are averaged out.

storm surge     A storm-generated rise in water above normal tidal level. In most cases, the largest cause of storm surge is strong onshore winds in a hurricane or tropical storm.

Texas     The second largest state in the United States, located along the southern border with Mexico. It is about 1,270 kilometers (790 miles) long and covers an area of 696,000 square kilometers (268,581 square miles).

trillion     A number representing a million million — or 1,000,000,000,000 — of something.

tropical depression    This is a low-pressure storm system that forms in the tropics and has wind speeds no higher than 61 kilometers (or 38 miles) per hour. It’s a serious storm, but well below hurricane status.

water vapor     Water in its gaseous state, capable of being suspended in the air.

weather     Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.

Further Reading

Report: National Oceanic and Atmospheric Administration. Regional climate trends and scenarios for the U.S. National Climate Assessment: Part 1, Climate of the Northeast United States. NOAA Technical Report NESDIS 142-1. Washington, D.C. January 2013.

Report: National Oceanic and Atmospheric Administration and Army Corps of Engineers. Probably maximum precipitation estimates, United States East of the 105th meridian. Washington, D.C, June 1978, 100 pp.

Educator Guide: Bureau of Economic Geology, University of Texas at Austin. Sea Level Changes and the Texas Coastal Environment. 17 pp.