I was watching these 'what if' parachute failure videos on YouTube and everywhere they say do not choose water over land. Why should we not choose water and what happens if we land in water?

One such video:

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    $\begingroup$ You can't drown on land. $\endgroup$ – Ron Beyer Nov 8 '17 at 12:25
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    $\begingroup$ @RonBeyer it depends how hard you try $\endgroup$ – BeB00 Nov 8 '17 at 12:56
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    $\begingroup$ @GdD The meta consensus so far is that questions about parachuting (and paragliding) are on topic. Many modern parachutes are basically flying wings so it's hard to see why we'd exclude them (and that's not even considering the many ways that parachuting is relevant to aircraft pilots). $\endgroup$ – Pondlife Nov 8 '17 at 13:39
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    $\begingroup$ Aim for a hospital. $\endgroup$ – Marc Bernier Nov 8 '17 at 19:37
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    $\begingroup$ It will be easier to find your body. $\endgroup$ – talex Nov 9 '17 at 3:20

If your parachute fails to open entirely you are almost certainly extremely dead no matter where you land, however occasionally people do survive. A partial failure of a chute is much more survivable. You will be coming down much faster than you would with a good chute, and you are going to get injured, probably badly. Think broken legs and arms with neck or back trauma. You may sustain a concussion as well, and you will certainly go into shock.

If you come down in the water you will be injured and unable to keep yourself afloat, and it will be much harder to rescue you. On land help will be much closer and, and as @RonBeyer says in comments, you can't drown on land.

Land has features which may help you survive: trees, vegetation, hay bales, crops, snow, and many other things may cushion your impact enough to make the difference between life and death. Water is the same wherever you go, and doesn't have nearly enough give to cushion an impact.

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    $\begingroup$ Some statistics: 100% (albeit being a small sample) of the persons listed here landed on land en.wikipedia.org/wiki/Category:Fall_survivors $\endgroup$ – Viktor Mellgren Nov 8 '17 at 15:54
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    $\begingroup$ @ViktorMellgren that's because it's possible to land on something yielding or on a steep smooth slope that can decelerate you at a survivable rate. At freefall speeds water might as well be concrete for all the yield it can give. $\endgroup$ – Dan Is Fiddling By Firelight Nov 8 '17 at 16:00
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    $\begingroup$ might be good to add how hitting water at speed compares to hitting something solid $\endgroup$ – Michael Nov 8 '17 at 17:42
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    $\begingroup$ @Michael That depends very much on the attitude at which you enter the water. $\endgroup$ – reirab Nov 8 '17 at 17:54
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    $\begingroup$ related : Why is jumping into water from high altitude fatal? $\endgroup$ – J... Nov 8 '17 at 18:57

From a jump instructor, whose chute failed:

You landed in a blackberry bush, right? Yeah, it was less than a meter high and it wasn't super dense but it was better than hitting than the hard floor or hitting the lake. If I'd landed in the water I would have been knocked out just the same and broken the exact same bones. But my lungs would have collapsed and I would have drowned, because I was unconscious.

So this instructor had studied the problem enough to know that he didn't want to land in the water. He is not alone.

Also, years ago, I remember meeting a woman who was in the Army, doing a jump in North Carolina, and her chutes failed to open. She targeted a pile of hay, and survived.

The terminal velocity of the human body is about 120 MPH, and may be less if the jumper can increase their drag. Picking the right landing spot, such as soft vegetation, appears to increase survivability. Landing in water seems to cause complications with breathing and also with the ability to swim if limbs are broken or consciousness is lost.

A co-worker was a base commander when a F-4 went down and the pilot's chute failed to deploy in the North Sea at night. The pilot survived, and his injuries were limited to compressed discs and hypothermia. It took them about 70 minutes to fish out the pilot.

I do not know what the statistics are for water landings vs land landings, but it is generally recognized that a land touchdown provides more opportunity to steer to favorable soft targets.

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    $\begingroup$ "Landing in water seems to cause complications with breathing..." Excellent!! $\endgroup$ – FreeMan Nov 8 '17 at 18:06
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    $\begingroup$ While water displaces nicely at swimming displacement velocities, it does have about the same inertial mass as the body striking it, and there is further displacement resistance. So a body traveling at 120 MPH hitting water meets an effective mass with greater net force than if it just met a similar piece of jelly (water) in free air which could deform and spread with only the resistance and inertial properties of air. Instead it has the inertial properties of the water around it, and the compressibility of water, rather than air. Bottom line, it's a bigger ouch. $\endgroup$ – mongo Nov 8 '17 at 20:56
  • $\begingroup$ I'd have thought trying to aim for a tree or forrest type of area would be better than land or sea? $\endgroup$ – mickburkejnr Nov 9 '17 at 17:31
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    $\begingroup$ @mickburkejnr Well, you'll generally find more trees and forests on land than on water. Ergo, first step is to aim towards land instead of water (in case e.g. you are above water and can't make out features in the landscape, it's best to get closer to the land before trying to aim for a specific spot on the land). $\endgroup$ – Delioth Nov 10 '17 at 18:01

An impact on land has a small chance of survival, an impact on unbroken water has none.

Falling from thousands of feet without a parachute is very likely a death sentence, but there are a handful of cases in which people have survived. In nearly all of them, it is because the person landed in particularly hospitable terrain, like hitting a number of branches on the way down to slow their fall, or rolling down a steep hill.

All of these stories have one thing in common: slowly breaking your fall

What kills you isn't really the impact, it's the deceleration of the impact. You could be slowly lowered from 10,000 feet by a crane and you'd be just fine. But when you fall from great height, you build up a lot of speed as energy that has to be dissipated upon impact, and if it can't be dissipated into your environment it gets dissipated into you.

Your body can absorb reasonable impacts from reasonable heights, but it has limits. When you slowly break your fall, you're essentially splitting one unsurvivable impact into many smaller survivable ones.

What does this all have to do with land versus water?

Land has terrain. Water doesn't. If you hit the side of a grassy hill and roll down hundreds of feet before finally stopping, you've dissipated all this energy into the hill, while splitting up all the impact on your body.

If you hit the water, it really doesn't matter whether it's hot water, cold water, saltwater, freshwater, mineral water, branded water. It's going to be a very, very hard impact, and it's going to be head-on, because water is always level to gravity, so no hills or angles to dissipate energy. Water's very high surface tension means that at speed, the surface of water behaves much like the surface of a brick.

In Short:

Avoid water if you're falling without a parachute. Aim for trees. Or hills. Or peat bogs. Or giant trampolines. Or something that isn't flat and uniform like water.

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    $\begingroup$ It is not surface tension that causes the surface of the water to behave like a brick, it is the quasi-incompressibility of water. The body hitting the water will generate a large pressure at the impact point, but the water itself won't compress to absorb the shock. Surface tension force, which scales as $$gamma/R$$ where R is the radius of curvature and $\gamma$ the surface tension of a fluid, has nothing to do with it since the radius of curvature of a flat surface is, by definition, infinite $\endgroup$ – BlaB Nov 8 '17 at 21:45
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    $\begingroup$ @BlaB Interesting. Feel free to edit my answer with the extra information :) $\endgroup$ – TheEnvironmentalist Nov 8 '17 at 21:48
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    $\begingroup$ If you hit water with substantial numbers of air bubbles in it, you get much the same cushioning effect as if you'd hit a tree or a haystack. Of course, conveniently-placed waterfalls or swimming pools filled with seltzer water are significantly less common than conveniently-placed forests... $\endgroup$ – Mark Nov 8 '17 at 22:11
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    $\begingroup$ "...slowly lowered from 10,000 feet by a crane and you'd be just fine if you didn't suffocate on your way down." There's plenty of oxygen for survival at 10k feet. $\endgroup$ – Wayne Conrad Nov 8 '17 at 22:19
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    $\begingroup$ @Seph We'll send our condolences. $\endgroup$ – T.J.L. Oct 31 '19 at 17:41

At a freefall speed of 120MPH, water would provide a drag of about 1000 Gs which would be the same as hitting the ground and stopping in 6 inches (15cm). Better than concrete but still not survivable.

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If you see a large water body around you, direct yourself to that.

Carry something which can cause a large concussive force just as you're about to impact. Say you're about to hit the water, you lob in object X which causes a large boom. The concussive force of the blast pushes you back and cushions you using the water as a "sofa" of sorts. You have to time this perfectly though, too soon and you miss it, too late and you get caught in it yourself. You can always try practicing by jumping from a low enough bridge into the water and trying, have enough health insurance and you'll be fine.

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    $\begingroup$ A "lob" of an object toward the ground while falling at terminal velocity seems somewhat difficult to achieve. $\endgroup$ – Ken Williams Nov 11 '17 at 4:57
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    $\begingroup$ Didn't Mythbusters do this in 2003? en.wikipedia.org/wiki/… Yes, yes they did. $\endgroup$ – Criggie Nov 11 '17 at 23:12
  • $\begingroup$ Its also covered in this question on Worldbuilding worldbuilding.stackexchange.com/questions/15661 $\endgroup$ – Criggie Nov 11 '17 at 23:12
  • $\begingroup$ @Criggie According to the linked description, the mythbusters episode was throwing a hammer at the water to "break the surface tension" rather than throwing an explosive at the water and using the blast force to provide extra drag. In theory, causing the air to move rapidly upward a bit before you hit the water would indeed slow you down. Of course, you will run into the problem that Ken mentions: the object you throw down won't be moving downward much faster than you are, so it's quite likely to explode right beside you and reduce, not increase, your chances of survival. $\endgroup$ – reirab Nov 12 '17 at 8:43
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    $\begingroup$ @Mast It seems borderline ironic. I'm not sure the OP is really serious about it or it is just joking. $\endgroup$ – Lorenzo Donati -- Codidact.com Nov 12 '17 at 19:46

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