The wind gradient

Why the wind slows close to the ground, how sinking through that slower air steals airspeed on your final glide, and why keeping your speed up protects you — especially over rough ground and behind trees.

In this lesson you will

On a breezy day at the training hill, your final glide looks perfect until the last few metres. Then the wing seems to go soft and sink, the grass comes up faster than you expected, and the landing is firmer than it should have been. You have just flown down through the wind gradient.

The wind gradient is the slowing of the wind close to the ground. It is invisible, it is there on every windy day, and it acts exactly where you have the least height to spare. The flare lesson tells you what to do on final; this lesson explains why.

Why the wind slows near the ground

Air moving over the ground rubs against it. Friction slows the wind near the surface — more over rough ground, and more in strong wind — and the effect fades with height until it is small above the lowest few hundred metres to a kilometre or two¹. Don’t confuse this with the gradient wind, forecasters’ name for the wind above that friction layer.

In windy, overcast weather over even ground, the wind grows with the logarithm of the height: it climbs quickly in the first few metres, then ever more slowly¹. How quickly depends on how rough the surface is²³:

Upwind surface	Wind at 2 m7 ft, compared with 10 m35 ft
Open water	About 85%
Open grass	About 72%
Low crops with hedges	About 65%
High crops, scattered obstacles	About 56%
Bushes, very rough ground	About 46%

Over grass, then, a wind of 20 km/h12 mph at 10 m35 ft is about 24 km/h15 mph at 30 m100 ft and only 14–15 km/h9–9 mph at 2 m7 ft. Gliding down the last 30 m100 ft into wind, you lose roughly 9–10 km/h6–6 mph of headwind³.

Note For the curious: the log law

In neutral air over uniform ground, the wind at height z₂ is the wind at z₁ multiplied by ln(z₂/z₀) / ln(z₁/z₀), where z₀ is the surface’s roughness length: tiny for water, larger for grass, largest for forest and towns¹². Real profiles vary, so treat the numbers as rough guides³.

Figure: Change the surface, the wind and the height you sink from. Notice how the arrows shorten sharply in the last few metres, more over rough ground — and that both pilots lose the same airspeed, but the braked one starts much nearer the stall. The figure shows the worst case: the full loss of headwind coming off your airspeed.

Change the surface, the wind and the height you sink from. Notice how the arrows shorten sharply in the last few metres, more over rough ground — and that both pilots lose the same airspeed, but the braked one starts much nearer the stall. The figure shows the worst case: the full loss of headwind coming off your airspeed.

Note Wind gradient and shear

Pilots use “wind gradient” for this steady slowing near the ground. Wind shear is the wider term for any sudden change in wind speed or direction over a short distance; low-level shear comes with fronts, thunderstorms, inversions and strong winds aloft of more than about 25 kt⁴.

The weather changes the wind gradient too. In stable air — at night and early in the morning over land — the wind is slower near the ground and faster aloft than the log law predicts, and strong wind shear often forms across a temperature inversion⁵. When that inversion breaks up later in the morning, stronger wind from above can reach the ground quite suddenly. On a sunny afternoon the thermals mix the air, and the wind is nearly the same at every height above the lowest tens of metres⁵.

Higher up, the wind is usually both stronger and turned: about 600 m1,950 ft above the ground it typically blows 20–40° to the right of the surface wind in the northern hemisphere, and to the left in the southern⁶. A calm landing field (LZ) can sit under a windy launch, and on high ridges the lower slopes can be almost calm while the top is in strong wind⁷.

What the wind gradient does to your airspeed

Your wing flies through the air, not over the ground. On final into wind, as you sink into slower air, the headwind drops. For a moment the wing keeps its groundspeed, so the lost headwind comes straight off your airspeed. The wing then dives a little to win the speed back, but that takes time — and height⁸.

If the wind gradient is abrupt, the airspeed can drop suddenly; close to the ground there may not be enough height to recover, and you can land short and hard⁸. One school wing’s manual warns that gusts, wind gradients or turbulence near the ground can cause a sudden loss of lift or an unintended stall on any paraglider⁸.

That is why speed is your margin. A wing flying hands up has plenty of airspeed to lose before the stall. A wing already slowed on the brakes starts much closer to it, and the same loss can take it there⁹. Try both in the explorer above.

Turns low down are the second trap. In a strong wind gradient the higher wingtip sits in faster wind than the lower one, which is one reason to keep the bank small near the ground⁸. One manufacturer advises against tight turns below about 30 m100 ft, because the wing must dive afterwards to regain speed¹⁰.

Keeping your speed on the final glide

The training systems agree on the answer: a straight final into wind at or near trim speed, hands up, with speed in hand for the wind gradient and turbulence near the ground¹¹¹².

Through the wind gradient on final

Arrive on a long, straight final, hands up, at or near trim speed.
Cue Steady wind noise, firm wing, time to settle before the last metres.
Why Speed is your margin against the wind gradient and gusts¹²¹³.
Expect the last 30 m100 ft or so to feel sinkier, and often bumpier, on a windy day.
Cue The wing feels softer and the ground comes up faster.
Why The wind gradient is taking headwind away, and the air near the ground is often turbulent³⁹.
Keep your hands up through it — no extra brake to “stretch” or slow down.
Cue The wing dives a little and picks its speed up again.
Why Braking spends the margin the wind gradient is already eating⁹.
Keep the wing straight; small corrections only.
Cue Level wing, eyes on the far end of the field.
Why Low turns meet uneven wind across the span and cost height you do not have⁸¹⁰.

Standing up, the flare and the run-out are in Final approach and the flare.

Standards differ The wind gradient in the first-rating syllabus

Common ground: USHPA, APPI and SafePro all teach a straight, hands-up final with speed for the wind gradient¹¹¹³.

USHPA (USA): P2 ground school includes extra speed for handling wind gradient and turbulence; P3 requires proper airspeed control when descending through a wind gradient¹¹.
BHPA (UK): The Club Pilot environment exam for hill pilots covers the wind gradient, together with rotor, ridge etiquette, top landing and wave¹⁴.
APPI (international): The wind gradient is first-level theory, and APPI’s approach rules ask for a final long enough to gain speed for it¹⁵¹³.
FAI/CIVL SafePro (international reference): Its second stage asks for exactly that: hands up, a straight final, overcoming the wind gradient with speed¹¹.

Summarised from each body’s published material, which changes over time. Check the current official documents and follow your school.

Behind trees and obstacles

Trees, hedges and buildings upwind of a field make the wind gradient much sharper. Research on tree windbreaks measured how far their shelter reaches in a 32 km/h20 mph wind¹⁶:

Distance downwind of a medium-density tree line	Wind speed, compared with the open field
5 tree heights	About 30%
10 tree heights	About 50%
20 tree heights	About 75%
30 tree heights	About 95%

A final that sinks below tree-top height close behind a tree line drops out of the full wind into air moving at a third to half its speed. That is a far bigger loss of headwind than over open grass, and very dense barriers also pull the air coming over the top downward into turbulence¹⁶. How far that turbulence reaches is in Rotor, venturi and compression.

Common mistake A slow final “to land softer”

Symptom: The wing feels mushy in the last metres; you sink fast and land short or hard.
Cause: Brakes held on final, just where the wind gradient takes airspeed away.
Fix: Hands up on final, and save the brakes for the flare⁹.

Common mistake A low turn onto final

Symptom: The wing swings you out, you lose height fast, and the ground arrives during the turn.
Cause: Turning late and steeply near the ground, through uneven wind.
Fix: Plan the approach so you turn onto final high and fly a long, straight final⁸¹⁰.

Common mistake Setting up the final close behind a tree line

Symptom: The wind seems to vanish below tree-top height and the air gets rough.
Cause: You descended into the trees’ shelter and wake.
Fix: Choose a touchdown point well away from obstacles upwind, and keep your speed¹⁶. See assessing the landing field.

Instructor's note Stronger wind, bigger wind gradient, smaller flare

In stronger wind the wind gradient costs more speed¹, so keep your hands up and expect the sink. But your groundspeed is already low, so the flare itself is smaller¹⁷. Students sometimes mix the two up and brake early to “soften” the arrival; they get the sink without the speed. Keep the speed, then size the flare to the wind.

Instructor's note Big ears and the wind gradient

Big ears already lower your airspeed. Release them before the flare, and avoid them on a windy or bumpy final; one manufacturer warns of a stall in the wind gradient¹⁸. In the German federation’s 2024 accident statistics, a very serious accident followed very large ears, a strong wind gradient and a possible error opening the ears close to the ground¹⁹.

Questions students ask

Why does my final feel sinky on windy days?

You are sinking into slower air, so the wing loses a little airspeed until it dives to regain it, and the air near the ground is often bumpy too⁸. Hands up and straight is the answer.

Does the wind gradient matter on launch too?

Yes, the other way round. Your wing rises into stronger wind than you feel at head height, so it can pull harder than you expect; many schools warn of up to about 10 km/h6 mph more²⁰.

Why is it calm in the landing field but windy on launch?

The wind usually gets stronger with height, and the landing field sits deep in the wind gradient. On high ridges the lower slopes can be almost calm while the top is in strong wind⁷.

Should I push the speed bar on final for extra margin?

No. Manuals say to avoid accelerated flight close to the ground and in turbulence²¹. Hands up is your margin.

Key points

Friction slows the wind near the ground; the effect is strongest in strong wind and over rough ground, and it fades with height.
Over grass, the last 30 m100 ft can cost about 9–10 km/h6–6 mph of headwind in a 20 km/h12 mph wind; more over rough ground and close behind trees.
Sinking through the wind gradient takes airspeed away until the wing dives to regain it; near the ground there may be no height to spare.
Fly a long, straight final hands up; never brake to slow down or stretch it, and keep turns away from the ground.
Land well away from trees and obstacles upwind, where the wind gradient is sharpest and the air is turbulent.

Ground to Solo is a study aid. Paragliding is learned in person with a qualified instructor at a recognised school; nothing here certifies you to fly.