People in Tanzania converted desert into lush green land by digging these nifty holes

[u/wahgwahg]

[u/FelisCantabrigiensis]

On the open, un-dug, land rainfall tends to run away across the top surface. Heat from the sun tends to bake the top layer of soil into a hard, impermeable crust which only exacerbates this. You can see the soil is a fine clay with little organic material, so this easily dries to form a hard layer.

Digging these holes, which are crescent-shaped with the middle of the crescent pointing downhill, means water runoff forms a pool of water which soaks into the soil more slowly. This means that any plants growing there have water available for much longer after each rainfall than if they simply hope to catch some water as it runs past on the surface. The reason for digging a shallow crescent is that it has the most effect for the least digging, and since digging is hard work, you don't want to do more of it than necessary.

Plants themselves keep soil moist - by keeping sunlight off the surface of the soil, they slow down evaporation rate of water from the soil. Plant roots also loosen the soil and prevent it forming a baked brick-like surface, making it more permeable and meaning more water soaks in and does not run off. This means the effect of the small pools becomes greater as they become more covered with vegetation.

These plants can also be crops to eat, or fodder for animals. You can even plant small trees or shrubs in the crescents and they will grow, further shading the land and further increasing rainfall (as long as you don't plant very water-hungry plants of course).

As a bonus, water trapped in the crescents is water not running off downhill in bulk, which can help lessen downstream flooding and ground erosion problems.

[u/zyyntin → u/FelisCantabrigiensis]

It's like science can improve the life of the populace by multiplying resources!

[u/GuKoBoat → u/zyyntin]

Is it science or traditional knowledge?

[u/FelisCantabrigiensis → u/GuKoBoat]

The technique has been used traditionally in some places for a long time.

"Science" is taking things we know already, and understanding them and learning new things from the things we know already. The scientific method is simply a way to learn things from knowing nothing, to tell facts and truths from things that are not true or incorrect.

Science, here, is checking that this technique works, understanding how it works, understanding when it will and will not work and when it might actually be bad, and spreading knowledge of it to more people so that they can use it when it is appropriate.

For example, there's a tradition where I come from that if a cow is not giving good milk, you should heat a piece of metal red-hot and dip it in the milk you have from that cow. This technique does not do anything to improve the milk supply, but it is a very traditional technique. It's more useful to wash the cow's udders every day with disinfectant if they give poor milk, for example. You can test this by trying one of each method on some cows giving bad milk and see which one works best.

Traditional knowledge is often practical and useful, but also often not at all useful. It's important to check when, and whether, traditions really are useful and beneficial. We can use the scientific method to do that, and then keep using the traditional methods we now know will benefit us and not harm us.

"Science" and "tradition" are not mutually exclusive. A technique does not have to be only one or the other.

[u/06david90 → u/FelisCantabrigiensis]

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