The most common way to die in the desert is dehydration. The second most common is drowning. Drowning in the desert may seem like an oxymoron, but it illustrates the tricky nature of dealing with water in desert climates; when it rains in a desert, the result is flash floods.
Floods form in deserts because of the lack of foliage. In non-arid climates, plants’ root systems aerate the soil and increase the amount of water the soil will absorb, and the plants themselves slow water flow. Here in the desert, the mitigating effects that plants would normally have on water flow are almost non existent, so the soakage capacity of the land is very low. Moreover, 100% of rain that hits exposed rock becomes runoff. These mountains are almost all rock, so rain gathers speed and power up high, and collects in the wadis, and rushes onto the flood plains, until it reaches the sea. The floods that form in the bigger wadis here in the Hijaz contain billions of liters of water and have enormous destructive power.
More than a few families in Al Baydha have lost loved ones, animals, and farms to floods.
Floods not only cause significant damage, but they also make most of the water inaccessible, as the big floods quickly empty most of the water into the red sea.
In this image from 2007, following some of the larger wadis in the mountains
South of al Baydha clearly show the paths floods have taken from the
mountains to the sea.
Any successful attempt at greening the desert must first increase the amount of available water. In the case of the Al Baydha Project, and many other deserts, that means slowing down the flash floods. Slowing the water down decreases its destructive force and makes it much more accessible and controllable.
Simply slowing the water, however, introduces the second major problem of desert water systems: evaporation.
We’ll talk about evaporation in a subsequent post.