The Hijaz has Diarrhea

The Hijaz has Diarrhea

In the last post, I wrote about how the cycle of desertification in the Hijaz and much of rural Saudi Arabia was started through the unintended consequence of a Saudi national policy in 1954, after a sustainable, traditional land management system called the hima was abolished.  We’ve also seen how desertification is a self-reinforcing feedback loop that builds on itself and makes it more and more difficult to turn back the desert and bring life and productivity back to the land.  In this post you will learn one of the fundamental methods for understanding your climate and diagnosing the causes of problems to be addressed, as opposed to the symptoms, which is the following:

1:  You cannot bring a desert back to life unless you understand how the water and nutrient cycles are functioning.

The various parts and functions of a healthy water cycle.

The various parts and functions of a healthy water cycle.

How nutrients and minerals cycle through plant and animal and soil life.

How nutrients and minerals cycle through plant and animal and soil life.

2:  You must cooperate with the existing function of those cycles to begin mimicking a healthy water/nutrient cycle and then healing them on a small scale.  That means you cannot start in the middle of the desert.  You have to start on an edge, where these cycles are functioning at least a little.

3:  Healing the water and nutrient cycles on a small scale will kickstart a cycle of life that counters the cycle of desertification.  Once that cycle reaches a certain tipping point, the system will take on a healthy function and become resilient, regenerative, and irreversible (disregarding shocks to the system such as warfare, major natural disasters, or sudden shifts in the larger weather patterns).

Those are the principles and theory.   Here is the application for one of the main edges that must be tackled to afforest/asavannahize the Arabian Peninsula:  The hijaz.


The hijaz is characterised by large wadi systems that flood when it rains.  These floods cause major destruction when they hit cities, as well as more ruralized devastation outside.  One of my worker’s uncles and 4 of his cousins died in a flood in Al Baydha 6 years ago, leaving a widow and two young children to be cared for by his extended family.  I am going to pick one watershed characteristic of the rest, and use that as our case study.  The watershed we will look at in this post is Al Lith, which is a 90 minute drive south of Jeddah.

As is typical of other hijazi watersheds, Al Lith has an extensive mountain watershed draining into a very short flood plain before it hits the red sea.

As is typical of other hijazi watersheds, Al Lith has an extensive mountain watershed draining into a very short flood plain before it hits the red sea.


Picture a flood the way you would a tree.  The way a tree’s leaves and branches collect sunshine, the mountains in Al Lith collect water.  There are main branches, small branches, eventually a trunk (where all the water collects and runs as a flood).  Then before it hits the red sea, it spreads out in an alluvial fan  and then in the hijaz, runs into the red sea.  In Al Lith, the catchment area (in the mountains) is approximately 35 x 55 kilometres.  If a rainfall of 25 mm (one inch) hits this whole watershed, that means there are 1,925,000 cubic meters of water (the equivalent of 1560 acre feet) hitting that watershed at one time.  Because these mountains are largely devoid of plant life, less than 10% of that water will soak into the shallow aquifers, and the rest will run into the red sea.  You can se in the picture the two alluvial fans that were created in the last floods from the watershed within the blue polygon.  But you can also see 4 other alluvial fans from other floods, and other watersheds just north and south of Al Lith.

Looking at the water cycle above, there are some parts of that cycle that are severely hampered or stunted in the Al Lith watershed.

  • The condensation of water droplets to create clouds (listed just as CONDENSATION in the graph above) is severely restricted by high surface temperatures relevant to the dew point, by dust in the atmosphere, and by the lack of potential water drop nuclei that would be produced by a less desertified environment.  This means that rainfall, rather than being a regular occurrence, only happens once a year, or sometimes once every two or three years.
  • Surface Runoff is the overwhelmingly dominant way water makes it to the ocean.
  • Infiltration of water into the soil is severely restricted by a few factors:
    • Topography (where most of the watershed is in the catchment and the available space for the trunk of the tree is very small)
    • The lack of plants and plant roots in the watershed, which facilitate infiltration, slow water flow, reduce erosion, and reduce the impact of falling water on bare soil
    • The inability of the soil to hold and retain moisture due to its sandy makeup and the lack of carbon and organic material.

The best analogy for this kind of water cycle is diarrhea.  The hijaz has diarrhea.  Within 24 hours of a rainfall event, 90% of that water is already lost to the sea, and only 10% is left to nourish all the plant life in the watershed until the next rainfall (which may not occur for another 1000 days!)

So let’s talk about the actual results of the Hijaz’s ailment.  A person with diarrhea is significantly less productive than he would be healthy.  The hijaz is no different:

A 1 inch rainfall in Al Lith results in an estimated 1,733,000 Cubic meters of water run into the red sea in the Al Lith watershed above.  Let’s put this in a more meaningful perspective since most people don’t intuitively think in acre feet or cubic meters of water.  That lost water from a one inch event in Al Lith is enough to irrigate 118,698 mature date palms for one year.  Assuming a low average of 70 kilos of dates per tree, that’s the equivalent of just over 8,300,000 kilos of dates per year, from one watershed.

The lost water from the flash floods is an enormous loss of potential, measured solely in the amount of dates you could produce if you were to only plant date palms.  That doesn’t account for any other ecological services or potential products provided by these imagined palm trees–fiber for traditional crafts, a reduction in dust, mitigating wind and dust storms, lowering ambient temperatures, shading the riparian areas, and providing more habitat for wildlife.  Aside from the lost water, which is the source of all life, Saudi Arabia is losing out on money, employment, higher public health (dust and fine particulate matter has been proven to increase the amount of asthma, respiratory diseases, and heart disease), and just a nicer, greener landscape.

There's some green in that watershed!  What if my 10% estimate is off?

There’s some green in that watershed! What if my 10% estimate is off?

Now, I can hear you critics saying, “What if your 10% number is off?  After all, Al Lith does have some greenery in that watershed, and it does have a small strip of running water most of the year.  Or what if your calculations on the size of the watershed are off?”  The size of the watershed doesn’t matter–the principles are accurate, and being off by a few square kilometres doesn’t change the numbers much.  But what if my estimate on the water absorption is off?  Let’s assume it’s off by a factor of 5, and 50% of the water is absorbed into the water cycle.

Well, that would mean that the amount of lost water is only 1,000,000 cubic meters in a one inch rainfall.  But guess what?  The average amount of rain in a year is not 1 inch.  It’s 70mm, or just under 3 inches.  Which means that even if 50% of the water is being retained, there are still 3,000,000 cubic meters of lost water per year, or the equivalent of 205,500 date palms irrigated per year–slightly less than double my original estimate.  And if my estimate of 10% water retention (which is based on studies done in the mountainous deserts of the SW United States) is accurate, then the lost water per year is equal to 5,199,000 cubic meters of water a year, or 25,000,000 kilograms of dates per year  (by the way, I am not suggesting that hundreds of thousands of dates should be planted in Al Lith.  I am simply trying to give a measurement of the lost water that is meaningful beyond acre/feet or cubic meters of water).

This is only one watershed.  There are at least 20 other watersheds up and down the west coast of Saudi Arabia that have diarrhea–some are bigger and some are smaller.  The lost production, lost employment, and lost water is worth billions per year in lost productivity, and this is in a country where 70% of all the consumed water is sourced from desalination plants.  This is in a country with no recognised rivers or lakes.  This is in a country where water and food security are so paramount that they are leasing hundreds of thousands of acres of land in Ethiopia, a land so famous for its food production that it has its own Wikipedia page on famine.

Clearly, if we could heal the Hijaz’s diarrhea it would be of enormous benefit to the county’s economy, food security, and water security.  This can only be done by understanding the water cycle and then working to get it regular.  In the next post, we will talk about the cure:  roughage.








  1. Hi Neal,
    in another website i read another explanation for the disappearing of clouds above desert/dry regions:

    “Disrupting the water cycle
    The temperature increases and evaporated moisture rises much higher. Because in a forest the evaporated moisture rises to only 60m, staying cool in the process, it is more likely to precipitate nearby. Once moisture rises to 200m, it will be transported much further and rain down somewhere else, where the temperature is cooler, such as the oceans, or the mountain tops. ”

    There is also a good sketch in this section in this page explaining the connection between forests and water cycle, which you also mentioned in one of your articles. This connection was at least published for the scientific community by two russian physicists in 2006:

    Biotic pump of atmospheric moisture as driver of the hydrological cycle on land
    A. M. Makarieva and V. G. Gorshkov
    Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg, Russia
    Published in Hydrol. Earth Syst. Sci. Discuss.: 30 August 2006

    This idea came up/was brought to the wider public again in 2009:

    Revolutionary new theory overturns modern meteorology with claim that forests move rain
    Jeremy Hance, April 01, 2009

    Here is a video of a speech of Douglas Sheil, a scientist from Norway which worked together with Gorshkov and Makarieva in the last six years on the new theory of connectiong forests and water cycle (the sound is during a part of this video a bit low):

    Douglas Sheil – Do forests attract rain?
    Center for International Forestry Research (CIFOR)

    Do you know if there is something more to be prepared for the second phase of the project (the bigger area right adjacent to the demonstration site)?

    • Hi Stephan

      The Biotic Pump concept is one i’m familiar with and have put out there in presentations here in the kingdom. It’s an exciting theory with global implications. There are things going on for the second phase of the project, but I can’t announce them publicly.



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