Trees Are More Awesome Than You Thought:  Hydraulic Redistribution

Trees Are More Awesome Than You Thought: Hydraulic Redistribution

One of the major obstacles to reforesting the desert through floods is getting foliage established, and one of the reasons foliage does not establish more readily is because when it does rain, water does not penetrate the thin layer of clay that forms before a flood flows.  You can see that clay layer starting to form  in the video posted below, only 2 minutes after the start of a 5 minute rainfall:

This rainfall did not cause a flood–but it did show what happens in a wadi before a flood occurs–clay layers form, and as clay is hydrophilic, they become saturated, after which more water cannot sink into the landscape unless there are strategies and structures put in place to make it do so.

One of the greatest tools to disrupt this clay plan & establish foliage at the same time is to plant trees that can perform Hydraulic Redistribution.  Hydraulic redistribution is the ability of some trees to use their shallow roots and taproots as pumps.  When the shallow soil is saturated or wet, these trees can pump that water through the tap root deep into the soil, and keep that water in reserve until a drier period.  In that drier period, it can pump the water in the lower levels of the soil up to the shallow roots, thus cooling the soil temperature, making water available to other plants in the tree’s vicinity, and allowing the tree to continue to respirate even in very hot and very try times.   Here is a graphic of how it works:


Graphics courtesy of FC Meinzer, USDA Forest Service.

This is a truly awesome function that you can stack with trees.  The known desert species that perform hydraulic redistribution are acacia tortilas and prosopis, whose taproots can reach up to 120 feet (about 40 meters) below the surface.

Thus in only one function of some trees, we can penetrate the clay layer of floods, and literally pump flood waters into the ground when it is wet.  Then when times get dry, the trees themselves will bring that water back to the surface to nurture other plants growing in their root zone.

To do this without the assistance of a tree would require digging holes, laying pipe and filters, and installing cisterns–just to get the water into the ground.  Then to bring it back up we would have to install pumps and irrigation systems.  That is what some would recommend, and that is actually the function of some standard dams in Saudi Arabia.  Why do that when we can do this passively by understanding how nature works, then tailoring our designs to facilitate her wonders, and then simply cooperating with her?  That is what we can do with hydraulic redistribution.

Why Sustainability Is A Terrible Goal

Why Sustainability Is A Terrible Goal

I hate the word sustainable.  Yes I use it to describe some of the things I do in my Linked-In account, but only because it’s the vernacular word that most people think of to describe the ultimate “green stuff.”   Google brings up nearly 80,000,000 entries for a search on “sustainable development,” 50,000,000 entries for “sustainable business” and 11,000,000 for “sustainable agriculture.”  Clearly many people are thinking about “sustainability.”  It’s become a buzzword, a keyword for greenwashing, and even though it is popularly used, it’s poorly defined.  But that’s not why I dislike sustainability.  I dislike sustainability because it is an insufficient, mediocre goal.

Here are some situations that demonstrate sustainability:

1:  Living paycheck to paycheck .

2:  A marriage that doesn’t result in divorce.

3:  susbsistence farming.

4:  serfdom.

On the scale of awesome, i think all of the four situations above all would qualify as, “not awesome.”  Let’s go a little deeper:

1:  I’ve lived paycheck to paycheck before.  It’s not a lot of fun.   But it is sustainable–as long as someone doesn’t get sick, as long as there is a job paying minimum wage, someone can live for a long long time without problem.  That’s a sustainable situation.  Who aspires to live paycheck to paycheck?  People who are very hungry.

2:  This isn’t my analogy–I saw it on a TedX video somewhere, but I don’t recall whose.  But if you were asking someone, “so how is marriage treating you?” and he replied, “well, you know, our marriage is sustainable.”  What impression would you have?  That the marriage is good or not?

3:  Subsistence farming is exactly that–subsisting.  Sustaining life.  It can go on (essentially) forever.  When you have asked a kid what he wants to be when he grows up, does he ever say, “I want to grow just enough food to eke out my existence!”  No.  But it would be sustainable!

4:  Serfs revolted from serfdom because sustainability wasn’t good enough for them.  It’s not good enough for us, either.

Sustainability means breaking even.  It means that you are producing no less than you consume, and also no more than you consume.  Unfortunately, 99% of all human society on the planet is entirely unsustainable, and over the last 40 years or so more and more people are beginning to realize it, and that is a terrifying realization to have.  That doesn’t mean we should simply go for broke.  We need to add some resilience to the system, and some regenerative ability.  Here is what I mean.

Resilience is the ability of a system to go back to a steady state after experiencing a shock.  On a personal financial level, this would be losing your job and yet having the ability to take care of yourself despite the loss in pay.  That shock (you’re fired!) to the system can be absorbed by substituting for what was lost (finding another job, having enough savings to get by, etc.)  The only way a system can be resilient is if it is producing more than it consumes, leaving some of it in storage to be used when shocks occur.

On an ecosystemic level, this is like a forest regrowing (resilience!) after a forest fire (the shock).   Or a watershed that has been dammed for 100 years (the shock)  filling back up with life and spawning salmon returning (the resilience!) after the dam is removed.

A resilient marriage is a marriage that can handle a lot of problems and keep going–shocks like unmet expectations, illness, the death of a child, financial difficulty, etc.  All those are shocks to a marriage relationship and unless there is some resilience, that system will fall apart.  Shocks happen to every system.   People are resilient but most of our built systems are not:  electric grids are notoriously fragile; political systems are fragile.  Trade and distribution networks,  food and water systems:  These are systems that are not built to withstand shocks, but built to be as inexpensive or as exploitative as possible.

But beyond resilience, there is regeneration.  A system that is regenerative is a system that is not only resilient, but that expands without interference–that perpetuates itself while moving into other domains.  This is a truly permanent system.  If an unsustainable system is in the negative, and sustainability is 0, then a regenerative system is positive.  If we want to have a truly permanent society, then we must build systems that do not consume their resource base (this is essentially every human system in the oil age), but that produce more than they consume.  I am not talking about a perpetual energy machine or any such flim-flammy chicanery.  I am talking about building human societies the way nature itself is built–by deriving all energy for our systems from the sun, and by redesigning how we design, produce, distribute, consume, and discard the products of human society.

Lots of people talk about saving the planet–the planet is fine.  But human society is destroying its resource base.  When our agricultural systems destroy soil and riparian areas, it should be obvious that those systems will not persevere, and that they are unsustainable.  When our methods of managing the oceans increase oceanic acidity and decimate fish and coral populations, it should be obvious that one day our progeny will not eat saltwater fish, unless those methods are redesigned and repurposed.  When people are instigating the next great extinctions, even while we depend on natural systems to keep us alive, it should be evident to anyone with his eyes open, that we are going the wrong way.   Something that cannot go on forever, won’t.

The right way is not sustainable.  The right way is regenerative and resilient.

Floods Can Reforest The Hijaz.

Floods Can Reforest The Hijaz.

In my last post, I talked about how the water cycle in the Hijaz is disrupted, or sick.  Accurately diagnosing the causes of that disrupted functioning gives us a good idea of how to go about healing the water cycle, and also points to the resources available to us to do that in a sustainable, or even regenerative way.

That post was the last in explaining the environmental and climatic sources of the problem facing the Arabian Peninsula vis-a-vis the lack of rainfall and increasing desertification, as well as some of the political complications involved.  Here is a  summary:

The collapse of traditional rangeland practices in the 1950s lead to a tragedy of the commons and a self-replicating  cycle of desertification that increased dust in the atmosphere, increased surface and atmospheric temperatures, and eliminated many of the organisms that were producing nuclei required for rainfall.  Due to overgrazing and woodcutting, and as the cycle of desertification takes hold, vast swaths of once-lush valleys and mountains are becoming nearly devoid of life, leading to a dramatic loss of productivity and a disrupted water cycle that causes the only renewable source of freshwater to be lost in dramatic flooding events.  As this cycle continues, more and more water will be lost, less and less rain will fall, temperatures will increase, and the productivity of the land will approach 0.

At this time, I am not going to go into the political, social, or economic implications of these facts.  Instead, from this post on, I’m going to be explaining what I believe to be the only sustainable solution that has a chance at saving Saudi Arabia’s and the Arabian Peninsula’s water and food security issues.

The most valuable resources in the current water cycle are the floods that periodically rush through the wadi systems of Saudi Arabia’s west coast.  These floods (and other rains) constitute the only sustainable source of water in the entire Kingdom.  Fortunatey, these floods can be used to establish systems that will make the water cycle more regular, that will increase its cyclical frequency, as well as amplify the total amount of rain that falls.  In short, we have to use the floods to bring the rain back, and it can be done in such a way that the total precipitation increases, and the frequency of rain events increases.

The first part of this series will be all about trees and the wondrous effect they can have on the water cycle.  Here is the map, tho not a table of contents:


A pictured Mongongo Tree

Moderating Rainfall, Surface Water Flow & Water retention. 

1:  Clay pan penetration

2:  Erosion reduction, soft rain catching

3:  Hydraulic redistribution

4:  Soil moderation–increasing carbon & soil life increases water retention

Tackling the Problems of Dust, High Surface Temperatures, & Lack of Raindrop Nuclei

5:  Evapotranspiration–VOC’s, vapor, & litter

6:  Moderating hot, dry winds

7:  Extending evaporation periods while reducing evaporation from bare soils

8:  Shade, specific heat, and lower soil temperatures

9;  Wind & dust break

Providing Additional Sources of Precipitation

10: Increased condensation

This is going to get sciencey, but I promise that it will be awesome.   Here’s the first taste of awesome:  Did you know that trees can store water in the soil near their taproots during wet times and then pump it back up to their shallow roots when the soil is dry?  This is called hydraulic redistribution and will be the topic of the next post.

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.







The Catalyst of Desertification

The Catalyst of Desertification

In the last post I discussed the cycle of desertification and its effect on weather patterns, and how dust, high temperatures relative to dew point, and the lack of suitable ice nuclei for cloud formation prevent more rainfall from occurring in the Arabian Peninsula.  The next few posts are going to focus on  the Hijaz–the strip of land on the west coast of the Arabian Peninsula between the red sea and the mountains.   In this post you will learn how the cycle of desertification was set off in the Hijaz in the recent past, as well as how it has been a recurring event in human history.

The hijaz has sustained nomadic pastoral tribes for thousands of years, and over that time, a land management system known as Hima was brought into practice.  This system predates Islam, and has been amended over the years to constitute a reserve or protected area, managed by the local tribe, to maintain rangelands and grazing.  Shortly after the advent of Islam, the Hima became recognised as a place to provide for the general welfare of the people, particularly the poor.

The caliph Omar ibn al-Khattāb (reigned 634-644 CE) instructed the manager of Rabadhah himā by saying: “Lift your wing from the people! Heed the complaint of the oppressed for it will be heard by God. Let enter those who are dependent on their camels and sheep; and turn away the livestock of Ibn ‘Awf and Ibn ‘Affān (two rich Companions of the Prophet), for they can fall back to their palms and fields if their livestock should perish. Whereas the needy ones, if their livestock perish, will come to me crying (i.e. asking for financial help). (from O. A. Llewellyn, “The Basis for a Discipline”, p. 213)

In the middle ages, Himas were given as waqf surrounding the cities.  In the rural areas,  local inhabitants established environmental planning and management strategies which balanced the settlements’ growth and natural resources uses according to Islamic laws and the tribal self-government. Tribes were given the authority by the Prophet, PBUH, to be the custodians of their himā-s, and to control them on behalf of the central government. (S. al-‘Ali, “The himā in the first hegira century (7th century CE)” (in Arabic), al-‘Arab (Riyadh), 7 April 1969: pp. 577-95.  Also see here)  Violators of the rules of the hima–those who brought unpermitted animals in, were either beaten, or had some of their animals confiscated as punishment.


Thus we have a very brief overview of a political system that sustainably  managed lands teetering on the desert for thousands of years, and which, contrary to many other human societies, maintained the relative health of their land while caring for the poor.

Hunting was another activity managed through the Hima to maintain stocks and prevent extermination.

Hunting was another activity managed through the Hima to maintain stocks and prevent extermination.

This system thrived throughout the Arabian Peninsula and the Levant until very recently.  In Saudi Arabia, as in so many other cases throughout history, unintended consequences of policies led to severe deforestation.  Here I quote directly from Lutfallah Gari:

In Saudi Arabia the government wanted the tribes to be unified under one umbrella; hence it took the responsibility of management and security of the rural lands through governmental agencies. In 1954 a decree was issued designating the Ministry of Agriculture and Water as the custodian of the rural lands in this country. This created a new statute for the himā-s that became public lands. There was no immediate alternative conservation system. The first national park in the country (i.e. ‘Asīr National Park) was established in 1980. The National Commission for Wildlife Conservation and Development (NCWCD) was established in 1986. The period between the banning of the himī system and the start of constructing national parks and protected areas was a period characterized by severe destruction of the plant cover through overgrazing and felling of trees as well as over-hunting of wild animals… An estimated three thousand himā-s existed in Saudi Arabia in the 1950’s…A report issued by the NCWCD in 2003 mentions only four remaining that are called “old himā-s” that are managed by the Ministry of Agriculture, in addition to a few dozen himā-s that are still managed by local communities in “isolated” rural areas. The NCWCD report says: “Many of the traditional himā s as well as many terraces have been either abandoned or disappeared under fields that are suitable for mechanical cultivation. In some cases, this has replaced sustainable systems of land use with ones that require increasing inputs of water and management to maintain their productivity, but is has also markedly reduced the diversity of habitats” [45].

The effects of this policy are being felt acutely in the hijaz and many other rural areas of the kingdom.  When the Himas were disbanded and tribes lost the legal right to manage their land, A tragedy of the commons took place that resulted in massive deforestation, overgrazing, and environmental destruction that continues today.  This is compounded by a surging population (set to double to 50 million by 2035!), and along with it a surging demand for red meat.

The people in Al Baydha, where I work, are the prime subjects of this issue.  They have no legal right to manage their land, nor to prevent others from bringing their animals to graze when it rains in Al Baydha.  One man I know owns two hotels in Makkah and his hobby (like many of his compatriots) is to keep a large herd of camels, and go out on the weekends to camp, roast a goat, and drink camels milk.  When it rains in Al Baydha, he brings some 200 head of camels (worth an estimated 1.2 million USD) into Al Baydha to graze.  The people in Al Baydha welcome him because of their sense of hospitality, yet cannot maintain 20 head of goats on their land because of visitors like him.  They have no right to forbid others from coming and overgrazing their land, yet bear the full brunt of desertification’s consequences.

Conversely, because they do not own the land, they have disincentives to develop it.  There is a real risk that if someone manages land and tries to bring it back to productivity, that it will be seized by the government because that is who owns the land.  This scenario is the reality for thousands of rural communities throughout Saudi Arabia–they cannot manage the land, and if they begin to improve it, it could be seized from them.  In Al Baydha, they have responded by cutting down trees to be sold as charcoal in Makkah.  In turn, the trees’ ecological services are lost, and the cycle of desertification intensifies and progresses more rapidly.

As recently as 40 years ago, this was a forest, with trees so big "you could not reach your arms all the way around them."  as related by Abdul Rizaq al Aduani, pictured above.

As recently as 40 years ago, this was a forest, with trees so big “you could not reach your arms all the way around them.” as related by Abdul Rizaq al Aduani, pictured above.

Thus we see the interplay of policies, unintended consequences, the collapse of a traditional land management system, and as a result, massive desertification, loss of productivity, and a collapsing way of life for many rural peoples in Saudi Arabia.  Without exception, every person I talk to in this country who is older than 50 years old has fond memories of visiting a green, lush wadi, filled with date palms, jujubes, acacias, fish,  running water, or forest.  When they revisit these areas now, they are dry, dead, treeless, and prone to flooding.

As the land dies, it becomes more and more difficult to bring it back.  Soil life dies, erosion increases, and the land’s ability to absorb water ebbs away.  As plant life decreases, soil temperatures increase, making it even harder for plants to become established.  Finally, the 3 main impediments to rainfall–dust, high temperatures, and the lack of particles that form ice nuclei and clouds, dominate the climatic situation.  The water cycle becomes erratic and unhealthy, and the mineral cycle ceases to function as even bacteria cannot decompose plants or animals because of the dryness.

This is the reality for much of the Arabian Peninsula.  People have been the catalyst for desertification in many cases throughout history–in the fertile crescent, on Easter Island, in the western United States, China, and much of Africa.  This is now the case in the Arabian Peninsula today.  In the next few posts, I will go into more detail on the water and mineral cycles, after which we will get into the solutions of these problems–how people can also be the catalyst for regeneration of their land, their environments, and their economies.

More Resources:

On The Hema:

From King Abdulaziz University

A downloadable PDF in Arabic, French, and English

Omar Lutfi’s “Ecology in Muslim Heritage”

Google Books Sources: