Soil & Water

Soil & Global Warming

Surface Carbon Temperature Biota

The untold story of intensive 'western' agriculture' is how much water, often from elsewhere, it uses. Instead of capturing and utilising rainwater, water is pumped from aquifers and/or stored behind huge dams and piped countless miles to the point of use. This water is used to grow crops which are then transported - often by air - to countries with more than enough water. It's a prescription for drought and disaster. If we were to get serious about using our own rain to grow food, and encourage others to harvest rainwater, those landscapes would attract rainfall and hold onto rainwater.

The cultivation of these products requires water for irrigation, crop maintenance, and post-harvest processing. In many cases, water-intensive irrigation methods, such as sprinkler or drip irrigation, are used to support the growth of crops. The exact amount of water used varies depending on factors like crop type, farming techniques, and local water availability.

This use of water was coined as ‘Virtual water’ by Tony Allen, Prof of Geography at Kings College. It has been estimated that about 20 ‘Niles worth’ of virtual water is used in Africa each year to provide fruit and veg to Europe. I would like to thank Tony for all the help he gave me designing a Masters degree in Regenerative Farming for Plymouth University. He would always remind me of the key importance of water. Without it nothing grows.

WRI Aqueduct water report 25% of all crops are now threatened by water crisis

Global Commission on Economics of Water

Water Risk across world

Heat exchange

A significant proportion of heat transfer on this planet is via water. The greenhouse gases (GHGs) account for much less.

Many of the events which are said to be related with ‘climate change’ involve water - like flooding, droughts and fires. We’ll find how floods and droughts are interconnected.

The Earth's heat transfer facilitated by water, come through processes like evaporation, condensation, and ocean currents.

Key Ways Water Contributes to Heat Transfer:

Evaporation and Condensation:
- Evaporation: When water evaporates, it absorbs heat from its surroundings (latent heat), which cools the surface and transfers heat into the atmosphere. This process is a major way heat is redistributed, especially in tropical and subtropical regions.
- Condensation: When water vapor condenses into clouds or precipitation, the stored heat is released back into the atmosphere, warming it. This cycle of evaporation and condensation plays a crucial role in the global energy balance and weather systems.
Ocean Currents:
- Oceans act as massive heat reservoirs, absorbing heat from the sun and redistributing it via surface and deep-sea currents. These currents move warm water from the equator toward the poles and cold water from the poles toward the equator. This redistribution helps moderate global temperatures and is vital for regulating climate.
Water’s Heat Capacity:
- Water has a very high specific heat capacity, meaning it can absorb and store large amounts of heat without significantly changing temperature. Oceans and large bodies of water store solar energy and release it slowly, which moderates temperature extremes and plays a huge role in climate regulation.
Atmospheric Moisture:
- Water vapor in the atmosphere is also a significant greenhouse gas, contributing to the trapping of heat and regulating Earth's temperature through the greenhouse effect. It helps to prevent heat loss to space and keeps the planet's surface warmer than it would be otherwise.

Other Heat Transfer Mechanisms:

Conduction and Convection: Besides water, heat is also transferred through direct conduction (in solids, like the Earth's surface) and convection (in fluids, such as air in the atmosphere and magma in the Earth's mantle).
Radiation: The Earth gains energy from the Sun through radiation, and it also loses energy to space via infrared radiation.

Thus, while water (in its various forms—liquid, vapor, ice) plays a massive role in global heat transfer, other processes like atmospheric circulation, conduction, and radiation are also significant. The 90-95% figure likely emphasizes the dominant role of water in heat redistribution, especially through evaporation, condensation, and ocean currents, but the full picture is more nuanced.

Cycle

The hydrological cycle, or water cycle, is the continuous movement of water on, above, and below the Earth's surface and describes the processes by which water circulates through the air, the land, and bodies of water. The hydrological cycle moves between gas liquid and solid forms of water. involves several key processes, including evaporation, condensation, precipitation, and runoff.

Evaporation is due to heat from the Sun and causes water from oceans, lakes, rivers, and other bodies of water to evaporate and transform into water vapour. Part of this is evapotranspiration, where plants release water vapour through their leaves.

Condensation is where the water vapour that rises into the atmosphere cools down and condenses to form tiny water droplets, which gather to create clouds. This process occurs due to changes in temperature and pressure and when the water droplets in the clouds become too heavy to remain suspended, they fall to the Earth's surface in the form of precipitation, we call rain, snow, sleet, or hail.

Rain

When that rain reaches the Earth's surface, it may flow over the land as runoff, forming streams, rivers, and eventually making its way back to the oceans, or it may infiltrate into the ground to become groundwater. This is a vital part of the cycle, as the precipitation soaks into the ground and may be stored in porous layers of soil or rock, before replenishing surface water bodies. Or it may evaporate from the surface quickly.

Water that evaporates from the land and sea eventually returns to Earth as rain and snow. Global warming intensifies this cycle because as air temperatures increase, more water evaporates into the air. Warmer air can hold more water vapour, which can lead to more intense rainstorms, causing major problems like extreme flooding. While some areas are experiencing stronger storms, others are experiencing more dry air and even drought. As temperatures rise, evaporation increases and soils dry out. Then when rain does come, much of the water runs off the hard ground into rivers and the soil remains dry with still more evaporation from the soil. And the soil becomes warmer.

Through the water cycle, heat is exchanged and temperatures fluctuate. As water evaporates, for example, it absorbs energy and cools the local environment. As water condenses, it releases energy and warms the local environment. The water cycle is about temperature all the way through.

Forests

Plants also take up ground water through their roots, transport it to their leaves where transpiration through stomata occurs to release water vapour. Evaporation comes from the soil, so the two together are called evapotranspiration and provide the moisture for about 2/5 of all rainfall. Forest, water and energy interactions provide the foundations for cooling terrestrial surfaces and for distributing water resources.

Forests & Decisions

Forest-driven water and energy cycles are poorly integrated into regional, national, continental and global decision-making on climate change adaptation, mitigation, land use and water management. This constrains humanity’s ability to protect our planet’s climate and life-sustaining function….Our call to action targets a reversal of paradigms, from a carbon-centric model to one that treats the hydrologic and climate-cooling effects of trees and forests as the first order of priority" (Ellison et al 2017)

One study found that in temperate regions, forest cover contributed to cooling compared with cropland in most seasons. They said that “this can be added to the numerous other ecological benefits of afforestation"

They do this is a number of ways. 1. Trees, and other forms of vegetation, collect rain and spread the water about Cooling is explicitly embedded in the capacity of trees to capture and redistribute the sun’s energy. 2. Going through the tree the moisture rises along with volatile organic compounds and microbes, which create ‘precipitation triggers’ (yellow dots). trees’ microbial flora and biogenic volatile organic compounds can directly promote rainfall. 3. Forest-driven air pressure can be much stronger sending that moisture great distances 4. Water rising into the air condenses to produce clouds that deflect additional radiation from terrestrial surfaces, bouncing the heat back out. 5. Trees draw additional moisture out of the atmosphere when it is fog and cloud, putting moisture into the soil. Trees infiltrate water and recharge groundwater 6. They keep conditions more stable , so that along with all the rest, distribute water gradually moderating floods 7. Trees are increasingly being planted for 'carbon offsets', but they also provide these other benefits, particularly cooling.

Soil Sponge

These water/energy/temperature cycles have been disrupted by deforestation and agricultural practices that destroy the soil so that it can no longer hold water. The water holding capacity of the soil can be likened to a sponge. We can liken it further when we realise that original sea sponges are the elastic and absorptive skeletons (of glass-like material) of various sea creatures, such as the Spongia.

“The soil sponge (or “soil carbon sponge”) is a living matrix that soaks up, stores, and filters water; holds landscapes in place; and provides nutrients for an entire food chain, from what would otherwise be bare rock, hardened clay, and desert sands."

The term ‘soil-carbon sponge’ was coined in 2017 by Walter Jehne to demonstrate the capacity for healthy soils to cool the planet by restoring the water cycle and sequestering carbon. He often quotes the sponge being made of ‘springs’, that can be squeezed and extended, depending on circumstances and they have the control over water-holding. Anybody who has read this book will know that these are mechanical predictions of what we’ve seen evolving over the last 400 years, aggregates. The minerals and debris are glued together by springtail and mite poo. For lots of that there needs to be lots of bacteria and fungi. These aggregates are totally accidental constructs and must vary all the time with the various stresses put on.

Click graphiic for understanding soil porosity and water-holding capacity using sponges Cornell SIPS

2/3 volume of soil is empty. While there is this space, soil can hold water and air, and increase the availability of nutrients, all exposed to microbial activity which provides the food for the rest of the soil biosystem, Where roots go down further than 6inches, and the potential to create biosystems all depend on those voids. But to have these voids we have to have these resilient structures to hold them open. The size of pores determines how the soil structure behaves with water. Large pores allow water to go down, small pores hold it.

Water Holding

This soil structure enables water to be absorbed, that can be released at various rates later. We saw how this property started around 350mya and evolved into the soil texture and organic matter that are the key components that determine soil water holding capacity There are three main terms to describe soil moisture states - saturation (where all pores filled with water), field capacity (=amount of water soil can hold against gravity - lost from large pores but held by small) ) and permanent wilting point. (where still water but held so tightly roots cannot get the water).

based on studies that have examined the relationship between soil organic matter and water holding capacity in different soil types and regions. The relationship between soil organic matter and water holding capacity is not necessarily linear, meaning that the rate of increase may vary at different organic matter levels. Nevertheless, increasing soil organic matter through various practices does not just add nutrients but can significantly enhance the water holding capacity of soils, contributing to improved soil health. There should be a great deal more research on this.

There are several studies indicating that an increase in soil organic matter (SOM) enhances soil's water-holding capacity. you can find various amounts with differing soils. Specifically, a 1% increase in SOM can lead to a around holding an extra 20,000 litres per hectare.

General Relationship:

For every 1% increase in soil organic matter, the water-holding capacity of the soil increases by approximately 16,000 to 24,000 liters per hectare for every 30 cm (12 inches) of soil depth. This estimate can vary depending on soil type, structure, and climate, but it is a commonly cited range.

Sources:

NRCS (Natural Resources Conservation Service, USA): The NRCS has documented that increasing SOM by 1% can improve water retention by up to 24,000 liters (24 mm) per hectare for the top 30 cm of soil.
University of Nebraska: Research from the University of Nebraska shows that each 1% increase in SOM can increase the soil’s water-holding capacity by about 20,000 liters per hectare, depending on the specific soil type.
Journal of Soil and Water Conservation: In a study published by this journal, it was shown that for a 1% increase in organic matter, soils could store between 16,000 to 24,000 liters of additional water per hectare.

Mechanism:

Organic matter in the soil acts like a sponge, absorbing water and releasing it slowly over time, which increases water retention in the soil. This is particularly important in drought-prone areas.
Higher SOM improves soil structure by increasing pore space and aggregation, allowing soils to absorb and hold more water.

Variability:

The exact amount of additional water-holding capacity varies depending on soil texture (clay, loam, sand), local climate, and cropping systems. Clay soils may experience slightly lower gains, while sandy soils might see greater increases in water-holding capacity with improved SOM.

Thus, a 1% increase in soil organic matter can lead to an additional 16,000 to 24,000 liters of water being held in the top 30 cm per hectare of soil, which is a valuable figure for water conservation and sustainable agricultural practices.

hectare

Here’s how it works. The organic matter itself, decomposed plant and animal residues attract water, acts as a sponge, just like the original sea sponge. Soil structure by binding soil particles together with the glue poo creates the pore spaces or aggregates in the soil, allowing for better water infiltration and retention so the pore spaces act as reservoirs. This is referred to as soil’s porosity. Larger bits of organic matter form larger stable aggregates that create larger and more interconnected pores. These enable movement of water between smaller pores, so reducing runoff. The smaller pores - Micropores - hold water against the force of gravity, while Macropores facilitate drainage and aeration. It all adds up. This ability of soil to hold water is determined by its total pore space and the size distribution of those pores and is called the water holding capacity. Organic matter contributes to the formation of micropores (small-sized pores) and macropores (large-sized pores), which affect the soil's ability to retain water.

The concept of increasing soil organic matter (SOM) to improve water-holding capacity (WHC) and potentially mitigate global warming has been explored, but the calculations and analysis you are referring to are relatively complex and less commonly discussed compared to carbon sequestration's role.....

While enhancing the water-holding capacity of soil by increasing SOM could theoretically reduce global warming through mechanisms like reduced irrigation energy use and increased evapotranspiration cooling, it is a complex area that hasn't been widely studied in isolation. More modelling and research would be needed to calculate the precise impact on global temperatures. But here goes..
Soil Organic Matter and Water-Holding Capacity

When organic matter in the soil increases, it significantly enhances the soil's ability to retain water. On average, 1% of SOM can hold between 16,500 and 24,000 liters of water per hectare (depending on soil type), with 20,000 liters being a reasonable estimate. This enhanced water-holding capacity has multiple positive effects:

Improved Drought Resistance: It makes soils more resilient to drought by retaining moisture for longer periods, reducing the need for irrigation.
Reduced Evaporation and Surface Runoff: By holding water more effectively, soils with higher SOM lose less moisture through evaporation and runoff, leading to more efficient water use.
Climate Impact via Reduced Irrigation: Reduced need for irrigation can decrease energy use (e.g., pumping groundwater or desalination), leading to reduced CO₂ emissions associated with energy consumption.
Cooling Effect from Evapotranspiration: As soil moisture increases, so does plant growth and transpiration. Higher evapotranspiration from plants has a cooling effect on local climates, potentially lowering surface temperatures.
Soil Health and Productivity: Enhanced soil moisture improves agricultural productivity, which could help sustain ecosystems and food systems under climate stress.

Estimating the Global Climate Impact

While the carbon sequestration potential of increasing SOM has been widely studied, the cooling effect purely from enhanced WHC is less frequently quantified. Some studies estimate that global land management changes, such as regenerative agriculture and better soil management, could make a measurable contribution to mitigating climate warming, though primarily through carbon sequestration.

Water-Holding Capacity and Climate: Increasing SOM by 1% globally would increase the soil's WHC by approximately 20,000 liters per hectare. This could reduce irrigation needs and cool the atmosphere through increased evapotranspiration.
Potential Global Area Impact: With about 5 billion hectares of arable land and grasslands globally, increasing SOM by 1% could theoretically lead to an additional 100 trillion liters of water stored in soils globally. However, the direct impact of this water storage on global temperature is challenging to quantify without modeling the feedbacks, including changes in local climate systems, irrigation needs, and overall surface cooling due to enhanced plant transpiration.

Research Gaps

Despite the potential, this idea is less well-documented in terms of its direct contribution to mitigating global warming. Most soil-related climate strategies focus on carbon sequestration and less on water-related climate feedbacks, which are harder to measure and model globally.

Climate models would need to factor in localised cooling effects, changes in the hydrological cycle, and how these changes interact with broader weather systems. While this has been studied on a regional scale (e.g., drought resilience), it's less explored on a global scale for temperature reductions specifically from WHC increases.

Organic matter also affects the chemistry. It enhances the cation exchange capacity (CEC) of soil. High CEC soils generally have greater water holding capacity than low CEC soils. A higher CEC usually indicates more clay and organic matter.

And then there is the biological. We know that soil organic matter isn’t just lumps of carbon, but also microbes & fungi and moving carbon in the form of trillions of tiny creatures, chewin’, pooin’ and gluein’, that make the architecture that supports life underground.

FAO Global Symposium on Soil & Water 2023

Water-holding capacities of soil don't appear to be factored into any governmental initiatives to hold/sequester carbon on the soil and cool the planet down. We should be investing much more research into how the water, soil, temperatures and organic matter interact in all sorts of situations so that we can directly control soil surface temperatures in order to reduce global warming. Lots of small direct improvements all over the world could add up to a lot.

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