Australia does not suffer from a lack of rainfall. What we suffer from is a failure to capture it. Most rain falls in small, frequent events that wet the soil and then evaporate, never reaching dams or rivers. Climate change is increasing evaporation and raising the rainfall threshold required for runoff. This article explains why traditional water systems are failing, how vast quantities of water are wasted, and why community-based water harvesting using soil, percolation, and local storage is essential for long-term resilience.
Living With Uncertainty
We live in an age of uncertainty. No one knows exactly how climate change will unfold, how fast it will progress, or how severe its impacts will be. Some people believe the problem is exaggerated, others believe it is already out of control. What matters is that the risk is real enough that ignoring it is reckless.
In the short term there is little we can do to reverse the forces driving climate change. What we can do is adapt. The greatest immediate threat most communities face is not temperature itself but water scarcity. Longer dry periods interrupted by intense but irregular rainfall events are becoming more common, and this pattern undermines traditional water systems.
Governments reassure us that water supplies are secure and that planning is underway. To some extent this is true, but the era in which governments could guarantee abundant, cheap, centrally supplied water is coming to an end. The future requires a different approach.
The Real Problem: Rising Runoff Thresholds
The core issue is not simply how much rain falls, but how much rain is required before runoff occurs. Hotter temperatures and stronger winds increase evaporation. Dry soils absorb more water before becoming saturated. As a result, rainfall that once flowed into streams and dams now disappears into the soil and atmosphere.
Historically, a rainfall of around 20 millimetres might have generated runoff in many catchments. Today, that threshold may be 50 millimetres or more. In the future it could approach 100 millimetres. This change alone can drastically reduce the amount of water captured by dams.
This effect is rarely discussed in public debate, yet it explains why dams remain empty even after rain. Our water infrastructure was designed for a different climate and different soil conditions.
Climate Change Amplifies the Losses
Even if total rainfall does not decline significantly, climate change still reduces effective water capture. Increased evaporation means less water reaches storage. Modelling shows that relatively small increases in evaporation can halve dam inflows. Combine this with reduced rainfall and effective water availability may fall to a quarter of previous levels.
This is why relying solely on dams and large catchments is increasingly dangerous. These systems depend on rare, high-intensity rainfall events, which are becoming less reliable.
How Much Water Actually Falls
If the total rainfall over Australia is divided by the population, the result is astonishing. On average, close to one million litres of rain falls per person per day. This is many thousands of times more than we need for drinking, sanitation, and food production.
The problem is not lack of supply but the way rainfall is distributed and harvested. Most rain falls as small or medium events that never contribute to runoff. Our infrastructure ignores this water entirely.
The Opportunity in Small Rains
Small and medium rains occur frequently, even during droughts. These rains are far more reliable than the large storms we depend on to fill dams. Harvesting these rains across a wide area offers far greater security than chasing rare extremes.
The technologies required already exist. What is missing is the social and institutional willingness to deploy them at scale. This is not primarily an engineering problem. It is a governance and mindset problem.
Rethinking the Role of Dams
Dams are still useful, but their role must change. Instead of supplying everyday water, they should be treated as strategic reserves for prolonged dry periods. Routine water use should be supplied locally wherever possible.
The danger is political short-termism. When heavy rain finally fills dams, restrictions are lifted and complacency returns. This cycle guarantees future crises.
Micro Dams and Percolation Holes
Micro dams are deliberately designed to be temporary. They are not meant to store water on the surface. Their purpose is to slow water long enough for it to soak deep into the ground, where it is protected from evaporation.
Percolation holes beneath roads, drains, and channels allow runoff to recharge soil and shallow aquifers. Globally, the amount of water stored in soil far exceeds the volume stored in dams and lakes. Soil is the largest water reservoir we have.
When water is later drawn from a dam or bore, surrounding groundwater slowly moves back toward the extraction point. This natural recharge can dramatically extend usable supply.
Using Roads as Water Catchments
Urban roads collect enormous volumes of water. By modifying drainage systems to encourage infiltration rather than rapid discharge, this water can be stored underground instead of being lost to the ocean.
This water does not need to be drinking quality. It is perfectly adequate for irrigation, gardens, and general cleaning. Treating all water to potable standards is unnecessary and wasteful.
Catching Water in Vegetated Land
Water harvesting is not limited to urban areas. Percolation holes and micro dams can be used throughout vegetated landscapes. Australia lacks large mountain catchments but has vast areas of land that can function as distributed water storage.
Only a small percentage of soil volume needs to hold water to create massive storage capacity. The challenge is ensuring water penetrates beyond the evaporation zone.
What Happens After Rain
After a light rain of less than 10 millimetres, water is absorbed into the surface soil and evaporates. There is no runoff. Medium rains between 10 and 50 millimetres often produce scattered puddles that never connect into streams.
As rainfall increases, small flows form and then disappear as the water reaches flatter ground. Australia is full of these ephemeral creeks that start and stop. Shortly after rain ends, the remaining water evaporates.
Rainfall Per Person
When viewed per person, Australia’s rainfall is immense. The fact that we experience water shortages is not due to scarcity but to failure of capture. Coastal regions, where most people live, receive reliable medium rains even during drought. These are precisely the rains we waste.
The Insulating Soil Crust
In arid and semi-arid regions, the top layer of soil forms an insulating crust that protects deeper moisture from evaporation. Desert plants survive because of this. However, that crust must first be wetted before water can move deeper, and the water used to wet it is usually lost.
Percolation holes bypass this loss by directing water straight into deeper layers.
Wicking Beds: From Storage to Irrigation
Wicking beds began as a simple attempt to store water locally. Their broader implications were not immediately obvious. My involvement began in Ethiopia, where famine was driven not by lack of rain but by erratic rainfall timing.
Crops could look healthy, then fail completely after just a short break in rain during seed development. The solution was short-term local storage.
The earliest wicking beds were simple channels lined with plastic and refilled with soil. Later, pipes were added to distribute water efficiently. This eliminated the need for high flow rates and reduced losses.
Water Amplification
By extending the plastic liner beyond the bed itself, rainfall can be funnelled into the base of the bed. This captures even small rains and protects them from evaporation. Larger rains are also retained instead of draining past the root zone.
Grey Water and External Sources
Most wicking beds still rely on some external water. Grey water can provide a steady supply, but plant demand varies. Oversupply during wet periods must be avoided, and dilution is essential to manage alkalinity.
Why Productivity Improves
Wicking beds often outperform conventional beds. Roots are wetted from below, drawing air down as water is used. A moisture gradient forms, ensuring roots always have access to an optimal balance of air and water.
Successful beds also require better soil construction, often including organic matter and biological inoculants. This combination creates healthy, resilient soil.
Scaling Up
Initially seen as a home-garden solution, wicking beds can be linked and cascaded for larger systems. On sloping land, contour-aligned beds with cut-off valves can replace inefficient flood irrigation.
Anticipatory Irrigation
Anticipatory irrigation means applying water before stress occurs, often immediately after rain, when evaporation losses are lowest. The goal is to refill the soil profile efficiently.
There is always a threshold volume required before water penetrates deeply. Applying too little repeatedly wastes water. Applying enough at the right time reduces losses.
Measuring What Matters
Soil moisture probes measure local conditions but do not show total wetted volume. The key is to measure how much water is required to refill the profile, just as you would fill a jar of stones rather than calculate empty spaces.
Learning Through Feedback
By estimating crop water use, applying water, and adjusting based on results, systems can be tuned accurately. Software tools can simplify this process using predictor-corrector methods.
Conclusion
Australia’s water crisis is not caused by lack of rain. It is caused by systems that ignore small, reliable rains and rely on rare extremes. Community-based water harvesting using soil, percolation, and local storage offers resilience in an uncertain climate. The choice is not whether change will occur, but whether it will be intelligent.
