Image Source: Jana Skokan, Be ready - Water Cycle Restoration & Rainwater Harvesting for Municipalities.
When it comes to talks about water and climate, something gravely overlooked is the water cycle itself. We tend to see water as different parts of a whole: either as stormwater that needs to be controlled, rainwater that can be harvested, flood waters that need to be pumped out of cities, or freshwater that is used for drinking and day-to-day needs. But if we want to solve climate change and increase our freshwater supply, we have to begin thinking and acting like water as a whole: as a water cycle.
In the article by Alpha Lo on the “Map of the small water cycle” (30 May 2024), he talks about the most underrated yet critical piece in the water sustainability puzzle: micro-water cycles or what he calls “moisture recycling.” Moisture recycling is the concept of recycling evaporated water over and over again to return as much moisture back to the water cycle in the form of rain, also known as rainfall recycling. The dutch hydrologist Hubert Savenije and his student Ruud van der Ent have taken on studies which show that moisture recycling actually increases freshwater supplies.
“Globally, recycled moisture multiplies our fresh water resources by a factor 1.67, but locally this can amount to a factor three (e.g., the Río de la Plata basin in South America), or even a factor ten in western China.”
Yes, you heard it! We can increase freshwater supplies globally simply by focusing on the evaporation-precipitation relationship of water in the water cycle.
“We conclude that continental moisture recycling plays an important role in the global climate…. we have stressed the fact that all water that evaporates eventually precipitates: what goes up must come down. Although this is popular knowledge, in hydrology this idea is not mainstream. In most water resources studies evaporation is considered a loss to the system. In addition, precipitation is often merely seen as external forcing.”
Evaporation, unlike precipitation, isn’t as visible to the naked eye. And what isn’t visible is usually taken for granted. But the idea that the semi-invisible moisture from evaporation is critical to our water security unlocks a whole new approach to sustainable water management. So how do we recycle this evaporated moisture?
Simple: By focusing on land use practices that maximize groundwater infiltration and reduce stormwater runoff.
“Recent research demonstrates that impacts resulting from land-use change are more important than the greenhouse effect to explain regional climate change, occurrence of droughts and desertification.”
This just goes to show that changing the naturally intended use of land can have drastic repercussions on the moisture recycling of an area. But equally empowering is the knowledge that we can change land use for the better if we engineer our land to maximize moisture recycling. Looks like carbon capture isn't the only ally in the climate change arena: enter in moisture recycling.
“In this light, it is remarkable that in the international research environment so little attention is paid to the analysis and quantification of moisture feedback processes, whereas enormous research efforts are dedicated to global warming and GCM predictions, which will not yield any tangible actions to be taken locally. The problem of desertification, however, having its cause in local anthropogenic influences on the land-atmosphere interaction, can be addressed by local and regional management actions. ...Land use practices that minimize runoff, and hence maximize moisture feedback, do not only prevent erosion and nutrient losses, but they also sustain continental rainfall.”
The topic of climate change and global warming is usually addressed as a global problem and consequentially, restrict or limit local actions. But the idea that the way we use land can actually be a climate solution when designed with the intention to increase moisture return into the atmosphere and reduce stormwater runoff is a game changer. We can now more concretely begin to address global problems on a local scale – beginning with land.
To design and use land with the idea of moisture recycling in mind, we must think like the water cycle. Therefore, to recycle more moisture, the following need to be taken into consideration:
To increase evaporation: plants, trees and green spaces should be present to induce evapotranspiration (evaporation of water from soil + transpiration of water through the leaves of a plant)
To decrease stormwater runoff:
Use permeable surfaces that infiltrate water back into the ground (try substituting cement, concrete, and conventional construction materials with more permeable and porous pavement and greenery)
Limit use of chemical pesticides, insecticides and fertilizers especially on agricultural land which destroy the soil’s microbiome and induce heavy flooding
Keep soil moist with groundcover (exposed bare soil results in cracking and acts like cemented pavement, increasing stormwater runoff)
In other words, nature is an asset, not just an aesthetic. With more greenery and mindful urban design, we can optimize moisture recycling to increase our rain and freshwater supplies. By telling the story that land use affects moisture recycling, what we’re really saying is that global issues can be addressed on a local scale. Now, the control of global problems has been shifted to a much local and practical scale. We have the power to help turn the tide against climate change and the water crisis – if we design and use land with moisture in mind.
To learn more about moisture recycling, read on here:
Key Findings of the Study by Savenjie and Van der Ent (2010):
1. The way we use our land affects the amount of rain we get in return
2. The way we use our land affects the amount of rain neighboring countries get in return
3. We can design and use land to increase moisture recycling
4. Most of the rain we get in the PH (~90%) comes from oceans, ~10% comes from evaporation from land
References
Lo, Alpha. "Map of the small water cycle." Climate Water Project (2024).
Van der Ent, Rudi J., Hubert HG Savenije, Bettina Schaefli, and Susan C. Steele‐Dunne. "Origin and fate of atmospheric moisture over continents." Water Resources Research 46, no. 9 (2010).
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