A Novel Method for Woodland Water Resource Management
taylorvich writes:
https://phys.org/news/2024-03-method-woodland-resource.html
Vegetation plays a vital role in regulating the percentage of precipitation reaching the ground to nourish the root systems of plants both in the canopy and undergrowth, which consequently supports the survival of the entire forest ecosystem. Water arrives to the ground via multiple mechanisms, including throughfall (water falling directly through the canopy) or stemflow (water flowing down stems and trunks), while some is intercepted by the canopy leaves and does not reach ground level.
New research, published in Water Resources Research, has focused on pour points, locations where water flowing under the branches detach. These are distinguished from the large drops falling from leaves, known as drip points.
A pour point is formed when the raindrops, initially intercepted by leaves or the top half of the branch, flow to the underside of branches, coalesce with other droplets to form a rivulet, but fall before becoming a part of stemflow.
The detachment of the rivulet can occur where multiple branches converge or where a single branch changes in angle, leading to a pour point. These are important as they considerably increase water received from the canopy to the forest floor at fixed points, thereby supporting enhanced infiltration of water to the ground.
The volume of water received at pour points is impacted by a number of factors, such as the structure of the branches, leaf surface area (foliation), and the volume of rainfall. The larger water droplets occurring at these points have more kinetic energy than normal rainfall, meaning that they create more pronounced dips in the soil upon impact, thus augmenting infiltration efficiency.
[...] Measuring the water content of soil directly below pour points, the research team found 20%-30% of the seasonal rainfall volume infiltrated to a depth of 1 m here, compared to just 5% in control test areas away from pour points. This makes pour points important zones for groundwater recharge and storage in the forest ecosystem, although in the study site one pour point was identified per ~30 m2, matching the distribution of banksia trees, being one pour point per tree on average.
This particular study site in Western Australia is important as it overlies a significant source of groundwater that supplies the population of Perth. Therefore, the ability of pour points to potentially recharge groundwater supplies at this site (and at others via other trees globally), is vital for supporting water resources management both for forests and humanity.
More information: Ashvath S. Kunadi et al, Introducing Pour Points: Characteristics and Hydrological Significance of a RainfallConcentrating Mechanism in a WaterLimited Woodland Ecosystem, Water Resources Research (2024). DOI: 10.1029/2023WR035458
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