Development Aspects Impressum Editors

Key components of natural water infrastructure

The following are illustrations of some components of ecosystems with key func- tions as water-related infrastructure. However, the interconnected nature of the water cycle means that identifying manageable elements of the ecosystem is, in fact, a matter of scale. Most considerations for natural infrastructure are at the ecosystem, that is landscape, level.

1. Plants as land-cover

Plants covering the land surface perform numerous functions, including contribut- ing (through their roots) to soil water infiltration and stabilizing soils, and thereby regulating soil erosion, and through water transpired through their leaves, etc., contributing to humidity levels and thereby regulating local and regional climates. In many areas, particularly the humid tropics, the bulk of rainfall actually arises (or is being recycled) locally through plants. Forests are often the most widely recognized land cover (infrastructure) type and are widely used to protect water supplies. Other land-cover types, such as grasslands, however, can perform similar functions. Depending on the objectives, the land cover does not necessarily need to be “natural”. Agricultural crops should also be considered, and managed better, as potential infrastructure. The agriculture–water dialogue is currently dominated by the irrigation debate, in itself an important topic, but there is a great need to focus also on how better management of crops as land cover can be part of the solutions to better water management in the broader landscape.

The majority of the water recycled by plants is recharged (one way or another, and as for most water) through precipitation. There are, however, examples of ecosystems in which plants are directly the original source of recharge of water, including in some cases being the only source: an example is some coastal de- sert areas that depend almost entirely on plants capturing water from humidity (via condensation), which would otherwise not fall in that area via precipitation; tropical “cloud forests” function similarly, but in this case condensation in the tree canopy is not the major source of water.
It is important to note that because it is widely (mis)understood that plants “use” water (through transpiration) it can often be assumed that removing them increases water availability for other purposes. The evidence, in fact, strongly dis- credits this notion (although this is very much case specific). Removing land cover can reduce soil water infiltration and accelerate evaporation from land: desertifica- tion, for example, is a phenomenon driven in part by the degradation of land cover through, for example, overgrazing of livestock.

2. Soils

What happens in the below-ground part of the water cycle, in terms of manage- ment, is very often a case of “out of sight out of mind”. Groundwater usually re- fers to water stored deeper underground, for example in aquifers, whereas “soils” refers to the thin and biologically active surface layer of the land. Soils play a very significant, and often underestimated, role in the water cycle and should be man-

aged as such. The life associated with soils (soil biodiversity) is usually naturally extremely diverse, even in natural deserts, ranging from larger animals such as mammals (moles) and earthworms, through to microscopic bacteria and fungi. These function collectively to support soil health, including regulating (together with land cover) how water enters and stays in the soil (soil moisture) and thereby enables soils to function properly as aquatic systems, and so underpinning other soil ecosystem services, such as erosion regulation, nutrient cycling and carbon storage. Among other things, soil functions underpin the entire world agricultural (and forestry) production and therefore food security. Sustaining soil functionality is therefore a major aspect of water security for food security.

The actual amount of water stored in soils, or rather recycled slowly through soils, is globally and locally significant. Soil is also partly, together with other sourc- es, responsible for recharging groundwater. Degrading soils by, for example, over disturbing them, removing land cover or over applying chemicals essentially results in the loss of these functions and benefits. However, maintaining or restoring this natural infrastructure of soils offers significant opportunities to manage water bet- ter, not just for crops, but also for other benefits in the landscape setting.

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