Land management and hydrology

The concept of hydrological drought (as distinct from meteorological drought) helps explain the success of these age-old techniques to enhance surface and groundwater supply. Meteorological drought is the occurence of abnormally low rainfall for a given region. Hydrological drought is a consequence of meteorological drought – it happens when surface and ground waters run low thanks to a prolonged rainfall shortage compared to historical conditions for a region. Human water consumption for irrigation, industry and household use intensifies hydrological drought [Wada 2013].

Yet, as seen in the examples above, proper land management can raise the water table in an area in spite of occasional episodes of meteorological drought. In other words, while we cannot directly control when and how much rain falls, we can manage what happens to water once it reaches the ground.

Rain falling on much of our modern built environment is managed with ditches, gutters, drains and sewers designed to whisk it away as quickly as possible, rather than absorbing it in place. Farmland too is sometimes fitted with underground “tiles” (pipes) to drain fields, or with dikes to keep water out. Moreover, by the very absence of design, nearly all conventional farmland is so lacking in organic matter that it can barely absorb rainfall, which instead runs off the soil surface carrying soil with it.

In short, water hitting the ground in today’s world moves quickly. Stormwater moves in torrents over land seeking an outlet. That is until the outlet is full, at which point the water stagnates, rising like a bathtub, soaking and rotting property.

Ironically, the water we seek to drain away when there’s plenty becomes desperately lacking after the rain has stopped. Two sides of the same coin, flooding and drought often go hand in hand. By the same token, because a surfeit of impervious surfaces is at the root of these twin challenges, the solution of turning more land into a spongy surface helps resolve both problems at once. Spongy surfaces slow down water, allowing it to percolate into groundwater reserves.

Ecosystem restoration creates a spongy land surface by protecting soil with vegetation, thus allowing the soil to repair itself with biodiversity and organic matter, key ingredients of a good soil sponge. And beyond fostering drought and flood resilience, healthy ecosystems serve a myriad of protective functions, including cooling their surroundings, cleaning polluted water, drawing down CO2, and harboring the biodiversity that is the magic making ecosystems perform so many vital functions.

However, because the services rendered by nature go widely unrecognized or taken for granted, nature’s power as an ally is often shackled.

Human societies tend to value the potential benefits that a landscape might provide in a limited way, adjusting management practices towards desired outputs by maximizing the benefits gained from one or some of the services (often the provision of goods) leading to the loss of multifunctionality and the degradation of natural capital at the expense of human welfare [Schindler 2014: 230].

An example of a landscape with undervalued ecosystem function is a river floodplain. Because floodplains are often favored for agricultural, industrial, commercial or residential uses, rivers are constrained to their channels and their banks leveed, despite that a river and its floodplains are members of a single interdependent ecosystem. Through seasonal pulses of floodwater over the banks, like a heart pumping blood through a body, a river replenishes groundwater and nutrients throughout its floodplains, making these areas some of the planet’s most productive and biodiverse ecosystems [Sparks 1995]. Consider, for example, that the Amazon Basin is a floodplain, where fish biodiversity actually depends on riparian forest cover [Arantes 2017]. Fish swim into flooded forests during flood pulses and directly consume terrestrial floodplain vegetation (seeds, fruits, detritus).

In addition to supporting robust biodiversity, floodplain ecosystems give water somewhere to go during severe flooding events rather than damaging cropland, houses or other properties. By allowing water time to infiltrate into the ground, floodplains recharge groundwater, thus alleviating future droughts [Opperman 2009]. Riparian ecosystems also serve as a migration corridor for birds and fish especially, and also as a refuge from the heat of more exposed areas.

In other words, intact river-floodplain ecosystems perform multiple ecosystem services and thus help us manage some of our most pressing societal problems if only we acknowledge the value of floodplains in these terms.