Mapping degraded lands with applied geospatial knowledge
Tuesday, February 13, 2018
Will the restoration of degraded lands come to the rescue of a world short on water, arable land and space — a world long on polluted water, unusable land and mouths to feed, young and old?
The short answer is that it depends. At least geoscientists are well on their way to quantifying the potentially restorable areas.
An oft-downloaded article from the journal Applied Geography finally wrestles with the challenge, for surveyors, scientists and others, of defining, mapping and quantifying degraded lands. The authors, H.K. Gibbs and J.M. Salmon, point out that estimates of all global degraded lands vary widely from less than 1 global hectare (Gha) to more than 6 Gha.
The paper's major theme: New mapping regimens and procedures, leveraged on satellite technology, will hasten new geospatial business applications for degraded lands. These will be designed to help businesses and/or government measure the degraded areas and then possibly restore some of them to a productive condition.
But it would also be quite easy to overestimate the potential of degraded lands. In many ways, the focus on using them distracts and lulls both scientists and citizens into complacency.
It implies that mankind can easily keep meeting its needs for agricultural products by swapping patches of earth. Whereas, even degraded lands can't offer the world a magical pathway out of abject and/or structural famine, misery, poverty and insecurity.
It is true that certain lands can be delineated and rated on their ability to incentivize economic activity upon them. But so much then depends on the location and quality of a host of inputs — such as energy and labor — that may be necessary to effect a net-positive result. Gibbs and Salmon warn that any focus on revivifying degraded lands necessarily distracts from efforts to reduce food and agricultural waste or satiate the world's appetite for new land-borne products.
At least the various assessment methods are evolving quickly. They can be grouped into four broad categories:
- expert opinion
- satellite-derived net primary productivity
- biophysical models
- mapping abandoned cropland
Just as the concept of "degraded lands" is perhaps too broad, conversely, each of the above methods offers information on only limited types of ground conditions. So, unfortunately, none of them can give a full picture of degraded areas.
Satellite-based measurements tend to provide more accurate and detailed information on both vegetation and soils. In which case, scientists can ease up on the mainstay of assessment so far: the expert opinion approach. Satellites' remotely sensed data provide the chance for them to vastly improve assessments in a consistent way.
The overall measure of land health that the U.N. Food and Agriculture Organization (FAO) used in its landmark, ongoing satellite-based study — "Global Assessment of Lands Degradation" (GLADA) — was net primary productivity (NPP). The study utilizes satellite-derived measures — collected from a space-based Advanced Very High Radiometer (AVHR) — as a proxy for NPP.
Initial GLADA results showed declining NPP over 21 percent of the earth's land area, primarily in tropical Africa, Southeast Asia, China, north central Australia, the Pampas and large belts of boreal forest in Siberia and North America. It must be duly noted, however, that 16 percent of global land area is increasing in NPP, including 20 percent of all cropland, 23 percent of all forests and 43 percent of all rangelands — softening the blow of degradation a little.
Among all the assessment methods' demerits, say Gibbs and Salmon, is the lack of a standard definition of degradation.
The biophysical and abandoned cropland approaches to assessment remain viable only in the limited way the first two methods are — that is, they cannot give a full picture of global degraded lands. Yet "the development of relevant and consistent definitions of degradation is increasingly important as we attempt to establish policy- and market-based incentives to encourage production on these lands."
Worldwide land scarcity, it appears, will continue to dictate improved understanding of the global land base. So will the need to develop policies around bioenergy and large-scale land acquisitions.
Gibbs and Salmon provide a starting point for considering the potential of degraded land. More significantly, they point to the urgent need for new approaches that will likely combine innovative satellite data analysis with the taking of extensive field inventories for years to come.
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