At the global level, as the climate has been changing, the amount of vegetation in arid areas has been increasing. But scientists at the University of Copenhagen, Denmark, have, following analysis of 15 years’ worth of satellite imagery of vegetation and rainfall, identified a worrying trend: vegetation in arid areas in poorer developing countries is declining. It is vegetation in arid areas of richer developing (or emerging market) and developed countries that is increasing.
Arid regions comprise more than 40% of the globe’s ecosystems. Although the animals and plants within these regions are adapted to their savannah or desert environments, where water resources are scant, they are seen as very vulnerable to the effects of climate change. The study was conducted in such a way as to account for different quantities of rainfall in the different regions at different times, during the period 2000 to 2015, thereby giving a uniform basis for comparison. The study, which covered Africa, Australia, India and south-west Asia, Mexico and the south-west US and South America, looked at the differing amounts of vegetation that grew in these regions, in response to the same levels of rainfall.
“We observe a clear trend of arid areas developing in a negative direction in the most economically challenged countries,” reported University of Copenhagen Department of Geosciences and Natural Resource Management Professor Rasmus Fensholt. “Here, it is apparent that the growth of vegetation has become increasingly decoupled from the water resources available and that there is simply less vegetation in relation to the amount of rainfall. The opposite is the case in the wealthiest countries.”
The structure of the study makes it easier to identify human impacts on these ecosystems, and establish whether or not their exploitation is in balance (that is, not being overexploited) or if they are indeed being overexploited (which could cause irreparable damage to an ecosystem). “[O]ur results demonstrate that in arid regions, particularly those in Africa and Asia, less vegetation grows for the amount of rainwater that falls, while more vegetation grows in arid areas of South America and Australia,” highlighted Department of Geosciences and Natural Resource Management postdoctoral student and study lead author Christin Abel.
In India and south-west Asia, 37% of the arid areas showed vegetation growth declining relative to rainfall, and only 4% increasing relative to rainfall, while 59% retained a balance between water resources and vegetation growth. In sharp contrast, in South America (more specifically, Argentina, Bolivia, Brazil and Paraguay) only 7% of arid areas registered a vegetation decline while 31% saw an increase and 62% remained in balance. Note that relative vegetation increases were observed in all four of these South American countries, not just in rich Argentina and Brazil. In Mexico and the south-west US, 14% of the arid area saw a decline in vegetation, 13% experienced an increase and 73% was in balance. In Australia, 5% of arid land suffered a decline in vegetation, 19% benefited from an increase and 76% stayed in balance.
For Africa, 24% of the arid areas registered vegetation growth declining relative to rainfall, and only 8% increasing, while 69% remained in balance. The map published with the study report shows Kenya as one of the worst affected countries. South Africa, Morocco, Algeria and Tunisia, despite their relative wealth, are closer to the other African countries than they are to the similarly wealthy South American States. (South Africa does display some arid areas with increased vegetation growth.) Namibia is the country which seems to have a proportionally greater extent of increased vegetation growth than any other in Africa.
A possible explanation for the divergence between the richer and poorer developing countries could be rapid population growth in the latter, while the former are developed (and so rich) enough to be able to practise modern efficient agriculture, including fertilisers and use of irrigation systems. Certainly, the former seem to be coping better with the effects of climate change.
“We have been pleased to see that, for a number of years, vegetation has been on an upwards trend in arid regions,” pointed out Fensholt. “But if we dig only a tiny bit deeper and look at how successfully precipitation has translated into vegetation, then climate change seems to be hitting unevenly, which is troubling.”