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Deserts Will Confront Growing Pressures in Coming Decades

The impacts of changes in precipitation and temperature patterns due to global climate change will be highly variable from one region to the next, but they are likely to be felt the hardest in desert margins and in desert montane areas, as these are where the principal arid rangelands are located. Because deserts are driven more by climatic pulses than by average conditions, even moderate changes in precipitation and temperature may create severe impacts by shifting the intensity and frequency of extreme periods, and subsequently creating catastrophic effects on plants, animals, and human livelihoods.

Climate change is expected to affect less the total amount of available water, and more the overall water regime and the timing of water availability in deserts. Deserts and desert margins are particularly vulnerable to soil moisture deficits resulting from droughts, which have increased in severity in recent decades and are projected to become even more intense and frequent in the future. Conversely, flood events are expected to be fewer but more intense, in which case less moisture would infiltrate into soils, and run­off and eroded sediment would concentrate in depressions, reinforcing the patchiness of desert ecosystems.

Deserts fed by melting snow or ice, such as the deserts of Central Asia and the Andean foothills, will be particularly vulnerable to a changing climate. As the volume of snowpack diminishes, river regimes will change from glacial to pluvial and, as a result, total run-off is expected to increase temporarily and then to decline. Peak discharges will shift from the summer months, when the demand is highest, to the spring and winter, with potentially severe implications for local agriculture. Growing populations in deserts and accompanying aspirations for improved standards of living, will very likely increase water demand in expanding urban areas. The deterioration of both surface and groundwater resources by agrochemicals, mostly pesticides and fertilizers used in irrigated agriculture, and increasing salinity of return flow, are likely to continue into the future. Seawater intrusion into groundwater caused by sea level rises resulting from global warming may further deteriorate the quality of underground aquifers. Desert margins, oases, and irrigated lands within deserts have a higher biological potential and are subject to increasing population pressure, and thus tend to constitute potential hotspots of degradation. Land use will continue to intensify in the desert margins while expansion of croplands into deserts will be limited, except where fuelled by irrigation. Grazing by livestock and cutting of firewood will continue to increase inside deserts, but mostly concentrated in montane areas and on the desert margins.

A decline in the rate of expansion of irrigated areas is expected in the next decades, together with increased investments in drainage to fight salinization. This would still not be enough to stop the advance of this serious problem in potential degradation hotspots including the Nile delta, the Indus, Tigris and Euphrates, and northern Mexico. A considerable amount of unsustainable irrigated land will go out of production as aquifer exhaustion progresses, and new opportunities for rehabilitation of degraded lands and sustainable pasture management systems will emerge.

Piecemeal development of infrastructure, such as road networks, will occur more in desert sky-islands and, again, in desert margins. Desert wilderness areas (any area located more than five kilometres away from any infrastructure) are expected to decline from 59 per cent of the total desert area in 2005 to a low 31 per cent by 2050, a decline of 0.8 per cent per year on average. Species such as desert bighorn sheep (Ovis canadensis), Asian houbara bustards (Chlamydotis macqueenii) and desert tortoise (Gopherus agassizii), that are sensitive to fragmentation of habitat or poaching, induced by inreased access to the areas previously not accessible to people, will be affected significantly by this change. Relatively pristine natural rangelands inside deserts may decline by 1.9 per cent annually, and wetlands at an even higher pace, under pressure from irrigation and agricultural expansion. At greatest risk are the few patches of dry woodlands associated with desert montane habitats, which may decline by up to 3.5 per cent per year.

Currently, the desert biome holds on average an abundance of original species of 68 per cent, but the rate of biodiversity loss in deserts may double in the coming decades. A decline in original species to a mean of 62.8 per cent by 2030 and 58.3 per cent by 2050 is expected, as a result of the new pressures and impacts brought forward by agriculture and human land use (41 per cent of the loss), fragmentation associated with infrastructure (40 per cent), and climate change (6 per cent in 2000 and 14 per cent by 2050).

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