Potential future changes in water limitations of the terrestrial biosphere

Abstract

This study explores the effects of atmospheric CO 2 enrichment and climate change on soil moisture (W r ) and biome-level water limitation (L TA ), using a dynamic global vegetation and water balance model forced by five different scenarios of change in temperature, precipitation, radiation, and atmospheric CO 2 concentration, all based on the same IS92a emission scenario. L TA is defined as an index that quantifies the degree to which transpiration and photosynthesis are co-limited by soil water shortage (high values indicate low water limitation). Soil moisture decreases in many regions by 2071-2100 compared to 1961-1990, though the regional pattern of change differs substantially among the scenarios due primarily to differences in GCM-specific precipitation changes. In terms of L TA , ecosystems in northern temperate latitudes are at greatest risk of increasing water limitation, while in most other latitudes L TA tends to increase (but again varies the regional pattern of change among the scenarios). The frequently opposite direction of change in W r and L TA suggests that decreases in W r are not necessarily felt by actual vegetation, which is attributable mainly to the physiological vegetation response to elevated CO 2 . Without this beneficial effect, the sign of change in L TA would be reversed from predominantly positive to predominantly negative.

Global effects of doubled atmospheric CO2 content on evapotranspiration, soil moisture and runoff under potential natural vegetation

“…Costa & Foley, 1997;Cao & Woodward, 1998;Neilson & Drapek 1998). The magnitude of the CO 2 effect as simulated by the LPJ model is also in good agreement with experimental findings (see Introduction) and with field observations (Gerten et al, 2005a), although the results presented here may be exaggerated in some regions, for example because limitation of availability of nutrients such as nitrogen is not taken into account (for a detailed discussion see Gerten et al, 2006). It has to be stressed that the simulated CO 2 effects vary in sign and magnitude between different regions and are, in some areas, much more pronounced than the global average suggests (see Figs 1 and 2); this response pattern is relevant when assessing what consequences elevated [CO 2 ] may entail for different world regions.…”

“…Firstly and most importantly, an increase in [CO 2 ] will be necessarily accompanied by changes in the climate, which will surely modify the hydrological CO 2 effects. The CO 2 -induced reduction in g pot is shown by Gerten et al (2006) to be offset in many regions by enhanced atmospheric demand as a result of higher temperatures, which increase transpiration, deplete soil moisture and also increase limitation of plant function by water availability. However, in other regions, the CO 2 effect may even be amplified by climate change.…”

“…The following paragraphs briefly describe the way the main components of the water balance are computed. For a more detailed account see Gerten et al (2004Gerten et al ( , 2006.…”

A brief overview of the causes, impacts and amelioration of soil water repellency - a review

“…A shortage of usable groundwater has arisen not only because of the depletion of reserves but also salinisation and pollution. As the amount of water that can be exploited is declining, climate change models predict that soils will be much drier in summer months by 2070, particularly in northern temperate latitudes (Gerten et al 2007).…”

Vulnerability and adaptation in a dryland community of the Elqui Valley, Chile

“…These changing conditions are expected to affect natural resources and human livelihoods in many regions. In particular, water resources are highly sensitive to climate variability and change with implications for water-dependent communities and sectors (Miller et al 1997;Arnell 2004;Gerten et al 2007). The vulnerability of communities to climate change is influenced by the ways in which they are affected by climate conditions and by the manner in which they can moderate effects or risks through adaptive strategies (Adger 2006;Füssel and Klein 2006;Smit and Wandel 2006).…”