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

Abstract

Rising atmospheric CO 2 concentration affects the water balance through climatic changes and through changes in transpiration, vegetation structure and distribution. This study quantifies CO 2 effects upon evapotranspiration, soil moisture and runoff under conditions of potential natural vegetation globally, using a biosphere model forced by observed climate . Isolated CO 2 impacts were inferred from a 2 × CO 2 scenario, assuming no climate change. Global effects are moderate: evapotranspiration reduces by 7%, whilst runoff and soil moisture increase by 5% and 1%, respectively. But the effects vary regionally and seasonally, owing to the complex interplay between water and vegetation dynamics. For example, reduced leaf-level transpiration is outweighed by increased transpiration resulting from enhanced vegetation cover in semiarid areas; and seasonal transpirational water savings result in year-round increases in soil moisture in boreal regions. Overall, CO 2 effects impart significant variability to hydrological processes at all scales, so they merit consideration in assessments of future water resources.

Resistance and Resilience of A Stream Salamander To Supraseasonal Drought

“…Although studies with equilibrium vegetation models suggested that increased leaf area may offset stomatal closure (Betts et al, 1997;Kergoat et al, 2002), studies with dynamic global vegetation models indicate that the effects of stomatal closure exceed those of increasing leaf area. Taking into account CO 2 -induced changes in vegetation, global mean runoff under a 2×CO 2 climate has been simulated to increase by approximately 5% as a result of reduced evapotranspiration due to CO 2 enrichment alone (Leipprand and Gerten, 2006;Betts et al, 2007). [WGII 3.4.1]…”

Hydrological and vegetation response to climate change in a forested mountainous catchment

“…The water cycle controls the distribution and productivity of terrestrial vegetation (Stephenson 1990;Churkina et al 1999), and in turn, the vegetal cover type is a key determinant for evapotranspiration and global runoff (Dunn and Mackay 1995). The runoff is constrained by vegetation through stomatal conductance (Field et al 1995;Morison and Gifford 1983), root pattern, leaf area (Milly 1997;Betts et al 1997), interception and transpiration (Leipprand and Gerten 2006;Beaulieu et al 2010).…”

“…Previous studies based on modelling or experimental methods showed that stomatal conductance may decrease by as little as 25% (Field et al 1995) or as much as 40% (Morison and Gifford 1983;Luo et al 2013), since plants tend to close their stomata to maintain an optimal balance between water loss and CO 2 absorption (Van de Geijn and Goudriaan 1997;Woodward 2002). Under a doubled CO 2 concentration, global evapotranspiration is predicted to decrease by 7%, while runoff and soil moisture are predicted to increase by 5 and 1%, respectively (Leipprand and Gerten 2006).…”

A model-based constraint on CO<sub>2</sub> fertilisation

“…The parameter k 13 is held constant at 29 ppm throughout. Although the expression for CO 2 fertilisation parameterises the uncertain saturating increase in gross primary productivity (GPP) under elevated CO 2 , the simplified moisture balance formulation does not capture the changes in evapotranspiration, soil moisture and run-off due to the physiological effect (Leipprand and Gerten, 2006;Betts et al, 2007).…”