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Rainfall distribution is the main driver of runoff under future CO 2 ‐concentration in a temperate deciduous forest
Author(s) -
LEUZINGER SEBASTIAN,
KÖRNER CHRISTIAN
Publication year - 2010
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2009.01937.x
Subject(s) - surface runoff , deciduous , environmental science , temperate deciduous forest , transpiration , temperate forest , temperate climate , hydrology (agriculture) , precipitation , water content , soil water , temperate rainforest , atmospheric sciences , soil science , ecosystem , ecology , chemistry , geology , meteorology , geography , photosynthesis , geotechnical engineering , biology , biochemistry
Reduced stomatal conductance under elevated CO 2 results in increased soil moisture, provided all other factors remain constant. Whether this results in increased runoff critically depends on the interaction of rainfall patterns, soil water storage capacity and plant responses. To test the sensitivity of runoff to these parameters under elevated CO 2 , we combine transpiration and soil moisture data from the Swiss Canopy Crane FACE experiment (SCC, 14 30–35 m tall deciduous broad‐leaved trees under elevated CO 2 ) with 104 years of daily precipitation data from an adjacent weather station to drive a three‐layer bucket model (mean yearly precipitation 794 mm). The model adequately predicts the water budget of a temperate deciduous forest and runoff from a nearby gauging station. A simulation run over all 104 years based on measured sap flow responses resulted in only 5.5 mm (2.9%) increased ecosystem runoff under elevated CO 2 . Out of the 37 986 days (1 January 1901–31 December 2004), only 576 days produce higher runoff in the elevated CO 2 scenario. Only 1 out of 17 years produces a CO 2 ‐signal >20 mm a −1 , which mostly depends on a few single days when runoff under elevated CO 2 exceeds runoff under ambient conditions. The maximum signal for a double preindustrial CO 2 ‐concentration under the past century daily rainfall regime is an additional runoff of 46 mm. More than half of all years produce a signal of <5 mm a −1 , because trees consume the ‘extra’ moisture during prolonged dry weather. Increased runoff under elevated CO 2 is nine times more sensitive to variations in rain pattern than to the applied reduction in transpiration under elevated CO 2 . Thus the key driver of increased runoff under future CO 2 ‐concentration is the day by day rainfall pattern. We argue that increased runoff due to a first‐order plant physiological CO 2 ‐effect will be very small (<3%) in a landscape dominated by temperate deciduous forests, and will hardly increase flooding risk in forest catchments. Monthly rainfall sums are unsuitable to realistically model such CO 2 effects. These findings may apply to other ecosystems with comparable soil water storage capacity.