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要旨:
We analyse how climate change may alter risks posed by droughts to carbon fluxes in
European ecosystems. The approach follows a recently proposed framework for risk
analysis based on probability theory. In this approach, risk is quantified as the product
5 of hazard probability and ecosystem vulnerability. The probability of a drought hazard is
calculated here from the Standardised Precipitation Evapotranspiration Index. Vulnerability
is calculated from the response to drought simulated by process-based vegetation
models.
Here we use six different models: three for generic vegetation (JSBACH, LPJmL,
10 ORCHIDEE) and three for specific ecosystems (Scots pine forests: BASFOR; winter
wheat fields: EPIC; grasslands: PASIM). The periods 1971–2000 and 2071–2100 are
compared. Climate data are based on observations and on output from the regional
climate model REMO using the SRES A1B scenario. The risk analysis is carried out
for 22 000 grid cells of 0.25×0.25 across Europe. For each grid cell, drought vulner15
ability and risk are quantified for five seasonal variables: net primary and ecosystem
productivity (NPP, NEP), heterotrophic respiration (RH), soil water content and evapotranspiration.
Climate change is expected to lead to increased drought risks to net primary productivity
in the Mediterranean area: five of the models estimate that risk will exceed
20 15%. The risks will increase mainly because of greater drought probability; ecosystem
vulnerability will increase to lesser extent. Because NPP will be affected more than RH,
future C-sequestration (NEP) will also be at risk predominantly in southern Europe, with
risks exceeding 0.25 gCm−2 d−1 according to most models, amounting to reductions
in carbon sequestration of 20 to 80 %.
