Transcript Document

IPCC Model Uncertainty in Representing the
Global Water Cycle of the late 20th Century Climate
• Water Cycle quantities are ordered left
-> right in increasing uncertainty.
• Fluxes (red) show better agreement
than reservoirs (blue).
• Vapor ( ) and Liquid ( ) show better
agreement than Frozen ( ) water.
• Taking the above into consideration, it
can be seen that quantities that have
robust observational constraints, in
many cases from satellite, tend to
exhibit less model uncertainty.
• The most uncertain water cycle
components (e.g., snow, ice, cloud
mass) represent key climate feedbacks.
Complete Caption (top) Model-to-model agreement in globally-averaged, annual mean values of
important hydrological quantities from the 1970-1994 period of the 20th century GCM simulations
contributed to the IPCC 4th Assessment Report (20c3m scenario). Normalized percent differences are
relative to the multi-model mean (MMM) values [e.g., 16 models provide soil moisture values, the
standard deviation is about +/- 60% of the MMM, with a maximum (minimum) of about +100% (-100%)].
Quantities are ordered in increasing model disagreement using the standard deviation. (bottom) Same,
except for expanded y-scale. Horizontal labels consist of the name model variable and the number of
model contributions included in the analysis. Font color indicates whether the water cycle component is a
flux (red) or reservoir (blue). In addition, model variables are labeled with icons indicating whether the
flux or reservoir is associated with vapor (molecule), liquid (drop) and/or ice (snowflake).
Duane Waliser, JPL