CICERO - Center for International Climate Research
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Precipitation is arguably the most direct link between the climate and human society. We depend upon existing precipitation patterns for fresh water and food production, and global infrastructure is designed to withstand current precipitation extremes.

At the same time rainfall patterns are naturally highly variable. Their future trends depend upon many climate factors that are currently changing, such as global air and sea surface temperatures, water evaporation rates, atmospheric stability and wind patterns. Beyond changes in global and local mean precipitation, changes in rates and magnitudes of extreme rainfall events are also of high importance.

The NAPEX project brings together a core group of international climate scientists to perform a set of dedicated unified experiments using state of the art climate models. The future scenarios of precipitation changes from global climate models presently do not agree very well on global nor regional scale. However, recent studies from groups participating in NAPEX have shown that precipitation changes from particular drivers of climate change (such as greenhouse gases and various aerosol types) have striking similarities. A main hypothesis of NAPEX is that differences in anthropogenic and natural drivers of climate change, both distribution and treatment, are crucial factors for differences in precipitation response in current global climate models.

NAPEX partners have extensive experience with model intercomparisons. Results will be made available to the scientific community and a common protocol established to encourage participation from further international modelling groups. The experiments will provide answers to the key question of whether idealized and simpler climate drivers give more similar and robust precipitation changes compared to the mixture of drivers adopted in regular scenarios. A further innovative part of NAPEX is investigation of extreme events related to the various climate drivers.