National Climate Assessment: 21st Century Precipitation Scenarios

The National Climate Assessment (NCA) is a central component of the U.S. Global Change Research Program (USGCRP). Every four years, the NCA is required to produce a report for Congress that integrates, evaluates, and interprets the findings of the USGCRP; analyzes the effects of global change on the natural environment, agriculture, energy production and use, land and water resources, transportation, human health and welfare, human social systems, and biological diversity; and analyzes current trends in global change, both human-induced and natural, and projects major trends for the subsequent 25 to 100 years. A draft of the Third National Climate Assessment report is available on the Federal Advisory Committee website. The final report is slated to be released in 2014.

These visualizations show model projections of the precipitation anomaly from 2000 to 2100 as a percentage difference between the 30-year precipitation averages and the 1970-1999 average. The dates displayed represent the center of the 30-year average; so, the 30-year spans are +/- 15 years from the displayed dates. The percentages are computed as follows: 100% x ( (30-year span) - (1970-1999 span) ) / (1970-1999 span). Separate animations are shown for annual averages and for seasonal averages in the United States. Spring precipitation is displayed to demonstrate the strong drying signal in the southwest. Summer precipitation is displayed because of agricultural community interest. The other seasons are included for completeness.

The data are from fifteen coupled Atmosphere-Ocean General Circulation Models (AOGCMs) from the World Climate Research Programme (WCRP) CMIP3 multi-model dataset (PCMDI 2012). These models are CCSM3, CGCM3.1 (T47), CNRM-CM3, CSIRO-Mk3.0, ECHAM5/MPI-OM, ECHO-G, GFDL-CM2.0, GFDL-CM2.1, INM-CM3.0, IPSL-CM4, MIROC3.2 (medres), MRI-CGCM2.3.2, PCM, UKMO-HadCM3, and UKMO-HadGEM. In those cases where an ensemble of simulations was available from a particular model, only a single ensemble member was used.

These climate model runs use assumptions about possible future development patterns and scenarios of greenhouse gas emission rates. Two future scenarios are shown: B1 and A2.

• In the B1 scenario, global environmental concerns are emphasized. B1 is a lower greenhouse emissions scenario.
• In the A2 scenarios, future socio-economic development and regional issues are emphasized; and, worldwide cooperation on environmental issues is deemphasized. A2 is a higher greenhouse gas emissions scenario.

For each scenario (B1 and A2), five individual precipitation anomaly animations are shown for annual, spring, summer, fall, and winter periods. So, there are a total of ten individual animations:

• B1 Annual (lower emissions annual outlook)
• A2 Annual (higher emissions annual outlook)
• B1 Spring (lower emissions outlook during initial growing season)
• A2 Spring (higher emissions outlook during initial growing season)
• B1 Summer (lower emissions outlook during growing season)
• A2 Summer (higher emissions outlook during growing season)
• B1 Winter (lower emissions outlook)
• A2 Winter (higher emissions outlook)
• B1 Fall (lower emissions outlook)
• A2 Fall (higher emissions outlook)