SUMMARY

This  Lawrence Livermore National Laboratory (LNL) model dipicts five independent data sets showing warming trends in 1950-1999 California daily winter temperatures that cannot be explained by natural climate variability (blue bands). During 1950-1999 California summers, only minimum daily (nighttime) temperatures show a clear-cut warming trend, possibly because daytime temperatures were depressed by widespread use of irrigation.

Regional climate is the climate specific to a limited geographical area, in contrast to the aggregated global climate of the Earth as a whole. Defined by their temperature, rates of precipitation, or by their vulnerability to droughts, floods, or other extreme weather events, the climate of geographical regions can vary widely depending on a number of factors.

• Those factors include: Latitude, which influences the solar radiation received
• Hours of sunshine
• Main zonal features of th e atmos pheric circulation (e.g.: trade wind belts, mid-latitude westerlies) Proximity to oceans
• Oceanic circulation (and heat exchange)
• Other atmospheric circul ation features
• Spatial and topographic features Impact of urban or rural land use Terrestrial ecosystems and vegetation feedback
• Atmospheric carbon dioxide concentrations

Irrigation Studies

Lawrence Livermore National Laboratory (LNL) scientists have studied the regional climatic effects of irrigation in observations and in model simulations. They found that a rapid expansion of irrigated area (as had occured in California over the last 150 years) has had a large cooling effect on regional summertime average daytime surface temperatures, and negligible effects on nighttime temperatures. This irrigation-induced cooling may have masked a greenhouse gas-induced day-time warming signal in California.

Elevations of the Western U.S. (color shading), with mountainous regions, where climate change is attributable to human activities, indicated by colored circles. Go to this model.

GOALS

To explore the benefits of the regional modeling approach and to learn how climate change information is obtained and sorted out.

ACTIVITY DESCRIPTION AND TEACHING MATERIALS

Explore:  Regional Climate Modeling

TEACHING NOTES / CONTEXT FOR USE

By limiting the domain size, regional climate models can be run at comparatively high spatial resolution ( ~ 10-50 km grid spacing), potentially producing more realistic climate simulations due to better representation of fine-scale physical and dynamical processes.

To explore the benefits of the regional modeling approach, LLNL scientists have performed simulations of California climate using the Weather Research and Forecasting (WRF) regional climate model nested within the global Community Climate System Model (CCSM). The regional model was found to greatly improve the spatial pattern of surface variables, but to overpredict precipitation amounts, especially in mountainous areas. This precipitation bias is also a consistent deficiency of other regional models participating in the North American Regional Climate Change Assessment Program (NARCCAP).

The WRF precipitation bias was due to overprediction of the strongest rain events, motivating an analysis of the parameterizations of subgrid-scale processes relevant for precipitation formation. The parameterizations of cloud microphysics and (to a lesser extent) convection were found to dominate the precipitation response. The precipitation bias was also found to increase as the model grid size decreased, suggesting that enhanced model resolution may not be sufficient for improving hydrological variables in regional climate simulations.

ASSESSMENT

Assessment is at the discretion of the educator and how this model is applied.

REFERENCES AND RESOURCES

Additional Resources on this topic:

image

Pacific Northwest National Laboratory Global and Regional and Global Scale Modeling Regional and Global Scale Modeling gaols are: * develop regional climate models and conduct research on their strengths and limitations. * develop and apply regional climate models and other tools (e.g., crop production models) for understanding the effects of climate change and climate variability on climate-sensitive systems (e.g., water resources, agriculture, etc.) * use regional climate models to understand and parameterize the effects of small-scale climate features on the global climate system.

image

University of California-Irvine Center for Hydrometeorology and Remote Sensing In collaboration with UNESCO's International Hydrological Programme (IHP) and with the California Institute for Telecommunications and Information Technology (Calit2), and its Irvine Division, CHRS has developed a Google Earth application that provides access to visualization of CHRS's very high resolution (0.04°) global precipitation products in near real time to worldwide users. The application, which is developed in conjunction with UCI's participation as a founding member UNESCO's Water and Development Information for Arid Lands-A Global Network (G-WADI) initiative, aims at strengthening the capacity manage water resources around the globe

Regional Climate-Change Detection and Attribution

LLNL scientists have played a major role in climate-change detection and attribution studies at regional scale,  identifying the origins of climate change observed across the mountainous areas of the western U.S. since 1950. They focused on three “hydrologically relevant” variables: minimum winter-time temperature, the timing of streamflow in three major river basins, and snowpack depth; and they conclusively attributed the changes in these variables to human activities.

They also presented the first evidence of a long-term human influence on the Pacific Decadal Oscillation (PDO) index, a mode of natural decadal climate variability that strongly influences the climate in the western U.S. and other regions.

Cross-Institutional Collaborations

Regional climate studies also are being fostered by current collaborations between LLNL scientists and those in other Department of Energy laboratories or California universities:

• A collaboration with Pacific Northwest National Laboratory (PNNL) scientists to model groundwater and vegetative mechanisms that might trigger more frequent severe and persistent droughts in the Southwest U.S. under conditions of increased greenhouse warming;.

• A collaboration with scientists at the Lawrence Berkeley National Laboratory (LBNL) to model processes that might produce abrupt climate change in high Northern latitudes. These processes include an accelerated thawing of permafrost, associated methane releases that amplify greenhouse warming, and regional vegetation changes that alter the surface albedo;

• A collaboration with University of California scientists to conduct a risk assessment of the range of expected impacts of prospective future climate change on California's water resources.