Zooming in on Regional Climate

A thunderstorm cloud passes over the plains east of Denver. Researchers believe that some regions will see warmer and wetter weather, while others will have droughts. Most climate change simulations are created with models that simulate the global scale and produce global averages as their results. But to understand how global warming will affect drinking water storage or the ability to grow wheat, corn, and other staples, regional simulations and impact studies are needed.

Some Challenges of Regional Climate modeling

Regional models depict the climate of a smaller area in more detail, which is challenging because:

  • scientists are still studying the influence of clouds and local storms and how best to portray them in regional models; global models do not try to represent these fine-scale processes
  • many of the other equations created to represent physical processes in global models must have more spatial detail
  • the models must reflect changes in the atmosphere, land, oceans, and other parts of the envirronment over shorter time scales
  • all of this higher resolution usually requires greater computing power and longer time to run a simulation

NCAR scientists and their colleagues are addressing these issues through development of a nested regional climate model (NRCM). The model's developers plan to:

  • Seamlessly integrate the weather and climate models based at NCAR to capture all important spatial and temporal scales
  • Collaborate with impacts researchers to address both scientific and societal issues
  • Provide a new community model freely available to researchers around the world, such as the NCAR-initiated Community Climate System Model (CCSM) and Weather Research and Forecasting Model (WRF).

Scientists hope to improve understanding and simulation of complex, two-way scale interactions, with emphases on:

  • downscaling from global climate simulations (especially in investigations of societal impacts)
  • upscaling from regional processes, including the effects of land and ocean processes
  • the impact of regional weather, particularly the organization of moist convection on larger scales.

Our Current Understanding

Some aspects of regional climate change are already well established. For instance, high-latitude areas such as Canada, Russia, and the Arctic are warming more rapidly than the tropics, as predicted by computer models. This trend is expected to continue. In many nations, rainfall and snowfall are becoming more concentrated in heavier bursts, and regions poleward of latitude 40 degrees north are expected to see more days with heavy precipitation. NCAR scientists and colleagues are working to improve understanding of other potential regional changes in climate, such as where U.S. rainfall and snowfall patterns might shift.

Researchers are also working to improve techniques for assessing the impacts of a changing climate on environment and society. One method is to translate temperature changes from a model into trends that affect people's everyday lives. A 2004 NCAR study found that, by the period 2080-99, American and European heat waves will be more severe, frequent, and long-lasting.

A related study found that frost days (those in which temperatures dip to 0°C or 32°F) will decline in many parts of the globe by 2080-99. The largest decreases are projected across the northwest parts of Europe and North America, as mild marine air becomes more prevalent in winter. Such a change would affect agriculture and tourism as well as natural ecosystems.

Both of these studies, along with many others, have been used in preparing the 2007 IPCC assessment. One theme for the new assessment will be the extent to which our planet is committed to some amount of human-induced climate change, regardless of what actions we take in the future.

Uncovering North America's climate future

Researchers are developing new approaches to fine-scale computer modeling to allow greater focus on regional impacts of a changing climate. (Image courtesy North American Regional Climate Change Assessment Program, NCAR.)What will climatic conditions look like for the United States and Canada by the middle of this century? An international team of scientists is focusing in on North American climate from 2040 to 2070, laying the groundwork to create regional simulations with unusually fine detail.

Most projections of future conditions rely on global climate models run on supercomputers that, despite their sophistication, lack the detail to simulate behavior within a state or region. Led by NCAR, the North American Regional Climate Change Assessment Program (NARCCAP) will use an ensemble of global climate models and high-resolution regional climate models to produce simulations with about triple the resolution of most projections of future climate.

The combination of tools will allow scientists to incorporate relatively small topographical features, such as mountain ranges, lakes, and complex coastlines, that can have a significant influence on local and regional climate. An important research benefit of the effort, which is designed to complement similar projects in Europe and South America, will be the ability to compare the results of fine-scale with coarser-scale modeling to more clearly determine the added value of high-resolution projections of future climate.

NCAR scientists are collaborating with colleagues at U.S. universities and laboratories, the University of Quebec and the Ouranos Consortium in Montreal, and Britain’s Hadley Centre for Climate Prediction and Research. The project is expected to spawn additional international collaborations as researchers continue to fine-tune projections of the impacts of climate change on North America.