1. Global Circulation Models

2. GCMs
Global Circulation Model (GCM): physically-based complex mathematical representations of the planet’s atmosphere, ocean, atmosphere, land, and ice
Modern GCMs have fully coupled atmosphere and ocean components and are referred to as atmosphere-ocean general circulation models (AOGCMs).
First AOGCM was produced in the 1970s at the NOAA Geophysical Laboratory in Princeton, NJ while the development of atmosphere models first evolved in the 1960s from weather prediction models.
Numerically integrating physical, chemical, and biological principles and equations into a 3-dimensional grid, GCMs can be used to simulate the planet’s past, present, and future climate
Next generation models are moving into the realm of full Earth System Models

3. Global Circulation Models
Horizontal Resolution (i.e.– grid box size)
GCMs tend to have relatively coarse resolution (100+ km)
Limitation: they can’t represent local climate very well, especially in complex terrain

4. Global Circulation Models
Downscaling: refining coarse GCM data to a finer resolution for regional and local climate impact assessments
Dynamic Downscaling
Statistical Downscaling

5. Dynamic Downscaling Nest a regional climate model within a GCM
The GCM forms the boundary conditions for the regional model
Advantages:
Physically consistent—based on fundamental physical principles
Disadvantages:
Passes along biases of GCM
Computationally intensive

6. Statistical Downscaling
Downscale via empirical statistical relationships
Example: develop relationship between local variables (temperature, precipitation) and synoptic model output variables (pressure heights, temperature, humidity, winds, etc.)

7. GCM Downscaling Simplest statistical approach: the delta method
Simply add on projected changes to high resolution climate grid

8. GCM Downscaling Delta Method Step 2
Perturb fine-scale historical observations with the projected seasonal/decadal regional changes to produce climate change scenarios
Provides climate data sequences that preserve the historically observed fine-scale spatial/temporal variability but are modified for a climate change scenario

9. GCM Downscaling Delta Method Advantages Delta Method Disadvantages
Quick and easy
Easy comparison to historical conditions
Delta Method Disadvantages
Does not account for changes in variability or extremes
Assumes entire landscape will change by the same amount
High resolution != realism

10. Projected monthly change in average temperature (°F) for each climate division in Montana between 2040 and 2069 for RCP4.5 and 8.5
Montana Climate Assessment 2017

11. Projected monthly change in # frost free days (°F) for each climate division in Montana between 2040 and 2069 for RCP4.5 and 8.5
Montana Climate Assessment 2017

12. Precip Projections and Seasonality
Montana Climate Assessment 2017

13. Summary of Daymet Methods
Interpolate daily temperatures and precipitation between stations
Extrapolate temperatures and precipitation across topographic features
Estimate radiation and humidity

14. Overview of Current Products
Daily Tmax, Tmin, Prcp, Radiation, Humidity
1 km grid over the conterminous U.S.
Now a 34-year period:
Climatological summaries of the daily data
Special summary products tailored to particular applications
All products available over the Web

15. Map showing locations of weather stations,
available on the internet in real-time

16. Radiation estimated from temperature and precipitation