PRELIMINARY DOCUMENTATION - DEGREE-DAY MAPS
We are developing a series of degree-day accumulation maps that can be used for a number of purposes such as:
Note that these maps are preliminary and are subject to a more rigorous validation and development of algorithms to interpolate degree-days.
- Comparing different growing regions for relative heat unit accumulations
- Showing average heat units for prediction of upcoming events
- Comparing this year vs historical average heat unit accumulations
These maps are primarily based on the relationship between temperature and elevation. As you go higher up, temperatures decrease. This relationship is fairly consistent for a given region, but will differ significantly between regions. The PRISM model is an expert system approach to determining local relationships between climate and elevation. It was developed at the Oregon Climate Center at Oregon State University and has its own web site.
The PRISM model uses a state-wide spatial resolution of ca. 4 KM, meaning that the length of a cell (a "pixel" of data) border is 4 KM. After maps are computed, we use a simple 2-pass gaussian filter to "smooth" the data to a 2 KM resolution. This does not improve precision of the data, but it does improve its appearance somewhat.
On computing historical NORMAL maps:
We started with PRISM-built maps for Oregon monthly maximum and minimum temperatures that are on-line and available from the PRISM FTP site. At the same time, we formatted historical average weather data from 127 sites in Oregon, and calculated cumulative degree-days. Using a GIS (GRASS), we next computed degree-days from the PRISM data and found the difference between the two data sources. We then performed an inverse-distance weighted interpolation of the differences, and added these values to the PRISM-derived degree-days. TIGER (US Census bureau) highways and county boundaries were added for reference.
On computing daily updated maps:
For the present year maps, we use all available sites within the mapping region (Oregon and areas into S. Washington and W. Idaho, currently ca. 54 sites). Each day after the weather data has been updated, we re-calculate cumulative degree-days. If a site has bad or missing data, that site will be ignored untill the data are corrected. As with the NORMAL maps, we find the difference between the PRISM degree-days and the actual degree-days for each location. We then interpolate the differences and add these values to the PRISM maps.
On computing daily deviations between historical NORMAL and actual data:
Once the two map types have been re-calculated, we simply subtract the NORMAL maps from the actual maps, to obtain the DEVIATIONS from NORMAL. If it was 200 DDs cooler this year than NORMAL for a given location, it will be indicated using a dark grey scale (black in this case). For areas where it is warmer than NORMAL, the same color legend that is used for actual degree-days is used.
Preliminary Metadata Summary:
- Data Origin: Interpolated Oregon site calculated degree-days (41 and 50 F base threshold) from 127 sites [site list] obtained from the SAGE climate center (Reno, NV) website. See also PRISM Metadata summary.
- Spatial Resolution: 4 KM per cell border (2.5 min. lat-long, smoothed to approx. 2 KM per cell border (1.25 min).
- Temporal Resolution: PRISM data- monthly average daily maximum and minimum temperatures used. Site data- daily maximum and minimum terperatures.
This project funded in part by a grant from the USDA-Western Regional IPM program.
On-line since April 5, 1996
This page last updated May 28, 1998
Contact Len Coop at firstname.lastname@example.org if you
have any questions about this information.