Developing New PRISM Climate Maps of British Columbia

PRISM mechanics

Generating new climate maps for BC: New Data, Higher Resolution

Utility of climate data

Figure 1. The added detail that an 800 m resolution climatology provides. a) The July Tmax climatology for the Grand Canyon at 4 km resolution. b) same for 800 m resolution. (figure courtesy of PRISM Climate Group).

Figure 2. Example of PRISM weighted regression versus non-weighted regression for calculating climate normals. a) unweighted scatter plot. b) Weighted scatterplot. c) Weighted scatterplot with fitted temperature/elevation relationship

Figure 4. Map showing 1971 - 2000 station climatologies for daily minimum temperature for January.

Figure 3. Elevation distributions of station climatologies derived from the CRMP network data (black) and for Environment Canada data (grey).

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Figure 5. Flow chart depicting the work entailed in developing new PRISM maps as well as for performing quality control on the Provincial Climate Data Set. Yellow coloured polygons indicate PRISM work, blue colored polygons indicate work done at PCIC, and the green polygon indicates data passing through a map-based data portal.

Figure 6. A screen capture of the PCIC data portal. Data selection filters are shown on the right along with a status box indicating the number of stations selected. Metadata may be viewed by clicking on individual stations and by clicking the 'View Metadata" button. Access to station data and climatologies is gained through the "Catalogue" link.

Gathered data from existing and historical weather observing networks in British Columbia. Data is loaded into a database and accessible via web-based portal.

Developed a web map to allow users to select stations by selecting regions, desired variables or desired networks.

Calculated station climatologies from the provincial climate data for more than 1700 stations.

Have established the PRISM modelling domain and procedures for performing quality control using PRISM methodologies.

Will create preliminary PRISM maps by July, 2012.

Maps for stakeholder review will be made at the end of the calendar year.

Final PRISM maps complete by Summer, 2013.

Progress to-date and future work

Much of the work that PCIC does revolves around understanding how the climate of BC will change in the future and how those changes will impact communities as well as the larger scale hydrology of the province. To make an assessment of change, an accurate understanding of the province's climate in the present is needed. An example of the station climatology for January mean daily minimum temperature is shown in Figure 4. There are large gaps in the station coverage that can be filled with a spatial interpolator like PRISM. The station data that will be used for PRISM are also of great value to stakeholders in the province including researchers, the general public, industry, and even internally to PCIC. PCIC already responds to many requests for station data and gridded products based largely on Climate WNA and PRISM. With new station data and new climate maps we foresee these requests growing in number. Station data, station climatologies, and climate maps will be released to the public once they are generated and determined to be reliable. Data will be released primarily through a data portal that is in development at PCIC and will be announced in July, 2012. This portal, shown in Figure 6, uses a map to orient users and to allow them to subset station data and eventually PRISM data to ensure that unneeded data aren't downloaded. PCIC will also try to fill custom data orders where possible and in situations where the data portal doesn't meet the user's needs.

Although much of the population of British Columbia resides in locations where Environment Canada maintains a climate station, much of the economic activity (such as forestry, mining, hydropower generation, farming, fishing, and tourism) within British Columbia occurs outside of urban centers or relies on knowledge of weather and climate at the landscape scale. In 1994, the PRISM Climate Group at Oregon State University was contracted to generate climate maps of the province at a resolution of 4 km. Those maps have been used as a primary source of climate information and have been further downscaled within the Climate WNA (Wang et al., 2006) software which allows a user to obtain climate information at arbitrary points on a map. Since the time of production of those maps, PRISM has been improved (Daly et al., 2008) and is now capable of reliably producing 800 m spatial resolution climate maps (Fig. 1).

Furthermore, in 2010 the BC Ministry of Environment initiated the Climate Related Monitoring Program which enabled the transfer of historical climate data collected from more than 6000 stations to the Pacific Climate Impacts Consortium. At about the same time, an agreement between PCIC and the PRISM Climate Group was signed enabling PCIC scientists to work collaboratively with the PRISM Climate Group to create new climate maps of BC at a ~800 m spatial resolution. This agreement also allows PCIC to use and develop the PRISM software for climate mapping in the future including for creation of monthly and daily time series maps.

PRISM works by forming relationships between a predictor variable (such as elevation) and station climatology. A basic approach is illustrated in Figure 2a showing the relationship of all stations around a point to elevation. PRISM improves this method by weighting stations based on their climatic and topographic similarity to the point of interest (Fig. 2b). A relationship is calculated and used to determine the climate value at any given point (Fig. 2c). The new PRISM maps will be based on much more data than was previously used including much better coverage at higher elevations (Fig. 3). A map of

the distribution of stations with climatology is shown in Figure 4. Greater station density justifies the higher resolution and the need to create new maps for BC. The process of mapping climate with PRISM is shown as a diagram in Figure 5. Much of the work of involves data quality control and assurance. This diagram also indicates some of the milestones of the project and shows PCIC's priority of releasing data to the public as soon as it is available. End-users will benefit from the PRISM process at every step of map development.

Acknowledgements: This project is partially funded by support from the Pacific Institute for Climate Solutions. Ted Weick and all of the network managers from the Climate Related Monitoring Program are a critical part of the PRISM climate mapping effort. Although the actual PRISM mapping will be done within the Climate Analysis and Monitoring theme at PCIC, the Computational Support group did most of the development of the data portal and will be a key partner in the climate mapping efforts. Funding for development of the data portal was provided by BC Ministry of Environment.

References: Daly, C., M. Halbleib, J.I. Smith, W.P. Gibson, M.K. Doggett, G.H. Taylor, J. Curtis, and Philip P. Pasteris. 2008. Physiographically sensitive mapping of climatological temperature and precipitation across the conterminous United States. International Journal of Climatology, doi: 10.1002/joc.1688.Wang, T., Hamann, A., Spittlehouse, D., and Aitken, S. N. 2006. Development of scale-free climate data for western Canada for use in resource management. International Journal of Climatology, 26, 383-397.

Faron Anslow (fanslow@uvic.ca) Dave Rodenhuis and James Hiebert

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