1. http://rainfall.geography.hawaii.edu/
Abby G. Frazier, Thomas W. Giambelluca, Qi Chen, Donna M. Delparte,
and Jonathan P. Price
Hawai‘i Pacific GIS Conference 2012
5 March 2012

2. What is the Rainfall Atlas?
• The Rainfall Atlas of Hawai‘i is a set of gridded maps of mean
monthly and annual rainfall for the major Hawaiian Islands
• This is an update to the mean isohyetal maps created by
Giambelluca et al. 1986 in the original Rainfall Atlas. Our new
method fuses raingage data with spatial predictor datasets
• The web site allows all rainfall maps, data, and related
information to be easily viewed and accessed by users

3. Measurement and Mapping of Hawaiian Rainfall
• Earliest known RF observations taken in 1837 at Nu‘uanu
Avenue and Beretania Street
• 106 stations by 1900
• Number of stations increased with the growth of plantation
agriculture
• 422 stations by 1920
• Mapping of rainfall patterns began in earnest in the 1920s

4. Previous Efforts to Map Hawaiian Rainfall
Halstead and Leopold (1948)
Median January
Rainfall
Isohyets

5. Previous Efforts to Map Hawaiian Rainfall
Taliaferro (1959)
Median January
Rainfall
Isohyets

6. Previous Efforts to Map Hawaiian Rainfall
Meisner et al. (1982)
Median Annual
Rainfall
Isohyets

7. Previous Efforts to Map Hawaiian Rainfall
The Original Rainfall Atlas of Hawai‘i
Giambelluca et al. (1986)
Mean Annual
Rainfall
Isohyets

8. Previous Efforts to Map Hawaiian Rainfall
Daly et al. (2006)
Mean Annual
Rainfall
Gridded Map

9. The Rainfall Network
• We compiled a monthly RF database of 2,188 raingage sites
• 517,017 station-months (43,085 station-years) of data
• Average length of record: 40 years

10. The Rainfall Network
Number of stations operating at any given time
- Peaked at 1030 stations in 1968
Now only 340
raingages

11. The Rainfall Network
• Large number of stations, but . . .
• Stations active during different periods
– Need to have common base period for calculating means
– Previous efforts adjusted means
– We chose to do gap filling
• Not evenly distributed spatially
– Most previous efforts relied strictly on subjective, expert knowledge
– We supplemented raingage stations with “virtual raingage stations”
based on patterns of natural vegetation
– We used independent spatial predictor datasets:
• PRISM
• MM5
• Radar

12. Gap-Filling Station Data
Numerous statistical techniques were used to fill gaps, including
periods before and after a station’s period of operation

13. Gap-Filling Station Data
• Resulting estimates were rigorously tested and gap-filling
estimates were rejected in many cases
• Results greatly improve the spatial distribution of stations for
any given period
Raingages Operating in 1980 All Raingages

14. Estimating Mean Rainfall for Virtual
Raingage Stations
Moisture zones determined by patterns of natural vegetation
Jacobi (1989) Gon et al. (1998).

15. Estimating Mean Rainfall for Virtual
Raingage Stations
Sites with known
mean rainfall used to
calibrate the model…
…Mean rainfall estimated
for sites with no nearby
raingages
(Virtual Raingage Stations)

16. Base Period
• Natural multi-decadal rainfall fluctuations suggest using a long
base period
• Long-term secular trends in rainfall suggest using a short,
recent base period
• NOAA standard for computing normals: 30 years
• Our choice: Use the most recent available 30 year period:
1978-2007

17. Spatial Predictor Datasets
PRISM: Mapping system relying on statistical
relationships between rainfall and terrain
MM5: Mesoscale meteorological model
used for operational weather forecasting
Radar Rainfall: Radar used to monitor
rainfall and to identify intense rainfall
approaching the islands

18. Spatial Interpolation of Raingage Data
• Calculate 30 year means of station data
• To combine with predictor datasets:
Interpolate the mean station data (including virtual raingage
stations) for each month and island using ordinary kriging

19. Adjusting Predictor Maps Using Observations
• Each predictor map was tested against the observed rainfall,
and how well (or poorly) they matched the measurements is
expressed in terms of uncertainty
• This uncertainty was used to weight the different data sets
(lower uncertainty = better predictor = higher weight)

20. Fusing Interpolated Maps and
Predictor Datasets
Bayesian statistics were used to fuse the estimates to produce
the final maps

21. Checking the Final Maps
Mapped and observed mean rainfall lie along the 1:1 line

22. Final Products
Maps:
• 12 monthly maps and one annual map
– Inches and millimeters
– Gridded and isohyets
• Accompanying uncertainty maps for all months
• Spatial resolution: 250 m
Data:
• Mean station data for stations used in the atlas
• Monthly station data for all stations (original and gap filled)
• Station metadata (updated coordinates, elevation, station
name, etc.)

23. The Web Site
With the help of the EPSCoR Cyberinfrastructure Team at UH Hilo,
we developed a web platform for the new rainfall atlas

24. The Web Site
The Rainfall Atlas of Hawai‘i Web Site is up and running.
Let’s check it out:
http://rainfall.geography.hawaii.edu/

25. Coming Soon
Month/Year Maps from 1920 to 2007
1920
1990
1950 1970
1930
2000
1980
1960
1940
2007

26. Thank You

27. The Web Site – Interactive Map
The interactive map, developed by the team at UH Hilo using
ArcGIS Online, gives users the opportunity to get information for
all maps and station data, and display all layers without needing
to use a desktop mapping program.

28. The Web Site – Interactive Map
Pan, zoom, use the inset map, or type in
coordinates to get around
Choose your base map
and units

29. The Web Site – Interactive Map
Choose which layers to display
The legend displays which layers are
currently turned on
Maximize the display to
remove the top and
bottom banners

30. The Web Site – Interactive Map
Locate any point of interest on the interactive map and click to get
mean annual and monthly rainfall statistics

31. The Web Site – Interactive Map
Clicking on a station gives both map and
station estimates of mean annual and
monthly rainfall statistics
Print or download your graph
of mean monthly rainfall

32. The Web Site – Interactive Map
Need Help? We have answers to some FAQ and provide a thorough
tutorial for using this map

33. The Web Site - Downloads
Use the drop down menus to navigate to the type of files you would like to download

34. The Web Site - Downloads
Map Images
• *.TIF image files of gridded color maps and isohyets
• Available in inches or millimeters
• One download file per island (all monthly and annual images
are zipped into one file)

35. The Web Site - Downloads
GIS Layers
• GIS Layers of rainfall isohyets, rainfall grids, raingage stations,
and uncertainty grids
• Layer Formats:
– Isohyets & Stations: Shapefiles
– Rainfall and Uncertainty grids: ESRI grid and ASCII grid format
– All use Geographic Coordinates, WGS84 datum
– All accompanied by metadata file
• Available in inches or millimeters
• One download file per island (all monthly and annual layers
are zipped into one file)

36. The Web Site - Downloads
Google Earth Layers
• Zipped *.KML (*.KMZ) files for raingage stations, isohyets, and
color rainfall maps
• Isohyets available in inches or millimeters
• Color grid maps are best viewed with transparency in Google
Earth (no legend is available at this time)
Tabular Data
• Excel 2007 and CSV formats of raingage station data
• Each file includes an “About” tab that explains its contents
Report
• The final project report and technical appendix