Hawaii Pacific GIS Conference 2012: Water Resources - Online Rainfall Atlas of Hawaii


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Hawaii Pacific GIS Conference 2012: Water Resources - Online Rainfall Atlas of Hawaii

  1. 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. 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. 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. 4. Previous Efforts to Map Hawaiian RainfallHalstead and Leopold (1948) Median January Rainfall Isohyets
  5. 5. Previous Efforts to Map Hawaiian RainfallTaliaferro (1959) Median January Rainfall Isohyets
  6. 6. Previous Efforts to Map Hawaiian RainfallMeisner et al. (1982) Median Annual Rainfall Isohyets
  7. 7. Previous Efforts to Map Hawaiian Rainfall The Original Rainfall Atlas of Hawai‘iGiambelluca et al. (1986) Mean Annual Rainfall Isohyets
  8. 8. Previous Efforts to Map Hawaiian RainfallDaly et al. (2006) Mean Annual Rainfall Gridded Map
  9. 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. 10. The Rainfall NetworkNumber of stations operating at any given time- Peaked at 1030 stations in 1968 Now only 340 raingages
  11. 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. 12. Gap-Filling Station DataNumerous statistical techniques were used to fill gaps, includingperiods before and after a station’s period of operation
  13. 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. 14. Estimating Mean Rainfall for Virtual Raingage StationsMoisture zones determined by patterns of natural vegetation Jacobi (1989) Gon et al. (1998).
  15. 15. Estimating Mean Rainfall for Virtual Raingage StationsSites with knownmean rainfall used tocalibrate the model… …Mean rainfall estimated for sites with no nearby raingages (Virtual Raingage Stations)
  16. 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. 17. Spatial Predictor DatasetsPRISM: Mapping system relying on statisticalrelationships between rainfall and terrainMM5: Mesoscale meteorological modelused for operational weather forecastingRadar Rainfall: Radar used to monitorrainfall and to identify intense rainfallapproaching the islands
  18. 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. 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. 20. Fusing Interpolated Maps and Predictor DatasetsBayesian statistics were used to fuse the estimates to produce the final maps
  21. 21. Checking the Final MapsMapped and observed mean rainfall lie along the 1:1 line
  22. 22. Final ProductsMaps:• 12 monthly maps and one annual map – Inches and millimeters – Gridded and isohyets• Accompanying uncertainty maps for all months• Spatial resolution: 250 mData:• 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. 23. The Web SiteWith the help of the EPSCoR Cyberinfrastructure Team at UH Hilo,we developed a web platform for the new rainfall atlas
  24. 24. The Web SiteThe Rainfall Atlas of Hawai‘i Web Site is up and running. Let’s check it out:http://rainfall.geography.hawaii.edu/
  25. 25. Coming Soon Month/Year Maps from 1920 to 20071920 1990 1950 1970 1930 2000 1980 1960 1940 2007
  26. 26. Thank You
  27. 27. The Web Site – Interactive MapThe interactive map, developed by the team at UH Hilo usingArcGIS Online, gives users the opportunity to get information forall maps and station data, and display all layers without needingto use a desktop mapping program.
  28. 28. The Web Site – Interactive MapPan, zoom, use the inset map, or type in coordinates to get around Choose your base map and units
  29. 29. The Web Site – Interactive MapChoose which layers to displayThe legend displays which layers are currently turned on Maximize the display to remove the top and bottom banners
  30. 30. The Web Site – Interactive MapLocate any point of interest on the interactive map and click to get mean annual and monthly rainfall statistics
  31. 31. The Web Site – Interactive MapClicking on a station gives both map andstation estimates of mean annual andmonthly rainfall statistics Print or download your graph of mean monthly rainfall
  32. 32. The Web Site – Interactive MapNeed Help? We have answers to some FAQ and provide a thorough tutorial for using this map
  33. 33. The Web Site - DownloadsUse the drop down menus to navigate to the type of files you would like to download
  34. 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. 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. 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