hawaii pacific gis conference 2012: water resources - online rainfall atlas of hawaii

Abby G. Frazier, Thomas W. Giambelluca, Qi Chen, Donna M. Delparte, and Jonathan P. Price

Hawai‘i Pacific GIS Conference 2012 5 March 2012

http://rainfall.geography.hawaii.edu/

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

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

Previous Efforts to Map Hawaiian Rainfall

Halstead and Leopold (1948)

Median January Rainfall Isohyets

Taliaferro (1959)

Median January Rainfall Isohyets


Meisner et al. (1982)

Median Annual Rainfall Isohyets


Giambelluca et al. (1986)

The Original Rainfall Atlas of Hawai‘i

Mean Annual Rainfall Isohyets


Daly et al. (2006)

Mean Annual Rainfall Gridded Map


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


Number of stations operating at any given time

- Peaked at 1030 stations in 1968

Now only 340 raingages


• 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

Gap-Filling Station Data

Numerous statistical techniques were used to fill gaps, including periods before and after a station’s period of operation

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

Estimating Mean Rainfall for Virtual Raingage Stations

Moisture zones determined by patterns of natural vegetation

Gon et al. (1998). Jacobi (1989)

Sites with known mean rainfall used to calibrate the model…

…Mean rainfall estimated for sites with no nearby raingages

(Virtual Raingage Stations)

Estimating Mean Rainfall for Virtual Raingage Stations

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

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

• 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

Spatial Interpolation of Raingage Data

• 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)

Adjusting Predictor Maps Using Observations

Fusing Interpolated Maps and Predictor Datasets

Bayesian statistics were used to fuse the estimates to produce the final maps

Checking the Final Maps

Mapped and observed mean rainfall lie along the 1:1 line

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.)

The Web Site

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

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/

Coming Soon

Month/Year Maps from 1920 to 2007

1920

1930

1940

1950

1960

1970

1980

1990

2000

2007

Thank You

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.

Pan, zoom, use the inset map, or type in coordinates to get around


Choose your base map and units

Choose which layers to display


Maximize the display to remove the top and

bottom banners

The legend displays which layers are currently turned on

Locate any point of interest on the interactive map and click to get mean annual and monthly rainfall statistics


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


Need Help? We have answers to some FAQ and provide a thorough tutorial for using this map


The Web Site - Downloads

Use the drop down menus to navigate to the type of files you would like to download

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)


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)


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


hawaii pacific gis conference 2012: water resources - online rainfall atlas of hawaii

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