Weather data inputs

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Weather data inputs

Post by rcoville » Mon Aug 31, 2015 1:43 pm

Weather information is required for i-Tree Hydro simulations. Of the 3 options i-Tree Hydro provides for weather input (users can pick from a map; use raw data; or use processed data), the most common and practical route is to pick from a map. If the map doesn't have data for the area or time period you're interested in, the next best option is to use raw data.

Picking a weather station from a map:
Weather data for many locations around the United States is pre-loaded into i-Tree Hydro for the convenience of users, after having been screened for completeness. Such stations are available through the map selection option, limited to time frames between 2005 and 2012.

Using a raw weather file:
Standard weather data in the raw format (including stations pre-loaded into i-Tree Hydro) come from the National Oceanic and Atmospheric Administration (NOAA)'s Climate Data Online (CDO) database, also known as the National Climate Data Center (NCDC).
To manually obtain raw weather data in standard format navigate to and select the Mapping Tool. Select the 'Time-Related Maps' tab and the 'Hourly/Sub-Hourly' option in that menu. From this map we look at the Hourly Global layer, select the desired weather station, and click 'Get Selected Data'. Choose the 'Simplified' Data Access option. Make sure the dates for the weather data download will match your project's simulation period (researchers often use January 1st hour 00 to December 30 hour 23 and do a one-year simulation with pre-loaded data that way) and that you check off "Select Only Obs. on the Hour". Follow the instructions to continue and submit your request. You'll receive an email with the data you requested. Open the 'Surface Data Hourly Global - Data File', save it, or select all and copy and paste the data, into a txt file. That txt file can then be loaded into i-Tree Hydro as a raw weather file.
Here is an example raw weather file (headers may differ slightly): ... xample.txt
Here are definitions of abbreviations in the raw weather file: ... viated.txt

To obtain recent weather data:
Follow the instructions above for using a raw weather file, but in the CDO Mapping Tool legend, make sure there is an "A" not an "H" to the right of "Hourly Global" (this can be toggled by clicking on the A or H symbol). This way you will see stations which are currently active and are thus more likely to have recent data, rather than stations with historic data which may have stopped collecting data years ago.

International weather data:
As of January 2017 we are no longer processing international weather data for use in i-Tree Hydro. We are working to develop the i-Tree Database tool for importing data into i-Tree Eco and eventually i-Tree Hydro. At this time, we cannot provide support for international i-Tree Hydro projects. The below information is for reference only.

Downloading raw weather data works for stations worldwide, but stations outside of the United States we have tested often do not have sufficient data for i-Tree Hydro simulations. In those cases, international users would need to provide their own data time-series for their projects, merging that with other weather data from the most proximate viable NCDC station. Using NCDC data is necessary because Hydro is designed to work with that format, and NCDC data includes variables which are not easy to acquire otherwise but are needed by Hydro.

International users can attempt to use proximate NCDC data that will process in Hydro v6, then merge their own data into the processed weather file. The processed weather files in Hydro v6 use comma-separated values (CSV) formatting, which makes it possible to edit in spreadsheet software. Guidelines on how to modify processed weather data files are available in the following FAQ: Customizing timeseries inputs (e.g. weather, observed flow) in Hydro v6. Note that the i-Tree Team cannot currently provide any support for this process.

In choosing a proximate NCDC station, consider your Geographic Reference Location. That is a location which represents your project but which is located in the United States, since Hydro's location database only includes data for US based locations. Your project's Geographic Reference Location should be a city that has a similar climate in terms of rain, snow, temperature, vegetation abundance, elevation, leaf-on & leaf-off days, and latitude. As an example of how this method can work: if the Geographic Reference Location you decide is most proximate to your study location is Syracuse, NY, then you could obtain processed weather data for Syracuse during your desired project period, and then customize that processed weather data to include the localized data you have available and want to simulate with.

Valid project periods depend on what NCDC data is available, which can be explored with the instructions above on manually obtaining raw weather data in standard format. For example, if the nearest Hourly Global NCDC station to your Geographic Reference Location only has observations for 2010 to September 2014, you can only merge in hourly precipitation data from within that period as you would need to pair your data with that NCDC data.

Note that this method assumes your reference location and reference weather data is useful for making predictions about your study area and that the reference weather is compatible with the local weather data you merge into it. These assumptions are unlikely to be completely true, so it is important to recognize those limitations when assessing your simulation results. For example, at a time when it's raining in your local study area, the atmospheric conditions may not be representative of rain in your reference area's weather data. Due to the complex interactions between location data and different weather variables, each project's use of this method will have different strengths and weaknesses, and it is up to users to determine how valid this is for their needs.

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