Workflow - Precip compare
Precipitation Comparison Algorithms
This workflow will collect precipitation data from a given NCEI Station and compare it to data obtained from NLDAS, GLDAS, and/or TRMM, depending on the user''s preference. The comparison presents relevant metadata, a time series graph, the Pearson's Correlation Matrix, Co-variance, GORE, and a table of statistics performed on each dataset.'
The user can specify an NHDPlus COMID (catchment) or NCEI Station ID for data retrieval. If only a COMID is provided, data from the nearest NCEI Station will be used. If both a COMID and NCEI Station are provided, data from the specified NCEI Station will be used.
Data will be collected from January 1st of the specified start year through December 31st of the end year, and can be aggregated by Daily, Monthly, Annually, or Extreme Event temporal resolutions.An Extreme Event is defined as an accumulation threshold of precipitation during the five preceding days or daily precipitation exceeding a specified amount. There is no limit on the number of years that can be specified, although annual resolution requires 2 or more years, and some NCEI stations may not have data for all years.Handling Missing Data
Occasionally, some NCEI Stations will have periods of missing or invalid data. Days with missing data will be indicated in the output time series with values of -9999. However, days with missing data will be excluded for all datasets when calculating statistics. For extreme event aggregation, missing data will be replaced by the mean of the other datasets, or with 0 if the mean is negative.
Obtaining NCEI Station IDs
A map of NCEI Stations can be found here. Exit The Station ID, Name, Location, and Dates can be found by clicking on the map icon. Some stations may not show up until the map is zoomed into that location. It is recommended that you use NCEI Stations that support the 'Normals Daily' Precipitation Dataset, although stations that support the 'Precipitation Hourly' dataset will work as well.
Obtaining NHDPlus COM IDs
A map of NHDPlus COMIDs can be found here. To find the COMID for your region, expand the 'Surface Water Features' tab, and check the box labeled 'Catchments'. Click on the map to highlight a region of interest, which will bring up a window on the map. Click the three dots on the bottom right of this window and select 'View' in Attribute Table. This will bring up a table which contains the COMID, which is labeled as 'FeatureID' This ID contains commas, which will need to be removed when used in Precipitation Comparison Version 2.0.
NLDAS Precipitation
The North American Land Data Assimilation System (NLDAS) combines North American radar data and satellite data from CMORPH (https://www.cpc.ncep.noaa.gov/products/janowiak/cmorph_description.html). NLDAS has a one-hour time step on a 0.125-degree grid of North America, with an average time delay of four days for data retrieval. NLDAS has data coverage from January 1, 1979 to the present. NLDAS data are reported in UTC (GMT).
GLDAS Precipitation
The Global Land Data Assimilation System (GLDAS) combines satellite data and ground-based observational data to provide precipitation and other meteorological parameters. GLDAS has a three-hour time step on a global 0.25-degree grid. GLDAS-2.1 provides data coverage from January 1, 2000 to present, with an average time delay of one month for data retrieval. GLDAS data are reported in UTC (GMT).
TRMM Precipitation
The Tropical Rainfall Measuring Mission Multi-Satellite Precipitation Analysis Algorithm (TRMM) provides precipitation estimates in specified TRMM regions from 1998 to 2019. The data is presented in 3-hourly timesteps over a 0.25-degree spatial grid. TRMM data are reported in UTC (GMT).