Attributes for NHDPlus Version 2.1 Catchments and Modified Routing of Upstream Watersheds for the Conterminous United States: Mean Day of the Year of Last Freeze, from 30 Years of Record (1961-1990)

This tabular data set represents the mean Julian year day of the year of the last freeze, from 30 years of record (1961-1990) compiled for two spatial components of the NHDPlus version 2 data suite (NHDPlusv2) for the conterminous United States; 1) individual reach catchments and 2) reach catchments accumulated upstream through the river network. This dataset can be linked to the NHDPlus version 2 data suite by the unique identifier COMID. The source data for the mean day of the year of a last freeze, from 30 years of record (1961-1990) was provided by the Environmental Protection Agency and is included with this data set (Ryan Hill, EPA, written commun., 2006). The values represent the Julian year day of the last freeze. For example, value of 300 is the 300th day of the year (Oct 27th). Values > 365 mean that the last freeze occurs after Dec 31. It is done this way so that (first_freeze - last_freeze) should always give a positive number; high numbers for an area with a long frost-free period (e.g. Florida), low numbers for an area with a short frost-free period.Reach catchment information characterizes data at the local scale. Reach catchments accumulated upstream through the river network characterizes cumulative upstream conditions. Network-accumulated values are computed using two methods, 1) divergence-routed and 2) total cumulative drainage area. Both approaches use a modified routing database to navigate the NHDPlus reach network to aggregate (accumulate) the metrics derived from the reach catchment scale. (Schwarz and Wieczorek, 2018).

[
  "010:12"
]

[
  "geospatial"
]