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

This tabular data set represents the mean Julian year day of the year of the first 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 first 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). Values of 0 indicate there is no freeze. 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).