Details of ISMN networks used in this study. Local extent means the network spans parts of one (or for ARM, two) states; regional networks span many states, and often all of the conterminous United States. Interval indicates typical interval; for some networks labeled “hourly” some subset of instruments may report 3- or 6-hourly. Years and days indicate the smallest span that incorporates all data. The instruments column indicates the sum of the max number of each unique type or uniquely labeled type of sensor deployed at any site. SM levels indicates the total number of unique depths of sensor placement for the network.