The Influence of Climate Variability on the Accuracy of NHD Perennial and Nonperennial Stream Classifications

Abstract

National Hydrography Dataset (NHD) stream permanence classifications (SPC; perennial, intermittent, and ephemeral) are widely used for data visualization and applied science, and have implications for resource policy and management. NHD SPC were assigned using a combination of topographic field surveys and interviews with local residents. However, previous studies indicate that non-NHD, in situ streamflow observations (NNO) frequently disagree with NHD SPC. We hypothesized that differences in annual climate conditions between map creation years and the years NNO were collected contributed to disagreement between NNO and NHD SPC. We compared NHD SPC to 10,055 NNO (classified as "wet" or "dry") collected in the Pacific Northwest between 1977 and 2015. Annual climate conditions were described with the Palmer Drought Severity Index (PDSI). Stream order was added as a covariate to account for different effects along the stream network. NHD SPC agreed with 80.5% of NNO. "Dry" NNO were five times more likely to disagree with NHD than "wet" NNO (p < 0.0001). Disagreement was greatest on first-order streams. When NHD SPC were collected during a wetter period than NNO the probability of disagreement increased by a factor of 1.17 (p < 0.0001) per unit difference in PDSI. The influence of climate on disagreements between NNO and NHD SPC provides support for the continued development of dynamic models representing SPC as opposed to static NHD classifications.

Beyond Streamflow: Call for a National Data Repository of Streamflow Presence for Streams and Rivers in the United States

“…A subset of these observations were used for the development of the streamflow permanence model, PROSPER, which provides spatially continuous probabilities of year round flow for streams aligned with the NHD medium resolution stream grids for the Pacific Northwest Region [ 7 ]. This dataset has also been used to evaluate the accuracy of existing streamflow permanence classifications [ 11 , 25 ].…”

“…Understanding the streamflow permanence of headwater streams is important for regulatory determinations and policy [17][18][19], water resource management [20], and ecological processes [4,10,[21][22][23]; however, streamflow data remain sparse for headwater non-perennial streams, and current streamflow permanence classifications (perennial or non-perennial) often disagree with in situ observations [24][25][26]. Given the abundance of non-perennial streams both within the U.S. (Figure 1) and globally [11], and the prospect of declining stream flows in the future [16,27,28], accurately characterizing streamflow permanence represents a major challenge to understanding water availability now and throughout the 21st century [24,25]. Consequently, there have been several recent calls to fill this critical data gap [29][30][31], with van Meerveld et al [31] aptly likening the lack of knowledge of non-perennial headwater streams to, "a puzzle with most pieces still under the carpet."…”

“…Given the well-known issues with hydrography and streamflow permanence classifications within the NHD [15,24,25], the USGS has established a NHD Stewardship Program in partnership with federal, state, and local agencies that leverages local knowledge of watersheds to facilitate ongoing updates that include stream and river flowline attributes including streamflow permanence classifications [38]. However, the task to update the hydrography and streamflow permanence classifications substantially outsizes the capacity and resources of stewardship programs so that for at least streamflow permanence classifications, classifications are sometimes decades out of date [25]. The dynamic nature of streamflow permanence in time and space in headwater streams [39][40][41][42] suggests that information on location, extent, and timing of streamflow permanence as well as changes in permanence through seasons and across years are needed.…”

“…In the U.S., the first delineations of streamflow permanence, most of which are still used today [ 25 ], resulted from ground-based surveys and hand-drawn maps of streams produced by the USGS. These hand-drawn maps were digitized to create the National Hydrography Dataset (NHD), which maps the locations of streams and rivers.…”

“…Streamflow permanence classifications (hydrographic category; Table 1 ) are attributed to these flowlines. The definitions of these classes have changed through time, creating subsequent inconsistencies between classifications (reviewed by [ 25 ]; Table 1 ). Current definitions focus on the presence or absence of surface water instead of surface flow and formally include a definition for ephemeral streams.…”