Surface water matters for both nature and people — and with climate change, worse droughts, and changing water and land use, it's expected to keep declining in many places, including much of the western United States (Seager and others, 2013). Knowing where and when water will be available, at every scale, is crucial for managing wildlife, recreation and energy development.
Indices exist for particular kinds of water, such as streams or wetlands, but not one that covers all major surface water together. The U.S. Geological Survey's Surface-Water Index of Permanence (SWIPe) aims to fill that gap, giving a reliable measure of how permanent surface water is — from a single river reach to a whole region — to guide land management and policy.
What goes into it
SWIPe covers the upper Missouri River Basin and combines three existing USGS products:
| Dataset | What it adds |
|---|---|
| Dynamic Surface Water Extent (DSWE) (Jones, 2019) | where surface water appears, from satellite imagery |
| Probability of Streamflow Permanence–Upper Missouri (PROSPERUM) (Sando and others, 2022a) | how likely streams are to flow year-round |
| Seasonal vegetation characteristics (Sando and others, 2022b) | likely places where groundwater and surface water interact |
Example SWIPe output: surface-water permanence, in percent. USGS
A planned web tool
An interactive, web-based tool for stakeholders is planned. It would:
- produce situational maps, such as dry-year versus wet-year simulations;
- analyze predictions for a chosen place and time;
- overlay gridded climate data to compare past climate with surface-water conditions.
SWIPe highlights. USGS
Test case: the northern leopard frog
The northern leopard frog (Lithobates pipiens) historically ranged across north-central North America. Populations east of the 100th meridian are considered stable; those to the west are less so, based on genetic assessment (Stockwell and others, 2016), and the Rocky Mountain populations are listed as endangered under Canada's Species at Risk Act.
- Why it declined: mainly overharvest in the 1960s and 1970s for education and research (Gibbs and others, 1971); recovery is now held back in places by climate change, invasive species, disease and habitat loss.
- Why water permanence matters: the frog overwinters in permanent water and breeds in seasonal water. Seasonal pools are vital for young frogs; permanent ponds keep scattered populations connected.
SWIPe is meant to show where suitable habitat and permanent water refuges exist for the frog across its northwestern range.
Probable historical range of the northern leopard frog (modified from Smith and Keinath, 2007); inset photo by Roy Sando, U.S. Geological Survey
More: Climate Adaptation Science Centers projects.
Sources
Based on Martin A, Sando R, Thurman L, McLean K, Wurster P, Jones J, Sarbanes A, "Development of a Surface-Water Index of Permanence to Assess Surface-Water Availability for Ecohydrological Refugia," U.S. Geological Survey Fact Sheet 2023–3045, U.S. Geological Survey; a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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