Association of State Wetland Managers - Protecting the Nation's Wetlands.

The Compleat Wetlander: National Wetlands Inventory Turns 40

By Jeanne Christie

2015 is the 40th anniversary of the National Wetlands Inventory.  It is one of the largest databases of its kind in the world with over 20 million polygons of individual wetlands in the United States.  It gets over one million website views (@ 2700 per day) each year.  It is easily accessible through google earth and the Fish and Wildlife Service’s wetland mapper.  The National Wetlands Inventory is also part of a number of GIS Services from ESRI ArcGIS Online to the USGS National Map, USGS US Topo, and NWI+.

Who uses wetland maps?  What do they use them for?  The Association of State Wetland Managers (ASWM) has explored this topic and identified 24 separate major groups of users in the government, nonprofit and private sector.


Wetland maps have many applications by states and other parties for making decisions that affect people, wildlife populations, and overall aquatic health.  Some of these are obvious and others are not.  ASWM has documented the various ways that wetland maps are used specifically by states (just one of the 24 major user groups identified) and this information is available here.  State uses range from wildlife and habitat conservation and wetland restoration and real estate and permitting decisions to storm surge and sea level rise analysis and transportation and agricultural planning.


But the decisions made are only as good as the data used to make them.  Maps that were made decades ago don’t reflect changes.  They don’t identify where wetlands have been lost or where they have been restored by programs such as the North American Waterfowl Management Plan or the Wetlands Reserve Program.  They don’t show how areas like the Louisiana coast are giving way to the sea.  And that is a serious problem for the National Wetlands Inventory users groups.  The great majority of maps were made using imagery from the 1970’s and 1980’s.


The United States is a big country and it is reasonable to expect that in some places there has been little change in the past 30 or 40 years.  But in other places there has been enormous change not only in wetlands, but in other landscape features such as forests, farmlands, urban areas, coastlines and more.

In recent years, budget cuts, competing priorities, sequestration and other factors have led the U.S. government to reduce its investments in updating many of its mapping products and one of these is the National Wetlands Inventory.  People that are concerned, but have little direct experience with wetland mapping, will ask if it can be automated, done more cheaply or done by another party such as the states, foundations, or the private sector.  The answer to the first question is no, there is no way that has been identified to automate wetland mapping so it can be done solely by a computer.  The answer to the second is that other parties are doing some work in areas around the country, but it is spotty, not always done consistent with the National Wetlands Inventory requirements, and at current funding levels, the National Wetlands Inventory staff are not even able to keep up with the work needed to add those few maps that are being completed.

The ASWM hosts regular webinars for the Wetland Mapping Consortium and the purpose of the consortium is to explore questions like these as well as ways to improve accuracy and usefulness of wetland maps, share new applications and so on.  It is possible to view all of the webinars held on these topics from 2012 to today here.  Anyone can join the consortium simply by signing up for a future webinar here.

Inaccurate maps can lead to poor decisions that increase costs at the private, local, state, and federal level. But an increase in investment in wetland mapping will only occur if the many parties that use the maps communicate to decision-makers – those who control budgets – that it makes sense to invest resources to create more accurate wetland maps to save both money and essential natural resources now and in the future.

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