Research to Inform Planning and Implementation of Nature-based Solutions
You may have heard President Biden talk about “nature-based solutions” and “green or natural infrastructure.” This language refers to the ability of ecosystems to provide benefits to people particularly as we tackle challenges like adapting to rising temperatures or sea levels due to climate change. There is a growing recognition that natural ecosystems can help to mitigate some climate change impacts and can be part of our adaptation and resilience planning efforts. We are excited to share that the Climate Research & Development program has conducted research that can help to inform those implementation efforts and support both policy and decision making. Here we explore only a subset of the relevant research the program is doing that can help inform nature-based solutions efforts.
The first example, from USGS research scientist Martha Scholl and colleagues was a study of the role of forest cover in regulating the timing and volume of streamflow in Puerto Rico. They determined that watersheds with more forest cover generated a net increase in hillslope infiltration and storage, inferring that forest cover functions to create soil structure, decrease soil temperature through shading, and slow overland flow. On balance, the forested watersheds converted more precipitation into groundwater that maintains streamflow than the less- or non-forested watersheds. In other words, protecting or restoring forests, especially in mountainous environments, can help mitigate the impacts of drought.
Another example is a recent review by Dr. Ken Krauss and colleagues, where they examined the storm protection value of coastal wetlands. They determined that tidal wetlands are effective in weakening normal short-period waves or small storm-induced waves. At the same time, however, they also determined that long-period (larger) storm surges, which elevate sea levels up to several meters for up to more than a day, are attenuated less effectively, especially when wetland fringes are narrow. Thus, it depends on the storm conditions as to how much storm protection can be expected from this nature-based solution.
A third example is recent work by Dr. Peter Ibsen and colleagues on the role of trees and grass to mitigate urban heat, which we have already detailed in another article.
It is important to recognize, however, that even as ecosystems are providing nature-based solutions that can help people adapt, we are also discovering that climate change in many cases is having negative impacts on the very ecosystems we are hoping can help us.
For example, forests are discussed as a very important natural climate mitigation opportunity. Trees take up carbon and store that carbon as plant biomass. Therefore, reforestation and urban forestry in addition to maintaining the health of our existing forests are all good nature-based strategies for mitigating some of our nation’s greenhouse gas emissions (of note, trees in urban areas also help provide important air quality and human health benefits in addition to carbon sequestration).
However, as documented in a recent study by Dr. Adrian Das and colleagues, large-scale and severe tree mortality events have begun to emerge worldwide as a consequence of increased temperatures and drought. This is particularly concerning, as many of these ecosystems had previously been considered either tolerant of these extreme conditions or not at risk of exposure. This raises concerns about climate change risks to the health of forests around the world; climate change may affect forests and their ability to provide desired benefits including carbon sequestration. In response, USGS researchers and their collaborators are working to develop tools to aid forest managers in targeting treatments to increase forest resilience.
In a second example of climate change negatively impacting the ecosystems that we are looking to for adaptation benefits, we again turn to coastal wetlands. Although coastal wetlands can reduce storm and erosion risk as discussed above, sea-level rise is also threatening their long-term health and survival. In a recent study, Dr. Glenn Guntenspergen and colleagues determined that tidal marshes in the Holocene to today could generally keep pace with rates of sea-level rise below 5mm per year because of biological processes facilitating adjustment to sea-level rise, but that there is a breakpoint between 5- and 10-mm per year, where tidal marshes are not likely to be able to accrete enough sediment to keep up with sea level rise. These rates of sea-level rise are anticipated to occur by mid-century under high emissions climate scenarios and by the end of the century under mid-range emissions scenarios. Under these circumstances, tidal marsh survival will increasingly depend on their ability to migrate landward.
Another recent study by Dr. Mike Osland and colleagues determined that even with landward migration, the U.S. is still likely to lose some of its coastal wetland area due to constraints on where wetlands can move and rates of sea-level rise that may be too fast for some wetlands to keep pace. As wetlands are lost, society will lose the benefits wetlands provide including storm and erosion risk reduction.
Thus, even as we can be excited about the benefits that nature-based solutions can provide, we must also study the impacts of climate change on ecosystems and green infrastructure to better understand what future conditions may be like and the extent of mitigation and adaptation benefits we can expect.
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