Climate change causes declines and greater extremes in wetland inundation in a region important for wetland birds

Wetland ecosystems are vital for maintaining global biodiversity, as they provide important stopover sites for many species of migrating wetland-associated birds. However, because weather determines their hydrologic cycles, wetlands are highly vulnerable to the effects of climate change. Although changes in temperature and precipitation resulting from climate change are expected to reduce inundation of wetlands, few efforts have been made to quantify how these changes will influence availability of stopover sites for migratory wetland birds. Additionally, few studies have evaluated how climate change will influence inter-annual variability or the frequency of extremes in wetland availability. For spring and fall bird migration in 7 ecoregions in the south-central Great Plains of North America, we developed predictive models associating abundance of inundated wetlands with a suite of weather and landcover variables. We then used these models to generate predictions of wetland inundation at the end of the century (2069–2099) under future climate change scenarios. Climate models predicted the average number of inundated wetlands will likely decline during both spring and fall migration periods, with declines being greatest in the eastern ecoregions of the Great Plains. However, the magnitude of predicted declines varied considerably across climate models and ecoregions, with uncertainty among climate models being greatest in the High Plains ecoregion. Most ecoregions also were predicted to experience more-frequent extremely dry years (i.e., years with extremely low wetland abundances), but the projected change in inter-annual variability of wetland inundation was relatively small and varied across ecoregions and seasons. Because the south-central Great Plains represents an important link along the migratory routes of many wetland-dependent avian species, future declines in wetland inundation and more frequent periods of only a few wetlands being inundated. resulting in an uncertain future for migratory birds as they experience reduced availability of wetland stopover habitat across their migration pathways. 

Methods
We estimated the number of inundated wetlands in the southern Great Plains for each year from 1991–2020 using the USGS Dynamic Surface Water Extent Product. The DWSE is a free remote sensing data product that is available online through the USGS. Number of inundated wetlands was estimated for two time periods relevant to migratory birds in each year the spring migration as 1 March–31 May and fall migration as 1 September–31 November. Wetlands were determined to be inundated at in a given season if they were observed to have water in at least 2 Landsat/DSWE images. 

Data was summarised into 10 x 10km grid covering the entire southern great plains in addition to the number of inundated wetlands per grid cell in each year we also recorded a number of variables related to weather and land cover. The weather variables include: total precipitation (mm), mean daily average temperature (°C), precipitation balance (measured over 3 time scales: 3 months, 6 months and 12 months prior to migration), and mean daily maximum temperature. Land cover included % cover of crops, grasslands, trees, and development as well as terrain roughness index and the number of wetland basins. A full description of how each of these variables was derived can be found in the full text of the associated manuscript.