1. Citation: Halabisky, Meghan A, Moskal, LM 2013. Monitoring Wetlands Dynamics Across Spatial Scales and Over Time. Factsheet # 7. Remote Sensing and Geospatial Application Laboratory, University of Washington, Seattle, WA. Digital version of the fact sheet can be downloaded at: http://dept.washington.edu/rsgal/ http://dept.washington.edu/rsgal/ THE ISSUE: Wetlands have complex hydrological regimes, which are not well understood as it is time consuming and expensive to monitor landscape level wetland dynamics using current field methods. The consequences of this data limitation have prevented assessment of regional trends over time. These consequences are now becoming increasingly severe since it is unknown how climate changes will alter the hydrological dynamics of wetlands and small ponds. THE KEY QUESTIONS: How does wetland hydrology change over time? ⓒ RSGAL 2013 Monitoring Wetland Dynamics Across Spatial Scales and Over Time Factsheet # 7 Understanding multiscale dynamics of landscape change through the application of remote sensing & GIS This research is funded by the NW Climate Science Center, the Washington State Conservation Commission, and the Precision Forestry Co-op. Introduction: Wetlands provide critical habitat for plants, fish and wildlife, influence biogeochemistry, and provide services to humanity valued in trillions of dollars. Despite their critical value and the widespread need for wetland assessment and planning, wetlands are understudied, in part because of inadequate methods for modeling wetland dynamics. The need amongst natural resource managers and conservation planners has only grown, however, since wetlands are especially sensitive to climate change. A small change in precipitation can significantly impact wetland surface area and alter wetland hydrology, with dramatic impacts on ecosystem services, such as changes in biodiversity, water storage and availability, and recreational values. Remote sensing has provided an effective means to map and study the changes of wetlands. However, most remote sensing of wetlands has focused on detecting change between a few dates and often at a scale that ignores small, yet valuable wetlands. This research combines field data and aerial imagery with multi-temporal Landsat satellite imagery to map and capture wetland dynamics at a finer scale than previously attained. Methods: To understand wetland dynamics at both intra- and inter-annual scales we used over 200 dates of Landsat satellite imagery to reconstruct the hydrograph of each wetland within our study area in the Columbia Plateau ecoregion for 30 years (1984 – 2011). Through use of a remote sensing technique called spectral mixture analysis we can derive the percent of wetland inundation for each date of Landsat imagery (Fig. 1). Date Rainfall % Surface Area Hydroperiod: Wetland habitat types are largely determined by their flooding regime, called the hydroperiod. In arid and semi-arid regions the surface water of wetlands is in constant flux as they flood and dry up throughout the year. Figure 3: Adding a spatial component allows us to identify spatiotemporal patterns and identify areas that may be drying up at a faster rate than others. Figure 1 (above): A time series of Landsat satellite imagery can be used to determine the hydroperiod of a wetland as shown here for 10 wetlands in Douglas Co., WA. Results: Preliminary results suggest that many of the wetlands in Douglas Co, WA are drying up (Fig.2). DATE 4/27/11 10/10/11 Figure 2 (a). Example of the theoretical wetland hydrograph characterized by inter-annual long-term metrics derived from the modeled amplitude. A progressive loss in amplitude would suggest that a wetland is slowly drying up due to changes in climate Figure 2 (b). Example of a wetland drying up over time and the corresponding hydrograph. Note that the wetland is now at 50% volume from 1984. 1984 2009 100% 50%