Caribbean Natural Landcover in Floodplains (Southeast Blueprint Indicator)

Reason for Selection Habitat near rivers and streams is strongly linked to water quality and instream flow (Naiman 1997), is easy to monitor and model, and is widely used and understood by diverse partners. Intact vegetated buffers within the floodplain of rivers and streams provide aquatic habitat, improve water quality, reduce erosion and flooding, recharge groundwater, and more (WeConservePA 2014). Natural floodplain landcover provides a “front line defense” for aquatic systems. Input Data * [Southeast Blueprint 2023 subregions]: Caribbean * [Southeast Blueprint 2023 extent] * [Federal Emergency Management Agency (FEMA) National Flood Hazard Layer] flood zones for Puerto Rico and the U.S. Virgin Islands, accessed 10-22-2022; to download the data, visit the [FEMA Flood Map Service Center], search by jurisdiction (Puerto Rico or Virgin Islands), download all FIRM (Flood Insurance Rate Maps) panels, and locate the “S_FLD_HAZ_AR” shapefile in each download package. We used the “FLD_ZONE” attribute of the S_FLD_HAZ_AR shapefile to define an estimated floodplain depicting areas predicted to be inundated by a 100-year flood (also known as the 1% annual chance flood). To create the estimated floodplain for Puerto Rico and the U.S. Virgin Islands, we combined all areas with flood zone codes beginning with the letter “A”. These zones represent the inland (non-coastal) portions of FEMA Special Flood Hazard Areas considered at high risk of flooding. This excludes coastal areas where the high risk of flooding stems from storm waves, areas of moderate-low flood risk, and areas with possible but undetermined flood hazards where no hazard analysis has been conducted. For more details on FEMA flood zones, [read this FEMA blog] or [visit the FEMA glossary] (detailed definitions are under “Z” for “zones”). * 2020 [LANDFIRE Existing Vegetation Type] (EVT) (v2.2.0) for Puerto Rico and the U.S. Virgin Islands; [access the data for U.S. Insular Areas] * [National Hydrography Dataset Plus High Resolution] (NHDPlus HR) National Release catchments and flowlines, accessed 11-30-2022; [download the data] Catchments A catchment is the local drainage area of a specific stream segment based on the surrounding elevation. Catchments are defined based on surface water features, watershed boundaries, and elevation data. It can be difficult to conceptualize the size of a catchment because they vary significantly in size based on the length of a particular stream segment and its surrounding topography—as well as the level of detail used to map those characteristics. To learn more about catchments and how they’re defined, check out these resources: * [An article from USGS explaining the differences between various NHD products] * The glossary at the bottom of [this tutorial for an EPA water resources viewer], which defines some key terms Mapping Steps * Convert the FEMA floodplain polygons to a 30 m raster, giving floodplain areas a value of 1. * Extract the stream and river lines from the NHDPlus HR flowlines (ftype IN (460, 558)). Convert extracted stream and river lines to a 30 m raster. Use the ArcPy Spatial Analysis Expand function to “buffer” the streams by 1 cell. This is the method that SARP uses to create a total stream width of approximately 90 m. * Combine the FEMA floodplains and buffered flowlines using the Mosaic function to make an enhanced floodplain layer. * Clip the 2020 LANDFIRE EVT to the enhanced floodplain layer. This limits the indicator values to the floodplain areas, where they are most relevant. * Reclassify the clipped 2020 LANDFIRE EVT to identify natural landcover. The following classes were considered not natural: Quarries-Strip Mines-Gravel Pits-Well and Wind Pads, Developed-Low Intensity, Developed-Medium Intensity, Developed-High Intensity, Developed-Roads, Developed-Open Space, Agriculture-Pasture and Hay, Agriculture-Cultivated, Crops and Irrigated Agriculture, Caribbean Bush fruit and berries. All other classes were considered natural. * The original NHDPlus HR catchment data was missing coverage of a small area on the west coast of Puerto Rico (just east of Parcelas Aguas Claras). Create an additional catchment polygon for this missing area so that the indicator covers the entire island of Puerto Rico. * The missing area is essentially outlined by extremely thin catchment polygons. To fill the gap, make a new rectangular feature class covering the missing area, then union it together with the original NHDPlus HR catchments. From that output, select the newly created polygon that fills in the hole. * The resulting polygon is a multipart feature, so use the explode tool to separate out just the missing catchment. Export it as a shapefile. * Union together the missing catchment with the other NHDPlus HR catchments and use that combined output as the catchment layer for the rest of the mapping steps. * Calculate the percent of riparian natural landcover inside each NHDPlus catchment using ArcPy Spatial Analyst Zonal Statistics “MEAN” function. * Reclassify the above raster into the 1-5 classes seen in the final indicator values below. * Clip the resulting raster back to the enhanced floodplain layer. It is necessary to do this again since the zonal statistics function outputs pixel values for the entire catchment. During this step, assign a value of 0 to areas outside the enhanced floodplain. Zero values are intended to help users better understand the extent of this indicator and make it perform better in online tools. * Clip to the Caribbean Blueprint 2023 subregion. * As a final step, clip to the spatial extent of Southeast Blueprint 2023. Note: For more details on the mapping steps, code used to create this layer is available [in the Southeast Blueprint 2025 Data Download] or [Caribbean-only Southeast Blueprint 2025 Data Download] under > 6_Code. Final Indicator Values Indicator values are assigned as follows: 5 = >90% natural landcover within the estimated floodplain, by catchment 4 = >80-90% 3 = >70-80% 2 = >60-70% 1 = ≤60% natural landcover within the estimated floodplain, by catchment 0 = Not identified as a floodplain Known Issues * This indicator does not account for the accumulated impacts of upstream riparian buffers. Buffers at the headwaters are treated the same as those downstream. * This indicator does account for river or stream size in relation to the estimated floodplain. Aquatic habitat needs may differ based on the river size class. For example, smaller headwater streams may need more natural landcover than larger rivers to maintain aquatic health. It also does not account for variation in buffer quality within the floodplain at a scale below the catchment. This means that within the estimated floodplain, loss of natural habitat adjacent to the river is treated the same as loss farther away. * The NHDPlus flowlines in the headwaters could represent intermittent or ephemeral streams. They were not excluded, so the indicator could be overprioritizing headwater areas relative to second-, third-, or fourth-order streams. * The National Hydrography Dataset digitizes surface water systems at the 1:24,000 resolution. It does not digitize every small, ephemeral stream. As a result, some stream channels that contribute excess sediment to downstream streams or the ocean are not included in this indicator. * NHDPlus HR contains multiple catchments that are very small. The reduced size of these catchments may result in exaggerating their values in the indicator. Other Things to Keep in Mind * Headwater streams are important to freshwater systems but are not always well-captured in the FEMA floodplain dataset. To better represent headwater streams in this indicator, we chose to buffer flowlines and include them as additional floodplain areas to give those areas the opportunity to be included in the Blueprint. * You may notice stream sections in this indicator that appear to be unconnected to other stream networks. These occur because the National Hydrography Dataset digitizes surface water streams that are not always connected to downstream stream segments. We assume that in these cases, the surface water streams sink into karst areas (e.g., in northwest Puerto Rico around Quebrada). We still included these stream segments in this indicator because they could provide freshwater water habitat for aquatic species. Disclaimer: Comparing with Older Indicator Versions There are numerous problems with using Southeast Blueprint indicators for change analysis. Please consult Blueprint staff if you would like to do this (email [hilary_morris@fws.gov]). Literature Cited LANDFIRE, Earth Resources Observation and Science Center (EROS), U.S. Geological Survey. Published August 1, 2022. LANDFIRE 2020 Existing Vegetation Type (EVT) Puerto Rico US Virgin Islands. LF 2020, raster digital data. Sioux Falls, SD. [[https://www.landfire.gov]]. Moore, R.B., McKay, L.D., Rea, A.H., Bondelid, T.R., Price, C.V., Dewald, T.G., and Johnston, C.M., 2019, User's guide for the national hydrography dataset plus (NHDPlus) high resolution: U.S. Geological Survey Open-File Report 2019– 1096, 66 p. [[https://doi.org/10.3133/ofr20191096]]. Naiman, Robert J., and Henri Decamps. “The Ecology of Interfaces: Riparian Zones.” Annual Review of Ecology and Systematics 28 (1997): 621–58. [[https://www.nativefishlab.net/library/textpdf/19487.pdf]]. WeConservePA. 2014. ConservationTools.org: The Science Behind the Need for Riparian Buffer Protection. [[https://conservationtools.org/guides/131-the-science-behind-the-need-for-riparian-buffer-protection]]. U.S. Geological Survey (USGS). National Hydrography Dataset Plus High Resolution (NHDPlus HR). Accessed November 30, 2022. [[https://www.usgs.gov/national-hydrography/nhdplus-high-resolution]].