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Project: Development of a Landscape Riparian Ecosystem Assessment Method: SCREAM Model

Background and Objectives

Southern California coastal wetlands and watersheds have been dramatically altered or destroyed by human activities over the past 150 years. Estimates of loss show riparian habitat reduced by 90-95%, much of this in recent decades. Development pressure on southern California continues to be intense, with a doubling of the 1995 population expected by 2020. Thus, attention has become focused on preservation and restoration of the remaining habitat. However, with limited funding available for conservation, it is important to set regional priorities. Priority setting should take into account several factors, such as an ecological assessment of the existing natural resources, socio-economic considerations (e.g. cost, equitable access to resources), and feasibility of preservation or restoration.

The objective of this project was to create an assessment tool for predicting the relative contribution of a riparian area to overall ecological function. The GIS-based tool, called the Southern California Riparian Ecosystem Assessment Method (SCREAM) can be used to assess the ecological condition and stressors affecting riparian habitat at a landscape scale. It considers both biological structure and physical processes within four primary functional components: habitat support, hydrology, sediment, and biogeochemistry.

Conceptual assessment framework for SCREAM (left); Greater detail of the metrics within the hydrology attribute (right)


This project was conducted from 2002 to 2007.


The SCREAM model was developed by the NOAA Coastal Services Center and SCCWRP in consultation with the Southern California Wetland Recovery Project (WRP) Science Advisory Panel. The foundation of SCREAM is a geospatial database (ArcGIS geodatabase) that is created using GIS data layers on the physical, biological, hydrologic, and chemical properties of a watershed. Input data layers include land use/land cover, channel properties (i.e., channelization), infrastructure (e.g., bridges), locations of known pollutant point-source discharges, soil characteristics, topography, and documented occurrences of sensitive and invasive species.

To utilize the SCREAM model, existing or new GIS data layers must first be compiled and organized. The information contained in those layers is then used to calculate hydrologic, biogeochemical, and habitat condition scores. First, the model queries the geospatial database and assigns scores to series of metrics using a defined set of formulas. All streams in a watershed are divided into “units of analysis” (UAs) and condition scores are calculated for each UA. Metric scores are then integrated into component scores, and finally into overall scores for hydrology, biogeochemistry, and habitat, using a series of rule based models. Condition scores are based on an integration of features within a specific UA as well as in surrounding or adjacent areas that may affect the overall condition of the UA. Specific scoring algorithms and weightings can be user-modified based on availability and confidence of specific data layers. The output of the model is a GIS coverage in which each UA is attributed with overall condition scores, as well as scores for the underlying metrics.


SCREAM is one of several decision-support tools used by the WRP and NOAA for planning and site prioritization. Potential uses include spatial data display, identification of high-quality habitat for restoration or mitigation sites within a watershed, and targeting areas for management measures such as BMPs.

Examples of application of SCREAM output data to restoration and management planning. The left panel represents a conservation example; the right panel represents a management example.


This project was conducted in collaboration with the NOAA Coastal Services Center and the Wetland Recovery Project’s Science Advisory Panel, Managers Group and County Task Forces.

For more information on Landscape Riparian Ecosystem Assessment Method, contact Eric Stein at (714) 755-3233.
This page was last updated on: 6/30/2014