Available with Spatial Analyst license.
The global Watershed function determines the contributing area above a set of pixels in a raster. Watersheds are delineated from a flow direction raster which identifies the flow direction from every pixel.
For more information, see the How watershed works topic in the Spatial Analyst tool help.
You will need to provide the locations from which to determine the catchment area. When a threshold is used to define a watershed, the pour points for the watershed will be the junctions of a stream network derived from flow accumulation. Therefore, a flow accumulation raster must be specified as well as the minimum number of pixels that constitute a stream (the threshold value).
The value of each delineated watershed will be taken from the pixel value of the pour point in the input raster.
Flow Direction Raster
The input raster that shows the direction of flow out of each pixel.
The flow direction raster can be created by running the Flow Direction function.
Pour Point(s) Raster
The input pour point locations.
This raster represents pixels above which the contributing area, or catchment, will be determined. All pixels that are not NoData will be used as source pixels.
This function requires that the ArcGIS Spatial Analyst extension to be enabled.