I want to delineate a watershed using ArcSWAT tool. Upon uploading the DEM from disk a window pops up & says: Dataset must have a projected coordinate system. The current coordinate system is geographic. Please define a projected coordinate system of your DEM dataset using ArcToolbox before proceeding. Where as the coordinate system of the DEM is GCS_WGS_1984. Could you help me i fixing it?
The message of the pop up window is telling you that your data must have a projected coordinate system, which means your DEM must be converted to meter/feet depending on the selected projection. Currently, your data is in WGS84 which is a geographic coordinate system and the horizontal unit for your DEM is in degrees. You must reproject your DEM so that your horizontal and vertical units are the same. One of the most common projection is Universal Transverse Mercator (UTM) which gives the horizontal and vertical units in meter. To reproject your data in ArcGIS:
ArcToolbox > Data Management Tools > Projections and Transformations > Raster > Project Raster
You can refer to this article to understand about coordinate systems, map projections, and geographic (datum) transformations