Drought & Surface Water Supply Index


The Colorado Water Conservation Board (CWCB) and DWR co-chair the Governor’s Water Conditions Monitoring Committee (WCMC) to monitor conditions that affect Colorado’s water supply, including snowpack, reservoir storage, streamflow, historical climate norms, long term precipitation and temperature outlooks, and climate variations.  WCMC meeting documents, including the brief Drought Update, are available on the WCMC webpage. Each month, DWR also generates the Colorado Water Supply Conditions Report and the supporting Surface Water Supply Index (SWSI), described below.


Important Links


Applications & Tools



Colorado Water Supply Conditions Reports

The Colorado Water Supply Conditions Update Reports are produced by DWR on a monthly basis.  The reports incorporate Division-specific information and the month’s SWSI maps and tables to produce a comprehensive review of water conditions for each of Colorado’s seven river basins.




Surface Water Supply Index (SWSI) 

The SWSI is calculated by DWR each month. It is an indicator of mountain-based water supply conditions in the major river basins and sub-basins of Colorado.  The SWSI compares the total volume of water in a basin or sub-basin against the volume available in the same month of historical years. The SWSI scale is from -4 to +4, where -4 indicates severe drought and +4 indicates abundant water supply. Since runoff forecasts are only generated in the winter and spring, the data considered in the calculation varies throughout the year as follows:

  • January 1 – June 1: Forecasted Runoff + Reservoir Storage  
  • July 1 – September 1: Previous Month's Streamflow + Reservoir Storage  
  • October 1 – December 1: Reservoir Storage

SWSI Map Tools

To view the SWSI map layer, open MapViewer, and, in "Map Layers", check the "Surface Water Supply Index (SWSI)" layer.  This displays the most recent month’s SWSI values on the map. SWSI maps and tabular data are also included in each monthly Colorado Water Supply Conditions report.

Colorado Information Marketplace (CIM)Tools include tabular datasets for SWSI