Water Use in Montana Active

As part of these efforts, county-level estimated use of water in Montana for 2015 was compiled for eight categories of use—irrigation, public supply, domestic, livestock, industrial, mining, thermoelectric power, and aquaculture.  In 2015, preliminary estimates indicate that a total of about 9,810 million gallons of water per day (Mgal/d) were withdrawn from Montana's streams and aquifers for these eight categories of use.

• Surface water withdrawals totaled  9,610 Mgal/d (about 98 percent of total) 
• Groundwater withdrawals totaled 200 Mgal/d (about 2 percent of total)

In 2015, about 2.5 million acres in Montana were irrigated based on the ArcGIS irrigated land coverage provided by the Montana Department of Natural Resources and Conservation.  The irrigation water use for Montana was estimated by using NWUSP-provided estimates of actual evapotranspiration based on 1-kilometer resolution satellite data which was analyzed through the Operational Simplified Surface Energy Balance (SSEBop) model (Senay and others, 2013) to assist in estimating consumptive-use of water on irrigated lands.  The consumptive-use estimates were combined with irrigation efficiencies and transmission-loss estimates to calculate irrigation withdrawals for the 2015 growing season (April through September).  Preliminary estimates indicate that irrigation accounted for about 9,450 Mgal/d or about 96.3 percent of total withdrawals for all uses.  Surface water was the source of about 99 percent of irrigation withdrawals and groundwater provided about 1 percent.  Not all water withdrawn for irrigation was consumed by plants or evaporated; much of the water withdrawn may result in return flow (surface runoff that reaches a surface-water source or water that infiltrates past the root zone to potentially recharge the groundwater system) thus returning to the local hydrologic system and potentially available for other uses.

Sources/Usage: Public Domain.

Water-use estimates for the remaining seven categories were based on a variety of sources and calculations. In general, publically-available metered or reported withdrawal information is very limited for the state of Montana. As a result, withdrawal estimates are often based on the interpretation of a limited amount of reported data that are in turn used to estimate withdrawals for other facilities or areas. For example, calculated per-capita water-use estimates from a set of public-supply systems with reported withdrawals were used to calculate public-supply water use in other areas of similar climatic conditions.  In addition, the USGS NWUSP provides national data sets for the livestock, mining, thermoelectric, and aquaculture categories.  In the pie chart above the approximate estimates for 2015 Montana withdrawals for all eight categories can be found.  Surface water was the dominant source for most water use categories, groundwater was the primary source for public supply, domestic, and industrial water uses.

Sources/Usage: Public Domain.