Water Demands in the South Platte Basin

Demand for water by sector (i.e. M&I or Ag) varies widely by sub-region. The following provides an overview of current and forecasted demands within each of the two major sectors in the South Platte:

Municipal and Industrial

Throughout the entire basin M&I demands account for roughly 25 percent of all diversions.  Driven largely by rapid population growth, demand for water in the South Platte has increased dramatically over the past several decades.

Between 1950 and 2000, population in the South Platte nearly tripled, increasing at an average annual rate of 2.7 percent per year. This growth, along with generally increasing per capita demands, has resulted in a shift in both the ownership and use of water for municipal and industrial (M&I) purposes throughout the South Platte. This growth is expected to continue, as total population within the South Platte is expected to more than double by 2050. Assuming current per capita consumption rates, total M&I demand is expected to increase by 480,000 acre feet over the next 30 years.

As of 2000, residents in the Central sub-region accounted for 68 percent of the basin’s total population. Between now and 2030, the Southern sub-region is expected to grow nearly three times faster than the Central region (3.56% to 1.33%). The Northern sub-region is expected to grow roughly 0.7 percent faster than the Central sub-region. While accounting for only 30 percent of the basin wide demand in 2000, the areas outside of the Central region are expected to account for 50% of the new demands forecasted for 2030.

In addition to questions surrounding the regional distribution of demands, intra and inter-annual variability in demands represents a significant source of uncertainty for regional planners. While agricultural demand occurs only during the summer months, M&I demands occur year round. Both of these demands fluctuate substantially depending on local climatic conditions.

This issue is illustrated to the left, where estimated total monthly M&I demand for the South Platte under 2000 and 2030 population totals are presented. In addition, estimated demands based on temperature and precipitation conditions from 1997 (wet) and 2000 (dry) are presented.

Agricultural

On average agricultural activities in the South Platte divert roughly 2.2 million acre feet of water annually. Despite rapidly increasing M&I demands and water rights transfers from Ag to M&I users, irrigated acreage and agricultural withdrawals have remained relatively stable over the last 40 years.

This is contrary to what is commonly believed and sometimes reported (e.g. Smith et al. 1996). However, analysis of USGS total irrigated withdrawal data for the period 1965 to 1999 does not reveal any significant trends in irrigated acreage or deliveries to agriculture. Considering the population boom described above it is surprising that, until the recent drought, the issue of water availability has not played a more prominent role in shaping development along the Front Range. There are two explanations for this. First, significant trans-basin imports early in this period helped relax the constraint on available water supplies. Second, roughly half of this growth occurred during the last twenty years a period that received precipitation amounts well above average.

Agricultural demands are typically located downstream of municipal users and rely heavily on their return flows. Year-to-year changes occur largely as a result of climatic variability. Because the system is already fully appropriated, the extent to which long-term changes in irrigation demand occur will depend largely on changes in how policies enacted to support M&I growth affect available agricultural supplies.