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~olorado Water Resources Research Institute. Water Demands in Colorado: Before we continue our discussion of the history of wet and dry periods in Colorado, and considering drought and drought preparedness, we should remember that precipita- tion - our source of water supply - is only half of the drought picture. The impacts of a lack of precipitation on humans and nature depend on several factors including: how water is used; when water is needed; how much water is needed; and how long water can be stored before use. Although this paper is based on research regarding the history of wet and dry periods in Colorado. some discus- sion is provided here of some of the major uses of water in Colorado to put these historic precipitation patterns in perspective. This is particularly important since the types and locations of water demands in Colorado have under- gone some dramatic changes, particularly in the last 20 years. In many cases, important uses of water in Colorado are "'non-consumptive", such as water in the form of snow for skiing or water in streams for recreation or habitat. Water is used multiple times between the time it enters Colorado as precipitation and the time it leaves the state as streamflow or evaporation. This discussion addresses the timing of water use and relative amount of water required for different demands in Colorado. As we have seen from the ski seaSon of '76- '77 or any of several droughts that have impacted important crops in Colorado, major impacts to any of the economic sectors dependant upon these water uses have serious impacts on the economy of the entire state. In addition to these in-state uses of water, we also have several interstate compacts or agreements requiring water to flow from Colorado to other states. Agricultural water supplies. This remains the number one water demand in Colorado:. However, Colorado agriculture has undergone recent changes, including the introduction of new types of crops, new irrigation tech- niques, renewed interest in non-irrigated agriculture, and more drought resistant strains of traditional crops. Agricul- turalusers have four sources of water: direct precipitation, streamflow diversions, reservoir storage and releases, and groundwater withdrawals. Storage of water in reservoirs is one form of drought mitigation. When more precipitation is available, however, farmers can rely less on their stored water supplies, and withdraw less water from streams and aquifers as well. Information on snowpack and precipita- tion that has fallen by early April is used to determine how the irrigation reservoirs are managed. Examples of irri- gated agriculture in Colorado include corn, sorghum, dry beans, barley, potatoes, sugar beets, and vegetables. Water demands for most irrigated agriculture begin increasing in late April, peak in early July, and drop off into late October. Non-irrigated or "dryland" crops are more susceptible to damage by droughts, especially "single season" droughts. Majer dryland crops, which include the largest acreage of crops in Colorado, include winter wheat How and when we use our water and beans, as well as pastureland. Winter wheat crops are successful if they have some precipitation in the fall to start germination of the plants. and some precipitation in spring to develop the grains. Pastureland is particularly important for livestock. Newer non-irrigated crops include sorghum. corn, canela, and sunflowers, which are more drought resistant but still need adequate soil moisture and timely precipitation for a successful yield. Municipal and industrial water supplies. Municipalities typically develop extensive storage facilities to ensure reliability of water supplies. For example, some cities have storage facilities in several different river basins, which allows them to use different sources of water in situations where one or more area has below normal precipitation. Water demands for industrial and many municipal uses are fairly constant throughout the year. However, about 50% of municipal water is used for watering oflawns and landscapes (e.g. parks and golf courses); these demands occur mainly in the summer. Recreation. There are many uses of water in the state for recreation. Typically, recreational industries require that precipitation falls or has fallen by a certain time of year. For example, ski resorts must have water available for snow making in October and November, and snow direct from snow precipitation by November and continuing through April to ensure a successful season. The most profitable period, however, is during the December/January holiday season, so earlier snows are critical. White-water rafting is also depen- dent upon winter snows, although the timing of the snowfall is less important. Water for rafting comes from melted snow in the spring. Peak streamflows from snowmelt occur in May and June, and decreases later in the summer. Summer recreation, particularly in lakes (e.g. fishing and boating) requires water available in May through September. Forests and Environmental Uses. National forests and parks are important for Colorado's economy both for timber re- sources and for tourism. Forest fire is also a major safety concern during droughts. In-stream uses of water to support animal and plant life and provide habitats is one of the more recent water demands of concern in Colorado. Water require- ments to support critical habitat for different species vary throughout the year. Water planning and the management of water facilities now often include some consideration of these demands. Hydropower A measurable amount of Colorado's power is generated in the form of hydroelectric energy, which can be provided when reservoir storage is high. If reservoir levels drop, the amount of energy that can be generated is reduced, and greater power demands by Colorado may impact "the Western Power Grid". Our peak power demands Occur at the time when our water levels are falling, in the heat of the summer. 11