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<br />';Water in the Balance';
<br />
<br />As summer comes to an end, the westerly winds aloft
<br />gradually increase again and low level moisture from the
<br />south and east retreat. The fall is often characterized by
<br />long periods of sunny, dry weather. Occasionally, however,
<br />Pacific moisture reaches western Colorado, sometimes in
<br />dramatic fashion as moisture from dissipated Pacific
<br />hurricanes sweeps northeastward. Infrequent but occa-
<br />sionally very heavy fall rains are an important part of the
<br />climate of western Colorado. A few storms will also
<br />harvest Gulf of Mexico moisture over eastern Colorado.
<br />
<br />These seasonal weather patterns and the shifting of
<br />moisture sources through the year are a natural part of
<br />Colorado's variable climate. In combination with the
<br />topography of the state, the r~sult is seasonal precipitation
<br />patterns that differ from north to south, from west to east
<br />and also locally as a function of elevation.
<br />
<br />Drought can be initiated by either a lack of moisture from
<br />one or more of these predominant supplies, or a lack of
<br />upward vertical motion to harvest the water vapor from the
<br />atmosphere. Due to natural variations in our climate, single
<br />season droughts over some portion of the state are quite
<br />common. However, with so much climatic diversity and with
<br />such a variety of moisture sources and precipitation
<br />mechanisms, it is historically rare for all areas to be deficient
<br />at the same time. For example, in any given year, winter
<br />snowpack accumulation may be subpar in some portion of
<br />the mountains, but summer storms may compensate.
<br />Likewise, it is very common to have very dry winters east of
<br />the mountains, but a few spring storms can make up for
<br />winter deficits.
<br />
<br />Multiple season and widespread droughts do happen,
<br />however, and we must be aware of their potential.
<br />
<br />Major Water Demands in the Seven Colorado Water Divisions
<br />
<br />The figure below shows the State of Colorado divided into the seven Water Divisions that are used for water right
<br />administration and management purposes by the Colorado Division of Water Resources. These Water Divisions corre-
<br />spond with the major river basins in the state, with some of the smaller river basins lumped together into a single division
<br />(e.g. the San Juan and Delores Rivers in the southwestern corner of the state, and the North Platte with the Yampa-White).
<br />Additional information on major water demands by basin available in Water, Colorado s Precious Resource, 2nd Edition.
<br />
<br />I,
<br />
<br />n___:_:.ft.:~_
<br />.........t'..."...n....
<br />Upper: Wet late Nov~May, Dry mid-Jun-Sep
<br />Wettest area in Colorado (one of two)
<br />Lower: No clear wet or dry seasons.
<br />Major Demands
<br />Dryland crops, livestock. skiing and other
<br />winter spons.
<br />
<br />
<br />Precipitation
<br />Upper: Wet Late Nov~Apr, Dry Jun-
<br />mid.Jul
<br />Lower: No clear wet or dry season.
<br />Major Demands
<br />Several of Colorado's biggest ski
<br />resorts, rafting, vineyards, dryland
<br />crops and pasture for caule.
<br />
<br />Precipitation
<br />Upper: Wet mid-Nov-Mar, Dry
<br />mid-May-mid-Jun
<br />Lower: No significant wet season.
<br />Dry lale May-Jun, slightly wet mid-
<br />Jul-Aug
<br />Major Demands
<br />Dryland crops, skiing, lake sports.
<br />
<br />Precipitation
<br />Upper: Wet Dec-Mar & late Jul~
<br />early~Oct, Dry May-early Jul &
<br />mid-Oct~mid~Nov Wettest area of
<br />Colorado (one of two).
<br />Lower: Wet Dec-Mar & late Jul-
<br />early-Oct, Dry May-early Jul &
<br />mid-Oct-mid-Nov
<br />Major Demands
<br />Dryland crops. com, apples,
<br />national parks, rafting, skiing.
<br />
<br />Precipitation
<br />Upper: Wet Dec.Apr, Dry Jun
<br />& Aug~Oct
<br />Lower: Dry Nov.~Feb., Wet
<br />Apr.-Jut
<br />Major Demands
<br />MunicipaVlndustrial, 1.4
<br />million irrigated acres. dryland
<br />crops for livestock, vegetables,
<br />fishing, hunting. wildlife.
<br />
<br />1
<br />
<br />South Platte
<br />
<br />2
<br />
<br />Arkansas
<br />
<br />Precipitation
<br />Upper: Wet Dec-Mar & mid-Jul-
<br />early Oct, Dry May~mid-JuL
<br />Lower: Dry Nov.Apr, Wet mid~
<br />Jul-Sep (Driest area of Colorado)
<br />Major Demands
<br />Mostly crops irrigated with
<br />groundwater from San Luis
<br />Valley aquifer.
<br />
<br />Precipitation
<br />Upper: Wet Dec-Mar & Jul-
<br />Aug, Dry May-Jun
<br />Lower: Dry Nov~Feb, Wet
<br />May~Aug
<br />Major Demands
<br />Some municipaVindustrial,
<br />dryland crops including com,
<br />. alfalfa, and pasture. and
<br />vegetables and melons.
<br />
<br />12
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