WSP10396

• File Number: 8056
• Description: Drought Preparedness
• State: CO
• Basin: Statewide
• Date: 1/1/1964
• Author: USGS
• Title: General Effects of Drought on Water Resources on the Southwest
• Water Supply Pro - Doc Type: Report/Study

B28

DROUGHT IN THE SOUTHWEST, 1942-56

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1915

FIGURE 6,- Yearly runoff in the Paolfio border zone.

1920

Mogollon Rim in Arizona-which provide water to the
Salt, Verde, and Little Colorado Rivers; along the
headwaters of the Gila River in New Mexico; and along
the middle Gila River and some of its tributaries in
Arizona, The total range of fluctuations in the period
of record (41,6 to 5 logarithmic standard-deviation
units) is slightly. greater than that shown by the group
of stations in the Pacific border zone; and the year-to-
year fluctuations are considerably greater, for many of
the changes in consecutive years are 3 to 4 units. The
resulting graphs are less regular and offer far less evi-
dence of alternate wet and dry periods than do those
shown on figure 6, This may reflect, in part, the dif-
ference in the precipitation pattern in the Sonoran bor-
der zone, where most of the annual total originates in
the Gulf of Mexico and occurs in thunder storms during
the summer.
In the Mogollon Rim region the 1-, 2-, 3-, hand 10-
year periods of least runoff all occurred during the
. 1892-1904 drought, Comparison of the two drought
periods suggests that the average runoff in 1892-1904
was 63 percent of the 50-year (1904-53) median and in
1943-56, 75 percent, In the groups of stations in the
Gila River drainage basin, whose records do not ex-
tend back to the 1892-1904 drought, the 1-, 2-, 3-, 5-, and
10-year periods of least runoff have all occurred within
the recent drought period. By comparison with either
1892-1904 or 1943-56, the drought of the 1930's was of
minor significance, although the runoff in certain years,
such as 1934, was.relatively low.

Shaded areas Indlcafe
periods when deviation
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Figure 8 shows the regional runoff trends for groups
of streams draining the High Plateaus of southwestern
Utah and the San Juan Mountain region of southwest-
ern Colorado, both within the Colorado Plateau hydro-
logic zone. Despite the geographic separation of these
two groups of stations, there is remarkable similarity in
the graphs, Generally the years of high runoff and
years of low runoff coincide in the two regions, There
are several indications that the stations in southwestern
Utah, which are closer to the Pacific Ocean, are also
more greatly influenced by it. Thus the stations in
southwestern Utah recorded a dry period in 1924-34,
concurrent with one recorded by stations along the Pa-
cific border (fig. 6) and distinct from the 1931-40
drought recorded in southwestern Colorado and in the
Great Plains. The recent Southwest drought is also
more clearly marked in southwestern Utah than in
southwestern Colorado and began in 1945 as it did in
California,
In the San Juan Mountain region, which includes the
headwaters of the Rio Grande and the Arkansas, San
Juan, Dolores, and Gunnison Rivers, the 10-year period
of least runoff occurred during the 1892-1904 drought,
but the 2-, 3-, and 5-year periods of minimum runoff
occurred during the recent drought, In southwestern
Utah, where records do not extend back to the 1892-1904
drought, the 2-,3-, and 10-year periods of minimum run-
off occurred during the 1943-56 drought. In both areas,
runoff in 1934 was less than in any year of the recent
drought, although the deviation below median flow dur-