Water Resources in the Desert Southwest - Design with the Desert: Conservation and Sustainable Development - page 79

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

30

(A)

25

20

15

10

5

0

30

(B)

25

20

15

10

5

0

30

(C)

25

20

15

10

5

0

30

(D)

25

20

15

10

5

0

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

FIGURE 4.4
Annual flow volumes for the Colorado River. (A) Colorado River below Hoover Dam, Arizona—Nevada (USGS
gauging station 09421500). (B) Colorado River below Parker Dam, Arizona—California (09427520). (C) Colorado
River above Imperial Dam, Arizona—California (09429490). (D) Colorado River below Yuma Main Canal
Wasteway at Yuma, Arizona (09521100).

Increasingly, surface-water supplies in arid and semiarid regions are overallocated
owing to the demands of agricultural production competing with the extreme growth and
water demands of urban areas. Water availability has become an increasing scientific chal-
lenge because of the interconnectedness of surface-water and groundwater systems and
the legal framework of water allocations. 24 Surface-water availability is likely to become
less dependable in the future as a result of the influence of sustained drought, increasing