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BOO ;'_ F. DROUGHT IN THE SOUTHWEST, 1942-56 . omy thus requires limitations in the natural advantages which might otherwise accrue to anyone who settled up- stream from the vaHey developments, In most States the limitation has been achieved as foHows: By repudi- ation of the traditional privileges of landownership and by declaration that water rights are based on priority in the beneficial use, irrespective of the location of use; by declaration that use for hydroelectric power (which is one of the principal uses of water in headwater areas) is subordinate to domestic and agricultural uses (which are chiefly in downstream areas) ; by development of headwater storage expressly for the benefit of the low- land users; or by some combination of these, Within each of the States in the Southwest, except Texas and' California, water rights to streamflow are based entirely on priority of beneficial use, so that up- stream position gives no advantage, and deliveries to downstream users may be required even though natural conditions are such that most of the water is lost in transport. Because the jurisdiction of each State is limited by its boundaries, however, each State neces- sarily has a separate and independent system of rights based on appropriation, For apportionment of the waters of interstate or international streams, it is nec- essary to rely either upon interstate compacts and in- ternational treaties or upon adjudications by Federal courts. These tend to provide security in water sup- plies for "the downstream areas by limiting the natural advantages enjoyed by the users in upstream areas. Some interstate compacts have been completed for apportionment of the water in relatively smaH streams, as for example the La Plata River Compact of 1922 and the CostiIla Creek Compact of 1944 between Colorado and New Mexico, Water rights in both States are based on priority, and the compacts provi<le integrated distribution and operation, which would otherwise be hampered by the conflicting jurisdictions of the two States, The compacts thus provide for apportionment compll.rable to that which could be provided by either State II.lone for !I. stream entirely within its boundll.ries. For both the Rio Grande II.nd the Colorll.do River there have been long histories of controversy between upstrell.m and downstream users. The instruments that hll. ve been negotill.ted for the purpose of achieving II.n equitable distribution of the WII.ter include the foHow- ing: The Rio Grande Convention of 1906 between the United Stll.tes and Mexico; the Rio Grll.nde, Colorll.do, II.nd Tijuanll. Treaty of 1944, ,also between the United Stll.tes II.nd Mexico; the Colorado River Compact of 1922, between Californill., Colorado, NevII.da, New Mex- ico, Utll.h, Wyoming, and eventuII.Hy Arizonll.; the Rio Grll.nde Compact of 1938 between Colorado, New Mex' ico, and Texll.s; II.nd the Pecos River Compa.ct of 1948 between New Mexico and Texll.s, A common feature of these instruments is that they do not admit that they establish II.ny principles or precedents of general II.p- plicII.bility. Nevertheless !I. few generll.lizll.tions mll.Y be in order. Several compacts and treaties include guarantees of certain minimum qUII.ntities of wII.ter to downstrell.m users, These minimum qUII.ntities II.re generaHy fll.r below the average flow II.vII.illl.ble to the downstream area, but have been greater thll.n the actual flow during some YCll.rs of the recent drought. The Rio Grll.nde Convention of 1906 caHed for delivery to Mexican water users nell.r JUII.rez of 60,000 II.cre-feet of wII.ter, which is less thll.n half the long-term II.verll.ge flow that has been available to them, AnnuII.I deliveries exceeded 60,000 acre-feet until 1951, when only 51,000 acre-feet WII.S anilable'; deliveries were less thll.n half of the specified 60,000 acre-feet in the dry years 1954 II.nd 1955. The treaty, however, hll.s !I. proviso thll.t in event of extra- ordinary drought the II.mount delivered to MexicII.n users shll.H be reduced in the sll.me proportion as the wII.ter delivered to IlI.nds of the Rio Grll.nde project in the United States (Thomas II.nd others, 1962), The Rio Grande, Colorado, and Tijuana Trell.ty of 1944, in its provision concerning the internll.tiollll.l reach of the Rio Grande below Fort Quitmll.n, Tex. (Thomll.s and others, 1962), apportions to the United Stll.tes one-third of the flow of certll.in named streams that enter the Rio Grande from Mexico, but gull.rll.ntees to the' United Stll.tes not less thaIl 350,000 acre-feet (II.nnuII.I II.verage in consecutive 5-yell.r cycles) from those strell.ms, The trell.ty specifies also that, in the event of extraordinary drought which prevents Mexico from making II.vII.illl.ble this qUII.ntity of water, the de- ficiency is to be made up in the next 5-year cycle, Dur- ing the recent drought, the inflow to the Rio Grll.nde from the nll.med tributll.ries reached a minimum annuII.I averll.ge of 647,000 II.cre-feet in the 5-year period 1951- 55, and the gull.rantee to the United Stll.tes would thus have required more thll.n hll.lf the flow of those tribu- taries. Both the Colorado River Compact of 1922 and the Rio Grande, Colorll.do, and Tijuanll. Treaty of 1944 were Iiegotill.ted prior to and in II.nticipII.tion of complete de- velopment of the water resources of the Rio Grande and the Colorado River, Thus, lI.1though protection 0:1 water rights II.lready estll.blished by use was one purpose of the negotiations, a prime objective was to apportion the water stiIl unll.ppropriated and unused. Apportion- ments mll.de by these compacts serve not only to guaran- tee rights to water for future development, but also to set upper limits on development in some arell.s and thus protect the development potentill.ls of other II.rell.S. In