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<br />331 JOURNAL OF APPLIED METEOROLOGY VOLUME 12
<br /> TABLE 4, Estimation of increase in spring runoff due to an increase in winter precipitation.
<br /> Percentage in-
<br /> crease in seasonal
<br /> runoff assumin:~
<br /> Mean seasonal l\.1ean winter precipitation Mean seasonal a 10% increase
<br />CSU runoff (inches) at gages runoff increase in mean winter
<br />number Station name (acre-ft) (inches) No, 1 No.2 No. J No. 4- (inches) (acre-fl) precipitation
<br />1375400 Lake Fork at 150,673 7,29 14,84 7,79 6,97 0,821 17,000 11.00
<br /> Gateview ,~
<br />1371520 Uncompahgre River at 149,610 6.40 6,97 5,35 5,22 0,61 14,200 9.55
<br /> (near) Chromo
<br />1277200 Dolores River at 270,647 9,13 11.41 9,74 9,06 7,70 1.10 32,800 12.10
<br /> Dolores
<br />1272445 San Miguel River near 135,282 8.33 7.83 7,67 0,791 13,000 9,50
<br /> Placerville
<br />1078000 'East Fork San Juan River 75,028 16,10 30,23 11.02 2.25 10,040 14,00
<br /> near Pagosa Springs
<br />1077400 San] uan River at 225,865 13,25 30,23 11.02 10,60 1.46 23,200 11.00
<br /> Pagosa Springs
<br />1077250 Rio Blanco near 51,398 16,50 .10,23 11.02 9,14 1.31 4,0.10 7.95
<br /> Pagosa Springs
<br />1077090 Navajo River at Banded Peak 61,878 16,.10 11,02 9.14 1.58 5,900 9,60
<br /> Ranch near Chroma
<br />1076420 Piedra River near 193,.124 9.68 10,68 8,22 0,88 17,410 9.10
<br /> Piedra
<br />1075830 Los Pinos River near 212,086 13,90 15,44 8,22 1.01 15,300 7,26
<br /> Rayfield
<br />1073480 Animas River at 6.1,397 21.60 16,94 11.61 1.98 .1,860 9,20
<br /> Howardsville
<br />10 73448 Hermosa Creek near 76,161 8,22 19,7 15.44 10,7.3 0,98 9,000 11.90
<br /> Hermosa
<br />1073436 Animas River at 479,575 12,30 10,73 8,22 1.01 37,200 8,20
<br /> Durango
<br />1073408 Animas River near 536,923 9,00 8..H 5,56 0,11 6,660 1.22
<br /> Cedarhill
<br />1073080 La Plata River at 27,186 13,.18 10.73 9,74 1.15 2,280 8,50
<br /> Hesperus
<br />
<br />precipitation, i.e., that
<br />i1Pw=kPw,
<br />
<br />in which i1P w is the mean increase of winter precipita-
<br />tion by cloud seeding, P w the natural winter precipita-
<br />tion, and k the ratio of mean increase of precipitation
<br />to the natural value or relative increase. The effect of
<br />cloud seeding is measured by the increase of usable
<br />runoff. It is assumed that runoff Q is a function of a
<br />representative precipitation P. Then, in the general
<br />form,
<br />
<br />Q= f(P).
<br />
<br />However, it is hard to find an integrated precipitation
<br />that represents the whole basin. Suppose that precipita-
<br />tion data Pj corresponding to Q are collected, as many
<br />as possible, in the basin in question. Eq. (10) is then
<br />modified as
<br />
<br />Q= f(P1,P2,' , .).
<br />
<br />In the case of precipitation management in the San
<br />Juan Mountains area, it is the seasonal runoff Q, caused
<br />mainly by winter precipitation, P wi> and partially by
<br />spring precipitation, Psi> which is of concern. The
<br />relationship is represented more precisely by
<br />
<br />Q= f(Pw1,P81,Pw2,Ps2,' . ,). (12)
<br />
<br />(9)
<br />
<br />Multiple linear regression analysis is applied to find
<br />the approximate relationship. Finally,
<br />
<br />Q=a+b1PWl+ClPsl+b2Pw2+C2Ps2+' . ., (13)
<br />
<br />in which a, bi> Cj are coefficients determined from
<br />available data.
<br />The increase of spring runoff, i1Q, caused by the
<br />increase of winter precipitation, i1Pw, is given by
<br />
<br />i1Q=bli1Pw1+b2i1Pw2+" '.
<br />
<br />(14)
<br />
<br />(10)
<br />
<br />Averaging over the period of record and substituting
<br />(9) into (14) yields
<br />
<br />i1Q=blklPW1+b2k2PW2+" '.
<br />
<br />(15)
<br />
<br />(11)
<br />
<br />By this procedure all i1Qi can be estimated in the
<br />target area. Because it is not possible to predict at
<br />present the average increase of precipitation due to
<br />cloud seeding, it was assumed that the ki did not vary
<br />from basin to basin. For the purpose of this study and
<br />for reasons previously discussed, a uniform k value of
<br />10% was assumed. Table 4 shows the results of the
<br />estimation of the i1Qi. Note that the percentage increase
<br />in runoff varies significantly from the assumed uniform
<br />10% increase in mean winter precipitation. It is
<br />recognized that these values of the i1Qi are only very
<br />rough estimates.
<br />
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