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00151)8 where the water supply is from spring snowmelt, from areas of uniform and restr'ictive soil profiles (Krimgold and Minshall, 1945), where the supply is largely from ground water or spring flow, and where extensive studies have been made of the runoff relations in the particular area. For most of the area of the arid West, however, where water supply for stock ponds is dependent largely on wet weather springs and on surface runoff from areas of highly variable SO ils, vegetation, and rainfall, one must conclude that an accurate estimate of water supply from precipita- tion and precipitation-runoff relations is not yet practical. The paucity of basic information is a further handicap in making such estimates. When water supply for the stock pond is from spring snowmelt, rather satisfactory estimates of the supply can be made from available information on snowpacks and the ir annual variation, together with snow- pack runoff relations. These relations have been established for many areas by the Soil Cons,ervation Service, Weather Bureau, and States and local agencies. Estimates of water supply from areas where the supply occurs largely as surface runoff in high intens ity storms involves: knowledge of the varying infiltration capacit ies of the soils as affected by vegetation, antecedent rainfall and storm characteristics, knowledge of the local precipitation intensities and their areal distribution and frequency, and knowledge of the interrelationship of soil moisture deficiences and precip- itation in the local area. In general, two methods of utilizing this infor- mation to estimate water supply are employed: In,one method', the rainfall excess is estimated by subtracting from the anticipated precip- itation intensity losses from interception, surface detention, and infiltra- tion, to give estimated surface runoff. In the alternate method, multivariate analysis is used to relate the runoff to the precipitation, soil moisture, and vegetation condition, and these relations are used to estimate surface runoff. The results of either method may be helpful -in adjusting known water yields 'from nearby areas. Pre cip itation intens it ies Prec ipitation intens ities and the ir frequenc ies may be estimated from published precipitation records and summaries. Maps of rainfall frequencies for durations from 30 minutes' to 24 hours and for return intervals from 1 to 100 years have recently been published by the Weather Bureau (Hershfield, 1961). The information extracted from guides to precipitation intensities ha.s been summarized for various subregions of the Pacific Southwest (see table 2). These intensities may be supple- mented by referral to local precipitation station records and knowledge of orographic and rain shadow effects. Some extrapolation is generally 17 ",