1054 
from those anticipated by the forecaster. Hence, im- 
provement of quantitative weather-forecasting tech- 
niques will materially aid the river forecaster, for he 
can treat weather forecasts in the same manner as 
observed data to synthesize the stream-flow situation 
which will develop. The U. 8. Weather Bureau uses a 
statistical approach to this problem in its water-supply 
forecasts, in which estimates of probable flow volume 
are given for maximum and minimum of record, quar- 
tile, and median precipitation during the late spring 
and early summer months. A system which would in- 
terpret the meteorological situation in terms of an ex- 
tended-range weather forecast would be much superior 
to such a statistical evaluation. 
Broadly speaking, the river forecaster needs two 
types of weather forecasts. For flood forecasting he 
needs a detailed forecast extending from 1 to 10 days 
into the future, giving the amount, time of occurrence, 
and areal distribution of precipitation and, if snow 
melt is involved, temperature. For water-supply fore- 
casting a less detailed outlook for 30 to 90 days ahead, 
indicating in general terms the precipitation anomalies 
and temperature trends, is necessary. Such forecasts 
would, in almost every case, give sufficient advance 
warning to permit carefully planned action, thus avoid- 
ing the waste and inefficiency of emergency methods. 
This need is highlighted by the existence of flood- 
control reservoirs which require a foreknowledge of the 
probable stream flow as much as thirty days in advance 
for successful operation. 
REFERENCES 
1. Brernarp, M., ‘‘The Primary Role of Meteorology in Flood 
Flow Estimating.” Trans. Amer. Soc. civ. Engrs., 109:311- 
382 (1944). 
2. Cuurcsa, J. E., ‘Principles of Snow Surveying as Applied 
to Forecasting Stream Flow.” J. agric. Res., 51:97-130 
(1935). 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
HYDROMETEOROLOGY 
. Harstap, K. C., “Reliability of Station-Year Rainfall 
Frequency Determinations.” Trans. Amer. Soc. civ. 
Engrs., 107:633-683 (1942). 
. Houzman, B., “Sources of Moisture for Precipitation in the 
United States.” U.S. Dept. Agric. Tech. Bull. No. 589, 
Washington, D. C. (1937). 
. Konter, M. A., and Liystey, R. K., “Recent Develop- 
ments in Water Supply Forecasting from Precipitation.’? 
Trans. Amer. geophys. Un., 30:427—486 (1949). 
. Linstey, R. K., Fosxert, L. W., and Kouurr, M. A., 
“Hlectronic Device Speeds Flood Forecasting.” Engng. 
News Rec., Vol. 141, No. 26, pp. 64-66 (1948). 
. Linsury, R. K., Kontmr, M. A., and Paunyus, J. L. H., 
Applied Hydrology. New York, McGraw, 1949. 
. Lunpquist, R. E., and Ricuarps, M. M., ‘‘Flood Forecast 
Centers—What Makes Them Tick.’ Engng. News Rec., 
Vol. 141, No. 24, pp. 98-100 (1948). 
. Meyer, A. F., Evaporation from Lakes and Reservoirs. 
A Study Based on Fifty Years’ Weather Bureau Records, 
56 pp. Minnesota Resources Commission, St. Paul, 1942. 
RicHarpson, B., “Evaporation as a Function of Insola- 
tion.”’ Trans. Amer. Soc. civ. Hngrs., 95:996-1019 (1931). 
Rouwer, C., “Evaporation from Free Water Surfaces.” 
U. S. Dept. Agric. Tech. Bull. No. 271, Washington, 
D. C. (1931). 
SHerMaN, L. K., “Streamflow from Rainfall by Unit- 
Graph Method.” Engng. News Rec., 108:501-505 (1932). 
Spreen, W. C., “A Determination of the Effect of Topo- 
graphy on Precipitation.’”’ Trans. Amer. geophys. Un.., 
28 :285-290 (1947). 
Surron, O. G., ‘‘Wind Structure and Evaporation in a 
Turbulent Atmosphere.” Proc. roy. Soc., (A) 146:701- 
722, (1934). 
TuHorNTHWwaITH, C. W., and Houzman, B., ‘“Measurement 
of Evaporation from Land and Water Surfaces.” U.S. 
Dept. Agric. Tech. Bull. No. 817, Washington, D. C. 
(1942). 
Wiuiiams, G. R., ‘‘Drainage of Leveed Areas in Mountain- 
ous Valleys.”? Trans. Amer. Soc. civ. Engrs. 108:83-114 
(1943). 
