Rainfall intensity and elevation in southwestern Idaho


  • Charles F. Cooper


There is no apparent relationship between elevation and the intensity of spring and summer rainfall in a 93-square-mile area with a range of 3500 feet in elevation in semiarid southwestern Idaho. Analysis covered four years' data from recording rain gages with an average density of 1 per square mile. Rainfall bursts amounting to 0.10 inch or more were considered. The maximum intensity recorded was 0.49 inch falling at 9.8 inches per hour. Rainfall in excess of 0.8 inch per hour occurred an average of once a year. The logarithm of the amount of rain falling in excess of a given intensity plots as a straight line against intensity. There is no difference in this relationship when the data are separated by elevation classes. The amount of rainfall decreases by about one-half with each 1-inch-per-hour increase in rainfall rate. This ratio may be a characteristic of the regional climate. It is suggested that data from accessible valley stations can be used to estimate the relative frequency of high intensity rains throughout an area of appreciable range in elevation.