MODELS OF SPATIAL AND TEMPORAL DISTRIBUTION OF THUNDERSTORM RAINFALL
A simplified stochastic model based on airmass thunderstorm rainfall data from the 58-square-mile Walnut Gulch Experimental Watershed in south eastern Arizona is being developed at the Southwest Watershed Research Center, Tucson, Ariz. Records from the 95 rain gage network on this watershed pro vide valuable information on airmass thunderstorm rainfall in the Southwestern United States. Proba bility distributions are being used to model random variables—number of cells, spatial distribution of the cells, and cell center depths—of thunderstorms in a summer rainy season. A computer program produces synthetic thunderstorm rainfall based on these distributional assumptions. The synthetic data are compared, with respect to storm center depths and isohyetal map characteristics, with data from the dense rain gage network on Walnut Gulch. The daily and hourly chances of occurrence of seasonal airmass thunderstorm rainfall are modeled. Efforts are being made to model the temporal dis tribution of rainfall from individual cells within the airmass thunderstorm. Finally, the question of model transferability to other regions and locations is tied to defining regional meteorology and local topography.
Climate of Arizona.
"THERE is probably no country on the globe that shows so many striking and picturesque topographical contrasts as does Arizona. Frightful chasms, dark and gloomy cafilons, massive mountains, rolling plains, rich and fertile valleys, arid wastes, and beautiful mountain vales form a panorama of nature at once in her wildest and most gentle mood. Here time has wrought mighty changes, and the face of the land yet bears the traces of the fearful convulsions which rent it from end to end. From Utah to Sonora, and from the great Colorado to New Mexico, the same physical features are met with. Mountain and valley, table-land and plain, barren peak and rocky gorge, and above all a sky without a cloud and a sun unequalled for brilliancy. Such a land is Arizona; a land blessed with many a gift, and showing a wild and attractive beauty that well becomes a clime that has given birth to a race wilder than its caflons and mountains, and with natures as fiery as its summer suns. In order to understand the nature of the climatic conditions found in Arizona, and to study the climate intelligently, it will be necessary to first glance at the geographical location, its area and topography. Arizona is situated between 310 and 370 north latitude and between 1090 and 114°.40' west longitude. It is bounded on the north by Utah and Nevada, on the east by New Mexico, on the south by the Mexican State of Sonora, and on the west
A hydraulic model for the catchment-stream problem. II. Numerical solutions
With the aid of kinematic-wave theory described in Part I for flow over a catchment and along a stream, the predicted form of stream hydrograph is calculated numerically, assuming that the rainfall is of constant intensity and of finite duration. The influence of the parameter λ, a measure of the ratio of stream “response time” to catchment “response time”, becomes significant for λ = 0(1); the general effect of large λ is to delay the arrival time of a flood peak and to reduce its amplitude. For λ small, the catchment discharge function is a good guide to the form of the stream hydrograph. With finite infiltration, the duration of catchment discharge is finite.