ESTIMATION OF MOUNTAIN FRONT RECHARGE TO REGIONAL AQUIFERS .1. DEVELOPMENT OF AN ANALYTICAL HYDROCLIMATIC MODEL

This paper addresses the hydroclimatic modeling of mountain front rech arge to regional aquifers. An analytical relationship between the mean seasonal precipitation and runoff is obtained based on a conceptualiz ation of the hydrologic processes occurring in hard rock mountainous t errain and a derived-distribution approach where the input variables a re considered to be stochastic and their probability distributions are transformed into the probability distribution of the output variable by using the deterministic physical process. In a first-order approxim ation a relationship between the seasonal values of precipitation and runoff is obtained. An analytical model of the seasonal streamflow is then developed where initial abstraction and the long-term effective s ubsurface outflow, or mountain front recharge, are viewed as unknown m odel parameters. In addition, a procedure that combines the water bala nce equation with a relationship provided by the so-called ''vegetal e quilibrium hypothesis,'' and which enables the estimation of effective soil-related parameters jointly with the mean seasonal evapotranspira tion and surface runoff, is introduced. This procedure is applied to a mountainous watershed in southern Arizona.