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

This paper addresses the hydroclimatic modeling of mountain front recharge to regional aquifers. An analytical relationship between the mean seasonal precipitation and runoff is obtained based on a conceptualization of the hydrologic processes occurring in hard rock mountainous terrain and a derived-distribution approach where the input variables are 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 approximation 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 subsurface outflow, or mountain front recharge, are viewed as unknown model parameters. In addition, a procedure that combines the water balance equation with a relationship provided by the so-called ''vegetal equilibrium hypothesis,'' and which enables the estimation of effective soil-related parameters jointly with the mean seasonal evapotranspiration and surface runoff, is introduced. This procedure is applied to a mountainous watershed in southern Arizona.