Analysis of Ephemeral Flow in Aridlands

An important parameter is found to be the flow duration, which describes the opportunity for natural recharge. Arid-land hydrology is, in effect, characterized by the absence of base flow, special precipitation patterns, and scarcity of data. A stochastic model of flow duration is developed for a stream near Tucson, AZ, using a regional model of rainfall. The number of flow events per summer seems to follow a Poisson distribution and that in winter, a geometric distribution, whereas the flow duration per event seems to follow a negative binomial distribution in both cases. Time series estimates of monthly streamflow of the Rillito Creek, AZ, are given to illustrate the correlation between various months and the difficulty of interpreting such time-lumped data.