Empirical Linear Model for Base Flow Forecast as a Function of the Rainfall Moving Average

Climatic variation may result in insufficient input of water in the water balance in a region, resulting in inconsistencies in the water rights permits. During droughts such reference discharges may not reach the water rights permits, requiring groundwater extraction to compensate this deficiency in surface water bodies. The aim of this study is to determine the integrated water availability (surface and groundwater), using an empirical linear model, proposed as a function of the average rainfall of previous periods related to the aquifer regulation time. Correlation and spectral techniques were employed for time-series analysis of precipitation (P) and base flow discharge (Q) in the Ribeirão da Onça watershed, to determine response times of Q as a function of P. The proposed methodology was developed for precipitation and discharge observed from 2003 to 2014 in a watershed with an area of 65 km². The obtained results indicate that the aquifer stores the rainfall water with regulation times of approximately 60 days for the subsurface flow, and approximately 2 years for the base flow. The methodology was also tested for two sub-basins of the Jacaré-Guaçú River watershed, with areas of 1867 and 3519 km².The proposed methodology allows the estimation of a sustainable reference discharge making it possible to predict the base flow variation during recession periods, since it is defined as a function of past rainfall.