Methodology to determine availability and deficit of surface water in basins: application case for the Mexican norms

Abstract

According to the Mexican National Waters Law, the existence of an annual mean availability of surface water is a condition for the authorization of new concessions or designations in a basin. The Official Mexican Norm NOM-011-CNA-2000 establishes the procedure for its determination. Although the concept of a deficit is opposite to that of availability, the former is implicit and the latter is a Mexican norm. Both concepts are analyzed in this work, and a general and consistent mathematical proposal is presented in order to independently determine both; decomposing total deficit into internal and external is also considered. The conceptual and numerical functionality is shown for the methodology proposed based on its application to the case of the Bravo River basin, presented as an example for demonstration purposes. The procedure developed is  applicable to any basin regardless of the country in which it is located,
and facilitates the interpretation by society of studies related to water availability and its use in water planning. The incorporation of the results of this work into the NOM-011-CNA-2000 will enrich this important normative instrument in Mexico.