Indices of water availability assessment on hydrological basins: A case in Mexico

Abstract

Water use and demand are increasing sensitive; all the productive sectors require bigger volumes with a minimal quality to complete the expectations in the requirements of food, goods, services and manufactured products. The hydrological systems are under increasing pressure and in Mexico City this need has led to severe crises owing to the inadequacy of the natural water supply to meet this demand. Particularly, water over-assignments phenomenon is present; the assignment to some users with volumes that overcome the natural capacity, due mainly to ignorance about the real watershed capacity, so these volumes lead to stressing of the hydrological systems, creating dangerous situations because the conflicts and social unbalances are increased, especially during shortage periods. Given the complexity and uncertainty on hydrologic phenomenon and the variability in time, if it is not properly assessed it can drive to over evaluating the water supply capacity and then to the creation of false expectations that potentially cause a crisis and negative impacts because of water inadequacy. In the face of this dilemma, it is essential to carry out hydrological balances keeping in mind that watershed is the unit of analysis, and considering the diverse water uses, individually and as a whole in order to evaluate the potentiality, as objectively as possible, of the water available related to water demand. This allows us to estimate the level of relative availability, and on this basis, to improve water planning with a reasonable risk of falling under conditions such that imply over exploitation and committing their sustainability. This acquires special importance for basins where hydrometric information is scarce or null, and then one has to apply indirect methods for water availability estimation; the results are expressed graphically as a semaphore plane.