Groundwater Flow Systems and Their Response to Climate Change: A Need for a Water-System View Approach

Abstract

Problem statement: The interest in early hydrogeological studies was the aquifer unit, as it is the physical media that stores and permits groundwater transfers from the recharge zone to the discharge zone, making groundwater available to boreholes for water extraction. Approach: Recently, the aquifer concept has been complemented by the groundwater flow system theory, where groundwater may be defined by local, intermediate and regional flow systems. This implies that groundwater may travel from one aquifer unit to another aquifer unit (or more) located above or below the former. Water in a local flow system takes months or several years to travel from the recharge to the discharge zone. These flows usually transfer the best natural quality water, so a reduction in precipitation would lessen recharge and diminish stored water, making them more vulnerable to contamination and variability in climatic conditions. Thus, there is a need to define local flows and to enhance actions to protect them from contamination and inefficient extraction. Results: In contrast to local flows, intermediate and regional flows travel from a region, or country, into another, with their recharge processes usually taking place in a zone located far away from the discharge zone (natural or by boreholes). There is a need of groundwater flow systems evaluation by means of an integrated wide system-view analysis of partial evidence represented by surface (soil and vegetation covers) as well as hydraulic, isotopic and chemical groundwater characterization in the related geological media where the depth of actual basement rock is paramount as well as discharge areas. The flow system definition may assist in extraction management strategies to control related issues as subsidence, obtained the water quality change, desiccation of springs and water bodies, soil erosion, flooding response, contamination processes in recharge areas, among others; many of which could be efficiently managed leaning on groundwater functioning. There is increasing evidence that climate becoming more variable and key driver of ecosystem health. Even with climate stability, most developing countries will confront serious water problems by the mid-21st century due to an insufficient knowledge of the functioning of their groundwater sources representing ≈ 99% of available water. Conclusion: Many such problems may be adequately controlled when local flows are defined, since changes in climatic condition are more prone to affect local flows rather than intermediate and regional flows. The value of the flow systems arises from the fact that a wide system view analysis allows adequate crossed examination among relevant data from where water management proposals might more adequately represent field conditions. Examples of successful application of the groundwater flow systems in Mexico and Argentina will be presented including: induced fluoride control, subsidence response, desiccation of springs, flooding water origin definition, basement position in flow-system control, inter-basin flow.