Global Groundwater Vulnerability to Floods and Droughts
Background:
Rising demands from global population growth, rapid urbanisation, intensification of agricultural production, as well as increasing industrialisation will require growing reliable quantity and quality of water. To meet these increased demands, policy makers, natural resource managers and planners have to stop focusing solely on surface water and consider conjunctive uses of both surface water and groundwater resources. Groundwater resources can represent an economical, reliable and sustainable contribution to water challenges. Furthermore, these resources are naturally less vulnerable and more resilient to external influences, such as floods and droughts, than surface waters. These extreme hydrological events can have devastating impacts on human life, generate economic loss and increase poverty and deprivation. Besides that, floods and droughts frequency is increasing due to the effects of climate change. Aquifers often offer opportunities for reducing the effects of the impact of these hydrological extremes and contribute to establish emergency water supplies.
Map "Global Groundwater Vulnerability to Floods and Droughts"
The Global Map of Groundwater Vulnerability to Floods and Droughts indicates the level of vulnerability of groundwater resources of the earth. It presents the intrinsic vulnerability of groundwater systems and the sensitivity or resistance of those systems to natural disasters. The map is the result of a joint effort of the projects "Groundwater for Emergency Situations" (GWES) and the "World-wide Hydrogeological Mapping and Assessment Programme" (WHYMAP). GWES is a UNESCO International Hydrogeological Programme (IHP) project aiming at providing best practices and guidelines to identify and adequately manage potentially safe groundwater resources with low vulnerability that could be used in emergency situations due to extreme events (natural and man-induced) that adversely impact human health and life. WHYMAP aims at collecting, compiling and visualising hydrogeological information at a global scale, to convey groundwater related data in an appropriate way for the global discussion on water issues and to give recognition to invisible underground water resources.
Concept:
The concept of groundwater vulnerability takes into account that the geological characteristics of the aquifers and the physical environment provide different degrees of protection against natural or human activities related impacts. Aquifers in karst formations or in fluvial unconsolidated deposits of large rivers are highly vulnerable to floods and droughts, and coastal aquifers are particularly prone to tsunamis, while the groundwater resources in deep-seated aquifers are naturally less vulnerable and more resilient to external influences due to their protection from the earth surface by geological layers with low permeability. Some of these aquifers, if accurately managed, could supply drinking water in the post-disaster emergency phase, replacing damaged water supply systems.
The assessment of groundwater vulnerability is usually based on a classification of various natural parameters, such as soil type, properties and thickness of the unsaturated zone, aquifer type, recharge rate and others. However, there is a lack of data in many regions of the world. Thus, the evaluation presented on this world map is mainly based on parameters that were globally available:
The groundwater vulnerability classification adopted for this map is intended for use as a global overview. Due to its scale, it cannot be used for site specific and local purposes. More vulnerability parameters based on relevant reliable data sets have to be applied to present groundwater vulnerability on maps at a large scale.
In order to obtain a numerical dimension of groundwater vulnerability, individual weighting and a rating scale have been assigned to the parameters "type of aquifers" and "groundwater recharge". According to their considered importance for the vulnerability assessment, a numerical score for both parameters has been calculated. The final result, called “Total Vulnerability Range”(TVR), is divided into three categories: low, moderate and high groundwater vulnerability. Generally, the lower the numerical score the lower the vulnerability and the higher the level of natural protection of groundwater against hydro-climatic disasters. Finally, the TVR for floods and the TVR for droughts have been combined. The resulting categories of vulnerability are depicted on the map in different colours.
Detailed information and the full scheme of vulnerability classification are provided in the corresponding explanatory notes.
References:
- RICHTS, A. & VRBA, J. (2016): Groundwater resources and hydroclimatic extremes: mapping global groundwater vulnerability to floods and droughts. - Environ Earth Sci 75: 926. doi: 10.1007/s12665-016-5632-3
- VRBA, J. & RICHTS, A. (2015): The Global Map of Groundwater Vulnerability to Floods and Droughts - Explanatory Notes. - Paris: UNESCO, p. 15. (PDF, 8 MB)
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