In the last years, water scarcity and drought severely affected southern Europe. Drought particularly afflicts Italy in different ways, mainly depending on the area hydrogeological setup and on the physical processes of precipitation-recharge interaction; the groundwater recharge decreases, due not only to rainfall reduction, but also to temperature increase. In southern Italy, the 1987-1993 period was probably the most critical, due to a long period of rainfall scarcity and historical minima of spring discharges. After this period, several drought years have been recorded (2002, 2007-2008, 2011 and 2017). The severity of these drought events has highlighted the need to evaluate the effects of possible future meteorological drought due to climate change on groundwater resource availability.
In this context, the Italian National Institute for Environmental Protection and Research (ISPRA) has developed the automatic “Nationwide GIS-based hydrological budget on a regular grid” procedure, named BIGBANG and currently at version 1.0, to evaluate the water budget components at monthly and annual temporal scale and in spatially distributed approach. This kind of approach also permits to analyze clipped parts (regions, hydrographic districts, river basins, etc.), to relate each other and to compare them to the whole territory as well. Moreover, the annual value of the water budget components can be evaluated by aggregating the monthly values or by calculating the water balance on yearly data. By using BIGBANG 1.0 procedure, the water budget comparison between a part and the whole territory provides a good agreement with local and more detailed analysis.
In the present study, the BIGBANG 1.0 procedure has been applied directly on a yearly basis as first approach to face the effects of possible future drought events associated to different climate change scenarios. BIGBANG evaluations are carried out, for Italy and for a region of southern Italy (Campania), at yearly scale and they are referred to four emission scenarios defined by IPCC in the Fifth Assessment Report and to short, medium e long time horizon.
Results suggest that, according to the RCP2.6 emission scenario, the reduction of groundwater recharge is quite constant for all time horizons for both Italy and for Campania region. On the other hand, the reduction of groundwater resources corresponding to the worst scenario in terms of GHG emissions (RCP8.5), is really critical, for Campania region and for Italy. Fortunately, there is still enough time to avoid severe situations, as predicted by the worst scenario, by means of the GHGs emissions reduction and of the sustainable management of the water resources.
This study could represent a “proof of concept” for the suitability of BIGBANG procedure, to simulate water balance under future climatic scenarios, to respond to the needs of decision makers, to plan water resources affected by climate change.