Vulnerability to drought of the main water supply systems in the Tiber basin. Definition of prevention and mitigation actions
Water availability is affected by the synergic action of antrophogenic and natural drivers, exacerbated by climate changes that seem to reduce precipitation and increase the variability of the phenomena, especially in the Mediterranean area. Water crisis in the last 20 years in Italy and Europe brought about an increased sensibility in water resources utilisation by users, policy makers and water managers, as well as a new definition in priorities for water uses. In this framework the Tiber River Basin Authority (ABT) entrusted IRSA-CNR with this research project, aiming at the implementation of water allocation scenarios in scarcity conditions, by means of the simulation code SimBaT (Bellezza et al., 2006), developed by the DICA (Dipartimento di Ingegneria Civile ed Ambientale) of the University of Perugia for the ABT. SimBaT is a decision support system that simulates water transfer, utilization and storage through a topology representing human made and natural connections by means of “nodes” linked by “arcs”.
The methodological approach was developed following two main lines: 1) the analysis of drought condition onset in the past through precipitation and discharge observations in the period 1952-2007; 2) the analysis of the water supply system of the area.
In the first line, an analysis conducted by means of standardized indices, allowed for the identification of meteorological and hydrological droughts in the past (half of the ‘50s, beginning of the ‘70s, end of the ‘80s, since 2000) as well as the comprehension of the dynamics of the basin; the final aim is the generation of synthetic time series of river and spring discharge, in which the drought conditions happened in the past have been exaggerated to simulate more scarce water availability conditions in the future.
The second line went through an accurate analysis of the available documents (historical documents, sectoral plans, administrative and policy provisions, water managers interviews), allowing for the verification of the correspondence among meteorological droughts and the onset of socio-economic crisis. Finally, the connections among the numerous water resources in the basin (springs, wells, reservoirs) and their end users, as well as the connections with the hydrographical network , were structured in a GIS scheme, in order to prepare the topology for the simulations. The year 2015 was chosen as a reference for the estimation of the demand and the status of completion of the main water supply system.
In this research a procedure for the implementation of a decision support system at the basin scale was drawn, founded on a simulation model for the water transfer, which allows for the assessment of the effects of realistic options to mitigating water scarcity due to climatic drivers. The final aim of this instrument is to prepare a discussion platform in order to facilitate decision making, to be shared among the main users, including the environment, and the water managers.