Climate Change Effects on Ecological Flow: A Case Study in Central Italy

Ecological flow is the discharge required to maintain the vitality of a water ecosystem and preserve biodiversity and ecosystem services. Ecological flow is thus a matter of both water quantity and quality as defined by the EU Water Framework Directive WFD (60/200/EC). Climate change might significantly affect ecological flow through alterations of precipitation regime and temperature. River District Authorities in charge of issuing Water Management Plans are required to determine ecological flows capable of preserving a good quality status with uncertain future climate conditions. The aim of this work is to determine the sensitivity of ecological flow and Water Exploitation Index to climate change with an explicit simulation of hydrologic balance. The hydrologic balance is evaluated by modelling of precipitation, runoff, evapotranspiration, and groundwater storage with a continuous, raster-based, distributed model. Fresh water withdrawals from domestic, agricultural and energy demands are also included. Future climate scenarios are based on the IPCC WGI Atlas dataset on mean temperature and total precipitation for the Mediterranean Region and several global warming scenarios. The method is applied to a river catchment in Tuscany (central Italy). The results show a 17% decrease in average annual renewable water resource for a +4°C global warming scenario and a 24% increase of number of critical days in which river flow is lower than the current minimum vital flow.