Can we use flood control infrastructures in forecast-based drought management in a drying climate?

In Southern Europe, the occurrence of increasingly frequent and severe droughts is challenging existing water resources management. This trend calls for a proactive approach to drought management through the development of efficient monitoring, warning and forecasting systems. In this study we demonstrate the potential of using drought seasonal forecasts for promptly activating a drought management strategy aimed at mitigating the conflict between competing water users in the Lake Como system (Italy). Historically, in this region, water abundance was often the primary concern rather than water scarcity; however, the system has recently experienced a number of severe droughts with a consequent progressive lowering of the average lake level that have exacerbated conflicts between agriculture and other sectors, including navigation, tourism, and ecosystems. In this context, we propose a drought management strategy based on the use of a mobile dikes system, originally designed to protect the shoreline of Como city from floods, as a means of reducing the impacts of drought. The intent is to lift the dikes in view of dry seasons to increase the storage capacity of the lake, with potential benefits both for irrigation supply and for low levels control. To operate the dikes only in the event of an actual drought, a seasonal drought forecast is generated with a statistical approach that relies on the teleconnection of El Niño Southern Oscillation (ENSO) with local hydro-climatic conditions. When drought emergency conditions are detected, the lake operations switch from the historical policy to a new strategy specifically designed to manage the system and address the tradeoffs between the competing users in drought conditions. Our results show that many of the resulting solutions successfully improve the historical operation of the system both in terms of irrigation supply and low levels control, without increasing the risk of flooding.