Water scarcity is a problem that is currently very much on our minds. However, it is not only due to drought, it is a structural problem: we speak of water scarcity when the demand for fresh water in a region is greater than the availability.

The climatic variability of the Mediterranean, where the alternation between periods of drought and more humid periods is a normal phenomenon, makes us already prone to water scarcity, but global warming, population growth and overexploitation of resources are factors that aggravate it even more.

Sustainable and efficient management of available resources is essential to face this future, and to do so it is necessary to understand how rivers respond to meteorological phenomena and human activity, such as the construction of reservoirs, wells to extract water from aquifers, or discharges into rivers.

Hydrological models – mathematical equations that allow us to simulate the processes that determine the water cycle – are a powerful tool that allows us to explore how climatic and anthropogenic factors have affected or will affect the availability of water in rivers, and therefore the use we can make of it.

The Catalan Institute for Water Research (ICRA) has developed a hydrological model that allows the reproduction of both natural and anthropogenic processes in internal basins of Catalonia. Specifically, the ICRA team has implemented a SWAT+ (Soil and Water Assessment Tool) hydrological model, which integrates the expert knowledge of agents involved in water management. The model incorporates a new calibration and validation approach designed specifically for basins that present great heterogeneity in space and/or time.

With this model it is possible to evaluate how different climatic and management scenarios – for example, the restoration of a wetland, the increase in ecological flows or the construction of a new reservoir – can impact water resources. The model therefore makes it possible to identify which management measures are most beneficial.

The model can also be applied to study in more detail the evolution of water resources in the past. In this study, ICRA has analysed the patterns and trends in water resources in internal basins of Catalonia over the last 20 years, identifying a clear reduction in flows and an increase in intermittency – that is, the temporary drying up of some stretches of river – in a large part of the territory despite not observing a significant reduction in them. There are also notable seasonal differences, with autumn being the season that is most affected, as well as an increase in the frequency, speed and magnitude of changes in flow in the short term, which can negatively affect river ecosystems.

Water management is a key point for the development of our society, and it is essential to understand how different factors, both natural and anthropogenic, impact the availability of water resources, in order to face current and future challenges. Tools such as the hydrological model developed by ICRA allow different scenarios to be characterised and assessed, and therefore support efficient, sustainable and resilient water management.