• A method developed by the Ephyslab group calculates river flow rates and simulates the damage caused by torrential rainfall.

The EphysLab team, from the Water Campus of the University of Vigo in Ourense, is finalising the creation of an early flood warning system for the Miño-Sil basin. This model runs daily and is connected to a graphic interface that uses simple visual language to estimate the risk of flooding and the extent of the flooded area. The system, made up of a hydrological module and a hydraulic module, was created as part of the international RISC_ML project, in collaboration with the Miño-Sil Hydrographic Confederation.

The system’s operating basis consists mainly of the fact that once Meteogalicia’s weather forecasts for the following 72 hours have been issued, they are used as input in the hydrological module to transform that rain into runoff and obtain the flow forecasts at different points of interest throughout the entire basin, both in the main rivers, the Miño and the Sil, and their tributaries. Once these flows have been obtained, they are used as input in the hydraulic module, which allows simulations of what the flood, if any, generated by these flows will be like.

Flood maps

In other words, a numerical hydraulic model is made in those areas and villages where there is a risk of flooding. When a flow rate is predicted that could cause flooding in each of these areas, it is used as input in the corresponding hydraulic model, which generates flood and associated risk maps. The areas where flooding is predicted to cause risk are those where the water level has a certain height or speed that exceeds pre-established thresholds.

The system is currently in the final phase of calibration and validation, and the next step is to make it fully operational, in order to help in decision-making, which is being carried out within a new international project awarded, the RISC_PLUS, which is a continuation of the previous one, and always in collaboration with the Miño-Sil Hydrographic Confederation.

Greenhouse effect

Diego Fernández is a researcher at Ephyslab. He analyses floods in particular, studying their dynamics and evolution in order to take the necessary mitigation measures and minimise the damage that these extreme events can cause.

‘The greenhouse effect has many impacts on many components of the climate cycle, but especially on the hydrological cycle. We are seeing that in many regions of the planet this warming is intensifying the hydrological cycle, which implies that we have more and more drought situations but also more risks of flooding. These impacts are also affecting Galicia. Our studies indicate that these extreme hydrological situations will become increasingly frequent and intense in our community. In recent decades we are already seeing this increase both in drought situations in our community, as well as in the risk of flooding, which has been intensifying in recent times. In fact, it is to be expected that even areas of Galicia where there were previously no floods could be affected in the future,’ highlights the physicist and doctor of marine sciences.

He is currently working on the design of this anti-flood system in the Miño river basin, and warns of the need to implement these measures in our territory. ‘Early warning systems are one of the most efficient mechanisms for minimising damage. In our specific case, when an extreme rainfall event is forecast, we try to see how it is going to affect our rivers and the flooding that it can cause so that the authorities and civil protection can then take measures in advance and thus reduce the damage caused by these events. This system, when faced with a rainfall forecast, transforms that into the corresponding flow rate. The same rainfall event will not always have the same impact on the flow rate as this depends on various factors such as the state of soil moisture, the water requirements of the vegetation…’, explains the UVigo researcher.

Less water in the rivers but heavier rainfall

Faced with these rainfall forecasts, what they do is transform this into flow rates and see how it will evolve over the next few days. They also carry out hydraulic simulations to see how these flows can flood some areas of the towns so that measures can be taken. This is all done in real time. Looking to the future, they input data from so-called climate models that reveal how rainfall may evolve over the next few years.

‘We put that data into our system and it already tells us how river flows will evolve. If we compare current flows with future flows, we can see how the situation will evolve. If we see an area that is not flooded now but could be flooded in a few years‘ time, it would allow us to take measures such as restricting construction in that area. The system has these advantages because it allows us to analyse what is going to happen in the next few days, but also what may happen in the future and mitigate those impacts’.

All this hydrological and hydraulic modelling of the Miño-Sil basin was also used to try to analyse how the river patterns in the basin will evolve in the future. For this, precipitation data from the regionalised climate models of the Coupled Model Intercomparison Project (CMIP), using climate projections up to the year 2100, were used as inputs in the system. In general, what is observed is a reduction in the water that the rivers in the basin will carry as the century progresses, that is to say, the annual average flow will be lower, so there will be less water available.

Risk of dry periods

Furthermore, this reduction will be more pronounced in summer, so the risk of dry periods will increase. ‘Studies estimate that the Miño River will have a 20% water loss by the end of the century. Knowing this, we can adapt to future scenarios,’ says Diego Fernández. ‘In the future we are going to have a greater risk of not meeting the ecological flow rate, especially in summer. At that time we are going to have less water than we have now. If we are below the ecological flow rate of the Miño, we will see a deterioration in water quality and biodiversity. Reservoirs can play an important role in the future. Their use can mitigate these impacts in summer, and in winter, they have the capacity to mitigate river flooding. We must be increasingly aware of the sustainable use of water because we are going to have less water available, even in an area like Galicia that is not dry,’ he argues.

Intensification of extreme rainfall

On the other hand, it has also been observed that extreme rainfall events and floods will intensify. This is due to the warming of the atmosphere associated with climate change, which increases its capacity to retain moisture, causing extreme rainfall events, in the case of the Miño-Sil basin mainly due to storms and their associated fronts, to be more intense. This means that as the century progresses, extreme rainfall events, and therefore floods, will increase in both frequency and intensity. According to the forecasts, this will mean that not only will the floodplains of the Miño-Sil basin flood more frequently and intensely, but also areas that do not currently flood may flood in the future.

The increase in extreme rainfall events can have significant consequences for populations, as they would be associated with river overflow events, which can lead to increasingly devastating floods, given that the models show an unequivocal and strong increase in extreme rainfall events in the near future.