The salty Po and the limits of adaptation

It is an alarm that we have all read about in recent days: in the Po delta, also thanks to its low level due to the drought of recent months, sea water is “going up” the river. In reality, already the rise in sea level and the strong draining of water of the last decades – which have lowered the land – were causing the so-called “saline wedge” to enter the interior. As you can see in the figure, in this situation the sea water can reach the wells, which then go to “fish” salt water from the aquifers. And, as is well known, with this water we can neither quench our thirst nor irrigate the fields. Now the situation is worsening and could lead to the salinization of several strata of fresh water.

What we are accusing at the moment is an extremely dry winter-spring semester, with little rain and snow, and with an increase in the snow quota that decreases the storage of water resources that can be used in the warmer months: if, for example, the snow today falls on average 200 meters higher than in the past, those 200 meters of rain we lose them almost immediately in the sea; if they were made of snow, we would exploit them slowly. One might think it is an “unfortunate” year, but in reality years of this type have been occurring at a much greater rate over the past 10-15 years.

In these drought conditions, many rightly demand a better management of water resources, avoiding waste, but also building new reservoirs where to keep the little water that comes down from the mountains for our uses, primarily agricultural activities. Except that the mountain-river-sea system is extremely interconnected and making many large reservoirs where to store the little water available will further lower the level of the Po and increase the intrusion of the saline wedge. In short, the deck is short: adapting to counteract the drought aggravates the problem of salinization of the aquifers at the mouth of the Po.

Drought: the Po has never been so dry for 70 years


Adaptation has limitations: this is also shown by the recent IPCC working group 2 report. The real problem, in my opinion, is knowledge and awareness. With our greenhouse gas emissions and deforestation we have triggered responses from nature, responses that seem slow to us all in all. What will you ever be an extra degree of temperature globally in the last hundred years? The fact is that we do not realize that the dynamics of nature is perhaps slow, but sometimes it can become inexorable. A clear example of this is the melting of Alpine glaciers.

Our glaciers are receding more and more, but the real problem is that today they are not in equilibrium with the current temperature, because they are still slowly responding to the warming of the last decades. Thus, the models clearly show that even if the temperature remained the current one, our glaciers would still lose about 30% of their surface and their volume from now to the end of the century. But beware: if the temperature rises following the scenario business as usual (BAU), by 2100 only 5% of their current surface and volume would remain.

The emergency

Drought, the Po so dry that you can walk on the seabed



In this situation, it is clear that we will see a certain reduction in glaciers anyway and we must adapt to this situation, but if we cannot mitigate global warming, we will not be able to adapt in any way to the final situation of the BAU scenario.

Environment

For over a thousand years, the Hani people have known the secret against drought

by Sara Moraca



In short, we have triggered a climate change and we will keep some damage already evident today also in the future; we must adapt to this inevitable condition. But we must avoid reaching unmanageable conditions, so we must mitigate and decrease our carbon footprint. And we must do it as soon as possible, because the entire climate system, like our glaciers, also has an inertia, due to the long time spent in the atmosphere by carbon dioxide and the heat trapped in the oceans. To avoid the worst climate impacts we need to mitigate from now to see results in a few decades. Waiting to see the worst impacts would be too late.

These days the Po is giving us a clear lesson: with the few water resources that will come down from the Alps in the future and the increasingly frequent droughts, even adaptation has limits. We must mitigate, and do it immediately.

(* Antonello Pasini is climate physicist at the CNR)

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#salty #limits #adaptation

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