Flooding

Rainfall in the north and west of the island has grown significantly over the century – that of County Donegal has already risen by more than one-third. Western winters are expected to get a good deal wetter, so that the River Moy in County Mayo, for example, will double its biggest floods and those of the Shannon basin will threaten even more farmland and human settlements. In many rivers, floods once expected every 50 years could happen every 10 years.

Freshwater Pearl Mussel

Freshwater Pearl Mussel

Courtesy of the Department of the Environment, Community and Local Government

Freshwater Pearl Mussel
Courtesy of the Department of the Environment, Community and Local Government

Freshwater Pearl Mussel

Freshwater Pearl Mussel

Courtesy of the Department of the Environment, Community and Local Government

Enlarge image

The impacts on nature will be myriad and mixed. Rivers have communities of aquatic plants, animals and invertebrates adapted to a particular range of flow, water chemistry, and grading of sediments. If extreme events of rainfall grow more frequent, raging floods could disrupt these ecosystems and impoverish their biodiversity. In the short ‘spate’ rivers of the western seaboard, little could be left of aquatic life, such as the freshwater pearl mussel, already inceasingly rare, or of the gravelly spawning beds of salmon and trout.

As lakes and wetlands spread, and floods last for longer, vegetation at the margins will change, favouring reeds, rushes and mosses. The rare orchids of limestone shores could disappear. On the Shannon Callows, floods from extreme events of summer rainfall could swallow the nests of breeding waders, such as lapwing, redshank, snipe and curlew.

A million waterbirds now use Ireland’s wetlands in winter, and given great expanses of floodwater, one might expect even larger flocks of migrant wildfowl. But warmer winters in the Arctic and northern and eastern Europe may make migration to Ireland less imperative. Climate change is already keeping the wading birds of Europe nearer to their breeding grounds in winter. Most of those that come to feed in Ireland’s estuaries or along the shore have migrated from Iceland and Greenland, so their winter response to climate change in Ireland is less easy to predict, but even if the Arctic gains a longer growing season, it will not lose its dark months in winter.

Marram grass growing along the sand dunes

Marram grass growing along the sand dunes

Marram grass growing along the sand dunes

Enlarge image

A big factor could be the impact of more intense storms and rising sea-level on Irish estuaries and coasts. The steady erosion of sand dunes and the biting away of sandy fields, accompanied by both stronger winds and tidal surges will cause challenges in terms of flooding. For every centimetre rise in sea-level, we are told, about a metre of soft shore will be lost. How long will the dunes survive, and the flat machair lawn of sandy grass behind them? How soon before the ocean drowns the saltmarsh, and floods the lagoons where Iceland’s whooper swans arrive in autumn?          

In Ireland’s estuaries, such vital staging posts for migrant birds, the pace of change could be crucial. Swans and geese are grazing birds and can swiftly adapt to cropping grassland – the Brent geese of Dublin Bay already commute to graze the sports fields of the suburbs. But the bay’s great flocks of winter waders have long and sensitive bills made for probing sand and mud for marine snails and other organisms.