Title: Impacts of changing climate on groundwater recharge in low storativity fractured-rock aquifers
Researchers: Elia Cantoni, Prof. Bruce Misstear
Groundwater resources are the largest store of available fresh water on the planet. For example, they play a key role as a water supply for population and food production, but also in nourishing river base flows, and ecosystems. Although most of the public water supplies in Ireland are obtained from surface water resources, approximately 25% come from groundwater resources, with the proportion rising in rural areas. Until recently, most Irish aquifers had never been considered to be under stress, so groundwater recharge mechanisms and their quantification had received little attention. Nevertheless, accurate estimates of groundwater recharge are essential in order to quantify and manage groundwater resources, understand the contribution of groundwater to rivers and dependent ecosystems, and delineate source protection zones around wells and springs among other issues.
In Ireland, a methodology has been developed for quantifying recharge using geological and hydrological information contained in a Geographical Information System (GIS). First, the hydrologically-effective rainfall is calculated using a soil moisture budget approach. Then a recharge coefficient is applied which determines the proportion of the effective rainfall that forms potential recharge. The main factors influencing the recharge coefficient are the permeability and thickness of the subsoils; the drainage characteristics of the topsoils; the presence of peat deposits; and the presence of karst features. The potential recharge is then adjusted by taking account of the ability of the aquifer to accept the recharge water. For aquifers classified as being poorly productive, recharge caps of 100 mm a-1 or 200 mm a-1 are applied (depending on the sub-category of aquifer).
This methodology has proven very useful for providing preliminary estimates of groundwater recharge in river basins across the country. However, further research is now needed on how the specific properties of the bedrock aquifers affect their ability to accept recharge. In addition, in the context of a changing climate, changes in precipitation distribution, amounts and intensity are anticipated. Whilst climate change projections are highly uncertain, there is wide agreement in the prediction of an intensification of the hydrological cycle which would lead to longer and drier summers, and an increase of high intensity rainfall causing flooding. This alteration of the hydrological cycle points at possible reductions in groundwater recharge.
The overall purpose of this research project is to evaluate future groundwater recharge in Ireland in the context of a changing climate. In other words, future recharge scenarios will be generated, and their consequences examined through subsequent climate and hydrological modelling. More specifically, the thesis is focused on answering the following key questions: 1. How do bedrock properties affect the response of the aquifer to present and future recharge? 2. How would climate change impact on our regional groundwater resources? 3. How would climate change impact on the Source Protection Areas (SPAs) which have been delineated around major wells and springs