WITHDRAWN: Mapping the groundwater memory across Ireland: a step towards a groundwater drought susceptibility assessment

Abstract

• National assessment of the memory of groundwater across the Republic of Ireland. • The machine learning model is able to simulate the observed memory. • The study provides a first known high resolution map of the groundwater memory. • Groundwater memory informs on the susceptibility of groundwater to drought. • Lowest drought susceptibility appears in low-elevated areas with thick overburden, and vice versa. The occurrence of groundwater drought is closely linked to the meteorological input but also to the surface and subsurface properties, which function as lagging filter for the input signal. Knowledge about the potential occurrence of groundwater droughts is relevant for existing and future groundwater users, particularly in regions where climate change is expected to extend or increase the number of dry periods. This study proposes a method to quantify the groundwater memory as basis for characterising the intrinsic susceptibility of groundwater to drought. The memory of groundwater was estimated using a sliding window autocorrelation function applied on 114 groundwater level time series. A Random Forest regressor then modelled the groundwater memory across Ireland, using national digital maps as input files. The key variables explaining groundwater memory are: the relative and absolute surface topography and a thick overburden (>10 metres). Accordingly, the lowest memory appears in elevated areas with overburden thicknesses of less than 10 m, and vice versa. Areas of low, moderate and high groundwater memory relate to high, moderate and low groundwater drought susceptibility. The uncertainty of the results is lowest in areas of low memory and highest in areas of high memory, presumably related to the distribution of the observations. The results are considered relevant in the context of water resources planning across sectors (agriculture, industry, domestic), particularly in the context of climate change adaptation.