Influence of climatological cycles on hydraulic heads across a Spanish aquifer

The purpose of the paper is to show that the groundwater impacts of climatic cycles vary spatially across the aquifer depending on local hydrogeologic characteristics. Spectral analysis was applied 53 piezometers to study cycles patterns of variability in time and space in the Vega de Granada aquifer. Other variables like rainfall data, flows of rivers, and temperature were also analysed in order to determine the influence of climatological cycles. A number of long-term cycles were detected in the data series, with a time evolution that was well reflected in most piezometers. Many of the piezometers have been registering the position of the hydraulic head on a monthly basis for the past 30 years. The climatological time series represent nearly 50 years of monthly recordings, while the time series of river flow covers more than 30 years. Using spectral methods, we distinguished four different cycles in the time evolution of the aquifer hydraulic head: a decadal cycle (peaks between 8 and 11 years), a 3.2 year cycle, an annual one, and a semi-annual period. We also detected a 22 year cycle in a rainfall time series, though with less clarity. Whereas the annual cycle is ubiquitous, reflecting the annual hydrological cycle, the decadal and 3.2 year periods show a much more interesting spatial distribution. The decadal cycle can certainly be traced to hydrological variations involving a climatological regimen, probably induced by North Atlantic Oscillation (NAO). Groundwater impacts of climatic cycles vary spatially across the aquifer depending on local hydrogeologic characteristics. Specifically, the piezometers Located close to streamflows reaching the aquifer, or along the main river in those areas where it recharges the aquifer, present a statistically significant decadal cycle. NAO wet periods imply more rainfall than average over Spain and thus more recharge into the aquifer increasing the water table. The opposite occurs during the dry periods. The presence and spatial distribution of the 3-year cycle would have an explanation similar to that of the decadal cycle, though it is identified at fewer points of piezometric control. (c) 2008 Elsevier B.V. All rights reserved.