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1 Instituto Geológico y Minero de España (IGME), Urbanización Alcázar del Genil 4, 18006 Granada, Spain (e-mail: ja.luque{at}igme.es)
2 CEAMA/Department of Geodynamics, University of Granada, Avenida Fuente Nueva s/n, 18074 Granada, Spain (e-mail: mchica{at}ugr.es)
The spectral analysis of waterhead measurements on a network of piezometers has allowed the analysis of the spatio-temporal variability of data in the Vega de Granada aquifer (southern Spain). This analysis has detected several long-term cycles in the piezometric time series for the period 1966–2001. A complete analysis, using different spectral methods of those time series, has detected four different cycles: a decadal period (11 years), a 3.2-year period, an annual period and a semi-annual period. The annual cycle is ubiquitous, as a reflection of the annual hydrological cycle. The decadal cycle can be traced to hydrological variations involving a climatological regime induced by sunspot activity (11-year cycle). The piezometers located close to streamflows reaching the aquifer or along the main river, in areas where the main river recharges the aquifer, present a statistically significant decadal cycle. The explanation for the presence and spatial distribution of the 3.2-year cycle is similar to the decadal cycle, though it is identified in fewer piezometers.
