Climatic and geologic controls on the piezometry of the Querença-Silves karst aquifer, Algarve (Portugal)

Karst aquifers in semi-arid regions, like Queren double dagger a-Silves (Portugal), are particularly vulnerable to climate variability. For the first time in this region, the temporal structure of a groundwater-level time series (1985-2010) was explored using the continuous wavelet transform. The investigation focused on a set of four piezometers, two at each side of the S. Marcos-Quarteira fault, to demonstrate how each of the two sectors of the aquifer respond to climate-induced patterns. Singular spectral analysis applied to an extended set of piezometers enabled identification of several quasi-periodic modes of variability, with periods of 6.5, 4.3, 3.2 and 2.6 years, which can be explained by low-frequency climate patterns. The geologic forcing accounts for similar to 15 % of the differential variability between the eastern and western sectors of the aquifer. The western sector displays spatially homogenous piezometric variations, large memory effects and low-pass filtering characteristics, which are consistent with relatively large and uniform values of water storage capacity and transmissivity properties. In this sector, the 6.5-year mode of variability accounts for similar to 70 % of the total variance of the groundwater levels. The eastern sector shows larger spatial and temporal heterogeneity, is more reactive to short-term variations, and is less influenced by the low-frequency components related to climate patterns

Identifying non-stationary groundwater level response to North Atlantic ocean- atmosphere teleconnection patterns using wavelet coherence

The first comprehensive use of wavelet methods to identify non-stationary time- frequency relations between North Atlantic ocean-atmosphere teleconnection patterns and groundwater levels is described. Long-term hydrogeological time series from three boreholes within different aquifers across the UK are analysed to identify statistically significant wavelet coherence between the North Atlantic Oscillation, East Atlantic pattern, and the Scandinavia pattern and monthly groundwater-level time series. Wavelet coherence measures the cross- correlation of two time series as a function of frequency, and can be interpreted as a correlation coefficient value. Results not only indicate that there are common statistically significant periods of multiannual-to-decadal wavelet coherence between the three teleconnection indices and groundwater levels in each of the boreholes, but they also show that there are periods when groundwater levels at individual boreholes show distinctly different patterns of significant wavelet coherence with respect to the teleconnection indices. The analyses presented demonstrate the value of wave- let methods in identifying the synchronization of groundwater-level dynamics by non-stationary climate variability on time scales that range from interannual to decada

The impact of atmospheric teleconnections on the coastal aquifers of Ria Formosa (Algarve, Portugal)

Fluctuations in groundwater level in the Ria Formosa coastal aquifers, southern Portugal, owe 80% of the variability to climate-induced oscillations. Wavelet coherences computed between hydraulic heads and the North Atlantic Oscillation (NAO) and East Atlantic (EA) atmospheric teleconnections show nonstationary and spatially varying relationships. The NAO is the most important teleconnection and the main driver of long-term variability, inducing cycle periods of 6-10 years. The NAO fingerprint is ubiquitous and it accounts for nearly 50% of the total variance of groundwater levels. The influence of EA emerges coupled to NAO and is mainly associated with oscillations in the 2-4-year band. These cycles contribute to less than 5% of the variance in groundwater levels and are more evident further from the coast, in the northern part of the system near the main recharge area. Inversely, the power of the annual cycle increases towards the shoreline. The weight of the annual cycle (related to direct recharge) is greatest in the Campina de Faro aquifer, where it is responsible for 20-50% of the variance of piezometric levels. There, signals linked to atmospheric teleconnections (related to regional recharge) are low-pass filtered and have periods >8 years. This behavior (lack of power in the 2-8-year band) emphasizes the vulnerability of coastal groundwater levels to multi-year droughts, particularly in the already stressed Quinta do Lago region, where hydraulic heads are persistently below sea level.FCTPortuguese Foundation for Science and Technology [UID/GEO/50019/2019]Fundacao para a Ciencia e Tecnologia (FCT)Portuguese Foundation for Science and Technology [SFRH/BD/131568/2017]info:eu-repo/semantics/publishedVersio

A risk society? Environmental hazards, risk and resilience in the later Middle Ages in Europe

Modern society is said to have restructured in reaction to contemporary hazards with the aim of improving its management of risk. This implies that pre-industrial societies were somehow fundamentally different. In this paper, we challenge that hypothesis by examining the ways in which risks associated with environmental hazards were managed and mitigated during the Middle Ages (defined here as the period from 1000 to 1550 AD). Beginning with a review of the many case studies of rapid onset disasters across Europe, we draw upon both historical and archaeological evidence and architectural assessments of structural damage for what is a pre-instrumental period. Building upon this, the second part of the paper explores individual outlooks on risk, emphasising the diversity of popular belief and the central importance of Christianity in framing attitudes. Despite their religious perspectives, we find that medieval communities were not helpless in the face of serious environmental hazards. We argue instead that the response of society to these threats was frequently complex, considered and, at times, surprisingly modern