Solar activity is the main driver for a number of electromagnetic effects in the Earth's environment as enhanced electric fields, currents, and energetic particle precipitation in the magnetosphere and the ionosphere. A whole field of study, Space Weather (SW), has grown in recent years to understand and minimize these effects which are vital for human activities. Magnetic observatories distributed over the globe are important sources of information, since SW events leave a signature in the geomagnetic field (GMF) variations registered there. This proposal concentrates on geomagnetically induced currents (GICs), an example of SW hazards felt on-ground. GICs are the result of Faraday induction of electric fields in the transmission power lines, due to strong values of dH/dt occurring during geomagnetic storms, where H is the horizontal component of the GMF measured on Earth. GICs in power distribution grids can damage transformers and perturbate the stability of grid normal operation. GIC intensities of around 10 A have been measured and modeled at substations in countries of latitudes close to ours'. The main, unifying goal of this proposal is to assess, for the first time, the geomagnetic hazard to power systems in Portugal mainland. In the long term, a deeper insight into GIC risks can provide information for planning and designing of resilient transmission systems and for equipment selection. Ionospheric and magnetospheric currents, as well as the local crust conductivity profile, all contribute to the induced geoelectric fields that drive GICs. The power system characteristics are also influential, as e.g. the "system length" and its associated resistance. This proposal covers the whole chain of physical processes and related observational and analytical methods linking the GMF variability to final effects at high tension power grids and modeling of GIC source currents. Taking into account these different processes requires a concerted action involving geophysicists (geomagnetic driving fields, magnetotelluric measurements), engineers/physicists (power grid characteristics, estimation of GICs) and physicists/mathematicians (modeling, data analysis). Portuguese research units (CITEUC and IDL) and the state laboratory IPMA (as a consultant) are involved in this proposal, supported by other external consultants of renowned reputation, to ensure the required expertise. Formation of young researchers is also a goal of this proposal and the dissemination plan foresees initiatives to be included in the outreach stategy of the Geophysical and Astronomical Observatory. The expected results will cover a number of applied and fundamental areas and will contribute to a better knowledge of the Portuguese territory, to an improvement of power transmission conditions and, in particular, to promote the Centre Region through the upgrade of the magnetic observatory of Coimbra and the increased expertise in the fields of Geomagnetism and Space Weather.