Metrological evaluation of the effect of the presence of a road on near‐surface air temperatures

With the purpose of revising World Meteorological Organization's Commission for Instruments and Methods Observation (WMO/CIMO) Guide #8 on weather stations siting, an experiment to evaluate metrologically maximum influence a paved road 2-m air temperature measurements (“road siting effect”) has been designed, installed run in Italy. It consists 100-m long array seven measurement stations, at increasing distances from local road, equipped with shielded Pt100 thermometers ancillary sensors. Data coming 1 year observations have analysed daily climatological metrics, finding that mostly effects minimum temperatures, average values ~0.30 ± 0.18 °C distance m; then, order quantify instrumental effect measurement, data were filtered by applying generalized additive model, selecting only times when is more intense (during nights, presence low winds road), calculated modelling differences using extreme analysis. The 1-year return value 10-min 1.22 0.30 m gradual decline (~0.1 °C·m−1), while extrapolation 100-year level gives 1.71 0.79 rate about 0.17 °C·m−1. This first step towards redefinition station classification scheme WMO/CIMO #8, together building tree experiments which parallel here presented will be elsewhere.