Evaluating the effects of changes in observatory position and surrounding urbanization on the historical temperature time series of the city of Trento in the Alps

Results from field measurements and numerical simulations are analyzed to evaluate microclimatic effects on temperature spatial variability in the urban area of Trento, in the Italian Alps. The analysis aims at gaining information supporting the reconstruction of the temperature time series of the city, dating back to 1816. This project offers several difficulties, mainly due to various changes of position of the observatory sites and the increasing effects of urbanization.

The field campaign was carried out from August 2009 to November 2010: five identical sensors were placed near the historical observatories of Trento, to monitor systematic temperature differences between these sites under various seasonal and weather situations. However differences measured nowadays may not be representative of those occurred in the past. Therefore numerical simulations were run with the Weather Research and Forecasting (WRF) model, coupled with an advanced urban parameterization scheme, using a historical land use, reproducing early XX century urbanization. Moreover, to test if the model is suitable to reproduce microclimatic differences in the urban area, simulations including the present land use, high-resolution urban morphology and anthropogenic heat sources were performed and compared against the observations carried out during the field campaign.

The validation highlights that the model well captures the thermal field inside the urban area and the average temperature differences between the urban sites. However it poorly reproduces variability connected with seasonality and weather conditions.

Finally results from “present” and “historical” simulations are compared, suggesting that urbanization has played a significant role on Trento temperature record, especially in sunny conditions, when the urban heat island is stronger.