Extreme weather exposure identification for road networks - a comparative assessment of statistical methods

The assessment of road infrastructure exposure to extreme weather events is of major importance for scientists and practitioners alike. In this study, we compare the differ-ent extreme value approaches and fitting methods with re-spect to their value for assessing the exposure of transport networks to extreme precipitation and temperature impacts. Based on an Austrian data set from 25 meteorological sta-tions representing diverse meteorological conditions, we as-sess the added value of partial duration series (PDS) over the standardly used annual maxima series (AMS) in order to give recommendations for performing extreme value statistics of meteorological hazards. Results show the merits of the robust L-moment estimation, which yielded better results than max-imum likelihood estimation in 62 % of all cases. At the same time, results question the general assumption of the thresh-old excess approach (employing PDS) being superior to the block maxima approach (employing AMS) due to informa-tion gain. For low return periods (non-extreme events) the PDS approach tends to overestimate return levels as com-pared to the AMS approach, whereas an opposite behavior was found for high return levels (extreme events). In extreme cases, an inappropriate threshold was shown to lead to con-siderable biases that may outperform the possible gain of in-formation from including additional extreme events by far. This effect was visible from neither the square-root criterion nor standardly used graphical diagnosis (mean residual life plot) but rather from a direct comparison of AMS and PDS in combined quantile plots. We therefore recommend perform-ing AMS and PDS approaches simultaneously in order to se-lect the best-suited approach. This will make the analyses more robust, not only in cases where threshold selection and dependency introduces biases to the PDS approach but also in cases where the AMS contains non-extreme events that may introduce similar biases. For assessing the performance of extreme events we recommend the use of conditional per-formance measures that focus on rare events only in addition to standardly used unconditional indicators. The findings of the study directly address road and traffic management but can be transferred to a range of other environmental variables including meteorological and hydrological quantities.