Weather reconstruction and application for Switzerland: Long-term changes of spring weather impacts since 1763

Numerous historical sources report on hazardous past climate and weather events that had considerable impacts on society. Studying changes in their occurrence or mechanisms behind such events is however hampered by a lack of spatial weather information. For Switzerland, we created a daily high-resolution (1x1 km²) reconstruction of temperature and precipitation fields for the years 1763 to 1960 using an analog resampling method based on observational data. The resampled fields are further post-processed by assimilating temperature observations and quantile mapping the precipitation fields. Together with the present-day meteorological fields, this forms a more than 250-year long gridded data set.

We use this data set to evaluate changes in spring weather impacts over the last 250 years. The spring season receives fewer attention since it has no extreme events in absolute terms. However, it is relevant since weather conditions in spring can delay vegetation onset and growth, and can create substantial vegetation damages due to for example late frost and snow events. We evaluate therefore the long-term changes of spring fresh snow days, late frost days, frost days, and warm days, and compare it to changes of spring onset and reconstructed phenological stages.