Case Study 1: Phenological Trends in Germany

The rise of air temperature as one result of climate change affects the developmental stages of plants. In Germany, systematic observation of plant phenology development is established by help of International Phenological Gardens (IPGs) and by the phenological network of the German Meteorological Service (DWD) with up to 6500 observation sites for 270 phenological plant phases. Case study 1 aims at quantifying the statistical association between distinct plant phenological phases (‘phenophases’) and measured air temperatures in Germany. This should help in future projections on possible impacts of climate change on plant development and distribution. Accordingly, data on mean annual air temperatures and country-wide observations on 6 phases indicating different plant phenological seasons were analysed by means of regression analysis. Within a Geographic Information System (GIS), Regression Kriging was applied for mapping the development of plant phenology in the past and also in future by using projected temperature data for the climate reference periods 1991–2020, 2021–2050, and 2051–2080 derived from two different climate models (REMO, WettReg) and two emission scenarios (A1B, B1). The results showed already for the comparison of the past climate periods 1961–1990 and 1991–2005 a distinct shift of phenological onset towards the beginning of the year by about 9 days in average for all 6 phases investigated. The strongest shift was observed for hazel bloom advancing 13 days to the beginning of the year. In future, a shift of up to 33 days was calculated comparing data of 1961–1990 and 2051–2080. Since WettReg projections assume a moderate temperature rise, the projected phenological shifts were not that pronounced compared to REMO scenarios. Hence for WettReg B1, a shift by only 17 days was calculated for the beginning of hazel bloom. The strongest relationship between annual air temperatures and phase onset was found for phenophases in spring and, accordingly, the shifts in the beginning of phenophases indicating the spring season were most intense. The algorithms describing the statistical relation between temperature rise and phenology development were integrated into the “Technical Information System on Climate Change and Adaptation Strategies” (Fachinformationssystem Klimawandel und Anpassung, FISKA) which was initiated by the Federal Environment Agency and administered by the Competence Centre on Climate Impacts and Adaptation (KomPass). For implementation, so called ‘calculation engines’ were developed for all 6 indicator phases, each calculating the beginning of the respective phenological phase in days after New Year based on the respective mean annual air temperatures. That allows for future assessments when improved emission scenarios or climate models are available in order to develop well adapted mitigation measures considering environmental, agricultural and economic issues emerging from changes in plant growth and distribution.