Spatio-temporal assessment of frost risks during the flowering of pear trees in Belgium for 1971–2068

Abstract

Over the last decades, fruit trees in Europe have tended to flower earlier due to warmer winters. The impact of destructive spring frosts remains considerable as exemplified by damage during pome fruit flowering in Belgium between 2017 and 2021. While several regional studies on the impact and evolution of this phenomenon exist, pear fruit (Pyrus communis) has received little attention. We focused on the commercially important pear cultivar ‘Conference’ in Belgium using data from 1971 to 2018, and climate projections to 2068. A calibrated phenological model was applied to selected members of the CMIP5 EUROCORDEX regional climate model ensemble for emission scenarios RCP 4.5 and RCP 8.5 to determine the timing of the flowering period and the coinciding frost events (<-2 °C). A recursive and multivariate quantile mapping correction on monthly series of minimum and maximum temperature provided the most consistent reduction of negative temperature bias in the climate time series as compared to the observations. Flowering in the current pear production area in Belgium started on average 7.5 (10.8) days earlier under scenario RCP 4.5 (8.5), and the last frost occurred on average 12.8 (17.9) days earlier in 2019–2068 compared to 1971–2018. Sen's slope coefficient indicated an overall advancement of 1.25 (1.55) days per decade for flowering; 2.06 (2.23) days per decade for the last frost and around 25% fewer frosts during a projected future flowering period. Pear orchards in northern lowlands were less exposed to frosts than orchards in regions with elevations above 300 m. While frosts remain a potential threat in a projected future, climate change did not induce more frequent frosts and production relocation is therefore not recommended.