Spring frost risk for regional apple production under a warmer climate

<div><p>Spring frosts, as experienced in Europe in April 2016 and 2017, pose a considerable risk to agricultural production, with the potential to cause significant damages to agricultural yields. Meteorological blocking events (stable high-pressure systems) have been shown to be one of the factors that trigger cold spells in spring. While current knowledge does not allow for drawing conclusions as to any change in future frequency and duration of blocking episodes due to climate change, the combination of their stable occurrence with the biological system under a warming trend can lead to economic damage increases. To evaluate future frost risk for apple producers in south-eastern Styria, we combine a phenological sequential model with highly resolved climate projections for Austria. Our model projects a mean advance of blooming of –1.6 ± 0.9 days per decade, shifting the bloom onset towards early April by the end of the 21st century. Our findings indicate that overall frost risk for apple cultures will remain in a warmer climate and potentially even increase due to a stronger connection between blocking and cold spells in early spring that can be identified from observational data. To prospectively deal with frost risk, measures are needed that either stabilize crop yields or ensure farmers’ income by other means. We identify appropriate adaptation measures and relate their costs to the potential frost risk increase. Even if applied successfully, the costs of these measures in combination with future residual damages represent additional climate change related costs.</p></div

Spring frost risk for regional apple production under a warmer climate - Fig 5

<p>Panel (a) Distribution of apple farmers’ annual income. The dark red area refers to the probability of a reduction in yield as experienced in 2016. The light red shading shows the probability of an income reduction higher or equal to the one experienced in 2017. Panel (b): Exceedance probability curve describing the average annual income loss (AAL) faced by Styrian apple farmers. The numbers are inflation adjusted and correspond to EUR 2005 values.</p

Number of frost days (temperature below –2.2°C) coinciding with blocked days (dark blue) as a function of the day of the year.

<p>Number of frost days during randomly drawn days, mean (light blue) and standard deviation (black bars) based on a Monte Carlo test with 1000 repetitions.</p

Apple production and prices in Austria from 2000 to 2017 (based on [26]).

<p>The prices for apples for processing are only available until 2015.</p

Evolution of the blossoming day of apple in Weiz from 1951 to 2100 from the 5-year smoothed multi-model mean (green line) plus standard deviation (green shading) as well as from phenological observations from 1951 to 2006 (gray line).

<p>Potential frost damages (temperatures below –2.2°C occurring within 10 days after blossoming) are indicated for different regional climate models under RCP4.5 (colored dots). The dot size indicates how many grid points around Weiz are affected. Note that climate projections are not initialized with recent climate observations so that the variability of the simulated blossoming in the historical period does not match the observations.</p