Master Thesis Defense by Sandra Maria Nygaard

Title: Future Agricultural Summer Droughts in Europe with a focus on Denmark - A Storyline Approach based on the summer 2018 for assessing 3 and 5 °C Warmer Climates 

Abstract:
Extreme drought events can result in severe impacts such as agricultural harvest losses but are challenging to predict in climate projections due to various uncertainties. In this thesis, a storyline approach is taken to investigate the severity of possible future 2018-like European agricultural summer droughts with a focus on Denmark (Extended Denmark) in a 3 and 5˚ C warmer climate. From ERA5-land monthly soil moisture the 2018-event was historically (1950-2023) an exceptional dry drought in the first 100 cm of the soil column covering large parts of central, western, and northern Europe, including Extended Denmark and with a low to no plant available water expressed in a soil wetness index (SWI). From the uppermost soil layer (7 cm) two metrics are selected to resemble 2018-like events (2018-analogous): 1. The lowest mean May-June soil moisture values, 2. The lowest mean May-August soil moisture values. From EC-Earth3 and EC-Earth3-veg large ensemble data, the upper soil moisture (10 cm) 2018-analogues are selected from the two metrics in a present-day, a 3 ˚ C warmer, and a 5˚ C warmer climate. A change in the mean soil moisture is found for both warmer climates in Europe primarily in the Mediterranean and central and western Europe in the entire period of May to August, and in Extended Denmark from July. The 2018-analogues are notably dryer in Europe and Extended Denmark, in the same month as the mean soil moisture. Compared to the present-day mean, the 3 and 5 ˚ C warmer climate contains 2018-analogous with a larger area extent of drought conditions. The SWI for the extreme 2018-analogues in the warmer climates results in larger areas with no available soil moisture in May-August, in large parts of Europe including Extended Denmark.

Supervisor: Jens Hesselbjerg Christensen
Censor: Martin Drews (DTU)