## 2 Methods
### Description of the Sites
#### 2.1.2 Meteorological Conditions
The period from 1901 to 2000 was used as a long-term reference [71; 73]. Figure 1: The meteorological conditions near the Klein Schietweld and Park of Brasschaat. The line plots represent the daily average relative humidity (%; **A**; red), the temperature (°C; **B**; blue), and the vapor pressure deficit (kPa; **C**; green), while the bar plots represent the daily precipitation (mm; **D**; light blue). The grey bands surrounding the line plots represent daily maxima and minima, respectively. The data were measured every half hour and were provided by the Flemish Institute for Nature and Forest (INBO), the Integrated Carbon Observation System (ICOS), and the Royal Dutch Meteorological Institute (KNMI). The vapor pressure deficit (kPa) was calculated using the formulas of [PERSON] [85] using data of the relative humidity and air temperature between 7 a.m. and 7 p.m. The volumetric soil water content data (Vol%; **E**), provided through the courtesy of INBO, were measured every hour following [PERSON] [74]. The blue, orange, red and green dots represent the volumetric soil water content at depth intervals of 0-5 cm, 5-20 cm, 20–40 cm and 40–80 cm, respectively. This figure is partly adapted after [PERSON] et al. [71] and [PERSON] et al. [73]. The climate at our study sites can be considered temperate maritime. Nevertheless, the weather during our study period was marked by a number of abnormal to exceptional events (Table 1). For example, in the summer of 2019, three heatwaves occurred, and the absolute maximum air temperature record for Belgium was broken. Consequently, the meteorological stations recorded an average air temperature and a total amount of sunshine falling in the three highest recorded values since 1981 [77]. Although, the autumn of 2019 could be considered normal, 2020 again recorded some abnormal to exceptional events [78; 79]. For example, the winter of 2020 was abnormally warm with an average air temperature and vapor pressure falling in the three highest recorded values since 1981 [80]. This was followed by an extremely dry and sunny spring with, for Belgium, record-breaking values in the average duration of the sunshine, the global solar radiation the, relative humidity, the vapor pressure, and the number of rainy days [81]. The summer of 2020 was also dry and warm with an average relative humidity and air pressure falling in the three lowest recorded values since 1981 [82]. Finally, 2020 ended with a very warm autumn with an average relative humidity again falling in the three lowest recorded values since 1981 [83]. The winter of 2021 showed meteorological values that can be considered normal given the reference period f 1991-2020 [84]. Data on the volumetric water content for 2019 and 2020 showed, especially in summer, relatively low values. Since 2017, the rainfall deficit also showed an increasing trend. In the hydrological years of 2019-2020 and 2020-2021, the rainfall deficit even reached values similar to the hypothetical values forecasted for a return period of 100 years [73]. Figure 2: The rainfall deficit for the meteorological station of the Royal Meteorological Institute (KMI) in Ukkel, Belgium. Colored solid lines represent the rainfall deficit for the hydrological years in the period of 2019–2021, while grey solid lines represent the long-term reference statistics (computed for the 100-year period of 1901–2000). T stands for the return period, which represents the mean time between two successive exceedances of a given deficit value, and it was computed in an empirical way [89; 90]. Panel **A** uses a continuous computation, while panel **B** starts from a zero deficit on the first of April (the start of the hydrological year). The colors represent the rainfall deficit in 2018–2019 (red), 2019–2020 (light blue), and 2020–2021 (purple). This figure was partly adapted after [PERSON] et al. [71] and [PERSON] et al. [73].