Climate data
Hourly air temperatures measured at 2 m above ground approx. 3 km
southwest of the research site at ClimateBasis Disko (69.24 °N, 53.53
°W, 1 m a.s.l.; Fig. 1b) covering the period 23.09.1993 – 31.12.2019
were downloaded from the GEM database (https://data.g-e-m.dk
accessed on 9.3.2021; ). Daily mean temperatures were calculated based
on these hourly measurements. Days with fewer than 16 hourly
measurements were not further processed. Mean monthly temperatures were
calculated based on the daily means for months with at least 20 daily
means. This resulted in a mean monthly temperature series from October
1993 to December 2019, with gaps in 1993 (December), 1995 (May-July),
1997 (January, September – December) and 1998 (January). These gaps
were filled and the monthly temperature record was extended back to 1880
with temperatures from the homogenized monthly temperature dataset from
Ilulissat (; https://crudata.uea.ac.uk/cru/data/greenland/
accessed on 19.03.2021). Monthly mean temperatures from this dataset
were transferred using linear regression between this dataset and the
ClimateBasis monthly means to match the level of the latter. These
records are strongly correlated for each month (0.79≤r≤0.99,
p<0.0001), with on average slightly lower temperatures
recorded in Ilulissat.
Monthly precipitation sums (1901-2019) were extracted from the monthly
gridded dataset CRU TS4.04 for the grid 69-69.5 °N, 53.5-53 °W
(https://crudata.uea.ac.uk accessed on 14.5.2021; ). This gridded
dataset was extended through regression with monthly precipitation sums
calculated from daily data measured at Ilulissat (1880-1991; 69.22 °N,
51.1 °W, 39 m a.s.l.) as obtained from the Global Historical Climatology
Network (GHCN accessed on 10.3.2021; ). Precipitation sums from these
records are strongly correlated (0.80≤r≤0.97, p<0.0001) with
slightly higher values recorded in Ilulissat than suggested for the grid
matching the research site. The resulting monthly temperature and
precipitation records span the entire period of shrub growth (1892-2013)
studied here.