README

--------Overview----------
Title: Spatial streamflow drought in the larger Alpine region
Contact: Joren Janzing, joren.janzing@slf.ch

Description:
This dataset accompanies the paper "Spatiotemporal dynamics of streamflow drought in the larger Alpine region" by Janzing et al. 2026 (WRR).
The dataset contains all modelled data needed to recreate the figures in the manuscript. All data is based on the runs with the PCR-GLOBWB2.0 model, run at a spatial resolution of 30 arcsec over 1990-2019 as described in Janzing et al., (2025).
The modelled domain is 2.5--18.5 degree longitude and 42.5--51.5 degree latitude. The analysis was caried out over a smaller study domain (3--18 longitude and 43--51 latitude).

References:
Janzing, J., Wanders, N., Van Tiel, M., & Brunner, M. I. (2026). Spatiotemporal dynamics of streamflow drought in the larger Alpine region. Water Resources Research. https://doi.org/10.1029/2025WR040503 Janzing, J., Wanders, N., Van Tiel, M., Van Jaarsveld, B., Karger, D. N., & Brunner, M. I. (2025). Hyper-resolution large-scale hydrological modelling benefits from improved process representation in mountain regions. Hydrology and Earth System Sciences, 29(23), 7041-7071. https://doi.org/10.5194/hess-29-7041-2025

--------Structure of the files----------
For more detailed descriptions of the data and considered variables, we refer the reader to the section on definitions below or the methodological section of Janzing et al., (submitted).

combined_intensities_30plus_20250926.pkl
What: Python dictionary containing pandas dataframes with spatially-averaged intensities [-] for each time step and for each sub-event in a spatial drought.
Dictionary keys: the detected events that exist longer than 30 days [#]
Columns: Sub-event out of which spatial drought event exists [#]
Rows: Date [YYYY-MM-DD]

combined_lengths_30plus_20250926.pkl
What: Python dictionary containing pandas dataframes with spatially-averaged channel length [m] for each time step and for each sub-event in a spatial drought.
Dictionary keys: the detected events that exist longer than 30 days [#]
Columns: Sub-event out of which spatial drought event exists [#]
Rows: Date [YYYY-MM-DD]

discharge_averaged_1990-2019_20250926.nc
What: Netcdf file of time-mean discharge [m3/s] over the modelled period.
Coordinates: lat [deg], lon [deg]

drivers_30days_20250926.pkl
What: Python dictionary containing pandas dataframes with spatially-averaged 30 day anomalies for each time step that a spatial drought event exists.
Dictionary keys: the detected events that exist longer than 30 days [#]
Columns: variable for which a 30 day anomaly is given ("RF": Rainfall, "SF": Snowfall, "S": Snowmelt, "I": Ice melt, E": Actual evapotranspiration) [m]
Rows: Date [YYYY-MM-DD]

drought_days_in_manuscript_20250926.nc
What: Netcdf file which contains maps of discharge deficit [m3/s] for the days shown in the manuscript.
Coordinates: lat [deg], lon [deg], time [YYYY-MM-DD]

map_localEventSize_20250926.npy
Map of average local event size [m] over all events in the modelled period (per grid cell).
Rows: lat [deg], columns: lon [deg]; (same coordinates as in discharge_averaged_1990-2019_20250926.nc)

map_localGrowingSize_20250926.npy
Map of average local growing size [m] over all events in the modelled period (per grid cell).
Rows: lat [deg], columns: lon [deg]; (same coordinates as in discharge_averaged_1990-2019_20250926.nc)

map_timeFractionInEvent_20250926.npy
Map of local time in event, the time each cell is part of a spatial drought event [-] over all events in the modelled period (per grid cell).
Rows: lat [deg], columns: lon [deg]; (same coordinates as in discharge_averaged_1990-2019_20250926.nc)

modelledDischargeStations_20250926.csv
What: Daily averaged discharge [m3/s]
Rows: Date [YYYY-MM-DD]
Columns: names of the discharge stations; Two letters indicate the country ("CH": Switzerland, "AT": Austria, "DE": Germany, "IT": Italy, "FR":France).
For the location of these discharge stations and the observations, we refer the reader to Table S1 in the Supporting Information of Janzing et al, submitted.

spatialDroughtMaps_20250926.nc
What: Netcdf file which contains maps of identified spatial drought events. The map displays the time [days] that each cell is affected by certain event over its lifetime.
Coordinates: lat [deg], lon [deg], cluster [#]

rainfall_anomaly_days_in_manuscript_20250926.nc
What: Netcdf file which contains maps of 30-day rainfall anomalies [m] for the days shown in the manuscript.
Coordinates: lat [deg], lon [deg], time [YYYY-MM-DD]

snowmelt_anomaly_days_in_manuscript_20250926.nc
What: Netcdf file which contains maps of 30-day snowmelt anomalies [m] for the days shown in the manuscript.
Coordinates: lat [deg], lon [deg], time [YYYY-MM-DD]

--------Definitions----------
Taken from: Janzing et al., (submitted)

Spatial streamflow drought or event
An extensive region where discharge is below the 20th percentile of its monthly value and that is connected in space and time.
We consider events that affect a minimum of 500 km of river channels on each day and last for at least 30 days.
A spatial streamflow drought can consist of multiple sub-events that merge or split.

Sub-event
Spatially and temporally connected region under drought that splits away from a larger region under drought, merges into a larger region under drought, or both.
They are thus part of an event. Sub-events also affect a minimum of 500 km of river channels.

Intensity
Difference between the drought threshold and the actual streamflow,
normalized by the annual mean discharge for a specific grid cell.

Local time in event
Fraction of total time a specific river cell is part of a larger spatial streamflow drought.

Local event size
Average event size of all events that include a specific river cell,
calculated as the average size of the drought event over all days
during which the cell is within a spatial drought.

Local growing size
Size of connected region that was not under drought on the previous day (day X − 1),
but is under drought on day X and that includes this particular river cell.