This repository contains the radar rainfall nowcasts for 80 high-intensity rainfall events spread over 5 urban areas (Amsterdam, the Hague, Groningen, Maastricht, and Eindhoven) in the Netherlands.
Rainfall events chosen criteria:
The high-intensity events were selected for each municipality by using RadarTools (http://radartools.nl). RadarTools can list the rainfall events based on the highest climatological rainfall accumulation at any 1-km2 grid cell within each municipality in the Netherlands since 2008. RadarTools sets different thresholds to select rainfall events of different periods. For example, the selection criteria for 1-h period is that the precipitation sum in any grid cell is above 15 mm. For 24-h period, the threshold is 30 mm. Rainfall is not necessarily continuous during the period. We selected the eight highest 1-h and eight highest 24-h events in each of the 5 municipalities from 2008 to 2021. When selecting the 24-h events, the events that covered the period of the previously selected 1-h events were excluded per urban area to ensure independence of the events. This selection procedure led to 5 (cities) × 2 (durations) × 8 (events) = 80 events.
Nowcasts:
For every five-minute time step in each of the events, a probabilistic nowcast was made by pySTEPS (v0.2 used) libraries (Ayzel et al., 2019; Pulkkinen et al., 2019).
We used the same Pysteps setup as in Imhoff et al. (2020, https://doi.org/10.1029/2019WR026723), which consisted of the STEPS (short-term ensemble prediction system) nowcasting method using a semi-Lagrangian advection method and the Lucas‐Kanade optical flow method (using the QPE from time t-3 to t). An autoregressive model of order 2 and 8 cascade levels was used.
All nowcasts have a time step of 5 min and a forecast horizon of 4 hours. Nowcasts are first run with real-time QPE from Royal Netherlands Meteorological Institute (https://dataplatform.knmi.nl/dataset/nl-rdr-data-rtcor-5m-1-0). The 1-h events before 2020 are also run with climatological (https://dataplatform.knmi.nl/dataset/rad-nl25-rac-mfbs-em-5min-netcdf4-2-0) and CARROTS-adjusted QPE (https://doi.org/10.4121/13573814). Hence, in total, there are 9,060 separate norecasts (each with 4-hour forecast horizon and 20 ensemble members).
The nowcasts are saved as netCDF files in folders with the following structure: event duration (1 or 24 hrs) and QPE products used (realtime, CARROTS, or climatological) > city name > event folder > individual nowcasts. The filenames of the event folder indicate the onsets of the high-intensity rainfall events in UTC. The filenames of nowcasts indicate the issue time of the nowcasts in UTC.
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