Downscaling an intense precipitation event in complex terrain: the importance of high grid resolution

Figures & data

Table 1. Overview of the locations for the HOBO rain gauges (P1–P12) and the meteorological stations (denoted by their national code)

Identity	Name	Latitude	Longitude	Altitude
P1	Hagavik	60.176^◦N	5.403^◦E	48 m
P2	Nesttun	60.319^◦N	5.373^◦E	58 m
P3	Hisdalen	60.397^◦N	5.690^◦E	140 m
P4	Dale	60.590^◦N	5.829^◦E	91 m
P5	Kaldestad	60.554^◦N	6.018^◦E	521 m
P7	Steine	60.667^◦N	6.200^◦E	485 m
P8	Sandfjellet	60.607^◦N	6.212^◦E	620 m
P9	Hodnaberg	60.561^◦N	6.214^◦E	618 m
P10	Dyrvedalen	60.653^◦N	6.335^◦E	355 m
P11	Flyane	60.602^◦N	6.319^◦E	436 m
P12	Vasslii, Voss	60.645^◦N	6.445^◦E	79 m
25830	Finsevatn	60.592^◦N	7.524^◦E	1210 m
29400	Sandhaug	60.183^◦N	7.481^◦E	1250 m
46430	Røldalsfjellet	59.832^◦N	6.733^◦E	1010 m
46450	Røldal	59.830^◦N	6.824^◦E	393 m
47450	Straumøy	59.653^◦N	5.434^◦E	36 m
47500	Etne	59.665^◦N	5.966^◦E	35 m
47600	Litledal	59.664^◦N	6.066^◦E	83 m
47610	Kritle	59.636^◦N	6.087^◦E	568 m
47820	Eikemo	59.859^◦N	6.279^◦E	178 m
47890	Opstveit	59.858^◦N	6.017^◦E	38 m
48450	Husnes	59.864^◦N	5.770^◦E	13 m
48500	Rosendal	59.991^◦N	6.026^◦E	75 m
48780	Mauranger	60.132^◦N	6.331^◦E	33 m
49080	Øvre Krossdalen	60.280^◦N	6.386^◦E	342 m
49490	Ullensvang	60.319^◦N	6.654^◦E	12 m
49631	Eidfjord II	60.465^◦N	7.069^◦E	20 m
49800	Fet, Eidfjord	60.409^◦N	7.280^◦E	735 m
50070	Kvamsøy	60.358^◦N	6.275^◦E	49 m
50080	Øystese	60.379^◦N	6.193^◦E	108 m
50110	Aksneset, Kvam	60.336^◦N	6.218^◦E	13 m
50120	Skulafossen	60.275^◦N	6.039^◦E	16 m
50150	Hatlestrand	60.042^◦N	5.906^◦E	45 m
50175	Austevoll	60.017^◦N	5.206^◦E	32 m
50310	Jonshøgdi	60.389^◦N	5.964^◦E	455 m
50450	Stend	60.273^◦N	5.331^◦E	54 m
50480	Sandsli	60.292^◦N	5.280^◦E	45 m
50540	Florida	60.383^◦N	5.333^◦E	12 m
51010	Fossmark	60.521^◦N	5.724^◦E	10 m
51250	Øvstedal	60.688^◦N	5.965^◦E	316 m
51440	Evanger	60.647^◦N	6.111^◦E	17 m
51470	Bulken	60.646^◦N	6.222^◦E	328 m
51530	Vossevangen	60.625^◦N	6.426^◦E	54 m
51800	Mjølfjell	60.702^◦N	6.937^◦E	695 m
51990	Myrkdalen	60.866^◦N	6.473^◦E	700 m
52170	Eksingedal	60.803^◦N	6.147^◦E	450 m
52220	Gullbrå	60.829^◦N	6.265^◦E	579 m
52310	Modalen III	60.856^◦N	5.973^◦E	125 m
52400	Eikanger	60.623^◦N	5.381^◦E	72 m
52475	Blomvåg	60.531^◦N	4.893^◦E	30 m
52601	Haukeland	60.835^◦N	5.583^◦E	325 m
52750	Frøyset	60.846^◦N	5.211^◦E	13 m
53160	Jordalen	60.900^◦N	6.724^◦E	614 m
53530	Midtstova	60.656^◦N	7.276^◦E	1162 m

Fig. 1. Map of the experiment area with altitude from the terrain database ASTER GDEM v1 (Tachikawa et al., 2011) contoured in colours. The deployed rain gauges are colour coded and the stations P1–P12 correspond to the line colours in Fig. 5. Black squares are the stations M1–M3 referenced in the text, triangles are the remaining precipitation stations in the area operated by the Norwegian Meteorological Institute (MET Norway). The red line shows the lower edge of the cross sections analysed in Section 3.4.

Fig. 2. Model domain set up for the WRF simulations. The domains d01, d02 and d03 have horizontal grid resolutions of 9 km, 3 km and 1 km, respectively.

Table 2. Overview of the physical parametrisation schemes used in the WRF simulations

Category of physics	Parametrisation schemes
Microphysics	Thompson (Thompson et al., 2004; 2008)
Short wave radiation	Dudhia shortwave (Dudhia, 1989)
Long wave radiation	RRTM longwave (Mlawer et al., 1997)
Planetary boundary layer	MYJ (Janjić, 2000)
Land surface model	NOAH LSM (Chen and Dudhia, 2001)
Cumulus (d01)	Kain Fritsch (Kain, 2004)
Cumulus (d02 and d03)	None

Fig. 3. Surface analysis chart from UK Meteorological Office, for 28 October 2014 00 UTC. Reproduced with kind permission of the Met Office.

Fig. 4. Specific humidity (g kg) at 850 hPa at 00 UTC on 28 October (coloured contours) and the 850 hPa wind (arrows). Data from the ERA-Interim reanalysis.

Fig. 5. The observed (a) and simulated (b) accumulated precipitation amounts during the days before the flooding event, from 25 October 06 UTC to 29 October 2014 06 UTC. The observations of the HOBO rain gauges are given as solid coloured lines and the corresponding results from the interpolated 1 km model simulations as dashed lines. Data from the MET Norway stations are indicated by the black diamonds.

Fig. 6. Comparison of four-day accumulated precipitation from 25 October 06 UTC till 29 October 06 UTC from the WRF 9 km, 3 km and 1 km model output, using the interpolated grid point, and the observations. There is one set of bars for each station and the labels on the horizontal axis show the station id.

Fig. 7. A Taylor diagram with the 9 km, 3 km and 1 km simulations marked as circles and the observations marked as a black star for reference.

Fig. 8. Cross sections (above the red line in Fig. 1) of vertical velocities (a–c) with potential temperature contoured in black lines, specific humidity (d–f), liquid water content (g–i) and the sum of liquid and ice water content (j–l) from the 1 km resolution run, at three selected times: 26/18, 27/06 and 28/06 (in the left, middle and right column, respectively).

Fig. 9. Cross sections (above the red line in Fig. 1) of vertical velocities (a–c), specific humidity (d–f), liquid water content (g–i) and the sum of liquid and ice water content (j–l) at time 28/06 for the 9 km, 3 km and 1 km runs (in the left, middle and right column, respectively.

Fig. 10. Accumulated precipitation (25/06–29/06 October) in part of the 9 km grid (a). The circles correspond to the HOBO stations, squares are stations from MET Norway. The inner parts of the markers show the observed accumulated precipitation amounts in the period. The other panels show the same for part of the 3 km domain in (b) and for the 1 km domain in (c).

Fig. 11. The upper panel (a) shows the variance spectrum of the terrain and the specific humidity cross sections (pressure level 850 hPa) shown in Fig. 8 from the 1 km simulations. The middle panel (b) shows the same from the 3 km simulation, and the lower panel (c) for the 9 km simulation.

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