Numerical simulations of winter cold damage to citrus
fruits using the WRF model
Yukitaka Ohashi1 and Hideki Ueyama2
1 Department of Biosphere-Geosphere Science, Okayama University of Science, Okayama City,Okayama, 700-0005, Japan
2 Western Region Agricultural Research Center, Zentsuji City, Kagawa, 765-0053, Japan

Correspondence: Yukitaka Ohashi (ohashi@big.ous.ac.jp)
Received: 3 November 2018 – Revised: 2 February 2019 – Accepted: 4 February 2019 – Published: 13 February 2019

Abstract. To numerically assess winter cold damages of citrus fruits, a cold duration of sub-zero temperature

was simulated using a high resolution configuration (500 m horizontal grid spacing) of the WRF numerical
weather prediction system. Japanese citrus is often cultivated on slopes made of a small hill and a valley. Hence,a high resolution spatial configuration is needed to simulate cold durations at complex micro-topographies. In
this study, detailed cold duration maps for sub-zero temperatures were produced to assess the spatial differenceof cold duration, as an example of a winter cold surge attack in west Japan in 2011. Our findings suggest that therecorded temperature (by automatic observation of the Japan Meteorological Agency), which was observed at aflat coastal plain, may underestimate cold damage risk for citrus fruit on narrow slopes, valleys and hilly areas.

1Introduction

In Japan, a strong cold surge (cold air outbreak by a synoptic
pressure pattern) in winters has often damaged citrus fruits
cultured in outdoor open fields, leading to a reduction inyields (e.g., Nakagawa et al., 1965; Ikeda, 1982; Matsumotoet al., 2018). An example of large-scale cold damage is theeconomic damage of JPY 750 million (EUR 6.1 million) reported in December 2005 in the west region of Ehime Prefecture which is a major production area of citrus fruits (EhimeNewspaper, 2005). This cold event induced a decrease in theproduction yield exceeding 6000 t. In general, many citrus
varieties are known as being vulnerable to sub-zero temperature conditions (e.g., Konakahara, 1984; Jackson, 1992; Inchet al., 2014). The past cold attacks from December to February have caused freeze damage to citrus fruits and physiological disorders of citrus rind, afflicting major Japanese citrus
farmers. Figure 1 shows a relationship between yearly yieldsof lemon (Citrus limon) and “Iyokan” as Japanese name (Citrus iyo) against cold duration defined as integrated hours ofsub-zero temperature. The yearly yield data in this figure
was provided by the Ministry of Agriculture, Forestry andFisheries (MAFF) in Japan. As can be seen in this figure,the long exposure of sub-zero temperature decreases citrus
Published by Copernicus Publications.

yields. Moreover, the global warming progress is likely tolead to a severe cold winter in mid-latitude Eurasian (Mori etal., 2014).
As many citrus orchards are locally spread and scatteredon the slope sides of small hills and mountains in Japan,
it is difficult to know how cold conditions affect actual orchard fields. The outdoor surface air temperature is continuously observed by the Japan Meteorological Agency (JMA),by their Automated Meteorological Data Acquisition System(AMeDAS). In fact, most AMeDAS observatories that areclose to major produce regions of citrus fruits are located atlowland sites near the coast.
A numerical weather prediction (NWP) model has beenutilized for the purpose of understanding the spatial distribution of near-surface meteorological elements, such as windspeed, air temperature, and humidity in numerous fields ofstudy as well as agrometeorology. The NWP model output
has the potential to evaluate the cold damage risk on complex
and micro-scale terrain. Hence, we examine an application ofa high-resolution NWP model to quantitatively assess wintercold damages of citrus fruits.

18th EMS Annual Meeting: European Conference for Applied Meteorology and Climatology 2018

Adv. Sci. Res., 16, 1–6, 2019https://doi.org/10.5194/asr-16-1-2019© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

2

Y. Ohashi and H. Ueyama: Numerical simulations of winter cold damage to citrus fruits

Figure 1. Relationship between the annual cold duration (h) less than −1 ◦ C and citrus yield amount (ton per 1 ha) for (a) lemon (2003–2015)

and (b) Iyokan (2007–2015).

Figure 2. Calculation areas and geographies of coarse resolution (d01) and fine resolution (d02) domains.

2

Numerical model and calculation settings

In this study, the Weather Research and Forecasting Model(Ver. 3.8.1 of WRF-ARW; Skamarock et al., 2008) was used
to simulate a field exposure of sub-zero temperature. A simulation period from 15 to 16 January 2011, was chosen as an
example of strong cold surge. Fruit (mainly citrus) damage
amounts of 839 t (652 ha) were reported during the winterof this year in Ehime Prefecture (Official Statics of Japan,2012). Simulation domains included Ehime Prefecture in thewest of Japan at which a citrus cold damage was reported byEhime Prefecture (2012). A coarse resolution was spatiallyresolved at 1500 m, while the finer resolution was done at
500 m (Fig. 2). For a vertical resolution, stretched grids wereprovided with the lowest height of 22 m up to 100 hPa. Ourmodel settings are summarized in Table 1. An initial time ofcalculation was set to 09:00 Japan Standard Time (JST) on
14 January 2011. The outputted data every 10 min were analAdv. Sci. Res., 16, 1–6, 2019

ysed from 09:00 JST on 15 January to 12:00 JST on 16 January.
Initial and boundary conditions of the model were assigned by the National Centers for Environmental Prediction (NCEP, 2019) final analysis, JMA meso-analysis (JMA,2019), and UKMO operational sea surface temperature andice analysis (OSTIA; Donlon et al., 2012) data every 3 h.
The land use (100 m resolution) and topographic data (50 mresolution) of the Geospatial Information Authority of Japan(GIAJ, 2019) were used in the model. Data assimilation was
not carried out in this study.
33.1

Results and discussion
Model validation

Figure 3 shows the simulated and actual observed cold durations between −2 and −1 ◦ C, those between −3 and −2 ◦ C,
and those less than −3 ◦ C at Omishima, Seto, and Misyo siteswww.adv-sci-res.net/16/1/2019/

Y. Ohashi and H. Ueyama: Numerical simulations of winter cold damage to citrus fruits

3Table 1. Model setting of grids, boundary condition, and physics for d01 and d02.

Horizontal grids

d01_pbl (Domain 1)

d02_les (Domain 2)

1500 m500 m

Vertical grids

44, 67, 112, 121, 153, 194 m ...

The number of grids

500 (we) × 500 (sn) × 34 (vert)

Initial and boundary conditionsJMA Meso analysis (5 km) and UKMO OSTIA SST (0.05◦ ) data

Model top level
Cloud microphysics

250 (we) × 355 (sn) × 34 (vert)

100 hPa
Morrison double-moment (Morrison et al., 2009)

Radiations

Shortwave Dudhia (1989)
Longwave RRTM (Mlawer et al., 1997)

Surface layer

Monin-Obukhov (Janjic Eta)

Land surface process
Atmospheric boundary layer

Noah LSM
PBL scheme of
Mellor-Yamada-Nakanishi-Niino(Nakanishi and Niino, 2009)

Urban canopy
Others

Large eddy simulation(full diffusion)

None
One-way nesting, slope shadow effect, fog gravitational settling

Figure 3. Cold durations (h) recorded between −2 and −1 ◦ C, those between −3 and −2 ◦ C, and those less than −3 ◦ C at (a) Omishima,(b) Seto, and (c) Misyo sites by the AMeDAS observation data, simulated d01, and d02 results.

(ref., each site location in Fig. 2). This cold duration was integrated during a period of the above-mentioned 09:00 JST on
15 January–12:00 JST on 16 January. The Omishima area has
major citrus producers of lemon and Iyokan, while the Seto
area has major “Kiyomi” (Citrus unshiu × sinensis) producers, and the Misyo area has “Kawachi-bankan” in Japanesename (Citrus kawachiensis) producers. Figure 3 indicates thecalculation results at model grids, including the AMeDAS
observational site in the d01 and d02 domains. Omishima(Fig. 3a) altitudes of observational site, d01 grid, and d02

www.adv-sci-res.net/16/1/2019/

grid are 16, 86, and 15 m above sea level (a.s.l.), respectively.
Seto (Fig. 3b) altitudes of observational site, d01 grid, andd02 grid are 140, 121, and 145 m a.s.l., respectively. Misyo(Fig. 3c) altitudes of observational site, d01 grid, and d02
grid are 17, 27, and 12 m a.s.l., respectively. The surface airtemperature in the model is a value obtained at a height of
2 m above ground level (a.g.l.), which is diagnostically estimated from the Bulk parameterisation for surface heat flux.
The AMeDAS temperature is also measured at a height of
1.5 m a.g.l.

Adv. Sci. Res., 16, 1–6, 2019

4Y. Ohashi and H. Ueyama: Numerical simulations of winter cold damage to citrus fruits

Figure 4. Simulated maps of cold duration (h) less than −1 ◦ C, which were produced for the (a) d02 entire domain and (b) enlarged rectangle

area in the left figure.

At the Seto area (Fig. 3b), the cold duration especially lessthan −3 ◦ C was well reproduced by both d01 and d02. Although there seems to be not a large difference between d01
and d02 results at Seto and Misyo (Fig. 3c), a cold duration ofd02 at Omishima agreed with the observed that betters thanthat of d01 (Fig. 3a). This may be because the Omishimasite is located at the narrow valley of a small island. In fact,
the d01 grid including the AMeDAS site has a significantly
higher altitude than those of the d02 grid and actual site andincludes not only the narrow valley but also the surrounding
hills. Therefore, a finer grid setting in the model is required
for simulating cold meteorological conditions on complex
micro-topographies, which will include narrow slopes, valleys, and hilly areas where citrus fruits are cultivated.
3.2Cold duration mapping

Here, calculated cold duration maps were produced to assessa spatial difference of cold duration less than −1 ◦ C, using
the d02 output data (Fig. 4). As an example, a region including the Misyo site was focused on the right side of Fig. 4.
These maps were drawn using the GMT software in which
the tone mapping is interpolated by the bicubic method. In
these figures, only areas less than 250 m a.s.l. were visualized
because of a cultivate elevation limit of citrus fruits. This wasachieved by using a land-use GIS map developed by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT)
in Japan. The figure revealed that the cold duration tended
to be longer at the foot of mountains, whereas the areas including the AMeDAS observatories of Misyo and Uwajima,
Adv. Sci. Res., 16, 1–6, 2019

which were located on the plain near the coast (as can beseen on the right-side figure), were estimated as having theshortest cold duration. The results suggest that temperatures
observed by AMeDAS sites may underestimate the risk ofcold damage for citrus fruit from the monitored temperature
data.
Figure 5a shows the cold durations simulated at slope grids(A and B) in addition to the simulated and observed cold durations at the Misyo site on the plain. The Misyo AMeDAS
site is located on at elevation of 12 m a.s.l., while elevationsof A and B are 126 and 83 m a.s.l., respectively, where citrus
cultivation fields spread (Fig. 5b). Simulated cold durations
less than −3 ◦ C recorded 4.5 h at both slope grids. This extreme cold condition was not simulated at the AMeDAS grid.
A relationship between air temperature observed at Misyosite and the yearly yield of Kawachi-bankan in Ehime Prefecture was analysed in the same manner as Fig. 1. That result showed a yield decrease of 1.5 t ha−1 for recorded temperatures (at Misyo site) of less than −2 ◦ C for 10 h. The
cold surge event also observed 5.2 h of temperatures less than−2 ◦ C at the Misyo AMeDAS. In this manner, visualizing acold temperature by maps provides knowledge of a spatial
heterogeneity of cold risk for citrus fruits.
4SummaryIn this study, winter cold damage of citrus fruits by cold surge
attack was simulated using a high resolution configuration ofthe WRF NWP model. Japanese citrus is often cultivated on
slope lands with a small hill and valley. Here, detail cold duwww.adv-sci-res.net/16/1/2019/

Y. Ohashi and H. Ueyama: Numerical simulations of winter cold damage to citrus fruits

5Figure 5. (a) Cold durations (h) observed at the Misyo AMeDAS site and simulated at the grids including the AMeDAS site, slope A, andslope B. (b) Simulated cold duration map (with temperature less than −2 ◦ C) and locations of AMeDAS, slope A, and slope B.

ration maps for sub-zero temperatures were produced to simulate a spatial heterogeneity of cold duration in west Japan
during the winter of 2011. The simulation results demonstrated that the temperature measured at AMeDAS sites atcoastal locations underestimated the risk of cold damage forcultivated citrus fruits on narrow slopes, valleys, and hilly
areas. This fact suggests a necessity for a numerical meteorological model for predicting cold damage, which canresolve complex micro-topographies where citrus fruits arecultivated. A higher resolution configuration such as of 100–
200 m may improve the accuracy of the sub-zero temperaturemaps further.

Data availability. Data are available via e-mail request to the cor-responding author.

Author contributions. HU provided the idea and motivation ofthis study and YO carried it out. YO performed the simulations andprepared the manuscript.

Competing interests. The authors declare that they have no con-flict of interest.

Special issue statement. This article is part of the special issue“18th EMS Annual Meeting: European Conference for Applied Meteorology and Climatology 2018”. It is a result of the EMS AnnualMeeting: European Conference for Applied Meteorology and Climatology 2018, Budapest, Hungary, 3–7 September 2018.

www.adv-sci-res.net/16/1/2019/

Acknowledgements. Input data of the WRF was arranged andprovided by Teruo Osawa in Kobe University, Japan. This study
was supported by JSPS KAKENHI Grant-in Aid for Scientific
Research (C) number 16K07963. The Generic Mapping Tools(GMT) graphics system (Wessel and Smith, 1998) was used fordrawing some figures.

Edited by: Keith Lambkin
Reviewed by: two anonymous referees

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