lare), and 
Eq. (1). 
Districts: 
T. Shoji, H. Kitaura | Computers & Geosciences 32 (2006) 1007-1024 1019 
  
  
  
  
  
  
  
t 
x 
= 
= 
a 
5 ChuKan Chubu 
Rl 
2 
o 
2 —O-— Average Precipitation/ mm-h^- 
© 1 (ChuKan) 
S - -& - Average Precipitation/ mm-h^- 
© 1 (Chubu) 
x - "E - Average Precipitation/ mm-h^- 
1 (Kanto) 
0 1 1 1 1 1 L J 
0 6 12 18 24 
Time/h 
Fig. 13. Averaged hourly precipitations at every time in a day through a year (‘99), when zero precipitation data are excluded. The 
averaged precipitations were calculated by Eq. (3). Districts: Chubu = dotted line with solid triangles, Kanto = dotted line with solid 
squares, and ChuKan = solid line with open circles. 
district at Time ¢ on Day d. Fig. 13 indicates two 
facts: (1) the average precipitation at each time is 
not different between Chubu and Kanto, and (2) the 
rain intensities seem to be slightly but remarkably 
strong around 17 o’clock in both districts. 
Figs. 12 and 13 show a daily cycle in rainfall. In 
contrast, most of temporal variograms do not show 
a daily duration. Only the variogram in Tsubakuro- 
dake (Fig. 10) shows a variation seeming to suggest 
a periodical cycle. The proportion of rainy hours is 
less than 10%, and a series of rain scarcely 
continues over a day. If a series of rain is defined 
by 1h break, the probability that a series of rain 
continues more than 24h is 0.3%. If 12-h break is 
applied (i.e. 11-h break is treated as a part of a series 
of rain), the proportion is 17%. Because of this low 
proportion, a daily duration does not appear on a 
variogram. 
6. Spatial correlation of short term rainfall 
It is necessary to estimate accurately rainfall in a 
short term for predicting natural hazards such as 
flood, landslide and others. AMeDAS records 
precipitation with a time interval of 1h. In order 
to know the spatial continuity of rainfall in a short 
term, experimental variograms of hourly precipita- 
tions has been calculated. The data studied came 
from August 13 to 14, 1999, because the rain caused 
a severe flood in Kanto. 
Fig. 14 shows averaged hourly precipitation p, at 
Time ¢ from 01 JST on 13th to 24 JST on 15th, in 
Chubu (solid line with open triangles) and Kanto 
(solid line with open squares), which is given by the 
equation: 
D = Y» 5. (4) 
Where pj, is the precipitation at Time f at Station i, 
and A, is the number of rainy stations at Time f. The 
figure also shows the proportion of the number of 
rainy stations to the number of total worked 
stations with dotted lines with triangles and squares 
in Chubu and Kanto, respectively. In Kanto, the 
rain started at about 13 o'clock on 13th, and 
became rapidly wide and heavy from the midnight. 
The intensity of rain became heavier from the 
morning of 14th.