The Kujukuri Coastal Plain located in Chiba Prefecture is a narrow elevated coastal plain stretching approximately 60 kilometers in length and 7_??_9 kilometers in width. Topography of this plain consists of sandy beach ridges (or sand banks) running in parallel to the coastline and marshy lowlands lying between these parallel ridges. Until recent it was said that, largely in conformity with these topographical features, the sandy beach ridges were used for settlements, upland fields, etc., while the marshy lowlands were used for paddy cultivation, creating such a characteristic land use of this coastal plain.
On the basis of 1 : 10, 000_??_1: 3, 000 large-scale maps, the present author carried out an investigation into the land use of this plain, and came to the conclusion that this view hitherto held as general knowledge was erroneous. In other words, the view that the sandy beach ridges are used by upland fields or that there are no paddy fields there is a fallacy. As a matter of fact, most of the sandy beach ridges include many island-like upland fields or “shimabata”, therefore even here, there are many paddy fields. Stating it in other terms, numerous paddy fields are found not only in the marshy lowlands but also in the sandy beach ridges.
As clearly presented by the author's survey on the distribution of “shimabata” in Japan (see Geographical Review of Japan, Vol. 41, No. 4, 1968), the Kujukuri Coastal Plain is an area noted for the distribution of “shimabata” landscape. The main purpose of the present paper is to clarify the reasons for the large-scale development of this type of land-scape.
Lagoons in the marshy lowlands and a few irrigation reservoirs built in dissected valleys of the diluvial uplands bordering the western boundary of the plain have long been used for paddy cultivation. However, paddy fields that could be irrigated by these sources amount to only a small proportion of the total paddy fields in the marshy lowlands, and so the majority were rainfed ones. Even if the sandy beach ridges were only slightly higher than the marshy lowlands by 50 centimeters or so, it was impossible to make any paddy fields unless the elevation of the ground surface was lowered. In order to expand paddy fields into the sandy beach ridges, the farmers dug the lower parts of the ridges. Cultivation was practiced on piled up spots, while in the dug places, paddy fields were realized. The result was the island-like upland field landscape where upland fields and paddy fields are found alternately. Groundwater table is generally high in the Kujukuri Coastal Plain, and so if rain falls at suitable intervals, rice can be grown well in rainfed paddy fields.
The reclaimed land of Chinkai Lagoon is located in the northern part of the Kujukuri Coastal Plain. This reclaimed land was created in the early years of the Tokugawa Period. This is an area always suffering from shortage of irrigation water. There is a wide distribu-tion of “shimabata” on this reclaimed lands, too. Blank parts enclosed by dotted lines in Fig. 2 indicate places where “shimabata” are found. The distribution pattern corresponds to the shallow lagoon bottoms that were reclaimed. Two sample areas were taken from the distribution areas of “shimabata” in Figs. 3 and 4. The black parts are “shimabata”, while blank parts show paddy fields. A complicated pattern shown in Fig. 3 is surprising. Difference in elevation between “shimabata” and paddy fields is, in general, 30 to 40 centi-meters. Slightly higher lands (about 50 cm) in this reclaimed land, the ground water table is relatively low. In order to have it closer to the groundwater table, earth should have been dug to make paddy fields. The result is the landscape of “shimabata”.
Figure. 4 shows the narrow “shimabata” made alternately with narrow paddy fields.

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In a summer half year, there are two rainy seasons ; Changma (early summer rainy season) and Kaul Changma (early autumn rainy season) in Korean Peninsular, correspond-ing with Baiu and Shurin respectively in Japanese Islands and with Maiyu in early summer in China.
In this paper, the writer analysed two rainy seasons by employing the occurrence frequency of bad weather index (Lee, 1974) and synoptical bad weather day. The bad weather day was classified synoptically as follows (Fig. 2) ;
1) rainy bad weather day (_??_ sign in Fig. 2) ; the day with ≥1.0 mm of precipi-tation, ≥threshold value of daily cloud amount and ≤ threshold value of sunshine duration or the day with ≥ 1.0 mm of precipitation and ≥threshold value of daily cloud amount.
2) cloudy bad weather day or scanty rainy bad weather day (_??_ sign) ; the day with ≥ threshold value of daily cloud amount and ≤ threshold value of sunshine duration.
3) showery bad weather day (⊕ sign) ; the day with ≥ 1.0 mm of precipitation and ≥ threshold value of sunshine duration or the day with ≥ 1.0 mm of preci-pitation.
4) cloudy bad weather day (_??_ sign) ; the day with ≤ threshold value of daily cloud amount.
5) scanty sunshine bad weather day (_??_sign) ; the day of C threshold value of sun-shine duration. The determination of the threshold values was referred to in the previous paper (1974).
Though the beginning of Changma is very irregular year to year, it dates on June 24 normally. The end of Changma dates on the second decade of July in the southern region and on the last decade of July in the central region of Korean Peninsular. The phenomenon of Changma gradually moves to north as the polar front advances to higher latitude. The seasonal trend of Changma has a various pattern according to the meridional shifting of the polar front (Fig. 5 and Fig. 2). The phenomenon of seasonal intermission of summer by returning of the polar front from higher latitude is also a typical bad weather situation of summer season.
Kaul Changma is a natural seasonal phenomenon which is caused by the stagnation of cold front from higher latitude and the stationary front. But, the Maul Changma season has shorter duration than the Changma season and its seasonal trend is very irregular year to year. In some years, Kaul Changma fails to appear.
Owing to the direct influence of the continental anticyclone, there is almost no autumn rainy season in China. In Japanese Islands, the Shurin season is much longer and receives plenty of precipitation because it is also a typhoon season. Put its appear-ence pattern is intermittent according to the stagnation of southward shifting cold front from higher latitude and the stationary front, and the bad weather climatic situation is very irregular year to year.
The position of polar front is intimately related to the advance and retreat of the North Pacific anticyclone as is shown in Fig. 7 and Fig. 8.

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The annual water balance in the Shinjo Basin was calculated by a climatological method. The Shinjo Basin, which is 205km² in area, is situated in the northern part of Yamagata Prefecture (Fig. 1) and receives abundant snowfall in winter. The drainage from this basin flows into the Sake River which is a tributary of the M ogami River.
It is said that the data of water balance components (precipitation, runoff, evaporation) of a drainage basin may contain considerable errors and that the accuracy will get worse in the order of precipitation, evaporation and runoff. So the author wanted to estimate runoff from precipitation and evaporation. Empirically, 60_??_70% of a small pan evaporation value are regarded as the actual evapotranspiration of the area. The author adopted 65% of this value in this calculation.
On the other hand, the author calculated evaporanspiration from the drainage basin by using the Penman's method for potential evaporation (Table 5). In the case of the Shinjo Basin, the actual evapotranspiration was obtained by multipling the Penman's value by the factor of 0.80 (Fig. 5). The result of water balance obtained from mean value for nine years are as follows; precipitation: 2220mm/year, evapotranspiration: 568mm/year, runoff: 1652mm/year, runoff ratio: 0.74.
Compared with the observed values in the Kamabuchi Experimental Watershed which lies about 15km to the north of this basin, the calculated ones for the Shinjo Basin shows close agreement. Consequently, the calculated runoff from precipitation and evaporation can be considered as appropriate for the Shinjo Basin.

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