The strong winds are observed over Japan, although the distribution is varied because of the mountainous terrain. The topography effect resulting in the strong winds associated with tropical cyclones (TCs) is intimately linked to the TC tracks. The purpose of this study is to examine the distribution of surface winds associated with TCs over Japan, based on numerical experiments. Using ensemble experiments with several TC cases, we detected the distribution of surface winds associated with TC tracks and developed a disaster-prevention graph so called “Typhoon Nomogram” at each location in Japan. The Typhoon Nomogram is useful for understanding the variability in the distribution of surface winds over Japan which depend on TC tracks and is useful for reducing the wind disasters caused by TCs.

抄録全体を表示

Observations of the solution rate of limestone tablets from 1993 to 1997 have been utilized to clarify the degree of karstification from northern to southern Japan.
Limestone tablets were placed at seven observation points stretching from northern to southern Japan : Toma, Abukuma, Chichibu, Akiyoshidai, Shikoku Onogahara, Ryugado, and Minamidaito. Three groups of four limestone tablets from Slovenia, Guilin (China), Chichibu, and the fourth tablet from limestone indigenous to the obsevation point, were arranged on three levels at each observation point : 1.5m above the ground, the A3 horizon, and the B₂ horizon. Measurements were taken of the solution rates of the tablets at each observation point from 1993 to 1997. Thornthwaite's method was used for calculating water balance to ascertain the relation between solution rate and water balance factors. The solution rates of limestone tablets placed 1.5m above the ground show a high correlation coefficient between (water surplus (WS) minus water deficit (WD)). On the other hand, limestone tablets planted in the soil had a solution rate from two to three times higher than those suspended in the air. The solution rates of limestone tablets located in the A₃ and B₂ horizons exhibited the highest annual precipitation correlation coefficient. The high CO₂values under warm, humid conditions may account for the higher solution rates of the tablets planted in the soil.
The solution rate tendency curve achieved its greatest range during the five years in direct proportion to the WS-WD ratio in 1993, when a cool, humid summer prevailed throughout most of Japan. The solution rate tendency curve marked its smallest range during the five years in proportion to the WS-WD ratio at all locations for limestone tablets suspended in air in 1994, under conditions of an extremely hot and dry summer, such as occurs only once in a hundred years. In general, however, the solution rates of the limestone tablets were high when the WS-WD ratio ranged between 1, 000 to 1, 600mm. Within this range, the solution rates at each observation point decreased slightly as the WS-WD ratio decreased.

抄録全体を表示

南大東島では大規模かつ効率的なサトウキビ生産が行われている一方で，サトウキビの単収は低く，年次変動が大きい．この理由として，夏場の降水量が少なくしばしば干ばつに見舞われることが挙げられる．島では積極的に灌漑設備の導入に取り組んでいるが，依然としてサトウキビ生産は降雨に大きく左右されている．その影響を解明し合理的な灌漑方法を提案するため，本研究では南大東島の過去の気象データに基づき株出しサトウキビ畑における水収支を算出し，特に夏季の水収支とサトウキビの生育および収量との関係について明らかにした．梅雨明け後の降水量は少なくサトウキビの消費水量が有効雨量を大きく上回ったため，7～9月における不足水量は多く，この3か月間の不足水量は年全体の46％にも相当した．そこで，7～9月に着目し解析を行ったところ，各月の不足水量と茎伸長量および単収との間には負の相関関係が確認され，特にこの時期の不足水量が増加するとサトウキビの成長が著しく制限され，収量を低下させると考えられた．また，この傾向は最大風速が25 m s^–1以上となる台風年度を除くとより顕著であった．非台風年度において7～9月の合計不足水量から合計伸長量および単収を推定する回帰式を用いると，この時期の不足水量が100 mm増加するごとに伸長量が25.1 cm，単収が14.1 t ha^–1低下することが明らかになった．以上より，7～9月の水収支がサトウキビの生育および収量に強く影響を与え，この時期における灌漑が高単収の実現に必要不可欠であることが本研究から改めて示された．

抄録全体を表示

Classification of the soils on the raised coral reef terraces of Minami-Daito Island, located in the humid subtropical region of Japan, were studied based on their general chemical properties and forms of free iron oxides. The results are as follows: 1) On the higher terraces, Haguue (45〜50 m.a.s.l), Red soil and Yellow soil are widely distributed. In the Red soil, the activity ratio of iron (Fe_o/Fe_d) ranges from 0.01 to 0.07, and the crystallinity ratio of iron [(Fe_d-Fe_o)/Fe_t ranges from 0.77 to 0.81, while in the Yellow soil, they range from 0.01 to 0.05 and from 0.78 to 0.85, respectively. The Red soil approximately corresponds to Haplic Lixisol close to Rhodic Nitisol (FAO-Unesco) or Typic Rhodudalf (USDA Soil Taxonomy). On the other hand, the Yellow soil corresponds to Haplic Acrisol or Typic Kandiudult. 2) On the lower terraces, Hagushita (15 m.a.s.l.), Terra rossa-like soil is distributed and approximately corresponds to Haplic Lixisol or Eutric Cambisol, Typic Hapludalf or Typic Eutrochrept, respectively. 3) On the sea side slope (20 m.a.s.l.), Terra fusca-like soil is distributed and corresponds to Chromic Luvisol or Typic Hapludalf. Consequently, the Red and Yellow soils distributed on the higher terraces of Minami-Daito Island are similar to the lateritic red soils widely distributed in subtropical South China, and considered to be older and more weathered than the Red-Yellow soils (Udults) which have hitherto been reported from Southwest Japan.

抄録全体を表示

In this paper, we describe the environment of domestic water systems, the people's opinions and the ways of water uses at Tonaki, Kitadaito and Izena island in Okinawa. And we analyse the suitable scale of equipments for rain water uses at Kitadaito island, using the simulation method. The main contents are as follows. At the islands with no tap water systems, the domestic water depends on well water and rain water in each house, and the well water influenced by the sea water and the sewage is restricted for using. At Tonaki island, mainly depended on well water, the rain water has been used for drinking. The other hand, at the island such as Kitadaito island, mainly depended on rain water for all uses in domesticities, the equipments for rain water using system so as the storage tanks are large in scale, and there are different ways of water uses as people's opinions for water conservation are high level in comparison to Tonaki island. Depended on the simulation results for using of rain water to Kitadaito island, it is showed that the usable amounts of rain water are the range between 600 and 700 (1/house, day) in many houses. We clarify the relation between catchment area (A) and storage tank capacity (B) for rain water collection system, and show that the effective ratio of (A) to (B) is at about 2 (m^2/m^3). The ratios in many houses are approximate to this value in Kitadaito island.

抄録全体を表示

気象庁の記録的短時間大雨情報は、大雨警報発表中に、数年に一度程度しか発生しないような短時間の大雨を観測又は解析したときに市区町村名等を示して発表されるもので、1983年に運用が始まった。その発表基準や運用等はたびたび見直されているが、気象庁はこの情報について一貫して、「現在の降雨がその地域にとって災害の発生につながるような稀にしか観測しない雨量であることを知らせるもの。」と説明している。一方、「避難勧告等に関するガイドライン」（内閣府）では、土砂災害に対する避難勧告等の判断に活用する情報の1つとしてこの情報が位置付けられている。しかし、記録的短時間大雨情報の業務的な変遷を纏めたものやこの情報が発表された際の災害発生率等について定量的に調査されたものはない。

本稿では、記録的短時間大雨情報の業務的な変遷を振り返るとともに、記録的短時間大雨情報が発表された事例について、市町村ごとの災害発生率等を調査し、防災情報としての役割等を考察した。記録的短時間大雨情報の対象となった市町村の61.6％で浸水害又は土砂災害が、大雨警報（土砂災害）と記録的短時間大雨情報が発表された市町村の43.5％、土砂災害警戒情報と記録的短時間大雨情報が発表された市町村の49.8％で土砂災害が発生していた。記録的短時間大雨情報は雨量の実況を知らせるものであるが、大雨警報を補足する防災情報としての一定の役割を果たしていると考えられる。

抄録全体を表示