Climate and Agriculture on the Hainan Island, South China

Geographical Review of Japan Vol. 57 (Ser. B), No. 2, 166-182, 1984

Climate and Agriculture on the Hainan Island,

South China: a Preliminary Study

Masatoshi M. YOSHINO*

Climate and agriculture on the Hainan Island is described based on the literature published in the recent years and on the author's study trip in January and February, 1984. First, the synoptic climatological background such as the frontal zones, cloud distribution, stream lines at the 850mb level, typhoon frequencies and fog distribution are described. The southwesterly winds and north easterly winds prevail at the surface level to the 850mb level and the typhoon plays an important role. Secondly, distributions of air temperature, rainfall, and durations of rainy and dry seasons are presented using the climatological records. Climatic division by Ha Daizhang is introduced to show the eight regions. Thirdly, agriculture in the Hainan Island is reviewed with special reference to climatic conditions. Rubber, rice and tea cultivations are dealt with in detail. In particular, the five areas of rubber cultivation were described in terms of cold and wind damages. The upper limit of rubber cultiva tion can be 300-350m a. s. l. in the northern part of the island, but 500m in the southern part. Of special interest is the recent development of hybridized rice cultivation. They grow in winter, ear and flower normally in middle and later March and mature in middle and later April in the southern part of the island. Then they are brought to the home regions in the other part of China and sown there in the normal growing season. Fourthly, typhoon damage and cold damage are described and damage classes are introduced. Especially, early rice and late rice cultivation and cold damages on rubber trees are dealt with, because they are most striking in the development of tropical crop agriculture on the Hainan Island. Lastly, a perspective is given for further development.

•@ are striking. I.Introduction The arable land area is 449•~103ha and tropical crop fields, such as rubber plantations, The Hainan Island, located on 18ß10•L-20ß occupy 227•~103ha. Lands for forestry and 10•LN and 108ß37•L-110ß03•LE, has an area of animal husbandry are 660•~103ha. Popula 33,907.7km2. It is the second-largest island tion is 5.4million, of which 1.6million is non next to Taiwan in China. The climate of the agricultural. The agricultural production Hainan Island is characterized by high tem amounts to about 500million U.•@S. dollars, perature throughout the year, plenty rainfall Main crops are rubber, rice, coconuts, oil palm, in summer and autumn, frequent typhoon pepper, coffee, coco, agave, fruits, etc. The visits, and clear difference between dry and economic tree species numbers about 2,900 and wet seasons. The terrain relief is intermediate, bird species 344. There are many wild species that is, low lands and hilly lands prevail of plants, such as wild rice and wild tea. broadly. The area lower than 500m a.•@s.•@l. In the present preliminary study, some occupies 74.6% of the island, surrounding the aspects of the agroclimate on the island will higher mountainous areas. Soils are reddish be discussed and the results recently published in color and develop deeply. mainly in China will be summarized, together Rivers are short, but the available water with some findings obtained by the author discharge is 297•~108m3/year. The seasonal during the study trip made in January and change and interannual variation of discharge February, 1984.

* Institute of Geoscience, University of Tsukuba. Sakura-mura, Niihari-gun, Ibaraki-ken 305, Japan. Climate and Agriculture on the Hainan Island 167

II. Climate of the Hainan Island 30ßN to 20ßN in January as shown in Figure 1 (YosHINO,1969, 1971). In the east of this 1.Synoptic climatological background frontal zone in South China steadiness is relatively high and about 75% over the Hainan In January, northeasterly winds prevail as Island. However, the northerly air flow from a winter monsoon. This winter monsoon, the main cold airmass located over the inner however, flows out originally from North China Asian continent occurs frequently toward the as a NW winter monsoon, changing to the N Hainan Island almost along 110ßE south of winter monsoon on the East China Sea, and to 35ßN. The details of this air flow should be the NE-ENE winter monsoon along the South studied synoptically, case by case, because China coast and over the South China Sea. A cold advection causes cold damages in the quasi-stationary polar frontal zone results in island, as will be mentioned later. From glum weather for many days in winter months winter to spring, the cold air from inland (called yin chun chun in Chinese) in South China causes fogs and drizzle when it flows China and in the northern part and central over the relatively warm sea surface. Such mountain regions of the Hainan Island. The a weather in spring is called monyu in so-called Kummin Polar Frontal Zone runs Chinese and has been called crachan in the from NNW to SSE along the 105ßE line from foreign literature (HE, 1980). The wind does not reach the southern part of the island, however, and the people enjoy the sun. The cloudiness distribution in the region surrounding the Hainan Island is given in Figure 2. Computing the divergence fields based on the data at the grid points at each 2.5ß•~2.5ß intersection, SADLER (1977) presented the tropospheric circulation over the global tropics. Generally, the regions of deep con vective cloudiness are associated with diver

gence and those of little cloudiness or low level stratus with convergence. Figure 2, extracted from these figures, makes clear the strong con vergence in South Asia to East Asia through South China in January. North of 30ßN, there is an observable divergence (2•~10-5 sec-1). The maximum cloudiness axis running in the meridional direction along 108ßE and another maximum axis from SW to NE along a line from Taiwan to Kyushu are striking in

January and correspond to the frontal zones shown in Figure 1. These conditions are reflected in the local weather, i.e., the foggy, drizzle weather in the northern and eastern

parts of the Hainan Island in January. As shown in Figure 3, streamlines over the South China Sea at the 850mb level are from NE to SW in January. However, over the continental South China, they are complicated, in the same month, indicating stationary frontal activities there. Figure 1. Positions of polar frontal zones In April, streamlines over the Hainan Island and ITCZ in January and July. are southwesterly, although they are originally 168 MM. YOSHINO

Figure 2. Divergence (10-5 sec-1) at the 300mb level (positive is divergence) and the mean cloudiness (oktas) in January and July. Compiled from the figures by SADLER(1977). easterlies over the Philippines and the southern Island in the summer monsoon months. part of the South China Sea. Contrary to the conditions in January, the The summer monsoon flow prevails markedly Hainan Island is placed in an area of divergence over the Hainan Island. According to Figures in July, which means a region of deep con 1 and 3, the southwesterly monsoonal flows vective clouds, as shown in Figure 2. In from the Indochina Peninsula and the South October, as shown in Figure 3, the streamlines China Sea prevails over South China, the at the 850mb level become ENE over the Yangtze River region, and the East China Sea Hainan Island, indicating the winter mon and reaches the Kyushu Island, Japan. It soonal circulation dominating South China. prevails over the Hainan Island and its eastern A marked difference between October and sea region, where the ITCZ is either absent or January is that there is no obvious frontal rarely present. Steadiness of the southwester zone in South China in October. lies in July is 50-75% over the Hainan In Figure 4, the occurrence frequency of Island, but it is more than 75% over the Gulf typhoons and mean paths are shown. These of Tonkin (YOSHINO,1969, 1971). This im fi gures were compiled from the figures based plies the stronger wind conditions with more on the statistics for 1949-1969 (Central desiccating effect on the western coast of the Meteorological Bureau, 1979). Typhoon fre Climate and Agriculture on the Hainan Island 169

Figure 3. Mean streamlines at the 850mb level over Southeast Asia. quencies were computed for each 2.5ß•~2.5ß Mostly there are 3-5 fog days in each month, quadrangle. The figures show that the north but in extreme months they are more than 10 ern part of the island is visited more in June, days. The sea surface temperature is lower

July, August and November+December, but than 25•Ž and the value [monthly maximum the southern part is in September and October. water vapor (aM) minus the saturation water Sea fogs are striking in the zonal sea region vapor for the sea surface temperature (am)] is with 100-200km width along the coast. Figure plus in these months. 5 shows the distribution of the number of days Typhoons hit the island from June to October with fogs over the sea along the South China generally. Their paths are mainly from ESE, coast from December to May (WANG,1983). i.e., from the direction of the Luzon Island of There are practically no fog days in the other the Philippines toward the north of the Hainan months in this region. Of much interest is the Island or toward the Leizhou Peninsula. As relatively high occurrence of sea fogs in the will be mentioned later, therefore, typhoons region extending from the northern part of cause frequent damage to the eastern part of the Hainan Island to Hong Kong, which is the Hainan Island. apparent especially from January to March. 170 M. M. YOSHINO

Figure 4. Occurrence frequency and mean paths of typhoons (Central Meteor. Bureau, 1979).

Figure 5. Distribution of the number of days with fogs over the sea along the South China coast. Compiled from the figures by WANG (1983). Climate and Agriculture on the Hainan Island 171

2.Distribution of climatic elements though the actual values range from lower than the above average in the central moun The Hainan Island receives insolation of tainous region to higher ones in the southwest 110-145kcal/cm2/ year on an average, al ern coastal regions, as shown in Figure 6-a,

Figure 6. (a) Insolation and (b) sunshine hours in the Hainan Island (after ZHOU, 1981).

Figure 7. (a) Annual mean air temperature, (b) observed record of minimum air temperature,

which was slightly revised from a figure given on the entire island, of which the Yaxian by ZHOU(1981). The eastern part is relatively County receives more than 9,000•Ž. Many lower than the western part because of higher tropical crops, such as palm, oil palm, and coco, cloudiness and rainfall in the former. Radia grow very well. Rice can be harvested three tion balance is also maximum on the western times a year in several parts of the island. coast; more than 70kcal/cm2/year in contrast Mean annual rainfall, which ranges 960 to to 64kcal/cm2/year on Mt. wuzhi, which is the 2,600mm from place to place, is about 1,500 lowest ever observed on the island. Location mm in most part of the island. The observed of Mt. wuzhi is shown in Figure 10. maximum annual rainfall was 3,600mm at Annual sunshine duration ranges from 1,747 Tianchi, a mountain station (760 m a. s.l.) on hours on the central mountains to 2,662 hours Is/It. Jianfengling in 1964. The western coast at Dongfang on the western coast. The is the driest in contrast to the central and southern coast receives 2,400 hours of sunshine, southeastern mountain regions which are the whereas the northern and northwestern regions wettest, as shown in Figure 8-a. The lapse recive 2,000 hours, as shown in Figure 6-b. rate of air temperature in the Hainan Island The percentage of actual over possible sunshine has been reported only for Mt. Jianfengling as duration is lower than 50% in the central shown in Table 1 by JIANG (1982). As far mountain region and 50-60% in the rest of as the values computed by the difference be the island, except for the western coast, which tween 68m and 760m a. s. l. are concerned, the registers more than 60% of sunshine. These conditions imply that the Hainan Island enjoys a plenty of sun light. Annual mean air temperature is higher than 22.5•Ž in most part of the Hainan Island. The highest is 25.4•Ž at Yaxian, as shown in Figure 7-a. Monthly mean air temperature higher than 20•Ž, under which vigorous growth of rubber trees occurs, begins from February - March and ends in November in the entire part of the island. Among these months, 4 months have the monthly mean air temperature higher than 26•Ž. The coldest month is January with the monthly mean of 16.2-20.8•Ž and the warmest month is June or July with 25.7-29.0•Ž. As shown in Figure 7-c and 7-d, the difference in temperature between the central mountain region and the coastal region is larger in

January than in July. In particular, warm conditions on the southern coast is remarkable. Cold waves spread over the island less than once a year on an average, but the southern part is free. During the surge of cold waves, minimum air temperature lower than 5•Ž continues for 1 to 2 days. The observed record of minimum temperature is shown in Figure 7-b, which indicates marked warm areas in the southern and southeastern coastal regions. The accumulated temperature of daily mean Figure 8. (a) Annual rainfall (mm) and (b) num air temperature of •†10•Ž is more than 8,400•Ž ber of ten-day periods of dry season. Climate and Agriculture on the Hainan Island 173

Table 1. The lapse rate of air temperature

at Mt. Jianfengling (18ß20•LN),

Hainan Island (JIANG, 1982). A. Winter (Jan., Feb. and Dec.)

B. Summer (June, July and August)

Figure 9. (a) Beginning of rainy season, and (b) end of rainy season.

indicates the dry condition of the west coast. The dry season is exactly twice as long on the west coast as in the central and southeastern regions where Tunchang and Wanning are located. September and October are the months with lapse rate is about 0.7•Ž/100m, which is larger monthly rainfall of more than 100mm, monthly than the one for the middle latitude mountains. mean air temperature of about 23•Ž and There are marked wet and dry seasons. The relatively large diurnal change of air temper months with rainfall of>100mm begin in ature, indicating that this is the period of the April and end in November (8 months) in highest yield of rubber trees on the island. southern and central counties, whereas they Using the year-climate method expressed by are from May to October (6 months) in north the KOPPEN's system of the climatic classifica western, northern, and northeastern counties. tion, it was indicated that BS (steppe climate) The period with monthly rainfall of>100mm occurs in Donfang on the west coast of the is the shortest from June to October (5 months) island in some dry years (YOSHINO et at., 1981). in western and southwestern counties. The This is an exceptional phenomenon in otherwise beginning and the end of the rainy season are wet Southeast Asia. shown in Figures 9-a and 9-b, respectively. In short, the regional difference in the cli The distribution of the number of ten-days of matic distribution can be more clearly depicted dry season is given in Figure 8-b. It clearly in the rainfall regime than in air temperature. 174 M. M. YOSHINO

3.Climatic subdivision prevailing wind direction is variable, typhoon winds are less strong, humidity is relatively

HE (1980) proposed a climatic subdivision of high, diurnal temperature range is large and climate, based on (i) the monthly mean dryness the local climate changes from place to place. Region I: Northeastern Qiongshan-Wenchang (r/E0)<1.2, where r is monthly precipitation and E0 is actual evaporation or monthly coastal climatic region. rainfall of<100mm for 6 months, (ii) monthly Region II: Northeastern Tunchang hill/shallow mean air temperature of the coldest month basin climatic region. with>18•Ž, (iii) normal coldest temperature Region III: Northwestern Lingao coastal cli matic region. (>5•Ž), (iv) 300m contour line, and (v) average wind velocity (3m/sec). The climatic sub Region IV: Northwestern Baisha mountain/ division is shown in Figure 10. Regions I-IV basin climatic region. are cool in winter, but Regions V-VIII are Region V: Southeastern Wanning-Lingshui warm. The eastern regions, i.e., Regions I, II, coastal climatic region. V and VI, are wet and frequently visited by Region VI: Southeastern Qiongzhong inland typhoons, while the western regions, Regions mountain/basin climatic region. III, IV, VII and VIII, are relatively dry and Region VII: Southwestern Dongfang-Yaxian experience less visits of typhoons. In Regions coastal climatic region. I, III, V and VII, prevailing wind velocities Region VIII: Southwestern Ledong inland are relatively high and the weather is fair and mountain/basin climatic region. dry. In Regions II, IV, VI and VIII, the

Figure 10. Climatic division of the Hainan Island after HE (1980) and HE et al. (1981). Climate and Agriculture on the Hainan Island 175

350m. An attempt to plant Hevea brasiliensis III. Agriculture in the Hainan Island to an altitude as high as 500m ended in failure. with special reference to climatic The upper limit of the plant in the southern conditions part of the island may be as high as 500m. Beyond 800m it will suffer from serious chilling injury. 1.General The island is divided into five regions in The productivity of crops in the Hainan accordance with the climatic conditions as Island is 1-3 times higher than that of the follows (SCATC, 1981) other subtropical or warm temperate regions of Region 1: Northeastern part of the island. China. For instance, sugar content per unit Possible light cold damage and heavy wind area produced in the Hainan Island is 1.4 times damage. Rational planning for protecting higher than that of the Suijiang Delta, 2.3 crops against strong wind damage is needed. times higher than Guangxi and Sichuan, 3.5 Region 2: Central and northern parts of times higher than Jiangxi and Hunan. The the island. Middle wind damage with light mean productivity of rubber in the Hainan to middle cold damage. In the low land, Island is about 60kg/ha/year, which is 2-3 shelter belts are necessary. In the hilly land, times higher than that of Zhanjiang, Shantou suitable cultivars should be selected in relation and Fujian. to the microtopographic conditions which, in In this chapter, the agricultural production turn, affect the local and microclimatic condi in the Hainan Island will be discussed with tions. In the mountainous region, water special reference to climatic conditions. contents in the soil should be managed rightly. Region 3: Central part of the island. Pos 2.Rubber, rice and tea sible heavy wind damage with middle cold It is said that the ratio of the present rubber damage. The cultivars should be selected in production to the potential production in the consideration of both cold and wind damages. Hainan Island is low in the state rubber farms Because of the greater topographical variations

(DENG and WEI, 1983). The absolute value is in this region, cultivation methods to be ap now 732kg/ha/year, but the potential seems to plied should change in accordance with local be 1,260kg/ha/year. Because of the favorate situations. climatic conditions in the Hainan Island com Region 4: Western part of the island. Pos pared with those in other tropical regions in sible light wind damage and middle cold China, the rubber tree area in the Hainan Island may be 10 times broader than the next production area of Xishuangbanna. The rub ber cultivation is generally possible below 350 m a. s. l. in the Hainan Island (HUANG et al., 1980). However, it can be cultivated in the southern areas of the island below 400m a. s. l. This roughly corresponds to 8,000•Ž of accumu lated temperature of•†10•Ž or annual mean air temperature of 22•Ž. JIANG (1982) pointed out that the upper limit of natural tropical plant communities may be drawn at about 500 m in the northern part of the Hainan Island, and at 800 or 1,000m in the southern part of the island. Cultivated plants, e. g., rubber trees

(Hevea brasiliensis), may be grown to 1,000m or even higher on the southern slope in Xi Figure 11. Regional division of rubber cultivation shuanbanna, but in the northern part of the in relation to climatic conditions island the upper limit can be recognized as 300 (SCATC, 1981). 176 M. M. YOSHINO

Table 2. Indices of damage on rubber trees and of the meteorological conditions (SCATC, 1981)

Figure 12. Rubber plantation in the Hongguang State Farm in the northern part of the island. In the right are the rub ber trees planted in 1960 and in the left are the shelter belt trees of Eucalyptus planted in 1950s. Dis tance between the shelter belts is 60-80m. (Photo taken by YOSHINO on January 27, 1984).

Figure 11. The indices of the cold and wind damages are given in Table 2. There are differences in indices between cold-registant cultivars and wind-registant cultivars and similar differences are also seen depending on differences in directions of slopes in the hilly and mountainous regions. As example of a rubber plantation in the Hongguang State Farm is shown in Figure 12. Average yield of rice on the island is now 6,263kg/ha/year, which is about 11% of potential productivity estimated for the Hainan Island. Early rice cultivars present the most im portant problem. They are sown from Decem ber to May and harvested in 160-170 days. During these days, solar radiation ranges from

* Cold damage classes 1-6 are shown in Table 6 and wind 388 to 485cal/cm2/day in the Hainan Island. damage classes in Table 3. These values are higher than the so-called ** Typhoon classes 8-12 are based on the Beaufort scale. full-harvest limit of 350cal/cm2/day. However, damage. Drought prevention systems as well 5/6 period of the growing season of the early as shelter belt networks should be considered. rice in the Hainan Island is the dry season. Region 5: Southern part of the island. Pos This means that no irrigation is necessary for sible light and middle wind damage and light early rice. Meanwhile, low temperature and cold damage. This is the most superior region, drizzle days, monyu as mentioned above, indicating high yield potentials and increased in the northern part, gingmingfeng (strong cultivation areas. In the coastal region, wind on around April 5) and dry, warm fohn stronger cultivars against wind damage should winds are in most cases not harmful for early be selected. rice. Since 1976, the cultivated area of early The regions mentioned above are shown in rice has increased to about 4/5 of late rice, but Climate and Agriculture on the Hainan Island 177

the yield of early rice is greater than that of late rice. The cultivated area of early rice was 49.2•~106ha in 1976, which was about 34% of the cultivation area for food crops. The total yield of rice is about 750•~106kg, which is about 50% of the total food produc tion. An experimental field has a record of 10,268kg/ha of early rice in 1979 (Guangzhou Institute of Geography, Laboratory of Cli matology, 1982). Since the 1970s, the international rice cultivar, IR, has been introduced. This made Figure 13. Cultivation landscape for developing possible to cultivate early rice (125-150 days) hybridized rice in Yaxian, southern and late rice (about 115 days) as well as winter part of the island (Photo taken by sweet potatoes (about 130 days), especially in YOSHINOOn January 29, 1984). the southwestern area. However, the crop

calendar differs from place to place and a to cultivate hybrid rice. The number of such

further detailed study is needed, because it people varied from year to year and reached depends strongly on the cold wave, winter the record of about 60,000 in the highest year. monsoon, and typhoons. There should be The area used for these cultivations was about combinations of crops, such as rice+rice+ 7•~103ha. Main crops cultivated for such a fl ower, rice+rice+maize and rice+rice+others. purpose are not only rice, but included about In making a combination, a consideration 20 other crops, such as sorghum, maize, wheat, should be given to such factors as the frequency millet, soy beans, peanuts, sunflower, cotton, of typhoon visit to the island in the middle of rape, tobacco, vegetables and watermelon. September, which is relatively low during the Therefore, the southern part of the Hainan typhoon season. Hanlufeng damage is not Island has become an important area for the seen anywhere except for only 5% of the experiments in agricultural sciences and hybri mountain area in the central part of the island. dizing cultivation fields. An example of the Hanlufeng will be mentioned later in detail. cultivation landscape for obtaining hybrid rice is shown in Figure 13. 3.Other crops In the southern counties, daily mean air Utilizing the warm climatic conditions in temperature is high enough to cultivate the winter, many other crops have been cultivated. crops in early spring; that is, early or middle

Of special interest is the recent development in January. On the southwestern coast of the the cultivation of hybrid rice, such as the one Yaxian County, frequently cultivated crops with male sterility and the one for the high include wax gourd (white gourd), cucumber, yield cultivar. They grow in winter, ear and kidney beans, tomato and other bean families fl ower normally in middle and late March and eggplant families. Watermelon is sown and mature in middle and late April in the in late December and harvested in March or southern part of the island. They were April in this county. They are big and red recently brought to other parts of China and inside with much juice and taste. The pro sown in the normal cultivation season. In ductivity is 37.5•~103kg/ha on an average but the 1960s, researchers from many parts of in the highest year it reaches 75•~103kg/ha. China came to the southern part of the Hainan On the coast of the Ledong County, winter Island and made experiments to breed good onion is produced intensively. Newly develop cultivars (HE, 1984). According to the sta ed cucumber, bitter gourd, etc. are harvested tistics of 1975-1976, about 30,000 people (not at the rate of 22-30•~103kg/ha on an average only scientists, but also farmers) from 27 and 75•~1.03kg/ha in the highest case. This provinces or cities, mainly in North China, means the income of more than 7.5•~103 US came to the southern part of the Hainan Island dollars/ha. 178 M. M. YOSHINO

Due to the less favorable temperature and Table 3. Classification of wind damage wind conditions of the Hainan Island, oil palm to rubber trees (SCATC, 1981).

yields are relatively low as compared with that in the Malayan Peninsula. If the absolute minimum temperature (Figure 7b) in winter

goes down below 3.0•Ž, the yield will drop to about 30% of that in previous years according to a study made in the farms on the Hainan Island (FANG, 1982). Typhoons cause severe damages to oil palms. For example, in the case of No. 20 Typhoon in 1972, the observed maximum wind velocity was 35m/sec at Wenchang and the nearly Nanhai State Farm suffered serious damage. Among the total number of 5,768 oil palms, 11% had a breakdown of new central leaves (22% in the worst plot) and 61.3% of old leaves (90% in the worst plot). On September 14, 1973, No. 14 typhoon hit the Qianghai coast with the maximum wind velocity of 80m/sec at the time when it landed. The Nanhai Farm had, therefore, changed to the cultivation of ly, because of the drag effect of terrains and land surface. In most cases, the eastern parts tea intercropped with rubber with systematic shelterbelts since 1973 and has been in success of the island are the wind-facing region and the western part the leeward region and this ever since. In short, the southwestern part of the island is most suitable for the oil palm difference causes a regionality of damages by typhoons. Percentage of breaking and lodging plantation. of tree trunks is 1% when the wind on the Beaufort Wind Scale is 8, about 6% when the IV.Agroclimatic problems wind scale is 9-10, about 10% when the wind scale is 10-11, and more than 20% when the 1.Typhoon damage wind scale is 12. If the wind scale is more Among the main meteorological damages, than 12, the damage will reach more than 50%. The percentage of breaking or lodging of wind typhoon damages are the most serious pro blems. According to the statistics for 1949 resistant rubber cultivars, such as Haiken 1 or -1977, 93 typhoons either landed or influenced the island (typhoon centers were within 100km from the coast) ; 3.2 typhoons per year on an average. From April to December, there is always a possibility of typhoon occurrence, but the months from July to October are the worst. The typhoon distribution for each month is shown in Figure 4. As mentioned above, a severe typhoon hit the island on September 14, 1973, and caused serious damages to farms cultivating rubber trees; number of trees with damage classes of 3 to 5 amounted to 7.313 million, which was Figure 14. Broken trunk of a rubber tree, caused 12.6% of the total (HUANGet al., 1980). Damage by the typhoon in August, 1983 classes are explained in Table 3. After landing (Photographed at the Nanhai State on the island, typhoons become weaker marked Farm by YOSHINOon January 31, 1984). Climate and Agriculture on the Hainan Island 179

PR 107, may be lower than 10% in the case Figure 1.5 shows an example of tea (Camellia of the wind scale of 12 (HUANGet al., 1980). An sinensis var. assamica) in the lower layer and example of breaking of rubber tree trunks is rubber trees in the higher layer. The planta shown in Figure 14. tion has a shelter belts. A result of observa To avoid the damages as well as to increase tion of tea production with and without rubber the production amount and to produce the trees as multistorey community is given in better quality of tea, cultivation method of Table 4 (FENGet al., 1982). As is clearly seen, multistorey and multispecific artificial com the tea production by trees with rubber trees munities has been developing on the island. is 3 times greater than that by trees without The multistorey artificial community can rubber trees. reduce the water loss and increase the amount 2.Cold damage of soil water and increase the soil fertility. Also, it reduces the soil erosion and shading In spite of its low latitude location, cold effect to the economic crops of the lower layer. winter monsoon invades the Hainan Island. According to the statistics of wind direction frequency for each ten-day period of each month (average of 1960-1969), winter mon soon with ENE wind direction prevails over Haiken from the first 1.0-day period of October to the first 10-day period of February (Go, 1983). The frequency of the ENE wind is 45-55% greater than the next frequent wind direction. This indicates that the cold air advection occurs easily on this island. During the last 30 years, 1950-1979, a severe cold damage occurred in 1955, 1963, 1967, 1974 Figure 15. Multistorey artificial communities: and 1976. Among them, the cases in January Rubber trees in upper layer and tea of 1955, 1963 and 1974 were the most serious in the lower layer (taken at the (JIANG, 1984). In the case of January 12, 1955, Nanhai State Farm by YOSHINOon minimum air temperature dropped to 0.4•Ž at Jan. 31, 1984). Danxian, and ten to thirty percent of young (1-3 years old) rubber trees suffered the cold Table 4. A comparison of tea production damage of classes 1 to 3. However, mature with and without rubber trees trees were damaged only on their branches. as multistorey community (FENG In the case of 1963, air temperature dropped et al., 1982). to -0.6 to 4.6•Ž in the northern part of the island. The cold damages were serious espe cially in low elevations. However, the cold registant cultivar, RRIM 600, showed no serious damage. In conclusion, the damages caused by severe cold waves occur in the central mountainous region north of Mt. Wuzhi and the north western region, but they can be minimized, if suitable caltivars could be selected, considering the topo-climatological conditions. For the cultivation of late rice, the main damages include typhoons first, secondly the so-called Hanlatfeng, cold-dew-winds or the winds blowing at the time of the cold-dew

(Unit is weight (g) of fresh leaves per one tea tree) festival during the flowering period, and thirdly 180 M. M. YOSHINO the cold damage during the irrigation period. in the Hainan Island. Quantitative studies on In some years, like 1976 and 1978, these three cold damage should also be performed in the damages will occur one by one continuously. future with this classification used as criteria. The daily mean air temperature lower than 23•Ž continuing for 3 days during the blossom V.Climatic superiority: a perspective period is harmful to rice (HE, 1980). In the As mentioned above, climate of the Hainan Hainan Island, such a condition occurs normal ly in the beginning of November, but occasion Island is better than the other tropical regions in China. For instance, photosynthetic po ally in the last days of September as in 1970. tential (dry matter production) is 106-138•~ In the central mountain region of the island, it is seen normally in the middle of October, 1,000kg/ha, which is about 10% higher than in Taiwan or South Guangzi. Other climatic but in some exceptional years, such as 1967, it comes a month earlier, as shown in Table 5. conditions are also more favorable in the Hainan island. It has a water-holding capacity The southern part of the island is an area without any damage by the Hanlufeng. of 3•~1010m3. Figure 16-a shows the varia Cold damage classes for rubber trees are tion in the cultivation area of (1) starch crops, shown in Table 6. Based on this classification, such as rice, sweet potato, maize, etc., (2) the study of cold damage has been carried out tropical crops, such as rubber, pepper, oil palm, coconuts, coffee, tea, etc., and (3) economic Table 5. Statistics of Hanlufeng or cold-dew crops, such as sugarcane, herb medicine,

winds, peanuts, vegetables, etc. (WEI et at., 1983). A sharp increase in the area of tropical crops can be observed during the last 30 years. The variation in production values of different crops are given in Figure 16-b, which also shows a striking increase of tropical crops. In the last 10 years, the production value of tropical crops grew by 5 times. Such an increase in tropical crops is, of course, supported by the climatic conditions of the island. The southwestern and southern parts of the island are particularly warm and dry. As has been reported by HUANGet al. (1982), these areas receive plenty of net radia tion (R). It amounts to 65-69kcal/cm2/year,

(Data Source: HE, 1980) but the ratio between the latent heat flux (LE) and R is 68-75% only, due to the deficit Table 6. Classification of cold damage of water in most months. The sensible heat of rubber tree (SCATC, 1981). flux (P) between the earth's surface and air is greater than LE or almost nearly the same with LE in half of the months in winter and spring. Pan evaporation (E0) may reach 1,500mm/ year, which is 500mm greater than annual rainfall. E0 exceeds rainfall in all months of the year, except August and September in the southwestern and southern parts of the island. Therefore, if the vegetation is carelessly destroyed, a savanna ecosystem will replace the present ecosystem, as pointed out by them. The other parts of the island are moderate or in superior climatic conditions. Therefore, if the Climate and Agriculture on the Hainan Island 181

Figure 16. Secular variations of production area (a) and production values (b) of various crops in the Hainan Island. A: starch food B: Tropical crops (rubber tree, pepper, oil palm, coconuts, coffee, tea etc.) c: Economic crops (sugarcane, herb medicine, peanuts, vegetables) (WEI et al., 1983).

ecosystem is rightly managed, that is, if the References land use plan is made with due consideration of climatological conditions, the development Central Meteorological Bureau (1979): Climatic atlas improvement and promotion of the tropical of People's Republic of China. Map Publ., Beijing, agriculture and forestry can be surely ac 226 p. (in Chinese). DENG,Honghai, and WEI, Lin (1983): An investigation complished. For this goal to be achieved, the on the present situation of agricultural resource use climatic and agroclimatic studies are urgent. in Hainan Island. Chinese Journal of Tropical Crops, 4. (1), 29-38. (in Chinese with English Acknowledgments abstract). We would like to express our sincere thanks to our FANG,Fuchu (1982): The climatic conditions in rela counterpartners in China. In particular, Prof. HUANG tion to oil palm cultivation on Hainan Island. Zongdao, President of the South China Academy of Chinese Jour. Trop. Crops, 3 (1), 81-93. (in Tropical Crop Science; Prof. JIANGAlliang, the Insti Chinese with English abstract). tute of Geography, Academia Sinica; and Prof. HAO FENG, Yaozong, WANG, Huihai, LONG, Yiming and Yonglu, the South China Academy of Tropical Crop ZHANG, Jiahe (1982): Tropical multistorey and Science. We are also indebted to the staff members multispecific artificial communities and its utilizable of the Guanzhou Institute of Geography, the Guan effects on sunlight, soil fertility and water. Col dong Academy of Sciences, and many other assistants lected Research Papers on Tropical Botany, Yunnan who lent us kind cooperation in many ways in the People's Pub., 42-55. (in Chinese with English course of field studies and in the offices. abstract). We would also like to thank the Bureau of State Go, Dianfu (1983): Preliminary analysis of the Guanxi Farms and Land Reclamation, the Ministry of monsoon and natural weather season. Scientific Agriculture, Animal Husbandry and Fishery in Study Report, Guanxi Inst. Met., No 1, 1-22. (in Beijing, for issuing the approval to our project, Chinese). studies. Guangzhou Institute of Geography, Laboratory of The present paper is a part of our preliminary study Climatology (1982): The utilization of the predom supported by the Ministry of Education, Science and inate agroclimate resource of Hainan Island. Tropi Culture in Japan (No. 58042002). Finally, I would cal Geography, No. 8, 6-13. (in Chinese). like to thank Dr. Y. NOGUCHIfor correcting English HE, Daizhang (1980): On the tropical climate of wording and Mrs. N. TOYOSAWAfor typewriting this Hainan Island. South China Teacher's College manuscript. (Natural Science Studies), No. 2, 114-122. (in Chinese (Received April 28, 1984) with English abstract). (Accepted July 7, 1984) HE, Daizhang et al. (1981): Characteristics of climates 182 M.•@M, YOSHINO

of Hainan Island. In: Bureau of Forestry Study Tokyo Press, Tokyo, 297-316. and Planning et al., (eds.): Forestry Data Collections SADLER,J. C. (1977): The upper tropospheric circula of Hainan Island., Guanzhou, 299 p., 21-39. tion over the global tropics, Part II Statistics. Dept. HE, Daizhang and WONG, Tongwai (1980): The rice of Met., Univ. Hawaii, UNMET-77-02, 24 p. cold-harm during later autumn and their suitable SCATC (South China Academy of Tropical Crop date to sow in Kwantung. Agricult. Meteor., Science) (1981): Rubber cultivation science. Chinese Beijing, No. 4, 59-64. (in Chinese). Forestry Publ., Beijing, 303 p. (in Chinese). HE, Daizhang(1984): Utilization of climatic superiority WANG,Binhua (1983): Sea fog. Ocean Pub., Beijing, of Hainan Island in warm winter and early spring. 352 p. (in Chinese). Geographical Knowledge, No. 1, p. ll. (in Chinese). WET, Lin, WANG, Jinghua and JING, Ke (1983): On HUANG,Runben, HUANGWeifeng and SEEN Xueping the agricultural superiority of Hainan Island. Acta (1982): On the formation of savanna ecosystem in Geogr. Sinica, 38 (2), 163-170. (in Chinese with southwestern Hainan Island. Studies on Tropical English abstract). and Subtropical Forest Ecosystem. No 1, 237-250. YOSHINO,M. M. (1969): Climatological studies on the (in Chinese with English abstract). polar frontal zones and intertropical convergence HUANG,Zongdao, ZHENG,Xuequin and HAO, Yonglu zones over South, Southest and East Asia. Cli (1980): Assessment of rubber planting areas in matological Notes (Tsuhuba), No 1, 1-71. tropical and subtropical zones of China. Chinese YOSHINO,M. M. (1971): Water balance of Monsoon Asia. Jour. Trop. Crops, 1 (1), 2-15. (in Chinese with Univ. of Tokyo Press, Tokyo, and Univ. of Hawaii English abstract). Press, Honolulu, 308 p. JIANG,Ailiang (1982): On the variation of temperature YOSHINO,M. M. and URUSHISARA,K. (1982): Regionality with height of mountainous regions in tropical of climatic change in Monsoon Asia. GeoJournal, 5 China and its effect on cultivation of rubber tree. (2), 123-132. Climatological Notes (Tsukuba), No 29, 19-29. ZHOU,Shuzhen(1981): On the climatic features of the JIANG, Ailiang (1984): Climate and agricultural land Hainan Island. Jour. East China Normal Univ., use in China. In: M. M. YOSHINO (ed.): Climate Natural Sci. Ed., No 1, 61-71. (in Chinese with and agricultural land use in Monsoon Asia. Univ. of English abstract).

華南海南島における気候と農業:予察研究

吉野正敏*

海南島における気候と農業について,最近の中国におるのは,最近の雑種交配種子の栽培である。それらは中ける文献と1984年1～2月の筆者の予察研究旅行の結果国各地から農民や試験者が島の南部にやってきて栽培さとによって記述した。まず,総観気候学的背景を前線帯れる。冬に成長し, 3月中・下旬に出穂・開花し, 4月・雲量分布・850mb面における流線・霧分布などによ中・下旬に成熟する。そして,とれた種子を中国の各地って示した。850mb面における南西の風と,北東の風, に持って帰り,そこで通常の栽培期間に栽培するもので台風が重要な役割を果たすこと,また気温・降水量・雨ある。季と乾季の長さなどを気候記録によって示した。何大章最後に,台風による事被害と,寒害について記述し,特による気候区分を紹介し,その8気候地域を示した。に,その分類基準を紹介した。また,近年の早稲と晩稲次に,海南島の農業について,その気候条件を考慮しの栽培の問題,ゴムの栽培における寒害の問題は,海南つつ,特にゴム・米・茶について,詳しく述べた。ゴム島の熱帯作物栽培の今後の発展に特に重要な課題なのでについては5地域に区分し,各々について寒害と風害に詳しく述べ,気候条件の研究が急務であることを指摘し

注目した。ゴム栽培の高距限界は島の北部では300～た。 350m,南部では500mである。米作のうち特に興味あ

* 〒305茨城県新治郡桜村筑波大学地球科学系