FIGURE 1-19 JAVA - TIMOR: REGIONAL SUMMARY TABLE JANIS 153 RESTRICTED General Summary of Climate Maps and Tables for this sector are contained in Chapter V, Climate and Weather. GENERAL The characteristic features of the climate of the Java - Timor Area are uniformly high temperature and humidity throughout the year; light winds that tend to undergo a seasonal reversal of prevailing direction characteristic of the monsoon regions; and a seasonal varia¬ tion in precipitation and cloudiness. The Lesser Sunda Islands and the north and east lowlands of Java receive moderate rainfall marked by a distinct dry season; some stations in the eastern part may receive no precipitation for a period of a month or more. Western, central, and southern Java receive abundant rainfall, the dry season being very short or lacking. In addition, local topography causes sharp contrasts in rainfall and cloudiness of nearby places. On basis of prevailing wind and rainfall the year may be divided into 2 seasons: the period of easterly monsoon (April through No¬ vember), the "dry” season; the period of westerly monsoon and transi¬ tion (December through March), the "wet” season. The precipitation occurs largely as intense showers, but drizzle may occur in mountainous areas and along the coasts in early morning. The dry season results from a lower frequency of showers rather than from a lessening in their intensity. For most of the weather elements the daily variation is more marked than seasonal variation. Monotonous similarity of weather day after day is characteristic, but, particularly during the months when the inter- tropical front is within the area, there is sometimes a tendency for the weather to fluctuate in spells of a few days’ duration. For example, on 3 or 4 successive days there may be each day a similarity of building up of cloud in the forenoon, a fall of rain in the afternoon, and clear¬ ance at night. After such a spell the weather type may change; for several days there may be no rain and the sequence of cloud build-up may take place later and/or the clearance earlier each day; or there may be a few days in succession in which the clouds are heavier and massed together all day long and perhaps during the night also. The occurrence of these nonperiodic spells of weather is a significant factor in the relation of weather to military operations and is a problem for the forecaster. In addition to the broad regional differences, there are pronounced local differences in climate related to topography and the degree of exposure to the monsoon winds. The lowlands are constantly hot, with light winds and frequent showers. The hills and mountain slopes are cooler, cloudier, and rainier. The few high mountain peaks are cold but have less rain and cloud than lands at medium elevations. . Windward slopes tend to have more rainfall and cloud than leeward WIND Generally throughout the area there is a seasonal monsoonal shift in wind directions. From April through November (easterly mon¬ soon), easterly to southeasterly winds prevail throughout the islands. During February (westerly monsoon) winds from a westerly quadrant prevail. During December-January and March (the transitional pe¬ riods) the intertropical front is over the area and winds are variable. Along the coasts, particularly in sheltered bays, there is a tendency toward a daily variation in wind direction. The sea (onshore) breeze usually sets in around midday and abates after sunset. The land (off¬ shore) breeze sets in late in the evening and abates in the early morn¬ ing. Where the monsoons are weak, land and sea breezes dominate the entire circulation. Where the monsoons are steady, the land and sea breezes either reinforce or diminish the strength of the monsoon winds. Topography causes local changes in the winds; many interior valleys experience daily shifts in wind direction. Mountain breezes (down- slope) are common at night and valley breezes (upslope) blow dur¬ ing the daytime. Wind speeds are usually light to moderate throughout the area. Mean velocities are 2 to 6 miles per hour in the early morning increasing to 3 to 12 miles per hour in the late afternoon. The wind often abates to almost calm at night on the plains and along the coast. No information is available on the frequency of gales but strong winds may be expected on exposed mountain peaks and during thun¬ derstorm activity. VISIBILITY Visibility is usually good through the area but is occasionally limited by rain, fog, or haze. Rain usually restricts visibility to less than 6 miles but may reduce it practically to zero in heavy showers. These torrential downpours are frequently limited in area as well as time. Visibility is reduced by precipitation more frequently during the westerly monsoon and transitional periods (December through March) than during the easterly monsoon period (April through November). Fog, reducing visibility to less than 1 mile, is rare at coastal stations. In the interior, however, dense morning fogs may be expected along many river valleys, lakes and swamps. It also may form at night over sheltered plains or plateaus on which rain has fallen during the evenin^Al^o^we^h^avj^^Timo^Are^^^h^mdiatiorwyp^ JAVA - TIMOR REGIONAL SUMMARY TABLE OF Relief, Drainage, Soil Trafficability, and Vegetation Figures II - 94 to II - 102, and Plans 2, 3, and 4 should be used concurrently with this Summary Table. FIGURE 1-19 JAVA - TIMOR: REGIONAL SUMMARY TABLE JANIS 153 RESTRICTED SECTOR A: JAVA AND MADOERA WEST JAVA Relief: Flat coastal plain along the north coast; narrow on west coast. Belt of wide alluvial terraces along inland border of northern coastal plain; terrace belt widest south of Batavia. Steep-sided but shallow north - south-trending ravines in terrace belt. Volcanic moun¬ tain chain in center is hook-shaped, enclosing series of flat mountain basins. Seaward sides of volcanic chain bordered by foothill ridges. Roughest terrain north of Wijnkoops-baai, and in area south of mountain basins. Narrow passes lead across volcanic chain into moun¬ tain basins and connect the basins. Southern coastal plain narrow and discontinuous. Drainage: No large rivers. Some flood danger on coastal deltas in wet season. Rivers normally fordable. Deep canyons cut by streams draining the mountain basins. Swamps, marshes and fishponds along most of north coast. Swampy coastal plain on west coast south of Laboehan, and stretch west of Wijnkoops-baai. Small ponds and marsh¬ es in Garoet Basin. Soil traffic ability: Generally poor in most parts. Sawahs (wet rice fields), which predominate in most lowlands and on some terraced slopes, are nontrafficable to wheeled vehicles most of year; dry crust formed during July and August where sewahs are fallow or planted to dry crops will not support heavy traffic. Swamps and marshes, im¬ passable to wheeled vehicles, are especially numerous along northern coast. Trafficability conditions are best on sandy beaches and on north¬ ern alluvial terraces where dry crops predominate. Most alluvial terrace soils of this and interior valley regions remain trafficable during non- persistent light rains and recover trafficable conditions rapidly after heavy rains. Best trafficability is from June through September; better in non-sawah areas north of mountains than elsewhere. Poor traffic- ability general during rest of year. Vegetation: Wet rice fields cover practically all of the northern coastal plain except poorly drained strip along the shore. Alluvial terrace zone mostly in dry crops with rice paddies in valley bottoms and on sides of valleys. Foothill zone mostly in secondary forest and scrub; a few tea and rubber plantations. Volcanic mountains have lower slopes in rice terraces. Plantations above rice; middle and upper slopes in rain forest. Mountain basins almost wholly in rice. Dense forests (secondary and rain) in southwestern area. Much brush and scrub back of south coast. Cross-country operations: Rice sawahs may be wet at any time of year. Double cropped in many places. Does not dry enough in short dry season for tank deployment. Best area for deployment of mechan¬ ized forces is along alluvial terrace zone. Many terraced rice fields in region are barriers to all types of vehicles. Many bottlenecks along roads south of coastal plain. Bad exits from beaches along south coast. CENTRAL JAVA Relief : Coastal plain not so wide or continuous as in West Java. Alluvial terrace zone fragmentary. Foothill belt well developed on both north and south sides of central mountain chain. Best north and south gaps through central chain are west of G. Slamet and between the volcanic cones near the east end. The Banjoemas Basin is separated from the southern coastal plain by a belt of ridges. The Tjitandoej lowland contains much poorly drained land. Plain near Jogjakarta provides low, level route from the east end of the southern coastal plain. Drainage: No large streams. Swamps along the Tjitandoej valley are the largest water barriers. Swampy strip along north coast not so continuous as in West Java. Soil trafficability: Generally poor in most parts of this region. Sawahs predominate in most lowlands and on some terraced slopes are non¬ trafficable during most of year; even during drier months will not support heavy traffic. Dry-cropped areas of alluvial terraces between northern mountains and northern coastal lowlands relatively small and discontinuous but trafficable except during, and for short time following, heavy rains or periods of frequent rains. Some areas of permeable ash loams with comparable trafficability on northern low¬ lands but many impassable fish ponds, swamps, and marshes along north coast. Extensive nontrafficable marshlands in Tjitandoej Valley and on shores of Segara Anakan (Kinder-zee). Best trafficability gener¬ ally from June through September, but during this period, non-sawah soils of northern plains and alluvial terraces are trafficable for longer and more frequent periods than elsewhere. During rest of year traffic- ability poor on most lowland soils and periodically poor on other types. Vegetation: Sawahs on nearly all level to undulating areas. Much secondary forest and scrub on hill ridges. Rain forest on mountain slopes. Scrub and grass on south coast dune ridges. Some teak on hills back of north coast. Cross-country operations: Best conditions are in eastern lowland areas during the dry season. All routes are constricted into botdenecks at several points. Central Mountain Belt is a formidable obstacle. Con¬ ditions generally not favorable for deployment of mechanized forces. EAST JAVA Relief : Northern coastal plain interrupted by volcanic peaks and by limestone hills at several places. West of Soerabaja are two east — west-trending belts of hills, separated by a flat to gently sloping plain. The central part consists of seven clusters of high volcanic cones, separated by wide basins or saddles. The eastern clusters of cones are closer together. Bordering the south coast are hills and low mountains, some parts of which are dry, dissected limestone plateaus. Two low¬ land areas on south coast. Exits from south coast poor. Drainage: Kali Brantas and Kali Solo are unfordable for long dis¬ tances in the wet season. Other streams small. Wide belt of fishponds and mangrove swamps along Straat Madoera. Swamps back of south coast beaches. Irrigation well developed along Kali Brantas and Kali Solo. Soil trafficability: Period of frequent widespread poor trafficability is shorter in parts of this region, particularly in northeastern and eastern lowlands, than in rest of Java. Sawahs, which predominate in most lowlands and on some terraced slopes, are nontrafficable to wheeled vehicles most of year. Swamps and fishponds numerous along northeast coast in vicinity of Soerabaja. Least favorable non-sawah soils are clays derived from belt of marls west of Soerabaja and in smaller areas near southern coast; and heavy alluvial clays of some valley and coastal lowlands. These soils are slippery and muddy whenever wet, and dry slowly. In other areas, permeable soils predominate; these soils remain trafficable during nonpersistent light or medium rains, and dry rapidly. In northeastern and eastern lowlands, favorable trafficability extends from March or April through October or November; during the remaining months trafficability of most lowland soil is generally poor, and even the better-drained upland soils are frequently non¬ trafficable to wheeled vehicles. In other regions best trafficability occurs from May or June through September or October, but in high moun¬ tains trafficability is frequendy poor throughout the year. Vegetation: Rain forest only at high elevations and in spots along south coast. Plains in rice and sugar, with maize or cassava during dry season. Much teak in hill country. Coffee and rubber plantations. Much scrub and secondary forest in hill country along south coast. Cross-country operations: Good for mechanized forces during dry season. Main obstacle is coastal swamps. Poor exits from south coast. Elsewhere, few bottlenecks. MADOERA Relief . Mostly rolling limestone hills and ridges oriented east - west. Many rock outcrops, several rocky gorges. Plains mainly on northwest side and on three deltas of south coast. North coastal plain narrow. Interior basins trend ease — west. Limestone caves. Drainage: Generally small streams with litde water during dry season. Tidal channels a barrier on southern delta plains. Mangrove swamps, salt pans and fishponds on these deltas. Soil trafficability: General trafficability in Madoera is better than in most parts of Java, because differences in relief are moderate, and most cultivated land is dry-cropped. Swamps and marshes in southern valley lowlands and near fishponds along the north coast. Sawahs nontraffic¬ able to wheeled vehicles during wet months and periodically at other times; sawahs restricted for most part to major river valleys. Sandy soils of good all-weather trafficability common along north coast. Heavy clay soils derived from marls in central longitudinal belt of island are slipper)' and muddy whenever wet and dry slowly. Non- sawah soils elsewhere mostly permeable clays and sandy clays which are trafficable except during fairly heavy rains or periods of frequent rains. Good trafficability conditions are characteristic from June through October, but during rest of year periods of poor trafficability are rela¬ tively long and frequent. Vegetation: Little dense forest. Largest area is in dry-crop fields Considerable scrub, bush savanna, and barrens. Rice mainly on delta plains, in Sokrok Valley, and near Bangkalan. Cross-country operations: Generally good for mechanized forces most of the year. Main obstacles are scattered sharp limestone ridges, rock outcrops, and swamps along south coast. Stone fences and wind¬ breaks would be local obstacles. SECTOR B: LESSER SUNDAS BALI Relief : A high volcanic range crosses the island from east to west somewhat north of the central axis. Range is more dissected in west. Highest cones in east. Steep slopes to narrow north coastal plain. Long, gentle slopes southward, cut by ravines. Limestone plateau (Tafelhoek) at south end of island. Isthmus north of the Tafelhoek is low and flat. Uplifted reef limestone platform at extreme north¬ western end. Drainage: Generally swift mountain streams with large seasonal fluctuations in volume. Streams are not barriers except when in flood. Soil trafficability: Trafficability for wheeled vehicles poor at most places as sawahs predominate in lowlands and also are common on terraced slopes. Sandy soils of good all-weather trafficability along northeastern and southeastern coasts, on isthmus of Tafelhoek, and on Noesa Penida. These soils rendered slippery and muddy by fairly heavy rains or periods of frequent rains, but dry rapidly. Trafficability most favorable from April through November in northern and north¬ eastern section, and in other regions from April, May, or June through September or October. In mountain and southern coastal regions, dry period less pronounced. Trafficability frequently poor everywhere dur¬ ing rest of year. Vegetation. Rain and monsoon forest at high elevations. Much brush on lower slopes in west. Savanna on lower slopes in northeast. Rice fields on plains and lower volcanic slopes in central Bali. Tafel¬ hoek is mostly savanna. Cross-country operations. Best along coasts. Difficult in interior owing to terraced sawahs and steep-sided ravines. LOMBOK Relief : High volcanic range, oriented east - west, crosses northern third of island. No good routes across this range. No distinct coastal plain along north coast. Central third of island consists of gently slop¬ ing plains merging with south-facing volcanic slopes. Southern part of island is a dissected hill country, rough and dry. Drainage: No large streams. Swamps border head of Ekas-baai. Soil trafficability: Trafficability similar to Bali, with many sawahs, but most dry-cropped soils are permeable and trafficable except during, and for short time following, medium or heavy rains or periods of frequent rains. Heavy black clays in vicinity of Praja, and soils with subsurface clay layers in vicinity of Selong, are slippery and muddy whenever wet, and dry slowly. Sandy soils of good all-weather traffic- ability in many scattered coastal areas and in fairly continuous strip along central part of west coast. Trafficability conditions most favor¬ able from April through November along sheltered southeast coast: elsewhere, conditions are most favorable from May through Septem¬ ber. During wet period, from November through March, trafficability is generally poor at most places. Vegetation: Main forest area is at high elevations in volcanic range. Much savanna on lower volcanic slopes, particularly in northeast. Cen¬ tral plains are mostly in rice fields; some grass in drier parts. Southern hills in grass, brush and scrub forest. Cross-country operations: Generally good on central plains during dry season. Poor in northern and southern parts of island. WEST SOEMBAWA Relief : Most of area consists of dissected hill country. A few moun¬ tain masses can be bypassed. Coastal plains small and discontinuous. A few upland plains. Steep headlands form obstacles to coastal land travel. Drainage: Streams not significant barriers except when in flood. Marshy plain north of Taliwang. A few patches of coastal swamps along northwestern coast. Rivers flood for short periods. Soil trafficability: Distribution and character of soils known only in general way, but apparently most soils in West Soembawa are per¬ meable types derived from limestone or volcanic rocks. These soils probably trafficable in most places except during heavy rains or pro¬ longed rainy periods. Deep loose volcanic ash along coast of Saleh-baai between Ampang and Plampang is always an obstacle to vehicular movement, regardless of precipitation. Alluvial soils of valley lowlands subject to flooding; fine-textured types of flat strips, mostly near coast, utilized for sawahs. Sawahs much less numerous than in western islands. Trafficability generally good in western and northern lowlands from May through September and frequently poor from November through March. Dry period probably less pronounced in mountains and southern lowlands. Vegetation: Mountain areas generally forested. Hill country is mostly in park-like tree and bush savannah. Forests are rain forest or secondary forest. Rice fields on flat lowlands near the coast. Cultivation elsewhere generally dry crops in scattered fields. Cross-country operations : Difficult even for foot troops in moun¬ tain areas. Mechanized forces could deploy locally elsewhere. Bottlenecks along any cross-island route. Many sites suitable for airborne landings. EAST SOEMBAWA Relief : Northern half has a series of high volcanic cones. Southern half consists of greatly dissected uplands, with narrow valleys. Flat plains at heads of bays. Headlands interrupt coastal routes. Largest terrain compartment is the plains area around Bima-baai. Drainage: Streams are small. Swamps at heads of most bays. Largest swamp at head of Tjempi-baai. Fishponds at head of Bima-baai. Soil trafficability: Soils of this area mostly permeable types derived from fragmental volcanic material or from limestone. Trafficability of these soils generally good except during fairly heavy rains or periods of frequent rains. Sawahs restricted for most part to local areas of clay soils in lower parts of stream valleys. Precipitation data available only for Bima, where dry period of good trafficability extends from March through October. During rest of year, periods of poor trafficability are fairly frequent. In mountain and exposed southern lowlands, dry period probably occurs about same time but is less pronounced. Vegetation: Most of area is jin savanna with scattered trees and bushes. Forests mainly at high elevations. Low flat areas are cultivated, mainly rice. Cross-country operations. Generally good for mechanized forces on lowlands during dry season. A few bottlenecks on cross-island routes. Steep slopes are the main barrier along exits from south coast. Move¬ ment difficult along all coasts. (except Timor) FLORES Relief: Most of island has rugged, mountainous terrain. Largest plains are along the north coast but are not continuous. Isolated vol¬ canic cones separated by ash-filled basins and saddles in eastern part. Several undulating to rolling plateaus in central part, surmounted by volcanic peaks and bordered by belts of rough terrain. Dissected limestone plateau country in northwest. Exits inland from beaches difficult except in eastern part. Several active volcanoes. Drainage: No large streams, but nearly all of them are in deep ravines and are subject to flash floods. Swamps at the heads of several bays. Soil trafficability: Generally good in open areas of moderate slope; soils mostly highly permeable types derived from young fragmental volcanic materials. Local areas of fairly heavy black clays, especially in valleys of southern slopes, are rendered slippery and muddy by moderate rains, and dry slowly. In large area south and east of Nanga- hale and in small scattered areas, soils derived from limestone and marl sediments. Information for most of these areas is insufficient to enable distinguishing limestone-derived soils that have rapid drain¬ age from marl-derived soils which are slippery and muddy whenever wet and which dry slowly. Flat areas of alluvial soils, restricted for most part to lower parts of stream valleys near coast, are subject to flooding. The relatively small areas of sawah are confined mostly to fine-textured alluvium. Considerable variation in rainfall from place to place but trafficability generally good from May through October ex¬ cept in mountains. From December through March trafficability fre¬ quently is poor. Vegetation: Largest forest area in western part. Forests elsewhere in patches at high elevations or along streams. Most of island in grass and brush savanna. Interior plateaus mosdy grassy. Largest cultivated areas on the plains of eastern Flores. Rice only in small patches, mainly in west. Coconuts at Ende, Maoemere and Larantoeka. Cross-country operations: Generally difficult for mechanized forces because of steep slopes; best in eastern part. Difficult even for foot troops in west. All roads on island pass through vulnerable defiles. Fair mobility possible on interior plateaus, but difficult to reach. SOLOR AND ALOR GROUPS Relief : Hilly to mountainous; small areas of level land on all islands. Volcanic cones on most of the islands. Coastal plains discontinuous. Some patches of level uplands on Solor, Pantar and Alor. Drainage: Small streams. A few coastal swamps. Soil trafficability General trafficability similar in all larger islands. Interiors are mostly rough or mountainous, and restrict movement of wheeled vehicles regardless of soil conditions. Soils mostly permeable- types derived from volcanic rock or reef limestone and are trafficable except during fairly heavy rains or periods of frequent rains. Probably considerable variation in rainfall from place to place but trafficability usually is good from May through October. During the rest of the year, frequent but usually short periods with slippery and muddy soil. Vegetation: Brush savanna, with some forest at high elevations and along streams. Dry crops on scattered upland fields; coconuts on beaches. Cross-country operations: Favorable for foot troops, but difficult for mechanized forces, except locally. Good natural conditions for defense. SOEMBA Relief: West, north and east coasts rise in series of broad flat to gently sloping terraces to rolling plateaus. Steep edge of plateau on south side. Several shallow interior basins. Most rugged part of island is in southeast. Steep gorges cut through the coastal terraces. Several flat, small isolated coastal lowlands on south coast. Numerous airfield sites on island. Good conditions for underground defenses. Drainage: Small streams, little flow during dry season. None of them are obstacles. A few swamps back of south coast beaches. Shallow ponds in interior basins. Soil trafficability: Poor in many areas during wet months, as most soils are plastic black clays and clay loams derived from marls or impure limestone. In many upland areas, however, soil is thin, and run-off of water is rapid, hence trafficable conditions are regained quickly after rains. Soils in some areas are derived largely from igneous rocks and have better trafficability. Sawahs fairly numerous, mostly in small scattered valley areas of heavy alluvial soils. Trafficability gener¬ ally good during period from May or June through September, October, or November, and frequently poor during remaining months. Vegetation: Mostly grassland, with narrow strips of trees along water courses. Massoe-gebergte, in southeast, forested; also steep south edge of plateau. Patches of forest on higher hills in interior. Rice paddies in west half of island, in Waikaboebak and adjoining basins, and in some south coastal valleys. Coconut groves along east coast. More scrub and brush in western part. Cross-country operations: Tanks could operate over much of the island. Terrace edges and ravines main obstacles. Not good in southern part of island. Rocky ledges would be troublesome locally. SECTOR C: TIMOR AND ASSOCIATED ISLANDS DUTCH TIMOR Relief : Mostly hilly to mountainous country on old hard crystalline rocks and limestone. Lowlands on north coast limited to a fringe less than a mile wide. Much of south coast is plain 4 to 8 miles wide, composed of narrow sandy beaches backed by swampy strip and zone of rolling plain. Stony valleys lead far into interior; some of these are broad but are broken by constrictions, terraces, and gullies. Interior of island is traversed from southwest to northeast by series of plains at elevations up to 3,000 feet. Drainage: Two fairly large river systems, but only small volume of water over their broad, rocky, and gravelly courses from November to April, inclusive. All streams fordable except for few hours to few days after rains. Flash floods common during period from November to April, inclusive. Swamps limited to narrow belt along parts of south coast, and scattered fragments along west and north coasts. Soil trafficability: Large number of rock types in this area results in great differences in soils and trafficability from place to place. Soils thin and well drained in most upland areas; many rock outcrops. Trafficability least favorable on heavy residual clays derived from marls, shales and mudstones, occurring most frequently in relatively low, central longitudinal belt and in parts of northwest uplands. These soils probably are slippery and muddy whenever wet, and dry slowly. Permeable soils derived from limestone are common in many areas, and are trafficable except during, and for short periods following, fairly heavy rains or periods of frequent rains. Large sections of the north¬ western uplands and smaller areas elsewhere have soils derived from igneous and metamorphic rocks; these soils are of variable texture and trafficability but, as a whole, trafficability of these types is intermediate between that of heavy clays derived from marls and that of permeable clays and sandy clays derived from limestone. Alluvial soils of lower parts of coastal lowlands and parts of wider valley plains or lowlands are heavy black clays; these are slippery and muddy whenever wet, and dry slowly. Sawah soils, for most part, are of this type. Marshes are common between these black clay soil areas and the shore, especially on the southern coast. Alluvial soils of valley and coastal terraces usually are coarse-textured, and are trafficable except during heavy rains; but soils of similar texture marginal to lower stream courses and in upper valleys are subject to inundation and flash floods. Traffic- ability generally is good from April through November in most of area, and from June through November along parts of southern coast. Dur¬ ing remaining months trafficability frequently is poor. Vegetation: Grass and scrub cover % of area. Scrub predominates in hilly country and grass on interior plains. Patches of open forest on some hill and mountain slopes. Casuarina, bamboo, and eucalyptus groves on southern coastal plain and along water courses. - Cro T T^rm mtry- rspc-ntt onr ■ L imited- i-n—general -wv -foot—sold iers and- pack units. No ready access from coasts to interior for motorized or mechanized vehicles. Several areas suitable for paratroop landings, es¬ pecially on interior plains. Areas suitable for glider landings on interior plains around Sbe and between Haliloelik and Atamboea. These areas have good exit roads. PORTUGUESE TIMOR Relief: Complex, mountainous country of ridges and valleys rising to central divide. Ridges of north coast are steep, high, and parallel to coast. North coast lowland less than a mile wide, cut by foothill spurs. South coastal plain, 4 to 10 miles wide, consists of many sandy beaches backed by narrow swampy belt, back of which is undulating plain. Valleys leading inland from coasts are broad, but are badly broken by rocky constrictions, terraces and gullies. High coral lime¬ stone plateau (Lautem Plateau) occupies eastern end of the island. Another (Baucau Plateau) along north coast; both have many caves. Low, heavy-soiled, interior plains (Nunura Plains) in northwest. Drainage: No large rivers. Small volume of water over broad, rocky, and gravelly courses during dry season (Augu.. to October, inclusive). Flash floods common during rainy season. All streams fordable except for few hours to few days after rains. Underground streams and caves in limestone areas. Soil trafficability: Conditions similar to those of Dutch Timor with thin soil and many rock outcrops in uplands. Where deep residual soils occur they are of three '"lain groups which, in decreasing order of trafficability, are: permeable clays derived from limestone which has wide distribution; fairly permeable clays, clay loams, and loams derived from igneous and metamorphic rocks of the northwest; and heavy plastic clays derived from marls commonly associated with limestone. Alluvial soils of tei ices are mostly coarse-textured and trafficable ex¬ cept during heavy ns; soil* of similar character adjacent to lower stream courses, ar. n jppt* stream valleys, are subject to flooding. Fine-textured alluvial soils, slippery and muddy whenever wet, are common on coastal plains and in wider parts of stream valleys (such as Nunura Plain). Marshes limited for most part to southern coastal regions and shores of Lake Ira-Lalaro (Lake Surubec). Good traffic- ability from April through November in western part of northern lowlands. Good trafficability apparently continues throughout year in eastern part of northern lowlands. Dry period at Hatolia from April through September; at Ainaro, Barique and Viqueque from July or August through October. During remaining months periods of poor trafficability are fairly frequent. Vegetation: Mostly scrub. Several areas of open forest and grass savanna, especially at intermediate and higher elevations. Prickly pear and thorn scrub on north coast, especially in central section. South coastal plain characterized by belt of mangrove backed by bamboo and eucalyptus groves with openings of alang-alang. Behind this, un¬ dulating savanna with Casuarina along watercourses. Cross-country operations: For the most part limited to foot soldiers and pack units. Tracked vehicles could operate locally over parts of southern coastal plain, parts of Lautem and Baucau limestone plateaus, -md-Nunura Plain.* Same areas aher suitable for paratroop* landings. Gliders could land on selected parts of coastal plain and Lautem Plateau. ISLANDS NEAR TIMOR POELAU SAWOE Relief : Poelau Sawoe is high, hilly plain becoming rugged toward southern end. Escarpment encircles island within mile of shore. Drainage: Streams small and almost all are intermittent. Can be forded anywhere and are subject to sudden flooding after rains. Vegetation: Grass predominates. Good grass cover in north. In south probably considerable scrub and light forest. Coastal belt includes many wooded areas. Cross-country operations: Tracked vehicles could not operate widely. Escarpment limits points of access from coast to interior. Paratroop landings could be made. POELAU ROTI Relief: Terraced limestone with considerable hilly land. Highest and steepest sections are back of the east coast in north-central part. South and east of Baa (Namodale) is level to undulating plain. Drainage: Several streams flow all year, but are easily fordable ex¬ cept for few hours after heavy rains. Considerable underground drain¬ age in porous limestone. Vegetation: Mostly scrub and grass. Rather densely populated island, with more gardens, paddies, and groves than neighboring islands. Open forest in scattered favored localities. Baa Plain is grassy. Cross-country operations: Terraces and solution-pitting of the lime¬ stone, as well as dissected hills, largely confine vehicular operation to roads. Baa Plain is an exception. POELAU SEMAOE Relief: Limestone island with steeply terraced coastal margins. In¬ land the terrain is rolling to hilly; highest and most dissected in north¬ east. Largest level area is near east coast at head of Pelikan-baai. Drainage: Almost all streams dry several months each year. Fordable except immediately after rains. Vegetation: Scrub. The island is only sparsely populated. Plain at head of Pelikan-baai is grassland. Cross-country operations: Limited for the most part to foot troops or pack units, owing to the rough surface and terraced slopes. Plain at head of Pelikan-baai well-suited to parachute landings. Soil Trafficability in Islands near Timor. On Roti, Semaoe, and Sawoe, soils are mostly clays and sandy clays derived from limestone and marl, with minor areas of variable texture derived from pre-Tertiary rocks. Trafficability generally good during dry period from April through November. During rest of year, heavy alluvial clay soils of coastal and valley lowlands and residual clay soils derived from marls are nontrafficable during fairly frequent but usually short periods. Part of isthmus near northeastern end of Ron is marsh¬ land. Sawah areas are fairly numerous but for the most part are on Roti. General Summary of Climate Maps and Tables for this sector are contained in Chapter V, Climate and Weather. GENERAL The characteristic features of the climate of the Java - Timor Area are uniformly high temperature and humidity throughout the year; light winds that tend to undergo a seasonal reversal of prevailing direction characteristic of the monsoon regions; and a seasonal varia¬ tion in precipitation and cloudiness. The Lesser Sunda Islands and the north and east lowlands of Java receive moderate rainfall marked by a distinct dry season; some stations in the eastern part may receive no precipitation for a period of a month or more. Western, central, and southern Java receive abundant rainfall, the dry season being very short or lacking. In addition, local topography causes sharp contrasts in rainfall and cloudiness of nearby places. On basis of prevailing wind and rainfall the year may be divided into 2 seasons the period of easterly monsoon (April through No¬ vember), the "dry” season; the period of westerly monsoon and transi¬ tion ( December through March), the "wet" season. The precipitation occurs largely as intense showers, but drizzle may occur in mountainous areas and along the coasts in early morning. The dry season results from a lower frequency of showers rather than from a lessening in their intensity. For most of the weather elements the daily variation is more marked than seasonal variation. Monotonous similarity of weather day after day is characteristic, but, particularly during the months when the inter- tropical front is within the area, there is sometimes a tendency for the weather to fluctuate in spells of a few days' duration. For example, on 3 or 4 successive days there may be each day a similarity of building up of cloud in the forenoon, a fall of rain in the afternoon, and clear¬ ance at night. After such a spell the weather type may change; for several days there may be no rain and the sequence of cloud build-up may take place later and or the clearance earlier each day; or there may be a few days in succession in which the clouds are heavier and massed together all day long and perhaps during the night also. The occurrence of these nonperiodic spells of weather is a significant factor in the relation of weather to military operations and is a problem for the forecaster. In addition to the broad regional differences, there are pronounced local differences in climate related to topography and the degree of exposure to the monsoon winds. The lowlands are constantly hot, with light winds and frequent showers. The hills and mountain slopes are cooler, cloudier, and rainier. The few high mountain peaks are cold but have less rain and cloud than lands at medium elevations. Windward slopes tend-to have more rainfall and cloud than leeward slopes. The land- and sea-breeze effect is more pronounced at sheltered coastal stations than at exposed stations. PRECIPITATION ( Figures V - 2 and V - 3). Over the Java — Timor Area precipitation varies from scant to heavy; average annual rainfall amounts range from 30 to over 185 inches a year. Regional contrasts are fairly regular and are controlled by air flow and local relief. Maximum precipitation occurs in the western portion of the area, where nearly all Javanese stations receive more than 50 inches a year. East of 115°E, precipitation amounts gradually decrease and are generally less than 50 inches a year in the vicinity of Timor. Rainfall is much heavier on exposed mountain slopes than in the lowlands. Seasonal variation in precipitation is pronounced in the Lesser Sundas and in eastern Java; but in western, central, and southern Java the dry season is short or lacking. During the period December through March, precipitation amounts are the highest for the year: mean monthly amounts range from 10 to 20 inches. During the easterly monsoon (April through November). there is a noticeable decrease in precipitation amounts in most sections of the area. Practically all lowland stations receive less than 8 inches a month in May, June, and November; and less than 3 or 4 inches from July through October. In the vicinity of Flores and Timor less than 1 inch per month is re¬ ported from July through October. At this time, long dry periods are frequent. For many stations in Java, entirely rainless months have been recorded 1 to 4 times in a 10-year period; over Flores and Timor an entire month without rain occurs 3 to 7 times in a 10-year period. Over the lowlands of the area, precipitation is usually in the form of showers. In the mountainous areas, rain is more persistent, some¬ times lasting for days with only short let-ups. TEMPERATURE In the lowlands, the temperature is constandy high; mean annual values range from 70 F. to 85°F. Stations at medium elevation (about 3,000 to 6,000 feet) experience mean temperatures around 65°F., while high mountain stations report annual means of 52°F. to 58°F. Mean temperatures below 65 °F. or above 95 °F. are rare. Throughout the islands, seasonal variation is slight, usually about 2°F. to 5°F. The diurnal variation is 13°F. to 16 L F. at coastal stations, 15°F. to 20°F. inland, and about 8 F. to 12°F. at high mountain stations. The diurnal range is particularly pronounced during the relatively dry season of April through November. Maximum temperatures of 85°F. to 90°F. at lowland stations and 75' F. at mountain stations are reached soon after noon. Minimum temperatures of 65°F. to 70°F. in the lowlands and 55°F. at mountain stations occur at sunrise. The high¬ est temperature recorded was 101 °F. at Sawahan and Koepang; the lowest, 30°F., at Kertasari which is located at an altitude of 5,300 feet. Pangrango Goenoeng, the highest mountain station (about 10,000 feet) for which data are available, has never recorded temperatures below freezing. The onset of the sea breeze helps to check the rise of the tempera¬ ture along coastal areas, but the principal cause of the drop in tempera¬ ture in the early afternoon is the increase in cloudiness and the onset of rain. During a shower temperature usually falls 5°F. to 10°F. WIND Generally throughout the area there is a seasonal monsoonal shift in wind directions. From April through November (easterly mon¬ soon), easterly to southeasterly winds prevail throughout the islands. During February (westerly monsoon) winds from a westerly quadrant prevail. During December-January and March (the transitional pe¬ riods) the intertropical front is over the area and winds are variable. Along the coasts, particularly in sheltered bays, there is a tendency toward a daily variation in wind direction. The sea (onshore) breeze usually sets in around midday and abates after sunset. The land (off¬ shore) breeze sets in late in the evening and abates in the early morn¬ ing. Where the monsoons are weak, land and sea breezes dominate the entire circulation. Where the monsoons are steady, the land and sea breezes either reinforce or diminish the strength of the monsoon winds. Topography causes local changes in the winds; many interior valleys experience daily shifts in wind direction. Mountain breezes (down- slope) are common at night and valley breezes (upslope) blow dur¬ ing the daytime. Wind speeds are usually light to moderate throughout the area. Mean velocities are 2 to 6 miles per hour in the early morning increasing to 3 to 12 miles per hour in the late afternoon. The wind often abates to almost calm at night on the plains and along the coast. No information is available on the frequency of gales but strong winds may be expected on exposed mountain peaks and during thun¬ derstorm activity. VISIBILITY Visibility is usually good through the area but is occasionally limited by rain, fog, or haze. Rain usually restricts visibility to less than 6 miles but may reduce it practically to zero in heavy showers. These torrential downpours are frequently limited in area as well as time. Visibility is reduced by precipitation more frequently during the westerly monsoon and transitional periods (December through March) than during the easterly monsoon period (April through November). Fog, reducing visibility to less than 1 mile, is rare at coastal stations. In the interior, however, dense morning fogs may be expected along many river valleys, lakes and swamps. It also may form at night over sheltered plains or plateaus on which rain has fallen during the evening. All fog over the Java - Timor Area is of the radiation ty pe, produced by nocturnal cooling of the surface air, and is therefore most frequent on clear calm nights and dissipates rapidly after sunrise. Fog or low clouds may seriously restrict visibility at mountain stations. Haze, another cause of reduced visibility, occurs most frequendy during the easterly ("dry") monsoon. It is particularly characteristic of the southeastern portion of the area during September and October. It generally reduces the visibility to 8 to 10 miles, sometimes to 3 to 4 miles. Haze is usually confined to the lowest layers of the atmos¬ phere and is densest between 3,000 to 6,000 feet. Its upper boundary is usually below 10.000 feet; above this level visibility is excellent. An increase in wind speed tends to increase the density of haze, and rains reduce its density. After the westerly monsoon rains set in haze is rare throughout the islands. CLOUDINESS AND CEILING Data on cloud amounts are available for relatively few stations within the area. These stations report moderate to high annual means in cloud cover; the range is from 40% to 70%. The variations of cloudiness, like that of precipitation, is influenced by local topography and the degree of exposure to the monsoon winds. Cloudiness is greater during the season of moist westerly air flow than during the season of dry easterly air flow. Most stations report their maxima in cloud amounts (60 % to 80%) from December through February and their minima (30% to 50 r i ) from July through September During the early morning hours, stratus and stratocumulus clouds pre¬ dominate. As the sun warms the air these clouds gradually dissipate and fair-weather cumuli form. During the afternoon these cumulus clouds frequently develop into cumulonimbus with showers. The frequency' of low ceilings varies considerably from place to place. Ceilings low enough to interfere with low-level operations are in¬ frequent over the lowlands. The bases of the lower clouds generally lie between 1,500 and 2,500 feet above sea level. However, the bases of isolated cumulonimbus clouds often lie below 1,000 feet or even below 500 feet in rain. In the mountainous areas, low ceilings are frequent and there is great local variation depending upon site and exposure. Great belts of deep clouds usually form on the windward slopes of the mountains, while leeward slopes have broken cloud cover. Like cloud amounts, low ceilings are more frequent during the westerly monsoon and transitional periods (December through March) than during the easterly monsoon (April through November). A belt of low clouds may be encountered #long the intertropical front. These frontal clouds are heaviest over the mountains, but even over the low¬ lands ceilings are occasionally very low. WEATHER AND GROUND OPERATIONS Ground operations may be hampered over the lowlands by frequent showers and constant high temperature and humidity. Over the low¬ lands of Java, rain falls on 75 to 100 days a year; lowlands of Timor, 40 to 45 days. At exposed mountain stations, precipitation may be expected on 200 or more days per year. Throughout all the islands, maximum rainfall amounts are generally reported from December through March and minimum amounts from July through September. Rain usually falls as intense showers which turn poorly drained soil into deep mud, and floods may make many of the roads impassable for short periods of time. The combination of high temperature and high humidity makes the weather of the lowlands very trying. This condition is particularly noticeable during the transitional periods ( December-January and March ). A more temperate climate prevails in the mountainous areas.