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Weather – April 2009, Vol. 64, No. 4 H-highlands; stippled-modification dueto altitude. Figure 1.Climaticzonesofthetropics: Af-tropical ; Aw/Caw-savannah; Am-; BSh-tropical ;BWh-tropical by mid-latitudeweather systems, orare dry. , theseareas have dominated ofsouthernAustralia. In andparts Paraguay, southeastern , northern Argentina, Uruguay,, northern Bolivia, tral southernChina,thetipof Africa, southwestnorth Asia, Tibet, cen- Mexico,, southernUSA,northern ing thosealongitspoleward limits:the air massinsummer(Galvin, 2007),includ- are onlyunder theinfluence ofthetropical this. removedalthough settlementhasoften sified according to theirnaturalvegetation, ment. The zones discussedbelow are clas- are made to theappearance oftheenviron- theclimate,affect assignificant alterations for food orlabour. These changesinturn almost allareas theyuseplantsandanimals distribution ofplantandanimalspecies;in as Figure 1. of theclimaticzones ofthetropics appears settled inalltropical environments. Amap the , thathave includinghumankind, relationship to theplantsandanimalsof describesthemajorclimates andtheir part in Part 1(Galvin, 2007),thispenultimate on from to theintroduction tropical experienced inthetropics.types Following Much ofthisserieshascovered theweather ExeterMet Office, J. F. P. Galvin The climates discussedincludethosethat manyIn places, humanshave altered the tropics, Part 9–, floraand The weather andclimate ofthe the high productivity oftherainforestthe highproductivity despite theshadefrom trees. Nevertheless, ration andwork rapidlycausestiredness, ishardronment. to loseheatby It perspi- tropicalthis themostuncomfortable envi- ally provided by theforest possiblymake temperature andhighdegree ofshelter usu- and 28 shown asFigure 2. Cebu, Philippines,location, Mactan, are than 10degC.Climate datafor atypical the andadailyrangeofrarely more 1 little. temperatures Mean are between 22 year anddayof rainfallevery length varies ‘’ receive more thanabout2000mm altitude. tance from themeteorological , and theme, ofrainfall, basedonseasonality dis- However, there are many variationsona as humid tropics whatisthoughtof andoften This isthearchetypal environment ofthe chapter5.pdf). chapter5.pdf). endangeredspecieshandbook.org/pdfslive/esh_ day, warmerby nightandwetter (http://www. the trueclimate isprobably somewhatcooler by climatic zone. thecaseoftropical rainforest, In thetemperaturefully reflect andrainfalloftheir the , soitcould beargued thattheydonot asare mostacross an opensite (onanairfield), are recordedtions mentionedinthisarticle at It shouldbenoted thatthedataforIt moststa- The highhumidity, high near-constant In thenon-seasonaltropics,In areas ofdense the tropical environment (Af inFigure 1). o C, withlittlevariationthroughout 1

o C the latosol under-storey. and there isgreater development inthe perature rangeisgreater, theforest thins zone, where rainfallislower andthetem- (Figure 3). or where trees have fallen,oralongcoasts light canpenetrate, suchasalongriversides, , except nearareas where more much oftheforest floorhasrelatively thin eventively around dark, midday. As aresult, and uptree trunks, sothejunglefloorisrela- of thezone withlianasgrowing between year. denseinmuch The leafcanopy isvery allows thetrees to grow throughout the there isnofrost andyear-round rainfall They live often hundreds ofyears, since (a result oftheleachedsoils, seebelow). many have so-called ‘buttressed’ trunks est zone. and SãoPaulo, liewithinthetropical rainfor- Two oftheworld’s ten largest cities, Jakarta settlement informerly inaccessible . along rivers, althoughthere isincreasing areas, settlementisinthecoastal zone, or alarge numberofpeople. many In supports given inBox 1. 2 ally oxidized andhave ashallow humus ing nitrate andphosphate. They are usu- deep, butare criticallyleachedoffertiliz- are well often developed andupto 30m A description of the types ofthetropics Adescriptionofthesoiltypes is The typical soilofthetropicalThe typical rainforest is Along thepoleward edgesoftheforest Trees are broad-leafed andevergreen; 2 (FAO-UNESCO, 1989). The and sub-tropical ; andsub-tropical desert; Weather and climate of the tropics - Part 9 Weather – April 2009, Vol. 64, No. 4 101 Fruit- reptiles. reptiles. ; 50% of the world’s ; 50% of the world’s ( and animals) (plants and animals) −1 3 yr −2 , 2006). This is mainly because growth is mainly because growth This , 2006). On the leached soils, new growth is very growth new On the leached soils, howev- rainforest, tropical archetypal The better are the trees high altitudes, At Productivity is highest of all the world’s world’s is highest of all the Productivity This is expressed in terms of the annual mass of the annual mass in terms is expressed This species of plants and animals live in these animals live species of plants and mineral of available level low The . an interesting has had however, nutrients, of and animal effect: the diversification extract to which must find ways species, ment (Fothergill the environ nutrient from et al. jungle The year. the throughout occurs plenti- with insectsteems and these provide mammals and for ful food also supportbearing trees some larger and apes. including monkeys animals, is insects, the mosquito Amongst many - particularly tropical to well-adapted – the parasite it comes With forest. that flourish diseases one of many bringing environment. equatorial in the warm, wet, dependent on the death of older trees, of in a matter which can be decomposed in this high-temperature, months or as well beetles, Thus moist environment. as other insects, bacteria which and fungi, do not depend on sunlight, but use un- are food, for matter organic decomposed important . inhabitants of this humidity and temperature, to is sensitive er, it soon gives a result, As rainfall changes. where forest tropical of other forms to way rainfall or where lower, are temperatures it is usually found a result, As is seasonal. there where within 200–500m of level is no long dry the main a result, . As the and are in which it is found areas the Congo peninsulas of southeast Asia, and the Irrawaddy river basins, and Amazon of the main equatorial Poleward system. may of modest altitude upland areas zone, because forest, maintain dense evergreen the year. rain falls throughout The changes in temperature. to adapted fall in humidity with altitude discussed in temperature 2008a) allows 3 (Galvin, Part even varyto during the day, more much alti- to freezing above though it remains On higher moun- tudes of 3000m or more. risk damaging frosts occasional where tains, 3 the (i.e. the environment from of carbon fluxed plant changed to amount of carbon dioxide vegeta- primarily by area: in a given material) Total animals. by then be eaten tion, which may productivity includes production of carbon by animals. and Mellor, 1995). Interestingly, however, however, Interestingly, 1995). and Mellor, the rainfall itself reduces canopy the forest leach- reducing the ground, that reaches and Ecology for at the Centre Studies ing. suggest that the Wallingford, Hydrology, reduction (Overton is as much as 30% and 2007). Strangeways, 1). (Table in these forests environments productivity total The reaches 4.5kg C m reaches totals vary as the ITCZ moves north moves through totals vary as the ITCZ downwards to make use of humus nutri- to downwards acid miner- leaching concentrates The ents. in particular and, including within als, aluminium (Ellis of high rainfall, this zone layer (http://uk.encarta.msn.com/media_layer 121627758/Typical_Latosol_Soil_of_the_ tend so that trees Tropical_Rainforest.html), than rather laterally their spread to Figure 3. Typical dense tropical rain forest at Latak waterfall, Lambir National Park, Sarawak. Sarawak. Lambir National Park, at Latak waterfall, forest rain dense tropical 3. Typical Figure (© Richard Young.) Figure 2. The climate of Mactan, Cebu, Philippines (10.3°N, 124.0°E, 24m) in the tropical rainforest rainforest 24m) in the tropical Philippines (10.3°N, 124.0°E, 2. The climate of Mactan, Cebu, Figure although monthly the year, throughout It is wet zone. the Philippines in June and July then returns between September and November. Drier weather Drier weather south between Septemberthe Philippines in June and July then returns and November. The incursions south between January and May. occasional make as northeastoccurs Trade on more is rain when there days is high, in particularnumber of rain between June and December, at http:// < 10 degC (sourced range, Note the small daily and annual temperature than half the days. www.pagasa.dost.gov.ph/cab/cab.html). 102

Weather – April 2009, Vol. 64, No. 4 Weather and climate of the tropics - Part 9 March (>12 degC), butcomparativelyMarch (>12degC), low during thewet summerseason. replaced natural forest inmuch ofthiszone. Thetemperature range November ishighbetween and make highrainfall forrapid useofthevery JuneandSeptember between growth. has period potentialevaporation exceeds . zone. Inthismonsoonclimate, there and earlyApril. this islittlerain During lateOctober between Figure 4.TheclimateofChittagong, Bangladesh (22.3°N,91.8°E, 6m)inthetropical deciduousforest Climatic zone Productivity (kg Productivity Cm Climatic zone tropical environments (from Fothergill Typical (measured asthefixingrate productivity ofcarbon by plants/phytoplankton) in Table 1 onan≤0.02 ~0.3 <0.03 ~0.1 0.2−2 1.5−5 1−3.5 ~1 Ocean –subtropical gyres –continental western margins Ocean –coastal zones Ocean –barrierreefs Mountain Arid zones Savannah evaporated rapidly. have highly limestone, theyform centration ofminerals, since thelow rainfalldoesnotleachthem. Where developed on occur, theyare poorlydeveloped andshallow, althoughtheymay contain ahighcon- crops commonly occur assmallmountainssurrounded by extensive . Where soils and fluvialdepositsincludingalluvialfans, lakesandoases. playas, Bedrock out- desert swelling clay. volcanic origin. The soilisregularly by overturned wetting, of dueto itshighproportion seasonally wet tropics where chemicalerosion whichisusuallyof affectsthebedrock, and that has a lack of a significant soil horizon because of a dry orcold climate.and thathasalackofsignificant soilhorizon becauseofadry tivation makesitespeciallysusceptible to erosion anddesiccation. containing large amountsofgravel. remains typically undernaturalvegetation, ascul- It ble minerals, suchascalciumandphosphorus. iron andaluminiumenrichmentisaresult ofhighrainfall, whichleachesthesoilofsolu- dolomite bedrock. occurs inhighland areas. typically It heavily cultivated, especiallywhennitrogenous are used. arid regions. Those inmonsoonalregions, however, have to acidifywhen atendency Box typesofthetropics 1.Soil (Courtesy surfaces. Desert Vertisol. Regosol. Leptosol. Latosol Grumusol. Andosol. Alfisol. Formed subsoil, ofmonsoonalandsemi- typical ofclay withnutrient-enriched . Asoilrichiniron, alumina,orsilicaformed inareas oftropical rainforest. The Asoilcontaining immature (swelling) clays, commonly found inthewet or Asoilformed from unconsolidated siltorclay thatmay beofalluvialorigin Ahighlyporous, darksoildeveloped from volcanic rocks: ash,tufforpumice. A very shallow soil(indicatinglittleinfluence ofsoil-forming Avery processes), often A brown, -rich soil of dry environments. Abrown, forms calcium-richsoilofdry over It limestone or Encyclopædia BritannicaEncyclopædia ofaridlandsare composed ofexposedbedrockThe surfaces outcrops rendzinas . However, theyare alsohighinsalts, since any rainfallis and et al specialized salt-tolerant ., 2006andLalliParsons, 1993). Wikipedia. Thus trees ‘hibernate‘ through thewinterand ) natural vegetation. −2 yr −1 ) perature may reach 40 12 degCormore. At timesinland, thetem- season, reaching is highduringthedry of theequatorial forests, thedailyrange mean temperature rangesimilarto that . northern subcontinent, ,Central Americaand oftheIndian Africa andeastern Brazil, parts are theclimax vegetation ofmuch West oftheyear.a proportion forests Seasonal ofthemonsoonwashthemoutfor returned to thesoil, althoughtheheavy somewhat more fertile, withmore nutrients but theannualleaffallallows thesoilsto be than inthepredominantly wet , The rate ofcarbonfixingissomewhatlower although evergreen speciesare alsoseen. season, soare present inmuchofthiszone, broad atthebeginning ofthedry adapted to thisregime, astheyshedtheir wet humidweather. son, foliage mustbeableto withstandvery oftheyear.a substantialpart thewet sea- In withstand dry, periodicallyhotweather for 1000mm; zone AminFigure 1),trees must forest (anannualrainfallmore thanabout extensive sufficient precipitation to support (Galvin, 2008c),where there is thelower-lyingIn tropics dominated by tropicalSeasonal forest temperatures. to steep slopes, thinsoilsand, attimes, low greater stress ontrees thatare notadapted there lessrainfallavailable, isoften placing conifers predominate. At thesealtitudes layer,the humidtropical boundary needle- trees inleafandwhichisusuallyabove as , trees are alsoacharacteristic zone across theEquator. Althoughdefined East Africa, the altitude andshelter extend of themonsoonforest zone, althoughin Caw inFigure 1)thus mainlylieto poleward the climaxvegetation. The savannahs (Aw, annual total ofabout800mm–grassland is extensive forestssupport –usuallybelow an Where rainfallisregular, butinsufficientto The savannahs ing someprotection from desiccation. tain arelatively moistenvironment, provid- grow. The trees themselves, however, main- large amountsofwater required for trees to annual rainfallisless, therelatively reflecting ofspecies.variety The forest thinswhere the larger animalsofagreat fauna –inparticular of awidevariety limit, andsoalsosupports towardsgrassland, itspoleward inparticular ble. The islocallyinterspersed with bamboo varietiesare perhaps themostnota- evergreen ofplantsasanunder-storey; ety this zone, are shown inFigure 4. data for Chittagong, Bangladesh,reflecting Although theseforests have anannual trees, are suchasteak, well Seasonal tropicalSeasonal avari- forest supports o C ormore. Climate Weather and climate of the tropics - Part 9 Weather – April 2009, Vol. 64, No. 4 103 ., 2006). et al C or more. Although C or more. o (Table 1) are fixed from from fixed 1) are (Table −1 ., 2006): a rate up to about up to ., 2006): a rate yr −2 However, most have a form a form most have However, 2 et al Where there is plentiful water, there is there is plentiful water, there Where flat this zone, over can be strong Winds Although dry part a large for of the year The grassland characteristically supports grassland The The mean temperature range of these range mean temperature The The soil types varyThe of the savannahs The large herds of animals, in their turn, of animals, herds large The support tropical species in most predator been a traditional and have continents Reptiles often humans. for of food source too. in this environment well live variety of species in the savan- a greater that flow rivers nahs and this is often from in this climatic zone, the year throughout though rainfall is seasonal – almost all even Not only is period. falling in a wet important it also this water vegetation, for supports animal species. many exerting little frictiongrasslands the air- on in predominate Winds Trade Drystream. although the summer brings pre- winter, flow. dominantly moist equatorial humid more than with much less growth the rate, of carbon fixing in terms areas, deservesavannahs the title of the world’s 0.2 Between most efficient environment. and 2kg C m characteristic of the zone. Leaching reduces reduces Leaching characteristic of the zone. of the sur- and mineral content the organic less leached but these soils are layer, face zone. of the rainforest than the latosols leaching in the both by formed are They dur- season and mineral differentiation wet ing the , when capillary action minerals towards dissolved brings lighter the surface. Much of the rainfall of the in short-period occurs savannahs heavy the poten- increasing however, downpours, the presence wash out, although tial for the impact reduce helps to cover of grass frosts are rare, they sometimes occur in win- they sometimes occur rare, are frosts Typical this zone. within in upland valleys ter at recorded the savannahs, data for climate shown are Australia Queensland, Croydon, 6. as Figure but also a vari- animals, of large herds many Indeed, fauna abound: ety of smaller ones. mass of animal is about 200 times the there in with that compared on the savannahs, life (Fothergill rainforest the tropical of much of this land, often occurring as small as small often occurring of this land, of much zone The of grass. areas large stands among season ‘winter’ dry a pronounced usually has by season characterized ‘summer’ and a wet in short falls of rain large periods. the 12 degC with oftenexceeds tempera- and largest highest temperatures during the dry range occurring ture season, 35 maxima reaching relatively scant resources by just a tenth just a tenth by scant resources relatively rainforest of the biomass of the tropical (Fothergill rainforest. times that of tropical four vertisols,between alfisols (Natural Conservation Service,Resources United 1999, DepartmentStates Agriculture, of bedrock, of limestone in areas 2006) and, grumusols. Figure 7. Chamber’s Pillar – a sandstone outcrop with vertical sides in the western , with vertical sides in the western outcrop – a sandstone Pillar 7. Chamber’s Figure only exist in deserts a lack of regular This landform can and indicates Australia. Northern Territory, and supports the rock through trees seeps gradually the scrubby rainfall meagre However, rainfall. Galvin.) P. (© J. F. its base. around Figure 6. The climate of Croydon, Queensland, Australia (18.2°S, 142.2°E, 116m) in the savannah 116m) in the savannah (18.2°S, 142.2°E, Australia Queensland, 6. The climate of Croydon, Figure is high in winter (>12 degC). is plentiful in summer and has the range Rainfall The temperature zone. evaporation potential though year-round even potential to support agriculture, highly productive dryis very at http://www.bom.gov.au/climate/averages/tables/ high; winter is generally (sourced cw_029012.shtml). Figure 5. Blaze in stands of trees in the savannah of Australia’s Northern Territory. The dry conditions Northern Territory. of Australia’s in the savannah trees 5. Blaze in stands of Figure Pettigrew.) & B. (© D. easily burning. trees ‘gum‘ Australian a near-constant fire hazard, make 104

Weather – April 2009, Vol. 64, No. 4 Weather and climate of the tropics - Part 9 setting fire to trees (Figure 5). derstorms occur, theirlightningtypically more humidairbegins to return, ‘dry’ thun- tion may as bedesiccated and, inparticular edges. Following season,vegeta- thedry towardszone, thepoleward inparticular available for irrigation. where soilsare richinmineralsandwater is inthiszone, inparticular important very farming, althougharable farmingisalso vate, dueto leachingandsofavour pastoral small. Savannah soilscanbehard to culti- season,however,dry the risksare relatively vest usuallyoccurs atthebeginning ofthe may bemore opento leaching. As thehar- ground isclearfollowing soils theharvest, similar –orbetter –shelter, butwhenthe of therain.Crops, astheygrow, provide latter. moisture from acoldsmall atLima(5–10degC), ocean limitingbothmaximaandminimaatthe environmentsture is notable:large range and inlandatAswān desert thetwo between (~15degC) scales inthesediagrams muchsmallerthanintheotherfigures. are very Thedifference intempera- Nomore thanatraceSahara desert. ofrain can tofall beexpected here. Notethattherainfall Figure environment atAswān, 8.(b)Theinlanddesert (24.0 °N, 32.8 °E, 194m)intheeastern bouring cool water ofthePeru Current. Note thelimittomaximumtemperature throu falls inwinterasuppertroughs bringoccasional mid-latitudedisturbances from higherlatitudes. Figure 8.(a)TheclimateofLima,Peru (12.0°S,77.1°W, Mostrain 13m)inthecoastal . Fires are ofthis anothercharacteristic gh thesummer, duetoseabreezes from theneigh- warm growing season. climates withadequate rainfallduringa ing thebenefitto humansofseasonal zones, reflect- oped intheseseasonallydry Mumbai, DelhiandShanghai,have devel- variable, however: in some years there is 300mm yr precipitation, whichisgenerally below Throughout theyear, evaporationexceeds ably highpopulation,despite their aridity. the ’s aremark- and support surface Figure 1) cover of more thanone-third These environments (BShandBWhin scrublands Tropical and deserts yr −1 Three of theworld’s ten largest cities: in the desert plains. Rainfall is very isvery plains. Rainfall inthedesert −1 andmore below 50mm typically at all, by ischaracterized water-retaining from Timbuktu, (Figure Mali 9). climate isillustrated by data (semi-desert) asshown inFiguredeserts, 8. The scrubland Egypt are oftheworld’s typical tropical water (Aquino andFord, 2008;Asif, 2008). need to findalternative sources ofdrinking in recent years, however, there isagrowing respectively. As theseglaciershave declined populations of10.8millionand8.9million, on neighbouringmountainsto support to supplyplentifulfresh water from andLimawereof Karachi founded onrivers environments.are indry The tradingports ingly, two ofthe world’s ten largest cities toareas . subject Perhaps surpris- ronments andhumanslive inmany tropical envi- represented orsemi-desert indesert ofanimalare allmajortypes Nevertheless, can maketheirown water metabolically. arid lands. Animalsusuallyretain water, or et al complexes, asdescribedinPart 8(Gaye comes from mesoscaleconvective estimated thatmuchoftherainfall may beaccompanied by . Indeed,itis as theSahel. lands (Figure Africa, thislandisknown 7).In burst ofthesummermonsoon,are scrub- polewardand Australia, closeto thefurthest Africa In cially attheedgeofdeserts. there is a large amountofbare soil, espe- hardySome grasses are alsoseen,although stands where sufficientwater isavailable. trees growing nearephemeralstreams orin ized by thisvegetation. and theAustralian Outbackare character- Parts ofsouthernandeastern Africa, India by drought-tolerant trees andhardy grasses. scrublandscomposed mainlyofstub- desert forests andsavannahs give way to semi- ground andinitsrainshadow, thetropical sonal rainfall. to findwater,of kilometres following sea- ofanimalsthatmusttravelvariety hundreds a not draininto thesea,butcansupport may attheedgeofKalahari, Okavango ecosystems. Ephemeralrivers, suchasthe have theirown peculiarenvironments and seeoccasional monsoonrain.Many deserts Part 5(Galvin andMembery, 2008). environments wereharsh dry presented in the maximumpossible. of Many aspects Sunshine totals may bemore than80%of temperature rangeof15degCormore. of Somalia, Yemen andOman)bringadaily Chile andPeru, aswell as, seasonally, those coasts ofNamibia,, the cool-ocean cover (away low humidity from andvery years there isnone. The usuallackofcloud relatively highrainfalllocally, whilstinmost Natural vegetation, where it cansurvive The climates ofLima, Peru andAswān, hardy inthe Life to mustbevery survive whenitfalls, intense isoften and Rain, needle-leafed hasmainlyshort, Scrubland manyIn areas, especiallyover higher scrublandsalongthefringesof Most ., 2005; Galvin, 2009). ., 2005;Galvin, Weather and climate of the tropics - Part 9 Weather – April 2009, Vol. 64, No. 4 105 (FAO- 2 C by day. It enough for is cold day. C by o , the air density little more than half , the air density little more −1 Although the Tibetan plateau provides an provides plateau Tibetan Although the Alpine grasses have adapted themselves themselves adapted have Alpine grasses At 4000m above sea level, the air is very sea level, 4000m above At UNESCO, 1989) vary mainly in their mineral UNESCO, under but most remain and origin, content In there their natural vegetation. the tropics near 4000m (but highly varia- to trees are scrub at higher altitudes ble), thin grassland on the ice-shattered rock bare to way giving rainfall does not erode Where highest peaks. (Ellis matter be rich in organic it may the soil, of ante- herds 1995). However, and Mellor, lope and horses typify the natural fauna of such a short sea- With growing the plateau. son and a desert productivity environment, and similar highlands. Tibet is very in low have the tropics study, to area interesting such as the other mountain areas, many modest areas Relatively Ethiopian plateau. wooded be more likely to are of high ground a from lands and benefit plateau than great that of surround- above high rainfall – well peaks of the towering The ing lowlands. so high that they are are plateaux great greatest The most rain-bearing . above about 1000m in rainfall is between increase of the air content and 3000m, the moisture High this level. above significantly reducing massifs of larger in the ground almost as dry remains as its surroundings, that at sea level. A lowland cumulonimbus A lowland that at sea level. at 750m and with a base cloud in the ITCZ, times as five contain may 000m deep, 15 plants and animals Humans, much water! must adapt to living in this environment in the dry levels, drought oxygen air and low the cold. as to as well very are few but there this environment, to soils: thin mountain The 11). (Figure trees andosols and regosols leptosols, of mountains. Almost all the plateau lies lies the plateau Almost all of mountains. summer, in high even so, 4000m and above with surfacecold it remains temperatures and reaching at freezing above barely than 20 more the ranges of mountains (the Tangula Shan) Tangula of mountains (the the ranges ice-covered remain plains to the that cross Lhasa, data for Climate the year. throughout points on the (at one of the lowest Tibet 10. as Figure shown are plateau) 60% of the oxygen barely thin, containing limiting more Still near sea level. available is plateau The of water. is the lack life for monsoon rains can- on all sides: sheltered the Himalaya and from not cross northernmore deposit meagre Shan, which Kunlun rainfall mainly on the Apart its northern a rim along forms border. mountains passes, deep narrow a few from the pla- surround 7000m or more reaching that does little rain and What teau. mainly from in summer, fall mostly occurs a base With cumulonimbus clouds. isolated little clouds contain near 5000m, convective they may though even water, precipitable humidityThe mixing ratio 000m deep. be 11 °C is only air at 5000m and 0 saturated for 9g kg One of the most extraordinary climates Mountain climates Mountain particularlyMountain are climates impor- drainage of the rain- the tropics; tant across often maintain fall they generate helps to or seasonally drypopulations on dry, lands stippled or are areas These them. around 1. H in Figure designated it expands pole- as zone, of the tropical is that of the in the northernward summer, Although much of the zone plateau. Tibetan the realm is a , its altitude brings it into Part 8: Galvin 2009). The return of the Trade Trade of the return The 8: GalvinPart 2009). bring plagues of locusts across may Winds in sum- moistened of seasonal growth, areas associated and the whilst mosquitoes mer, be brought occasionally risk of malaria may of high sum- flow the moist equatorial by mer. For much of the year, these zones have have these zones much of the year, For Low rainfall and high evaporation make rainfall Low Cool-water desertCool-water in particular – coasts relatively strong Trade Winds, blowing blowing Winds, Trade strong relatively flat land with little vegeta- relatively across tion, although summer brings periods of their from poleward moist monsoon flow 4 and 5 of equatorward fringes (see Figures productivity in the deserts low 1), (Table variation, is considerable although there dependent on the variability of annual rain- soil fertility. fall and potential those of the and Atacama – have an – have those of the Namib and Atacama dependent on dew and unusual vegetation, air carried ashore. cool in humid, plants. Otherplants. plants survive as drought rapidly dormant that germinate fall only one year rain that may following flowering these are in six. Characteristically, the plants and short-lived are of colour beautiful result. Figure 10. The climate of Lhasa, Tibet, China (29.7˚N, 91.1˚E, 3650m), typical of tropical highlands of tropical 3650m), typical China (29.7˚N, 91.1˚E, 10. The climate of Lhasa, Tibet, Figure and hot (considering air streams) of extra-tropical (under the influence with cold but wet, days are Many in summer. formed convection locally mainly from the altitude) with rainfall short relatively day. mainly late in the periods, over occurs rain Figure 9. The climate of Timbuktu, Mali (16.7°N, 3.0°W, 264m) on the desert fringe of the Sahel. Mali (16.7°N, 3.0°W, 9. The climate of Timbuktu, Figure late June to monsoon from of the summer excursions northward from comes Almost all the rainfall often in heavy and about bursts on only a few days during the summer, It occurs early September. 1997). The dramatic (Laing and Fritsch, associated with easterly waves squall lines, from half comes season is notable. during the rainy range reduction in temperature 106

Weather – April 2009, Vol. 64, No. 4 Weather and climate of the tropics - Part 9 - andsoconvergent descending water -ispresent across theEquator. NASA-GSFC.) (Courtesy Pacific (green andAtlanticOceans shades)isnotpresent where intheIndianOcean, theocean gyre the western coasts ofAfrica America, where andSouth values reach more than400mgCm where the ocean surface hasatemperaturewhere theocean surface somewhatwith Equator (varying season) and occur closeto 30 steep temperature gradients andsalinity that are found between therelatively For thetropical thepurposesofthis article, Tropical oceans andcoasts Highlands. of theMexican is founded ontherelatively equableclimate largest cities–at –oneoftheworld’s2008b). Mexico City of highground were listed inPart 4(Galvin, cantly increased rainfall. Many oftheseareas ics between theseheightshave asignifi- orseasonalareas ofthetrop- but many dry shades <100mgCm cator ofproductivity, ofoceanic 1997–August1998.Notethelow gyres productivity September (blue Figure 12. Theglobaldistributionofocean chlorophyll concentration -anindi- from satelliteimagery ofrural effect An depopulationisvisibleasruinedbuildingsinthemiddleground. (©NigelBolton.) altitude ofabout3500m),withfewtrees andscant vegetation, ManangHimalaya, 1992. Nepal, October Figure 11.Vegetation oftheHimalayan (above mountainzone, an essentiallyanuplandcold desert (yellow-orange). (~200mgCm The slightincrease inproductivity o an altitudeofabout2300m, southand35 –2 day –1 ) compared withtheproductive along areas ofupwelling -inparticular o north of the ofthe north above about22 peratures are locallywell below 22 ern coasts ofthecontinents, where tem- cold water thatliealongthewest- under theinfluence ofthesubtropical, water inthegreat oceansurface gyres, layer.in thesurface ensure someessentialmineralsare retained moderate to fresh Trade Winds, whichdo much ofthetropics, the notwithstanding mainly dueto therelatively lightwindsof low, since nutrientseasilysettleout. This is deserts. isusually very Their productivity oceans are equivalentto thecontinental included (seeFigure 2008a). 1,Part 3:Galvin, The convergence andsubsidence of Odd thoughitmay sound, mosttropical –2 day o –1 C. However, theareas of ) neartheEquatorin –2 day o C, are –1

the nutrientsupply islimited andthefish phenomenon. Without sufficient upwelling, December andJanuary. This isthe ElNiño to reachnormally beexpected apeak in odically decreases atatimewhen itwould Ecuador, thesupplyofupwelling water peri- PeruClose to theEquator in northern and This coast, however, isperiodicallycursed. anchovies, pilchards andjackmackerel. fish stocks are usuallyhigh. They include The result isacooling ofabout6degCand influence oftheoffshore Trade flow. underthe can readily riseto thesurface idly deepenoffshore, sothatdeepwater well-endowed. particularly The waters rap- America,southoftheEquator,of South is available asfood for fish. The west coast floating animals(zooplankton), whichare plankton), thephytoplankton form food for the nutrientfeeds plants(phyto- drifting to thenumberoffish,since is proportional Figure thisfigure,12. In thelevel ofnutrients them ahighnutrientsupply, as indicated by deeps to bringing riseto with thesurface, ing offshore causecool water from theocean of thetropical continents. Trade Winds blow- areas ofupwelling alongthewestern coasts offishintropicalcity oceans occurs inthe urchins). sea shellfish andechinoderms(e.g. starfish, the shelter ofthecorals live offish, avariety In with almostnosuspendedparticulates. onwarm,clear,ent for survival stillwater coral mineralastheydevelop, are depend- grow together asacolony, depositingthe Figure theseanimals,12.) Indeed which the chlorophyll concentration shown in ofnutrients,city thisisnotreflected in nutrient supply(Table 1).(Dueto thepau- are incredibly productive, despite thepoor environment, coral reefs blossom. These nental shelf. tropical Here, ocean inthedry there islittlerun-off, butashallow conti- remarkable, however,Most are areas where instreamsfrom andrivers run-off (Table 1). a muchgreater supplyofminerals, resulting the tropical oceans. coastal areas, In there is from theland. nutrients to thesea,someofitasrun-off andthetropical rainfalladds the surface 2008d). Large swell bringsdeepwater to weather following tropical (Galvin, asdoesthe increase inthemaritimeharvest, dominated by Trade Winds, bringssome supply.open oceans, isusuallyinshort the mainsource ofwhichisrainfallover the (Table 1). surface This meansthatnitrogen, also reduces nearto theocean productivity ofradiation theintensity Under clearskies, ter areas (thedoldrums)have lightwinds. areas receive littlerainfallandthewet- layer.sink below thesurface The windier and windensure thatmostnutrientssoon along withthedistributionofbothrainfall high- pressure belt(LalliandParsons, 1993), An important exception toAn important theusualpau- course,Of there isagreat across variety thehumidtropics,In thedrierseason, Weather and climate of the tropics - Part 9 Weather – April 2009, Vol. 64, No. 4 107

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2008. The The 2008. 63 63

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Soil map of the world: Weather : 32–38. Soil taxonomy: a basic Soil a basic taxonomy: Keys to soil taxonomy, to soil taxonomy, Keys de Felice P. de Felice

Weather Weather 64 1995. 1989. International Soil Reference Soil International Reference Daily Times 1999. 2006. . USDA: Washington, DC. Washington, . USDA: 2007. The weather and climate and climate weather The 2007. and cli- weather The 2008a. and cli- weather The 2008b. and cli- weather The 2008c. and weather The 2008d. 2009. The weather and climate and climate weather The 2009. : 306. : 245–251. : 31–36. : 129–135. Fritsch JM. Fritsch

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Q. J. R. Meteorol. Soc. J. R. Meteorol. Q. 2008. Water shortage hit drink- to Water 2008. . Routledge: London. London. . Routledge: 10th edition I. Overton A, Strangeways for report. Summer visit 2007 Centre Wallingford. and Hydrology, Ecology Weather Service, United States Department United States Service, of Agriculture. dailytimes.com.pk/default.asp?page=200 8%5C02%5C29%5Cstory_29-2-2008_pg7_ April 2008]. 20 34 [Accessed A. Ellis S, Mellor ment FAO-UNESCO. Asif Q. ing supplies. legend. revised Wageningen. Centre: and Information M, Brownlow V, A, Berlowitz Fothergill Linfield M. J, H, Keeling Cordey seen it before. never Planet earth – as you’ve BBC Books: London. Galvin JFP. – Setting 1 Part the scene. of the tropics, Weather Galvin JFP. – Synoptic-scale 3 Part of the tropics, mate systems. weather Galvin JFP. 4 – Forecasting Part of the tropics, mate weather. and associated cloud significant Weather Galvin JFP. 6 – Monsoons. Part of the tropics, mate Weather Galvin JFP. Tropical 7 – Part of the tropics, climate storms. revolving Galvin JFP. 8 – Mesoscale Part weather of the tropics, systems. Galvin JFP, Membery DA. Galvin JFP, 5 Part of the tropics, and climate weather – Dry environments. A, Gaye Squall lines and rainfall over western western Squall lines and rainfall over during summer 1986 and 87. Africa Phys. Atmos. Meteorol. Laing AG, population of mesoscale convective com- population of mesoscale convective plexes. Lalli CM, Parsons TR. Lalli CM, Parsons – an introductio oceanography Oxford. Press: Conservation Resources Natural Department States of United Service, Agriculture. for making system of soil classification soil surveys, 2nd edition. and interpreting accessed DC (updates Washington, USDA: http://soils.usda. on 5 July 2007 through gov/technical/classification/osd/index. html). Conservation Resources Natural Correspondence to: J.F. P. Galvin, P. to: J.F. Correspondence Devon, Exeter, Road, Met Office, FitzRoy EX1 3PB Email: [email protected] 2009, published with the Copyright, © Crown of HMSO and the permission of the Controller for Scotland. Printer Queen’s DOI: 10.1002/wea.312

Encyclopædia Peru bets on bets on Peru 2008. , at http://uk.encarta.msn.com/ Aquino M, Ford D. M, Ford Aquino supplies water desalination to ensure (http://uk.reuters.com/article/environ- mentNews/idUKN1161583720080311 20 April 2008]. [Accessed The final partThe agricul- will discuss tropical MemberyDavid made useful suggestions. References Acknowledgements availa- cities are world many data for Climate weather/world/ ble at http://www.bbc.co.uk/ descriptions of The city_guides/index.shtml. in the as given soil types are Conclusion In this part, it has been necessary divide to climate ‘typical’ to according the tropics long-term established by parameters, great of course, is, there However, means. and the zones variety discrete within these in truth, zones are, zones of climate margins change is also likely to of transition. Climate the limits of particularimpose changes to climatic regions. in effects on climate and the associated ture and as they are both at present the tropics, expected change during the twenty-first to century. dictionary Oxford The concise of Britannica, earth sciences and http:// medias_761576446/Soil.html soils.usda.gov/technical/classification/osd/ index.html. imported bottled water. The climate of Praia, of Praia, climate The imported bottled water. the 13) illustrates (Figure Islands Verde Cape drypredominantly of the oceanic weather scant rain falls relatively where , months of the year. only a few for The lack of rainfall in the oceanic deserts lack of rainfall in the oceanic The A variation on tropical forest is found along is found forest A variation on tropical Periodically, there is upwelling along other is upwelling there Periodically, Although the greatest stocks of fish are are of fish stocks Although the greatest can make living conditions difficult on on difficult can make living conditions islands – perhaps especially tropical remote those that, because of their sunshine and dry Desalination attract tourists. many weather, provide to a very way remains expensive but can be the only way drinkable water, the population and sufficient for provide to survive if tourists on even local agriculture, its brackish coastal limit: the for- its brackish limit: the mangrove coastal semi-submerged well grow est. a defence and provide in silt-laden waters surges The inundation. against coastal can be much storms revolving tropical from veg- low-lying this dense, by ameliorated as is regarded etation and its maintenance a very important part of of the protection in areas communities coastal the prevalent In addition, man- these storms. by affected and many the foreshore stabilize groves the out poisonous chemicals from can filter maintain its fertility. helping to water, tropical coasts – in particular coasts tropical of the those where Yemen, Gulf of Guinea, Somalia and of the summer southwesterlies the strong monsoon bring a good summer harvest parts as in many the Arabian Sea. Here, from occupa- fishing is a hazardous of the world, tion – every bit as taxing as in the western seas with rough of winter waters European hindering the fishing effort. found along the South American coasts, along the South American coasts, found America, of Central coasts those of the west and North also are Africa 1). important (Table the year throughout stocks reduce – at times causing a fail- – at times reduce stocks harvest, typically around of the ocean’s ure the phenomenon gave This Christmastide. its name – the Christ child. Figure 13. The climate of Praia, Islands (14.9˚N, 23.5˚W, 35m). This predominantly dry 35m). This predominantly Islands (14.9˚N, 23.5˚W, Verde Cape 13. The climate of Praia, Figure late in the summer when sea tem- anticyclones with most rainfall of the oceanic climate is typical day) to than 10mm per rain more average, heavy (on highest, allowing are showery rain peratures scant in Part 8: Galvin (described 2008e). The relatively often associated with easterly waves develop, the dry to last through be stored must season between December evaporation and July when rainfall Desert, off the These winds, regime. frequently Wind high in the northeastremains Trade of dust. bring outbreaks