STATE OF THE WORLD's FORESTs 2003 Sustainable use and management of freshwater resources. the role of forests D spendable freshwater supplies and the Technologies exist to deal with water scarcity bility to cope with the extremes of too little and to some extent with the effects of or too much water are requisites for sustainable hydrometeorological extremes( Brooks et al human development. Warnings of freshwater 1997). If they are to be turned into solutions scarcity issued at the end of the twentieth century several constraints must be overcome, including (e. g Falkenmark, 1989; Kundzewicz, 1997; land scarcity and inadequate policies an Vorosmarty et aL., 2000)are proving to be accurate, institutions that hamper an effective response to the point that lack of water now threatens food( Kundzewicz, 1997; Rosegrant, 1997; Scherr and security, livelihoods and human health(see UN, Yadav, 1996). Although land use and freshwater 1992: IFPRL, 2001). Worldwide freshwater are inextricably linked, they are rarely managed supports about 40 percent of all food-crop in concert. Upstream uses of land and water can production via irrigation, supports 12 percent of affect downstream communities and their use all fish consumed by humans and generates 20 of water. The converse is also true. Such percent of all electric power ohnson, Revenga linkages are readily seen with a watershed vernia, 2001). In addition to the direct perspective, but are not always fully taken into impact of water scarcity, impaired quality of account when responses are being developed at water reduces its usabilit the local national and international levels More than 3 billion people worldwide do not The International Year of mountains -2002 have access to clean water, and the problem is (iNternet:www.mountains2002.org)focused particularly acute in developing countries, where worldwide attention on land and water use in 90 percent of wastewater is discharged into mountainous watersheds. As the headwaters streams without treatment (ohnson, Revenga and for all major rivers of the world, many of which Echeverria, 2001). Of the more than 3 million are or were at one time forested these deaths that are attributed to polluted water and watersheds are a key to freshwater poor sanitation annually, more than 2 million are management. The relationship between forests children in developing countries(van Damme, and freshwater, in both tropical and temperate 2001). Furthermore, extensive loss of life and regions, therefore needs to be understood if economic productivity result each year from rain- forests are to be better managed to sustain the induced landslides, floods and torrents in productivity of uplands without affecting developed and developing countries alike. Water humans and the soil and water on which they and its management are therefore strategically depend. Enhancing the chances of achieving important to economies and the well-being of such objectives means taking a watershed people, and water management has become one of management perspective in the planning, the major challenges of this century. Conflicts over monitoring and implementation of forest, water water use will arise as water becomes increasingly resource, agricultural and urban development scarce, making action on many fronts imperative. pr
2003 FORESTS S’WORLD THE OF STATE 74 and use Sustainable of management :resources freshwater forests of role the the and supplies freshwater Dependable little too of extremes the with cope to ability sustainable for requisites are water much too or freshwater of Warnings. development human century twentieth the of end the at issued scarcity ;1997, Kundzewicz; 1989, Falkenmark. g.e( ,accurate be to proving are) 2000., al et Vorosmarty food threatens now water of lack that point the to ,UN see (health human and livelihoods, security freshwater, Worldwide). 2001, IFPRI; 1992 crop-food all of percent 40 about supports of percent 12 supports, irrigation via production 20 generates and humans by consumed fish all Revenga, Johnson (power electric all of percent direct the to addition In). 2001, Echeverria and of quality impaired, scarcity water of impact .usability its reduces water not do worldwide people billion 3 than More is problem the and, water clean to access have where, countries developing in acute particularly into discharged is wastewater of percent 90 and Revenga, Johnson (treatment without streams million 3 than more the Of). 2001, Echeverria and water polluted to attributed are that deaths are million 2 than more, annually sanitation poor ,Damme van (countries developing in children and life of loss extensive, Furthermore). 2001 in torrents and floods, landslides inducedrain from year each result productivity economic Water. alike countries developing and developed strategically therefore are management its and of being-well the and economies to important of one become has management water and, people over Conflicts. century this of challenges major the increasingly becomes water as arise will use water .imperative fronts many on action making, scarce ,scarcity water with deal to exist Technologies of effects the with extent some to and ,.al et Brooks (extremes hydrometeorological ,solutions into turned be to are they If). 1997 including, overcome be must constraints several and policies inadequate and scarcity land response effective an hamper that institutions and Scherr; 1997, Rosegrant; 1997, Kundzewicz( freshwater and use land Although). 1996, Yadav managed rarely are they, linked inextricably are can water and land of uses Upstream. concert in use their and communities downstream affect Such. true also is converse The. water of watershed a with seen readily are linkages into taken fully always not are but, perspective at developed being are responses when account .levels international and national, local the 2002 – Mountains of Year International The focused) org.mountains2002.www: Internet( in use water and land on attention worldwide headwaters the As. watersheds mountainous which of many, world the of rivers major all for these, forested time one at were or are freshwater to key a are watersheds forests between relationship The. management temperate and tropical both in, freshwater and if understood be to needs therefore, regions the sustain to managed better be to are forests affecting without uplands of productivity they which on water and soil the and humans achieving of chances the Enhancing. depend watershed a taking means objectives such ,planning the in perspective management water, forest of implementation and monitoring development urban and agricultural, resource .programmes
PART II SELECTED CURRENT ISSUES IN THE FOREST SECTOR Forested mountain watersheds are a key to dependable freshwater supplies(Switzerland) The loss of forest cover and conversion to other land uses can adversely affect freshwater upplies and compound human disasters resulting from hydrometeorological extremes ons can be improved ar overall water resource management facilitated if forests are managed with hydrological objectives in mind. While not a panacea for resolving water issues, forests can provide tangible economic and environmental benefits. A watershed framework helps identify these benefits in both Forests are found where there are large provide the greatest soil stability and the quantities of water, normally where precipitation lowest levels of soil mass movement, gully is abundant or in riparia erosion and surface erosion: moisture is high. Perception of the influence of export the lowest levels of sediment forests on water led to the establishment of the downstream national forest system in the United States, as forest cover was considered necessary to sustain FORESTS, ATMOSPHERIC WATER AND river flow(Lee, 1980). Most forests were WATER YIELD subsequently found to use great amounts of The relationship among forests, atmospheric water, contrary to early thinking. The present moisture and water yield has long been chapter summarizes the impact of forests on controversial. Lee(1980)noted that the natural freshwater and suggests how forests and forest coincidence of forest cover and higher management can help achieve water resource precipitation is at least partly responsible for the management objectives popular notion that forests increase or attract Forested watersheds are exceptionally stable rain, which leads to the assumption that their hydrological systems. In contrast to other land removal would significantly diminish healthy forests: precipitation. Globally, this is not the case; the strongly influence the quantity of water removal of all forest cover would only reduce ielded from watersheds global precipitation by 1 to 2 percent at most discharge the highest quality of water; (Lee, 1980). Calder(1999a)further suggested that discharge lower storm flow peaks and deforestation has little effect on regional volumes for a en ll precipitation, although exceptions could occur in moderate variation in stream flow between basins where rainfall largely depends on the high and low flows during a year, ternally driven circulation patterns such as the
75 SECTOR FOREST THE IN ISSUES CURRENT SELECTED II PART to conversion and cover forest of loss The freshwater affect adversely can uses land other disasters human compound and supplies .extremes hydrometeorological from resulting and improved be can conditions Watershed if facilitated management resource water overall objectives hydrological with managed are forests water resolving for panacea a not While. mind in economic tangible provide can forests, issues watershed A. benefits environmental and both in benefits these identify helps framework .areas downstream and upstream large are there where found are Forests precipitation where normally, water of quantities soil where areas riparian in or abundant is of influence the of Perception. high is moisture the of establishment the to led water on forests as, States United the in system forest national sustain to necessary considered was cover forest were forests Most). 1980, Lee (flow river of amounts great use to found subsequently present The. thinking early to contrary, water on forests of impact the summarizes chapter forest and forests how suggests and freshwater resource water achieve help can management .objectives management stable exceptionally are watersheds Forested land other to contrast In. systems hydrological :forests healthy, uses water of quantity the influence strongly• ;watersheds from yielded ;water of quality highest the discharge• and peaks flow storm lower discharge• ;rainfall of input given a for volumes between flow stream in variation moderate• ;year a during flows low and high the the and stability soil greatest the provide• gully, movement mass soil of levels lowest ;erosion surface and erosion sediment of levels lowest the export• .downstream AND WATER ATMOSPHERIC, FORESTS YIELD WATER atmospheric, forests among relationship The been long has yield water and moisture natural the that noted) 1980 (Lee. controversial higher and cover forest of coincidence the for responsible partly least at is precipitation attract or increase forests that notion popular their that assumption the to leads which, rain diminish significantly would removal the; case the not is this, Globally. precipitation reduce only would cover forest all of removal most at percent 2 to 1 by precipitation global that suggested further) 1999a (Calder). 1980, Lee( regional on effect little has deforestation in occur could exceptions although, precipitation on depends largely rainfall where basins the as such, patterns circulation driven internally watersheds mountain Forested dependable to key a are (Switzerland (supplies freshwater HOFER. T/0339-FO/DEPARTMENT FORESTRY FAO
STATE OF THE WORLDS FORESTS 2003 Amazon basin. Even then, it has been estimated documented, although research is under way that complete deforestation and replacement in Central America(Calder, 1999b, as with non-forest vegetation would reduce basin reported by Kaimowitz, 2000 rainfall by less than 20 percent( Brooks et al 1997) Non-cloud forests and freshwater yield There are circumstances, however, in which Outside fog or tropical montane cloud forest forests intercept fog or low clouds(cloud regions, forests generally consume large forests), adding moisture to the site that would quantities of water. More than 100 watershed otherwise remain in the atmosphere. The experiments around the world have shown tha relationship between forests and the yield of forest removal increases stream flow, which freshwater differs between cloud forest and varies in magnitude with climate and forest type non-cloud forest conditions and diminishes as forests regenerate(e.g. Bariet aL., 1996: Bosch and Hewlett, 1982; Lesch and Cloud forests and freshwater yield Scott, 1997; Verry, Hornbeck and Todd, 2000; Cloud forests occur along coastal areas in Whitehead and Robinson, 1993). When other results show th common. Forests intercept atmospher following moisture (horizontal precipitation), which Removal of forest cover increases annual condenses on and drips from foliage, adding water yield by 60 to 650 mm. The size of the moisture to the soil. Rainfall is not increased increase is generally proportional to the but forests add moisture that low-growing amount of biomass removed and is greater in regetation would not. The following are wetter areas. Little effect has been reported in examples of freshwater augmentation by cloud dryland areas where annual precipitation is forests less than 400 mm Coastal forests in the fog belt of western Flow during dry seasons generally increases Oregon, the United States, augment water after forests are thinned or removed yield(Harr, 1982; Ingwersen, 1985). The Forests with high interception rates(e.g removal of old-growth conifer forests from conifers)or high transpiration rates(e. g the municipal watershed of Portland, eucalypts) yield less water than those with Oregon, reduced summer stream flow, but lower interception and transpiration rates the regrowth of vegetation caused stream Water yield would therefore be expected to flow levels to return to normal within five to increase when conifer forests are replaced by SIx years broadleaf forests and to decrease when Water augmentation by tropical montane broadleaf forests, shrubs or grasses are cloud forests varies with altitude, location replaced by conifers(see Box opposite) nd season( Bruijnzeel and Proctor, 1993) The ratio of horizontal precip FORESTS, FLOODS AND DEBRIS annual rainfall was shown to vary between FLOWS 4 and 85 percent, with higher values Forests produce low levels of storm flow and orresponding to dry seasons, while average greater soil stability than any other vegetation horizontal precipitation varied between 0.2 type because of their high infiltration rates, and 4 mm per day. Annual stream flow from protective ground cover, high consumption of tropical montane cloud forest for a given soil water and high tensile strength of roots rainfall was higher than from other tropical These attributes are particularly beneficial in forests. The stream flow response to mountainous terrain that is subject to torrential conversion of tropical montane cloud forest rainfall. Forest removal and road construction to other land uses has not been widely are problematic in such areas because they
2003 FORESTS S’WORLD THE OF STATE 76 estimated been has it, then Even. basin Amazon replacement and deforestation complete that basin reduce would vegetation forest-non with ,.al et Brooks (percent 20 than less by rainfall .(1997 which in, however, circumstances are There cloud (clouds low or fog intercept forests would that site the to moisture adding), forests The. atmosphere the in remain otherwise of yield the and forests between relationship and forest cloud between differs freshwater .conditions forest cloud-non yield freshwater and forests Cloud in areas coastal along occur forests Cloud montane tropical in also and climates temperate are conditions cloud low or fog where regions atmospheric intercept Forests. common which), precipitation horizontal (moisture adding, foliage from drips and on condenses ,increased not is Rainfall. soil the to moisture growing-low that moisture add forests but are following The. not would vegetation cloud by augmentation freshwater of examples .forests western of belt fog the in forests Coastal• water augment, States United the, Oregon The). 1985, Ingwersen; 1982, Harr (yield from forests conifer growth-old of removal ,Portland of watershed municipal the but, flow stream summer reduced, Oregon stream caused vegetation of regrowth the to five within normal to return to levels flow .years six montane tropical by augmentation Water• location, altitude with varies forests cloud .(1993, Proctor and Bruijnzeel (season and to precipitation horizontal of ratio The between vary to shown was rainfall annual values higher with, percent 85 and 4 average while, seasons dry to corresponding 2.0 between varied precipitation horizontal from flow stream Annual. day per mm 4 and given a for forest cloud montane tropical tropical other from than higher was rainfall to response flow stream The. forests forest cloud montane tropical of conversion widely been not has uses land other to way under is research although, documented as, 1999b, Calder (America Central in .(2000, Kaimowitz by reported yield freshwater and forests cloud-Non forest cloud montane tropical or fog Outside large consume generally forests, regions watershed 100 than More. water of quantities that shown have world the around experiments which, flow stream increases removal forest type forest and climate with magnitude in varies et Bari. g.e (regenerate forests as diminishes and and Lesch; 1982, Hewlett and Bosch; 1996., al ;2000, Todd and Hornbeck, Verry; 1997, Scott other When). 1993, Robinson and Whitehead are increases flow, forests replace uses land the show results, exceptions few With. sustained .following annual increases cover forest of Removal• the of size The. mm 650 to 60 by yield water the to proportional generally is increase in greater is and removed biomass of amount in reported been has effect Little. areas wetter is precipitation annual where areas dryland .mm 400 than less increases generally seasons dry during Flow• .removed or thinned are forests after .g.e (rates interception high with Forests• .g.e (rates transpiration high or) conifers with those than water less yield) eucalypts .rates transpiration and interception lower to expected be therefore would yield Water by replaced are forests conifer when increase when decrease to and forests broadleaf are grasses or shrubs, forests broadleaf .(opposite Box see (conifers by replaced DEBRIS AND FLOODS, FORESTS FLOWS and flow storm of levels low produce Forests vegetation other any than stability soil greater ,rates infiltration high their of because type of consumption high, cover ground protective .roots of strength tensile high and water soil in beneficial particularly are attributes These torrential to subject is that terrain mountainous construction road and removal Forest. rainfall they because areas such in problematic are
PART II SELECTED CURRENT ISSUES IN THE FOREST SECTOR A lesson from Fiji Afforestation reduced water yield to a water supply reservoir with lower interception and transpiration rates would have in Fiji(Drysdale, 1981) been preferred over conifers On the leeward side of two of the largest Fiji islands, he experience in Fiji convinced the Beijing Water Conser- 0000haof Pinus caribaea, plantedtodevelopawood-based vancy Bureauto reverse its plans to replace Chinese locust and dustry, replaced shrub vegetation. Six years after the forest shrubs with pine in the catchment area of the Miyun Reservoir, was planted, dry season flows to a downstream water supply a key municipal water source for Beijing. Planners had mistak- reservoir had decreased by 50 to 60 percent. The areas affor- enly thought that conversion to pine would increase water ested were not in a cloud-forest environment Had freshwater yield to the reservoir, whereas the result would have been the resources been considered in the afforestation plan, species oppo construction(below ) in mountain increase the frequency and magnitude of landslides and debris flows(Sidle, 2000) However, there is a limit to the protection that forest cover provides, as was found in Taiwan Province of China(see Box on next page), where early and managed for slope stabilization and torrent control (Lu, Cheng and Brooks, 2001). As th amount of rainfall becomes extreme. the extent to which forests can help to prevent landslides, A frequently asked question is the extent to which forest cover affects flooding. In northern Minnesota, the United States, rainfall-generated peak flows up to the 25-to 30-year recurrence interval (Ri)increased when 70 percent of the forest cover on a small watershed was clear-cut (Lu, 1994; Verry, 2000). Larger floods(RI >100 years)were not affected by forest cover removal, supporting Hewlett's(1982)claim that changes
77 SECTOR FOREST THE IN ISSUES CURRENT SELECTED II PART of magnitude and frequency the increase .(2000, Sidle (flows debris and landslides that protection the to limit a is there, However Taiwan in found was as, provides cover forest where), page next on Box see (China of Province forested are watersheds mountainous all nearly torrent and stabilization slope for managed and the As). 2001, Brooks and Cheng, Lu (control extent the, extreme becomes rainfall of amount ,landslides prevent to help can forests which to .diminishes flooding and flows debris to extent the is question asked frequently A northern In. flooding affects cover forest which generated-rainfall, States United the, Minnesota recurrence year-30 to- 25 the to up flows peak the of percent 70 when increased) RI (interval cut-clear was watershed small a on cover forest 100 > RI (floods Larger). 2000, Verry; 1994, Lu( ,removal cover forest by affected not were) years changes that claim) 1982 (s’Hewlett supporting reservoir supply water a to yield water reduced Afforestation .(1981, Drysdale (Fiji in ,islands Fiji largest the of two of side leeward the On based-wood a develop to planted, caribaea Pinus of ha 000 60 forest the after years Six. vegetation shrub replaced, industry supply water downstream a to flows season dry, planted was freshwater Had. environment forest-cloud a in not were estedaffor areas The. percent 60 to 50 by decreased had reservoir species, plan afforestation the in considered been resources have would rates transpiration and interception lower with .conifers over preferred been and locust Chinese replace to plans its reverse to Bureau vancyConser Water Beijing the convinced Fiji in experience The ,Reservoir Miyun the of area catchment the in pine with shrubs water increase would pine to conversion that thought enlymistak had Planners. Beijing for source water municipal key a the been have would result the whereas, reservoir the to yield .opposite road and) above (removal Tree mountain in) below (construction erosion soil serious cause can areas (Nepal (landslides and HOFER. T/0285-FO/DEPARTMENT FORESTRY FAO HOFER. T/0286-FO/DEPARTMENT FORESTRY FAO Fiji from lesson A
STATE OF THE WORLDS FORESTS 2003 incentives for people to avoid them. Terrain analysis based on Geographic Information Typhoons,landslides and debris flows Systems(GIS)offers the means to mark in Taiwan Province of hina hazardous terrain in mountainous watersheds (Gupta and Joshi, 1990; Sidle, 2000), and methods to delineate floodplains and define Floods, landslides and debris flows, resulting from an zones according to the type and degree of risk three to four typhoons a year, cause extensive loss of life and prop- are well known(Bedient and Huber, 1988).An erty on the mountainous island of Taiwan Province of China. About example of an incentive to change people's 53 percent of the island has slopes steeper than 21, and more than behaviour is the federal flood Insurance 100 peaks exceed 3 000 m above sea level(Lee, 1981). With shal- Program in the United States, under which low soils overlying weak, fractured and weathered geological for- insurance rates in areas adjacent to rivers are mations, landslides load steep channels, which become primed for linked to the degree of hazard During the particularly destructive Typhoon Herb in 1996, rain- FORESTS AND SEDIMENTATION fall athigherelevationsexceeded 1 985 mmin 42hours(Lu, Cheng Because watersheds with healthy forests and Brooks, 2001). Landslides and debris flows occurred through- the lowest levels of sediment of any cover type out the island, many along roads and in drainage channels where Brooks et al., 1997), it is not surprising that native forest had been converted to grow tea, vegetable crops and forests are often looked to as a means of but many in forested areas as well. Given the reducing levels of downstream sediment in amount and intensity of rainfall, debris flows and flooding oc- water supply reservoirs curred regardless of land use. Larson and Albertin(1984 )recommended reforestation to reverse a threefold increase in sedimentation in the Alhajuela Reservoir in Panama following the clearing of 18.2 percent of the watershed. Few such studies forest cover have little effect on large floods in people therefore suggest that the benefits from streams. Importantly, the 1.5-to 2-year rI forest cover in reservoir protection have been peak flows more than doubled when forest cover overestimated(Kaimowitz, 2000). Reasons for such scepticism include Extreme hydrological events are the result of inadequate monitoring, and therefore limited natural processes of erosion and sediment empirical evidence linking forest changes to motion interacting with human systems(Davies, reservoir sedimentation levels 1997). Where land scarcity concentrates people the fact that forest cover changes have and their dwellings in hazardous areas, disasters occurred over such small areas of watersheds will occur whether uplands are fully forested or that little effect has been observed not. This is the situation in Taiwan Province of the distance between upstream watershed China, with a population density approaching projects and downstream reservoirs, which 600 inhabitants per square kilometre. People masks the effects living on steep slopes, in the mouths of small the recognition that other factors, such as drainage basins and in floodplains are bound to non-forest land use can increase stream flow be vulnerable. a coordinated watershed peaks and affect sedimentation management programme among government Downstream sediment delivery is affected agencies has been suggested in order to address both by changes in stream flow discharge from this threat for both upstream and downstream upland watersheds and by alterations in riparian communities(Lu, Cheng and Brooks, 2001). areas along stream banks(Rosgen, 1994 Hazardous areas must be identified, and Tabacchi et aL., 2000). Sediment levels of rivers policies and institutions established to provide are determined by both sediment availability
2003 FORESTS S’WORLD THE OF STATE 78 in floods large on effect little have cover forest in RI year-2 to- 5.1 the, Importantly. streams major cover forest when doubled than more flows peak .removed was of result the are events hydrological Extreme sediment and erosion of processes natural ,Davies (systems human with interacting motion people concentrates scarcity land Where). 1997 disasters, areas hazardous in dwellings their and or forested fully are uplands whether occur will of Province Taiwan in situation the is This. not approaching density population a with, China People. kilometre square per inhabitants 600 small of mouths the in, slopes steep on living to bound are floodplains in and basins drainage watershed coordinated A. vulnerable be government among programme management address to order in suggested been has agencies downstream and upstream both for threat this .(2001, Brooks and Cheng, Lu (communities and, identified be must areas Hazardous provide to established institutions and policies Terrain. them avoid to people for incentives Information Geographic on based analysis mark to means the offers) GIS (Systems watersheds mountainous in terrain hazardous and), 2000, Sidle; 1990, Joshi and Gupta( define and floodplains delineate to methods risk of degree and type the to according zones An). 1988, Huber and Bedient (known well are s’people change to incentive an of example Insurance Flood Federal the is behaviour which under, States United the in Program are rivers to adjacent areas in rates insurance .hazard of degree the to linked SEDIMENTATION AND FORESTS export forests healthy with watersheds Because type cover any of sediment of levels lowest the that surprising not is it), 1997., al et Brooks( of means a as to looked often are forests in sediment downstream of levels reducing .reservoirs supply water recommended) 1984 (Albertin and Larson in increase threefold a reverse to reforestation in Reservoir Alhajuela the in sedimentation of percent 2.18 of clearing the following Panama some and, exist studies such Few. watershed the from benefits the that suggest therefore people been have protection reservoir in cover forest for Reasons). 2000, Kaimowitz (overestimated :include scepticism such limited therefore and, monitoring inadequate• to changes forest linking evidence empirical ;levels sedimentation reservoir have changes cover forest that fact the• watersheds of areas small such over occurred ;observed been has effect little that watershed upstream between distance the• which, reservoirs downstream and projects ;effects the masks as such, factors other that recognition the• flow stream increase can, use land forest-non .sedimentation affect and peaks affected is delivery sediment Downstream from discharge flow stream in changes by both riparian in alterations by and watersheds upland ;1994, Rosgen (banks stream along areas rivers of levels Sediment). 2000., al et Tabacchi availability sediment both by determined are of average an from resulting, flows debris and landslides, Floods About. China of Province Taiwan of island mountainous the on ertyprop and life of loss extensive cause, year a typhoons four to three than more and°, 21 than steeper slopes has island the of percent 53 for primed become which, channels steep load landslides, mationsfor geological weathered and fractured, weak overlying soils lowshal With). 1981, Lee (level sea above m 000 3 exceed peaks 100 .flows debris Cheng, Lu (hours 42 in mm 985 1 exceeded elevations higher at fallrain, 1996 in Herb Typhoon destructive particularly the During where channels drainage in and roads along many, island the outthrough occurred flows debris and Landslides). 2001, Brooks and and crops vegetable, tea grow to converted been had forest native the Given. well as areas forested in many but, palm nut betel .use land of regardless curredoc flooding and flows debris, rainfall of intensity and amount flows debris and landslides, Typhoons China of Province Taiwan in