oki811ose

Dam reservoirForest clearcutForest managementJapan

s inwaw-re,

pan thervatonistry

and agricultural areas (Ministry of Land, Infrastructure, Transportand Tourism, 2009b).

Recently, dam reservoir development has drawn criticism fromthe viewpoints of biological and environmental conservation(Harada and Yasuda, 2004). There are frequent campaigns opposing

because forest management could reduce leaf area and henceevapotranspiration. This proposal is widely believed to be valid andmany local governments have thus introduced taxes to aid forestmanagement (e.g., Yorimitsu, 2001; Imawaka and Sato, 2008).

Researchers in Japan have reported an increase in low ow dueto forest management such as forest clearcutting (e.g., Tamai et al.,2004; Maita et al., 2005). On the other hand, researchers in Japandeveloped a method to evaluate the increase in low ow due todam reservoir development (e.g., Kume and Kubota, 1998; Komatsu

* Corresponding author. Tel.: 81 92 948 3109; fax: 81 92 948 3119.

Contents lists availab

Journal of Environm

ls

Journal of Environmental Management 91 (2010) 814823E-mail address: komatsu@forest.kyushu-u.ac.jp (H. Komatsu).Transport and Tourism, 2009a) owing to the countrys large pop-ulation relative to the land surface area (127,000,000 people in anarea of 378,000 km2).

A total of 2738 dams have been developed in Japan, anda further 331 are now under construction or have been proposed(Tonegawa Integrated Dam and Reservoir Group ManagementOfce, 2009). One purpose of dam reservoir development is toincrease low-ow discharge to secure water resources. Most damreservoirs are located in forested areas upstream of metropolitan

ning of coniferous plantation forests and conversion to broadleavedforests, as a possible alternative to the development of dam reser-voirs. Japan has developed large coniferous plantation forests fortimber production, and there was active management of forestsbefore the 1970s (Fujimori, 2000). However, forestmanagement hasnot been economically viable in recent years because of the rela-tively low price of timber and has not been actively performed forseveral decades (Fujimori, 2000). Researchers and journalists haveproposed that low ow could be increased by forest managementLow owWater resource management

1. Introduction

Despite higher precipitation in Jaregions (National Astronomical Obsages frequently occur in Japan (Mi0301-4797/$ see front matter 2009 Elsevier Ltd.doi:10.1016/j.jenvman.2009.10.011dam reservoirs across Japan. Using the relationship between annual precipitation and the low-owincrease due to deforestation, we estimated the potential increase in the low-ow rate for each damreservoir watershed if forests in the watershed were clearcut (dQf). Only 6 of the 45 samples satiseddQf > dQd, indicating that the potential increase in the low-ow rate due to forest clearcutting was lessthan the increase due to dam reservoir development in most cases. Twenty-ve of the 45 samplessatised dQf < 0.2 dQd, indicating the potential increase in the low-ow rate due to forest clearcuttingwas less than 20% of the increase due to dam reservoir development in more than half the cases.Therefore, forest management is far less effective for water resource management than dam reservoirdevelopment is in Japan.

2009 Elsevier Ltd. All rights reserved.

an in other temperatery, 2001), water short-of Land, Infrastructure,

proposed dams (e.g., Hoyano, 2001), and the removal of existingdams is also debated (e.g., Amano and Igarashi, 2004).

Some researchers and journalists (e.g., Tsukamoto, 1998;Yorimitsu, 2001; Kuraji, 2003; Amano and Igarashi, 2004) haveproposed forest management, such as patch clearcutting and thin-Keywords:between annual precipitation and the low-ow increase due to deforestation. We then examined theincrease in low-ow rates due to dam reservoir development (dQd) using inow and outow data for 45Accepted 23 October 2009Available online 22 November 2009 of forest management. We rst analyzed runoff data for ve catchments and found a positive correlationWater resource management in Japan: F

Hikaru Komatsu a,*, Tomonori Kume b, Kyoichi OtsuaKasuya Research Forest, Kyushu University, 394 Tsubakuro, Sasaguri, Kasuya, Fukuokab School of Forestry and Resource Conservation, National Taiwan University, 1 Sec. 4, Ro

a r t i c l e i n f o

Article history:Received 1 April 2009Received in revised form8 October 2009

a b s t r a c t

Researchers and journalistreservoir development forcompared the potential loreservoir development. He

journal homepage: www.eAll rights reserved.rest management or dam reservoirs?a

-2415, Japanvelt Road, Taipei 106, Taiwan

Japan recently proposed forest management as an alternative to damter resource management. To examine the validity of the proposal, weow increase due to forest clearcutting with the increase due to damwe focused on forest clearcutting as an end member among various types

le at ScienceDirect

ental Management

evier .com/locate/ jenvman

menet al., 2009b). Komatsu et al. (2009b) applied the method to eval-uate an increase in low ow for seven existing dam reservoirslocated upstream of the Tokyo metropolitan area. They reported anincrease in low ow due to the dam reservoir development.However, researchers in Japan have not compared the increase dueto forestmanagement with that due to dam reservoir development.Thus, the effectiveness of forest management in increasing lowow relative to dam reservoir development has not been evaluated.Consequently, the validity of the proposal of forest management inJapan has not been determined (Komatsu et al., 2009a).

This study compares the increase in low ow due to forestmanagement with that due to dam reservoir development toevaluate the effectiveness of forest management. Among varioustypes of forestmanagement, we focused on forest clearcutting as anend member. Changes in a ow regime due to forest clearcuttingare generally greater than changes due to other forest managementpractices such as patch clearcutting and thinning of coniferousplantation forests, and conversion to broadleaved forests (e.g.,Bosch and Hewlett, 1982; Scott and Lesch, 1997; Komatsu et al.,2009a,c).

Though our analysis focuses on Japan, our results are of use toresearchers in other countries. Many dam reservoirs have beendeveloped to secure water resources in other countries. However,the construction of dam reservoirs is criticized because it greatlychanges natural ow regimes and therefore affects biodiversity inriver and riparian ecosystems (Poff et al., 1997, 2007; Lytle and Poff,2004). Forest management might be an alternative to theconstruction of dam reservoirs in securing water resources.

2. Materials and methods

This study comprises three parts. First, we examined thedifferences in low-ow rates between forested and deforestedperiods using catchment runoff data obtained where deforestationand/or afforestation occurred in Japan. Second, we examined theincrease in low-ow rates due to dam reservoir development usinginow and outow data for dam reservoirs across Japan. Third, wecalculated the potential increase in the low-ow rate if forests ina dam reservoirs watershed were clearcut and compared it withthe increase due to the dam reservoir development.

2.1. Catchment runoff data

We obtained daily runoff data for ve catchments wheredeforestation and/or afforestation had occurred. There are severalother catchments such as Kamabuchi I and Jozankei catchmentswhere deforestation and/or afforestation had occurred (Maita,2005) but for which we could not obtain daily runoff data, and thuswe did not use data for these catchments.

Fig. 1 shows the locations of the ve catchments and Table 1briey describes the catchments. The catchments are located inwestern or central Japan, where water shortages are more frequentthan in northern Japan. Thus, the results of our analysis are morereliable for these regions than for northern Japan. In northernJapan, catchment runoff is often inuenced by snowmelt (Komatsuet al., 2008a; Shinohara et al., 2009), which contrasts to the case inwestern and central Japan.

2.1.1. Sarukawa I and III catchmentsThe Sarukawa I and III catchments are adjacent catchments. The

mean annual precipitation for 19592000 in these catchments was3032 mm and the standard deviation was 704 mm. Fig. 2a isa histogram of annual precipitation for 19592000. The annualprecipitation ranged between 1913 and 5710 mm. Fig. 3a shows the

H. Komatsu et al. / Journal of Environseasonal variation in precipitation based on data for 19671972 and19941999. Precipitation amounts and their variations weregreater in summer than in winter.

Broadleaved forests in Sarukawa I and III catchments wereclearcut in 1967. Coniferous trees (Chamaecyparis obtusa andCryptomeria japonica for Sarukawa I and III catchments respec-tively) were planted just after the clearcutting and broadleavedtrees naturally regenerated in the catchments. Thus, the catch-ments have been covered by coniferous plantation and broadleavedforests since the late 1970s (Shimizu et al., 2008). Daily runoff datafor 19682000 were available from the Forest Inuences UnitKyushu Branch Station (1982), Takeshita et al. (1996) and Shimizuet al. (2008). Thus, 19681972 data for the deforested period and19941999 data for the forested period were used in evaluating thedifference in low-ow rates between the forested and deforestedperiods. Note that some data for 1997 were missing and thereforedata for this year were not used in the analysis. More completedescriptions of the catchments were given by Shimizu et al. (2008).

2.1.2. Tatsunokuchi-Kita and Tatsunokuchi-Minami catchmentsThe Tatsunokuchi-Kita and Tatsunokuchi-Minami catchments

are adjacent catchments. The mean annual precipitation for19372000 in these catchments was 1232 mm and the standarddeviation was 221 mm. Fig. 2b is a histogram of annual precipita-tion for 19372000. The annual precipitation ranged between 499and 1680 mm. Fig. 3b shows the seasonal variation in precipitationbased on data for 19711980. Precipitation amounts and theirvariations were greater in summer than in winter.

Coniferous forests, comprising Pinus densiora, in the Tatsuno-kuchi-Kita catchment were clearcut in 1937. Broadleaved treesnaturally regenerated and the catchment has been covered withbroadleaved forests since the 1960s (Goto et al., 2006). Daily runoffdata for 19372000 were available from the Forestry and ForestProducts Research Institute (1961), the Forest Inuences UnitOkayama Experimental Site Kansai Branch Station, 1979) and Gotoet al. (2005). Thus, 19471951 data for the deforested period and19931999 data for the forested period were used to evaluate thedifference in low-ow rates between forested and deforestedperiods. Note that some data for 1995 and 1996 were missing andtherefore data for these years were not used in the analysis. A morecomplete description of the catchment was given by Goto et al.(2006).

The Tatsunokuchi-Minami catchment was deforested by forestre in 1959. Coniferous trees (Pinus sylvestris) were plantedimmediately after the forest re and the catchment was coveredwith coniferous plantation forests in the 1970s. However, therewas an insect infestation around 1980 and the coniferous forestsof the catchment were completely destroyed. Broadleaved treesnaturally regenerated and the catchment has been covered withbroadleaved forests since the 1990s (Goto et al., 2006). Dailyrunoff data for 19372000 were available from the Forestry andForest Products Research Institute (1961), the Forest InuencesUnit Okayama Experimental Site Kansai Branch Station (1979),and Goto et al. (2005). We performed three comparisons for thiscatchment to evaluate the differences in low-ow rates betweenforested and deforested periods: (i) 19601964 for the deforestedperiod versus 19731977 for the forested period; (ii) 19731977for the forested period versus 19801984 for the deforestedperiod; and (iii) 19801984 for the deforested period versus19932000 for the forested period. The comparisons evaluatechanges in low-ow rates due to coniferous afforestation, conif-erous deforestation, and broadleaved afforestation respectively.Note that some of the data for 1995, 1996, and 1997 were missingand therefore data for these years were not used in the analysis. Amore complete description of the catchment is given by Goto et al.

tal Management 91 (2010) 814823 815(2006) and Komatsu et al. (2009c).

H. Komatsu et al. / Journal of Environmental Management 91 (2010) 8148238162.1.3. Aichi-Shirasaka catchmentThe mean annual precipitation for 19301990 in the Aichi-

Shirasaka catchment was 1868 mm and the standard deviationwas286 mm. Fig. 2c is a histogram of annual precipitation for 19301990. The annual precipitation ranged between 1358 and 2426 mm.Fig. 3c shows the seasonal variation in precipitation based on datafor 19301938. Precipitation amounts and their variations weregreater in summer than in winter.

The Aichi-Shirasaka catchment was deforested in the 1930s byrepetitive felling for rewood. Such felling was not frequent afterWorld War II and broadleaved and coniferous trees naturallyregenerated. The catchment has been covered with broadleavedand coniferous forests since the late 1970s (Ariyakanon et al.,2000). Daily runoff data for 19301990 are available from TheTokyo University Forest in Aichi (1976, 1977, 1981, 1984, 1987,1999). Thus, 19301937 data for the deforested period and 19831990 data for the forested period were used in evaluating the

Fig. 1. Location of the catchments in this study. SI, SIII, TK, TM, and AS indicate Sarukawa I, Srespectively. Numbers in this gure correspond to the dam reservoirs in Table 2.

Table 1Description of the catchments in this study.

Catchment name Area (ha) Annual precipitation (mm year1) Annua

Sarukawa I 6.6 3032 13.2Sarukawa III 8.2 3032 13.2Tatsunokuchi-Kita 17.3 1232 14.3Tatsunokuchi-Minami 22.6 1232 14.3Aichi-Shirasaka 88.5 1868 15.4difference in low-ow rates between forested and deforestedperiods. A more complete description of the catchment is given byAriyakanon et al. (2000).

2.2. Inow and outow data for dam reservoirs

Daily inow Qin and outow Qout data for dam reservoirs areavailable from the Database of Dams (Ministry of Land, Infrastruc-ture, Transport and Tourism, 2009b). We selected 45 dam reser-voirs across Japan from the database following three criteria. First,one of the purposes of the dam reservoir must be to increase low-ow rates. Second, the dam reservoir must be located in the mostupstream reach of the river system. This criterion enables us toregard Qin as natural ow without modication by dam reservoirs(Kume and Kubota, 1998; Komatsu et al., 2009b). Third, most of thedam watershed must be covered with forest. Table 2 lists theeffective capacity, watershed area, and annual mean Qin of the dam

arukawa III, Tatsunokuchi-Kita, Tatsunokuchi-Minami, and Aichi-Shirasaka catchments

l mean temperature (C) Data years

Forested period Deforested period

19941999 1967197219941999 1967197219471951 1993200019731977, 19932000 19601964, 1980198419301937 19831990

men0

0.1

0.2

0.3

0.4

0 2000 4000 6000

a

H. Komatsu et al. / Journal of Environreservoirs. We used data for 19941999, when there were frequentwater shortages in downstream areas across Japan (Ministry ofLand, Infrastructure, Transport and Tourism, 2009a).

3. Results

3.1. Differences in low-ow rates between forested and deforestedperiods

Fig. 4 shows ow duration curves (FDCs) for the forested anddeforested periods of the ve catchments. In all cases, daily runoffrates for deforested periods were higher than those for forestedperiods for a percentage of time exceeding 50%. Note that wedetermined the forested and deforested periods for each case sothat the mean annual precipitation during the forested period was

0

0.1

0.2

0.3

0.4

0

0.1

0.2

0.3

0.4

500 1000 1500 2000

1000 2000 3000

b

c

Precipitation (mm year - 1 )

y c n

e

u

q e

r f

e

v i t a

l e

R

Fig. 2. Histogram of annual precipitation for (a) Sarukawa I and III, (b) Tatsunokuchi-Kita and Tatsunokuchi-Minami, and (c) Aichi-Shirasaka catchments.0

200

400

600a

J F M A M J J A S O N D

tal Management 91 (2010) 814823 817nearly the same as that during the deforested period (Table 3).Thus, differences in precipitation between forested and deforestedperiods have little impact on the FDCs.

The difference in the mean daily runoff rates for the percentageof time being 95100% between forested and deforested periods dqrangedbetween0.02and0.27 mm day1 for the sevencases (Table3).The dq values relative to mean daily runoff rates for a percentage oftime of 95100% for the forested periods ranged from 22% to 270%.The variation in dq for the three cases of the Tatsunokuchi-Minamicatchment (dq ranging between 0.02 and 0.04 mm day1) wasmuch smaller than the variation among different catchments (dqranging between 0.02 and 0.27 mm day1, Table 3). Thus, thedifference in dq due to deforestation and afforestation was rela-tively minor compared with the difference in dq among differentcatchments on the basis of our datasets. The differences in dq due

0

100

200

300

0

100

200

300

400

b

c

J F M A M J J A S O N D

J F M A M J J A S O N DMonth

Prec

ipita

tion

(mm

month

-1 )

Fig. 3. Seasonal variations in precipitation for (a) Sarukawa I and III, (b) Tatsunokuchi-Kita and Tatsunokuchi-Minami, and (c) Aichi-Shirasaka catchments. Vertical barsindicate standard errors.

menTable 2Description of the dam reservoirs in this study. The table does not include annualoutow data because annual outow was approximately equal to annual inow forthe reservoirs.

No. Dam reservoirname

Effectivecapacity (106 m3)

Watershedarea (km2)

Annual inow(mm year1)

1 Kanna 8 8 9362 Shinkawa 1 7 16763 Hekino 4 8 20804 Terauchi 18 51 12405 Matsubara 47 491 1829

6 Itsuki 12 34 672

H. Komatsu et al. / Journal of Environ818to forest type (coniferous plantation forests for cases 4 and 5 andbroadleaved forests for case 6) were relatively minor comparedwith the differences in dq among different catchments.

Fig. 5 shows the relationship between mean annual precipita-tion and dq. The positive correlation (p < 0.005) indicates greaterdq for higher annual precipitation. This relationship is used forcomparing low-ow rates for forest clearcutting and dam reservoirdevelopment in Section 3.3.

3.2. Increase in low-ow rates due to dam reservoir development

Using Qin and Qout data for the dam reservoirs, we arrangedQout Qin data according to the order of Qin (from higher Qin to

7 Yabakei 21 89 10508 Midorikawa 35 359 16779 Shimachikawa 20 32 161710 Haji 41 308 1121

11 Yasaka 106 301 71212 Nomura 13 168 90513 Ishitegawa 11 73 38214 Sameura 289 417 167315 Ohwatari 52 689 1333

16 Hitokura 31 115 76517 Shorenji 27 100 95018 Nunome 15 75 71519 Hasu 29 81 177520 Mikunigawa 20 76 4098

21 Koshibu 37 288 59122 Akigawa 44 82 128023 Yokoyama 33 471 195824 Ohmachi 29 193 288025 Naramata 85 60 2063

26 Kusaki 51 254 132227 Aimata 20 111 159828 Shimokubo 120 323 52829 Sonohara 14 493 83530 Kawamata 73 179 1274

31 Ikari 46 271 112932 Shichika 100 237 118433 Tamagawa 229 287 388834 Sagae 109 231 272835 Shirakawa 50 205 2457

36 Kamafusa 39 192 132937 Ishibuchi 12 154 252638 Asaseishikawa 43 226 173139 Iwaonai 96 331 146240 Isarigawa 14 113 1369

41 Kanayama 130 470 124642 Kanoko 36 124 57443 Jozankei 79 104 156544 Mirikawa 14 115 253545 Taisetsu 55 292 1478lower Qin). Fig. 6 shows the results for the Shimokubo dam reser-voir. This gure divides Qout Qin data into 20 classes according totheQin value and shows the averageQout Qin value for each class.Qout Qin values were negative for the percentage of time being025% and generally positive for the percentage of time being 25100%. Qualitatively, the same results were observed for most damreservoirs; that is, negative Qout Qin for higher Qin and positiveQout Qin for lower Qin. Thus, dam reservoir developmentgenerally decreased ow rates when natural ow (i.e., Qin) washigh and increased ow rates when natural ow was low.

Wedened theQout Qin value for the percentage of time being95100% as the increase in the low-ow rate due to dam reservoirdevelopment (dQd). dQd ranged between0.95 and 9.02 m3 s1 andthe mean plus or minus standard deviation was 2.63 4.12 m3 s1(Table 4). Here,Qin for the percentage of time being 95100% rangedbetween 0.00 and 8.63 m3 s1. dQdwas positive for 43 of the 45 damreservoirs. Thus, most dam reservoirs increased ow rates whennatural ow was lowest. Fig. 7 shows the relationship between theeffective capacity of dam reservoirs and dQd. A positive correlation(p < 0.001) indicates that larger dam reservoirs contributed moresignicantly to increasing low-ow rates.

We did not use FDCs to examine the increase in low-ow ratesdue to dam reservoir development in the above analysis. Analysisbased on FDCs can lead to misinterpretation of the effect of damreservoir development, as detailed by Komatsu et al. (2009b).Zero Qout is often recorded when high precipitation occurs,which can lead to an interpretation that the dam reservoirdevelopment decreases low-ow rates. This interpretation isincorrect because the zero Qout is due to the operation of thedam gate; when high precipitation occurs, the dam gate istypically operated as for Qout being zero in Japan to prevent oodow. Such misinterpretation does not arise from analysis basedon Qout Qin (Komatsu et al., 2009b).

3.3. Comparison of increases in low-ow rates for forestclearcutting and dam reservoir development

Regressing the relationship between mean annual precipitationand dq (Fig. 5), we obtained an empirical equation for calculatingthe potential increase in low-ow rates due to deforestation fromannual precipitation data. With the input of annual precipitation Pand the area for each damwatershed A, we calculated the potentialincrease in the low-ow rate due to forest clearcutting of the wholearea of each dam watershed dQf:,

dQfhm3 s1

i

0:000147P

hmm year1

i

0:0855A

hkm2

ik (1)

where k is a constant (86.4 106) for the conversion of units. Theabove equation assumes that the results from catchment-scaleexperimental studies are applicable at a watershed scale. Thisassumption is supported by results from the multiscale runoffstudy by Troendle et al. (2001). Annual precipitation for each damwatershed was estimated following the methods described inAppendix.

dQf values ranged between 0.01 and 1.51 m3 s1 (Table 4) and

the mean plus or minus standard deviation was 0.42 0.38 m3 s1.This mean value was lower than that for dQd (2.63 m

3 s1). Fig. 8shows the relationship between watershed area and dQf. Thepositive correlation (p < 0.001) indicates that the variation in dQfamong watersheds was primarily caused by the variation inwatershed area.

Fig. 9a compares dQ with dQ calculated in Section 3.2. Six of the

tal Management 91 (2010) 814823f d

45 samples satised dQf > dQd and the other 39 samples satised

0.01

0.1

1

10

100

0 20 40 60 80 1000.01

0.1

1

10

100

0 20 40 60 80 100

a e

Forested period Deforested period

H. Komatsu et al. / Journal of Environmental Management 91 (2010) 814823 819yad

m

-1 )

0.01

0.1

1

10

100bdQf < dQd. This indicates that the potential increase in low-owrates due to forest clearcutting was less than that due to damreservoir development in most cases. Twenty-ve of the 45samples satised dQf < 0.2 dQd (note that the ratio 0.2 was arbi-trarily determined), indicating that the potential increase in low-ow rates due to forest clearcutting was less than 20% of theincrease due to dam reservoir development in more than half the

Percentage

m( ff

on

uR

0 20 40 60 80 100

0.001

0.01

0.1

1

10

100

0 20 40 60 80 100

0.01

0.1

1

10

100

0 20 40 60 80 100

d

c

Fig. 4. Flow duration curves for the forested and deforested periods for (a) Sarukawa I,19731977), (e) Tatsunokuchi-Minami (19731977 versus 19801984), (f) Tatsunokuchi-Mi

Table 3Annual precipitation (P), low-ow rates for forested (qf) and deforested periods (qd) anqd qf). The low-ow rate is dened as the mean daily runoff rate for ow durations of

Case Catchment Forested period

P (mm year1) qf (

1 Sarukawa I 2881 0.12 Sarukawa III 2881 0.13 Tatsunokuchi-Kita 1189 0.04 Tatsunokuchi-Minami (19601964 vs. 19731977) 1197 0.05 Tatsunokuchi-Minami (19731977 vs. 19801984) 1197 0.06 Tatsunokuchi-Minami (19801984 vs. 19932000) 1204 0.07 Aichi-Shirasaka 1853 0.30.01

0.1

1

10

100fcases. Fig. 9b shows the relationship between watershed area andthe effective capacity of dam reservoirs classied by the relation-ship between dQf and dQd. Data satisfying dQf > dQd and 0.2dQd < dQf < dQd generally corresponded to greater watershed areaand smaller dam capacity. This indicates that forest clearcutting isrelatively effective for these specic conditions but is quite inef-fective for other conditions.

of time (%)

0 20 40 60 80 100

0.1

1

10

100

0 20 40 60 80 100

g

(b) Sarukawa III, (c) Tatsunokuchi-Kita, (d) Tatsunokuchi-Minami (19601964 versusnami (19801984 versus 19932000), and (g) Aichi-Shirasaka catchments.

d the differences in low-ow rates between forested and deforested periods (dq 95100%.

Deforested period dq (mm day1) dq/qf (%)

mm day1) P (mm year1) qd (mm day1)

2 2809 0.30 0.18 1500 2809 0.38 0.27 2703 1179 0.10 0.07 2339 1211 0.12 0.03 339 1205 0.11 0.02 227 1205 0.11 0.04 579 1806 0.59 0.20 51

R2 = 0.80

0

0.1

0.2

0.3

1000 1500 2000 2500 3000Precipitation (mm year-1)

dq (m

m da

y-1)

Fig. 5. Relationship between mean annual precipitation and the difference in themean daily runoff rates for ow durations of 95100% between forested and defor-ested periods dq. The regression line, determined by the least-squares method, isy 0.000147x 0.0855. The correlation is signicantly (p < 0.005) positive according

11 Yasaka 2.16 1.13 0.3112 Nomura 0.73 0.57 0.2113 Ishitegawa 0.23 0.04 0.0414 Sameura 23.05 1.43 0.9615 Ohwatari 2.57 5.50 1.27

16 Hitokura 1.56 0.28 0.1317 Shorenji 1.31 0.36 0.1318 Nunome 1.06 0.07 0.0819 Hasu 1.13 0.53 0.2020 Mikunigawa 1.67 2.79 0.42

21 Koshibu 1.58 0.18 0.2522 Akigawa 3.93 0.56 0.1523 Yokoyama 1.20 4.90 1.2624 Ohmachi 1.39 3.59 0.7525 Naramata 9.02 0.32 0.17

26 Kusaki 0.97 2.04 0.4727 Aimata 1.91 0.91 0.2428 Shimokubo 2.70 0.76 0.2529 Sonohara 0.95 1.67 0.5930 Kawamata 0.07 1.91 0.32

31 Ikari 0.23 1.66 0.4332 Shichika 2.91 2.33 0.3933 Tamagawa 4.84 5.92 1.5134 Sagae 4.90 5.42 0.86

H. Komatsu et al. / Journal of Environmen8204. Discussion

4.1. Differences in low-ow rates between forested and deforestedperiods

We observed increases in low-ow rates with deforestation anddecreases in low-ow rates with afforestation. This agrees withresults of many earlier studies in Japan (e.g., Tamai et al., 2004;Maita et al., 2005) and in other countries (e.g., Brown et al., 2005;Farley et al., 2005).

We found a positive correlation between mean annual precipi-tation and dq. This is supported by two other studies (Farley et al.,

to Pearsons correlation coefcient test.2005; Maita, 2005). Farley et al. (2005) summarized measurementsfor 26 catchments around the world and reported that changes in

-8

-6

-4

-2

0

2

Percentage of time (%)200 6040 10080

Qout - Q

in (m

3 s-1 )

Fig. 6. The difference in outow Qout and inow Qin arranged according to the orderof Qin for the Shimokubo dam reservoir. Vertical bars indicate standard errors.Table 4Increase in low-ow rates due to dam reservoir development (dQd) and forestclearcutting (dQf) and inow rates for the percentage of time being 95100% (Qinlow).

No. Dam reservoir name dQd (m3 s1) Qinlow (m

3 s1) dQf (m3 s1)

1 Kanna 0.16 0.00 0.012 Shinkawa 0.32 0.01 0.023 Hekino 0.04 0.11 0.034 Terauchi 0.35 0.42 0.095 Matsubara 0.10 8.63 1.23

6 Itsuki 0.07 1.90 0.037 Yabakei 1.33 0.29 0.138 Midorikawa 1.26 5.10 0.839 Shimachikawa 0.70 0.16 0.0710 Haji 1.26 1.71 0.48

tal Management 91 (2010) 814823low-ow rates due to afforestation correlated with changes inannual runoff. Maita (2005) summarized measurements for sevencatchments in Japan and reported that changes in annual runoffdue to afforestation and deforestation correlated with annualprecipitation. Therefore, a positive correlation between meanannual precipitation and the difference in low-ow rates betweenforested and deforested periods is expected.

4.2. Increase in low-ow rates due to dam reservoir development

Our results show that dQd was positive for most dam reservoirsand that dQdwas positively correlated with the effective capacity ofdam reservoirs. These results agree with ndings in a previousstudy (Komatsu et al., 2009b), which evaluated increases in low-ow rates for seven existing dam reservoirs located upstream of the

35 Shirakawa 2.55 2.67 0.69

36 Kamafusa 3.00 1.86 0.3537 Ishibuchi 2.67 1.49 0.5338 Asaseishikawa 3.49 4.31 0.5439 Iwaonai 9.96 2.25 0.5840 Isarigawa 0.16 2.60 0.18

41 Kanayama 12.84 4.98 0.6942 Kanoko 1.21 0.81 0.0743 Jozankei 5.37 0.52 0.2044 Mirikawa 1.06 1.72 0.3745 Taisetsu 0.90 4.05 0.52

homogenize natural ow dynamics. This agrees with what was

R2 = 0.64

-5

0

5

10

15

20

25

0 100 200 300

Dam reservoir capacity (106 m3)

dQ

d (m

3 s-

1 )

Fig. 7. Relationship between the effective capacity of dam reservoirs and the increasein low-ow rates due to dam reservoir development dQd. The solid and dotted linesindicate relationships for dQf dQd and dQf 0.2 dQd respectively. The regression line,

0

1

-5 0 5 10 15

dQ

f (m

3 s-

dQd (m3s-1)

200

300

ervo

ir ca

pacit

y (10

6 m

3 )

dQf > dQ

d

0.2 dQd

< dQf < dQ

d

dQf < 0.2 dQ

d

b

H. Komatsu et al. / Journal of Environmennoted by Poff et al. (1997, 2007) and Lytle and Poff (2004), whoexamined river ow data in the United States and reported thatriver ow dynamics are homogenized by dam reservoirdevelopment.

4.3. Comparison of increases in low-ow rates for forestclearcutting and dam reservoir developmentTokyo metropolitan area. Thus, the ndings of the previous studyhold not only in the specic area but all over Japan.

The positive dQd suggests that the dam reservoirs generally

determined by the least-squares method, is y 0.0585x 0.434. The correlation issignicantly (p < 0.001) positive according to Pearsons correlation coefcient test.We compared increases in low-ow rates for forest clearcuttingand dam reservoir development. In reality, forest clearcutting of the

R2 = 0.63

0

0.5

1

1.5

2

0 200 400 600Watershed area (km2)

dQ

f (m

3 s-

1 )

Fig. 8. Relationship between watershed area and the potential increase in low-owrates due to forest clearcutting of the entire watershed of each dam reservoir. Theregression line, determined by the least-squares method, is y 0.00192x 0.0265. Thecorrelation is signicantly (p < 0.001) positive according to Pearsons correlationcoefcient test.2

1 )

dQf = dQ

d

dQf = 0.2 dQ

d a

tal Management 91 (2010) 814823 821whole dam watershed area is unrealistic because it can causeenvironmental problems relating to oods, soil erosion, waterquality, and biodiversity (e.g., Tsukamoto, 1998; Ohte et al., 2001;Brooks et al., 2003). Realistic forestmanagementmethods that havebeen proposed by researchers and journalists and implemented bylocal governments in Japan are patch clearcutting and thinning ofconiferous plantation forests, and conversion to broadleaved forests(e.g., Tsukamoto, 1998; Yorimitsu, 2001; Kuraji, 2003; Amano andIgarashi, 2004). Changes in the ow regime following thesemethods are generally less signicant than those due to forestclearcutting of the whole watershed (e.g., Bosch and Hewlett, 1982;

0

100

0 200 400 600 Watershed area (km2)

Dam

res

Fig. 9. (a) Comparison of the potential increase in low-ow rate due to forest clear-cutting dQf with the increase due to dam reservoir operation dQd. Note that this guredoes not include the sample for the Sameura dam reservoir (dQd 23.05 anddQf 0.96) because of its extreme dQd value. (b) Relationship between watershed areaand effective capacity of dam reservoirs classied by the relationship between dQf anddQd, where dQf is the potential increase in the low-ow rate due to forest clearcuttingand dQd is the increase in the low-ow rate due to dam reservoir development.

menScott and Lesch, 1997; Maita, 2005; Komatsu et al., 2009b).Furthermore, changes in the ow regime due to thinning of conif-erous plantation forests becomes less signicant within severalyears of the treatment possibly because forest gaps developed bythe treatment are lled with branch extensions (Komatsu et al.,2009a). Thus, the effectiveness of forest management in realisticcases should be less than that evaluated in this study for the endmember case (i.e., forest clearcutting of the whole watershed).

To our knowledge, this study is the rst evaluating the potentialincreases in low-ow rates due to forest management relative tothe increases due to the dam development. The results of this studywould not be directly applicable outside Japan because increases inlow-ow rates due to forest management and dam reservoirdevelopment would vary with climatological conditions (e.g.,Fig. 5). However, our method of comparing the low-ow increasedue to forest management and that due to dam reservoir devel-opment is applicable to many other countries. Our method onlyrequires daily runoff data on deforested or afforested catchmentsand daily inow and outow data of dam reservoirs, which arereadily available in many countries. Thus, this study can enhanceexaminations on the effectiveness of forest management relative todam reservoir development for securing water resources.

5. Conclusions

The potential increase in the low-ow rate due to forest clear-cutting was estimated as being lower than the increase due to damreservoir development in most cases. Thus, our analysis clariedthat forest management is generally far less effective for waterresource management than the construction of dam reservoirs is inJapan. Only when the watershed area is great and the capacity ofdam reservoirs small can forest management be an effectivemethod of water resource management.

The Japanese public widely believes that forest managementcan be an alternative to dams and many local governments haveintroduced taxes to aid forest management. However, our resultsdo not support this common belief. Thus, the present public policyon water resource management in Japan needs to be reconsidered.

Acknowledgments

We express sincere thanks to Ms. Chiyoko Kumagai and Mr.Kenji Tsuruta (Kyushu University, Japan) for providing catchmentrunoff data. We also thank Mr. Yoshinori Shinohara (KyushuUniversity, Japan) for fruitful discussion on the selection of damsand accuracy of precipitation data. Thanks are also due to twoanonymous reviewers for their critical and constructive comments.This research has been supported by a Grant-in-Aid for ScienticResearch from the Japanese Ministry of Education, Culture, Sports,Science and Technology (#20780119) and a CREST project (Devel-opment of innovative technologies for increasing in watershedrunoff and improving river environment by the managementpractice of devastated forest plantation).

Appendix. Methods for estimating annual precipitation

Annual precipitation was estimated by summing the meanannual inow Qin and mean annual evapotranspiration for eachdam watershed. Mean annual evapotranspiration was assumed as600 mm year1 for the Hokkaido region, 1000 mm year1 for theOkinawa region, and 800 mm year1 for the other regions (Fig. 1),which were typical values (Komatsu et al., 2008b). Watershed-averaged precipitation is often estimated more accurately if basedon Qin data than if based on precipitation data taken at a station in

H. Komatsu et al. / Journal of Environ822the watershed or near the watershed in Japan (Tsuchiya, 2005;Sawano, 2006) owing to the large variation in precipitationamounts and sparse distribution of precipitation measurementpoints in forested areas.

Note that determination of annual evapotranspiration is notcritical for our results because variations in annual evapotranspi-ration between regions are much smaller than variations in annualrunoff (Komatsu et al., 2008b), and annual Qin is generally greaterthan annual evapotranspiration in Japan (Table 2).

When using precipitation data taken by the Japan Meteorolog-ical Agency (2009) at a station in/near each dam watershed, ourresults varied somewhat but not substantially. We compared thepotential increase in the low-ow rate when forests in each damreservoirs watershed were clearcut (dQf) with the increase due todam reservoir development (dQd) in Section 3.3. When themeasured precipitation data were used, four of the 45 samplessatised dQf > dQd and the other 41 samples satised dQf < dQd.Twenty-nine of 45 samples satised dQf < 0.2 dQd. Data satisfyingdQf > dQd and 0.2 dQd < dQf < dQd usually corresponded to greaterwatershed area and smaller capacity of dam reservoirs, similar towhat is seen in Fig. 9b.

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H. Komatsu et al. / Journal of Environmental Management 91 (2010) 814823 823

Water resource management in Japan: Forest management or dam reservoirs?IntroductionMaterials and methodsCatchment runoff dataSarukawa I and III catchmentsTatsunokuchi-Kita and Tatsunokuchi-Minami catchmentsAichi-Shirasaka catchment

Inflow and outflow data for dam reservoirs

ResultsDifferences in low-flow rates between forested and deforested periodsIncrease in low-flow rates due to dam reservoir developmentComparison of increases in low-flow rates for forest clearcutting and dam reservoir development

DiscussionDifferences in low-flow rates between forested and deforested periodsIncrease in low-flow rates due to dam reservoir developmentComparison of increases in low-flow rates for forest clearcutting and dam reservoir development

ConclusionsAcknowledgmentsMethods for estimating annual precipitationReferences