IJERD – International Journal of Environmental and Rural Development (2018) 9-1

Research article
erdApplication of TOPMODELs for Assessment of Ecosystem
Services: Regulating Service in Agricultural and Forest
Watershed
KOSUKE MUKAE
Graduate School of Agriculture, Tokyo University of Agriculture, Japan

KOJI MIWA
Institute of Environmental Rehabilitation and Conservation, Tokyo, Japan

HIROMU OKAZAWA*
Faculty of Regional Environment Studies, Tokyo University of Agriculture, Japan
Email: h1okazaw@nodai.ac.jp

TADAO YAMAMOTO
Research Faculty of Agriculture, Hokkaido University, Hokkaido, Japan

TAKASHI INOUE
Research Faculty of Agriculture, Hokkaido University, Hokkaido, Japan
Received 13 January 2018

Accepted 5 May 2018(*Corresponding Author)

Abstract According to Millennium Ecosystem Assessment, ecosystem services are divided
into four services. Among them, regulating services include water regulation and natural
hazard regulation which regulate water-discharge to rivers and mitigate flood risk by forest
ecosystem. This research investigated characteristics of river flow changes at the time ofrainfall runoff in two different land-use types, i.e.,1) watershed forest in Soebethu riverwatershed in Hokkaido and 2) intermixed watershed forest and pastureland in Igarashi riverwatershed in Hokkaido. A semi-distributed hydrological model, TOPMODEL was applied
to simulate the amount of water discharge to the rivers. The conventional TOPMODEL wasapplied to the watershed forest, and the developed version of TOPMODEL to theintermixed watershed and pastureland. Monte Carlo simulation was used to identify
unknown parameters required for the simulation. By comparing the identified parameters in
the two different watersheds, flood control effect was evaluated in both land-use watersheds
and each watershed and pastureland separately in the intermixed land-use. As the results ofcomparing the unknown parameters between the different land-use in the intermixed
watershed and pastureland, the model showed that watershed forest has higher regulating
service than pastureland. In addition, the research found that the difference of the type of
surface soil influenced the amount of water discharge, that is, flood control effect. As theconsequence, TOPMODEL was applicable for quantitative assessment of water regulation:
the regulating service of the forest ecosystems.
Keywords TOPMODEL, ecosystem services, hydrological model, watershed, land-use

INTRODUCTION
Ecosystem services that prosper by the coexistence with agriculture provide various benefits tohuman life. According to Millennium Ecosystem Assessment (MEA) initiated by the United
Nations, ecosystem services are categorized into four services, ‘Provisioning’, ‘Regulating’,‘Cultural’ and ‘Supporting’ services. Regulating services that this paper focuses on, contain theflood risk alleviation by water storing function of forests such as riparian forest, and risk reductionof flood and sediment disasters by vegetation cover. In general, valuing ecosystem services can bedone by monetary valuation such as hedonic approach and travel cost (Smith, 1993). However,Ⓒ ISERD

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IJERD – International Journal of Environmental and Rural Development (2018) 9-1

such monetary valuation is considered an incomplete method to evaluate ecosystem services (Kateet al., 2007). Although there is also qualitative method to evaluate environmental value except formonetary valuation, there is no previous study which evaluated the regulating service in Japan.
This research applied a hydrological model, TOPMODEL to evaluate the flood control effectof forestland and pastureland. The target areas are two watersheds which differ in land-use fromone another. One is a simplex land-use formed by only forestland, and another is the complex landuse by forestland and pastureland. TOPMODEL is a semi-distributed model, to predict waterrunoff within a watershed scale (Beyen et al., 1979), and a conceptual model where has been
confirmed its applicability in many parts of the world (David, 1993; Tada et al., 2002; Ali et al.,2015; Gao et al., 2015). TOPMODEL is a distribution model that divides a watershed into grids
and calculates the surface flow generated in each grid. However, it regards the groundwater flow as
a lumped model by considering the flow as one group in a watershed. Therefore, TOPMODEL iscalled a semi-distributed model. For this reason, the conventional TOPMODEL was applied to asimplex land-use watershed, and a developed TOPMODEL was developed to enable the prediction
in a complex land-use (Mukae et al., 2017). TOPMODEL is mainly applied to a watershedconsisted of a simple land-use, for example a watershed only consisting of forest (Tada et al., 2002).
On the other hand, there are few studies which applied to an agricultural watershed which both offorest and agriculture lands are mixed.
OBJECTIVE
This research applied the conventional TOPMODEL to a simplex land-use watershed and adeveloped TOPMODEL to a complex land-use watershed. It aimed to evaluate the applicability ofboth models for the prediction of water-runoff and the flood control effect in the different land-use
types of the watersheds. Unknown parameters between the conventional and the developed models
were compared to evaluate them.
METHODOLOGY
Research Site

Fig. 1 The Shubuto River Basin, Hokkaido, JapanThe objective sites of this research are watersheds of the Igarashi River and the Soebetsu River.
Both of them, in fact, are the size of stream rather than river and tributaries of the Shubuto River,located in southwestern Hokkaido, Japan (Fig. 1 and 2). The Igarashi River watershed has the areaof 6.9 km2 and the river length is 7.3 km. This watershed consists of a complex land-use with 2.7
km2 of pastureland in the downstream basin and 4.2 km2 of forestland in the upper and middle
basin, which covers 31% and 69% of the watershed respectively. This pastureland is mainly used
for livestock and there is cropland land in a part of the upper basin. Therefore, this watershed
contains the land-use of agricultural and forest lands. On the other hand, the watershed area of theSoebetsu is 11.5 km2, and the river length is 11.1 km. It is a simplex land-use only consisted offorestland. Since these watersheds are close to each other, the meteo-hydrological data such as
precipitation amount and evapotranspiration for the both areas are similar.
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IJERD – International Journal of Environmental and Rural Development (2018) 9-1

Fig. 2 Land-use of Igarashi River Watershed (Left) and Soebetsu River Watershed (Right)
This research used data of the daily record of river discharge and precipitation from June 1,
1998 to October 31, 1998 observed by Okazawa, et al. (2002). With these data, the applicability ofthe developed version of TOPMODEL is analyzed. Penman-monteith method (Allen, 1998) isapplied for calculation of daily evapotranspiration. The daily data of temperature, wind speed andhours of sunshine which are required to calculate daily evapotranspiration, are obtained from
AMeDAS in Kuromatsunai Town managed by Japan Meteorological Agency.
TOPMODEL
TOPMODEL is a semi-distributed model suggested by Beven et al. (1979). This model divides soil
layer into root zone, unsaturated zone and saturated zone. The semi-distributed model calculates
the upper layer which contains root and unsaturated zones by each grid as a distribution type. For
the lower layer, which is saturated zone, it is calculated as concentration type, thus every grid has
the same value. TOPMODEL has a character that calculates the status of drying state of surface
layer of basin from the topographical index (TI) induced from digital elevation model (DEM) andspatially evaluates the amount of the surface-flow. TI is calculated from flow accumulation areaand slope of each grid. If TI’s value is large, the grid can be storage more water. But, If TI's value
is small, the grid can be storage little water. So, Unsaturated zone is distribution model because it iscalculated using Topographic Index. So, Soebethu river watershed can be storage little water than
Igarashi river watershed.
Computational Procedure of TOPMODELTOPMODEL considers three storage parts, root zone, saturated zone and unsaturated zone as seenin Fig. 3, and calculates in each grid in the watershed as described below.

Fig. 3 Histogram of Topographic IndexⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2018) 9-1

a) Water balance equation of root zone: In root zone, the amount of water that can be stored
within the root zone is calculated from the water balance of rainfall (R) [L], actual
evapotranspiration amount (ETa) [L], water available amount within root zone (SRmax) [L] andstorage deficit in root zone (SRZ) [L]. When redundant water, (EXi) [L] is caused in root zone
(SRZ<0), the redundant water is supplied to unsaturated zone and added to storage water (SUZi)[L]in that zone. Potential evapotranspiration (ET0) is calculated by Penman-Monteith (PM) method,and ETa is treated as the function of ET0, SRmax and SRZ.
ET
E Aa

§
SRZ t ·¸¸
ET0 ¨¨1 © SRMAX ¹(1)b) Water balance equation of saturated zone: The base-flow Qsub [LT-1] from the wholewatershed is treated as the concentrated amount per watershed. Base-flow is calculated by thefollowing equation using the mean value of downslope transmissivity when the soil is just saturated(Te) [L2T-1], the mean topographic index of watershed (λ) [-], the mean storage deficit in watershed,( ) [L] and model parameter (m):
Qsub

§ S ·
Te exp  O exp ¨  i ¸
¨ m¸
©
¹

Si

m  ln

UZi

SUZi
Si  td(2)c) Water balance equation of unsaturated zone: Unsaturated zone is a temporary water storage
zone that connects between root zone and saturated zone. It is calculated as a distribution model.
The mean storage deficit amount in the watershed at the starting point of calculation, is obtained
from Eq. (3), assuming that the initial discharge at the start is Q0 [LT-1].
Q0
Te exp  O(3)
Si in Fig. 4 expresses the storage deficit of each grid [L] and obtained from Mukae et al.
(2017). UZi is the amount of water supply from unsaturated zone to saturated zone [L], i is thenumber of grid. However, because a grid which has the same value as TI is regarded ashydrological similarity, a grid is calculated in each status class of TI rather than that the wateramount is calculated in each grid (Fig. 4).
If Si is 0 or negative, that class is regarded as saturation. Therefore, the excessive water inflow
from root zone is return surface-flow (EXi). If Si is positive, the excessive water inflow is
temporarily added to SUZi. UZi is(4)
where td is a parameter that expresses the period of retention.
These [LT-1] are the concept of TOPMODEL. Operation of the model requires to determine
five unknown parameters,”m”, “Te”, “td”, “SRmax”, and “SRZ0”. This research determined the
optimal value of five parameters by Monte Carlo method. Monte Carlo method is the generic termof a numerical simulation that uses random numbers.

Fig. 4 Concept of TOPMODELⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2018) 9-1

TOPMODEL for Combined Forestland and Pastureland
In general, TOPMODEL is applied to a simple land-use at forest watershed. However, this study
discusses the applicability of the developed TOPMODEL which considers the difference of landuse between forestland and pastureland, that is, a watershed with a complex land-use (see Fig. 5).
The followings explain how this research calculated the complex land-use.
1) Land-Use Division
The area of forestland and pastureland in the Igarashi’s watershed is obtained from the 100 m meshdata of Land classification in National Land Numerical Information provided by the Ministry ofLand, Infrastructure, Transport and Tourism of Japan. The ratio of land-use for each forestland andpastureland was 61% and 39 % respectively. From this, the mean topographic index of forestland,(λ1) and pastureland (λ2) is calculated.
2) Computational Procedurea) Water balance equation of saturated zone: From Eq. (5), the base-flow of the wholeforestland, Qsub1[LT-1] and the base-flow of the whole pastureland, Qsub2[LT-1] are calculated. Then,the summation of the both values is regarded as the base-flow from the whole watershed.
(5)

Qsub = Qsub1 + Qsub2b) Water balance equation of unsaturated zone: It is necessary to gain the initial river discharge(Q01，Q02)[LT-1] from forestland and pastureland to gain the storage shortage (Si1, Si2) of each gridof forestland and pastureland. Here it assumed that the ratio of flow amount from the both offorestland and pastureland is always constant, and obtained the initial value of the river discharge
in the following equation.
Q0 = KQ0 + (1 - K )Q0(6)
Here, it assumed that the ratio of water outflow from the forestland to the whole watershed isK(0<K<1), the ratio of pastureland is (1-K), and K is an unknown parameter.
c) Other calculation: When it calculates root zone, UZi, it divides the watershed into forestlandand pastureland. From this, it determines the eleven unknown parameters “m1”, “Te1”, “td1”,“SRmax1”, “SRZ01”, “m2”, “Te2”, “td2”, “SRmax2”, “SRZ02” and “K” for the developed TOPMODEL.

Fig. 5 Concept of Developed Version of TOPMODEL
Method of Identification and Comparison of Unknown Parameter
This research determined the optimal values of the 11 unknown parameters for the developed
TOPMODEL by using Monte Carlo method. Through the method, generating random numbers forⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2018) 9-1

each 11 unknown parameter, “m1”, “Te1”, “td1”, “SRmax1”, “SRZ01”, “m2”, “Te2”, “td2”, “SRmax2”,“SRZ02” and “K”, 100,000 sets of combination were created. As the result of 100,000 times ofcalculation, it obtained the combination that accords the closest between the actual value of flow
amount and the estimated value.
RESULTS AND DISCUSSION
The actual value of rainfall and river discharge and the predicted values generated by bothconventional TOPMODEL and developed TOPMODEL are shown in Fig. 6 for the Igarashi and
Fig. 7 for the Soebetsu. Both models estimated changes of river discharge according to the changesof rainfall accurately. In addition, the developed TOPMODEL showed the closer value to the actual
value than the conventional one when the river discharge decreases after it reached the peak point.
The compatibility of the actual value of river discharge and the estimated value is evaluated byNash-Sutcliffe coefficient (NS value) and Root Mean Squared Error (RMSE). Regarding theaccuracy of prediction in the function value, the conventional TOPMODEL showed 0.823 for NS
and 1.069 for RMSE. On the other hand, the developed TOPMODEL showed 0.853 for NS and
0.973 for RMSE. From these values, it confirms that the developed TOPMODEL has the higher
accuracy of prediction of river flow changes by rainfall than the conventional one throughout thetarget period.
The optimal value of unknown parameters of the conventional TOPMODEL and thedeveloped TOPMODEL were determined by the Monte Carlo method as seen in Table 1. The
developed model showed the higher value in Te and td than the conventional one. Besides that, thedeveloped model showed that these two values are higher in forestland than those in pastureland.
As Te expresses the downslope transmissivity when the soil is just saturated, forestland has bettertransmissivity than pastureland. According to Ohte et al. (1989) and Ohta et al. (1989),
transmissivity of forestland is generally high in Japan. This is because the transmissivity inpastureland is lowered due to soils compressed by tiller machine or tractor. For this reason, it isvalid that Te is higher in forestland than pastureland.
A parameter, td expresses the delayed time caused by when water moves from unsaturated tosaturated zone. That is, it shows that water flows more slowly from unsaturated to saturated zone in
the developed model than the conventional one.
Comparting the unknown parameters between the forest watersheds in the Igarashi and theSoebetsu, the values except coefficient of saturated hydraulic conductivity showed the almost samevalues. The reason for the same value is that forest watersheds in the Igarashi and the Soebetsu are
adjacent to the watershed, both of which are considered to have forestland. On the other hand, thecause of the gap in the coefficient of saturated hydraulic conductivity is probably attributed to thesurface soil. The surface soil is composed by conglomerate and sandstone in the Igarashi watershed,
and by mudstone in the Soebetsu watershed. Since transmissivity is lower in mudstone thanconglomerate and sandstone (Ogata et al., 1992), it is considered that coefficient of saturated
hydraulic conductivity in the Soebetsu watershed is lower. From these, it confirms that in case thatwatersheds have the same water system and land-use, the unknown parameters except coefficientof saturated hydraulic conductivity can be the same values and the difference of the coefficient iscaused by the surface soil.
Table 1 Comparison of Unknown Parameters
unknown parameterm (mm)Te (mm/d)

td (mm/d)

SRZ 0 (mm)SR max (mm)Sobetsu (Conventional)

26.1

1.0×104

0.02180.13

0.88

Igarashi (Conventional)

46.0

2.5×1040.01040.52

0.62

0.02060.42

0.85

0.01980.43

0.49

Igarashi(developed)

forestland

24.5

9.0×104

grassland

81.6

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K

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IJERD – International Journal of Environmental and Rural Development (2018) 9-1

RainfallQobs

Qsim conventional model

Qsim developed model
0
50
100
150

10

200
250
300

Rainfall mm/d（(mm/d)
Rainfall（River-discharge（
mm/d（River-discharge (mm/d)

100

350
1
1-Jun

400
16-Jun1-Jul

16-Jul

31-Jul15-Aug30-Aug

14-Sep29-Sep14-Oct29-OctFig. 6 Comparison between the conventional and the developed TOPMODEL
RainfallQobs

Qsim Conventional
0
100
200

10

300
400
500

1
1-Jun

Rainfall mm/day（(mm/d)
Rainfall（River-discharge (mm/d)
River-discharge（
mm/day（100

600
16-Jun1-Jul

16-Jul

31-Jul15-Aug30-Aug

14-Sep29-Sep14-Oct29-OctFig. 7 Comparison between the conventional TOPMODELCONCLUSION
By comparing the unknown parameters between a simplex land-use and a complex land-use withapplication of the conventional TOPMODEL and developed TOPMODEL, it showed the result that
forest watershed has higher flood control effect than pasture watershed. Besides that, it is expectedthat the value of coefficient of saturated hydraulic conductivity is related to the type of surface soil.
For these reasons, this research clarified if the water system and land-use are the same, theunknown parameters except coefficient of saturated hydraulic conductivity in TOPMODEL gain
the close values, and coefficient of saturated hydraulic conductivity is influenced by surface soil.
Therefore, flood control effect as a regulation service which one of the ecosystem services isevaluated by the application of the conventional TOPMODEL and developed one.
For future study, this research result should apply to other agricultural and forest watersheds
and different water system by using the same method to evaluate the ecosystem service moreaccurately.
ACKNOWLEDGEMENTS
This research was supported by the grant-aid from Tokyo University of Agriculture in Japan, andby the joint usage/research program of the Institute of Materials and Systems for Sustainability(IMaSS), Nagoya University.
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IJERD – International Journal of Environmental and Rural Development (2018) 9-1

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