HYDROLOGICAL RESPONSE OF LAND USE CHANGE IN
MOUNTAINOUS SUB-WATERSHEDS OF THE MEKONG RIVER BASIN
Tsuyoshi Kinouchi
Department of Environment Science and Technology, Tokyo Institute of Technology,
4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan

ABSTRACTIn the Mekong River basin, Lao PDR, relocation of villages and governmental restriction
to the slash and burn agriculture has been in operation since 1980s. These social and politicalbackgrounds could possibly alter basin-wide land use and land cover status and cause adversehydrological impacts. However, no analysis was conducted based on measurement data to reveal
the land use change and relate it to watershed-scale hydrological responses. Thus, this study
aims at revealing the hydrological impacts of land use changes in mountainous sub-watershedsof the Mekong River basin by analyzing rainfall-runoff response and trends of monthly rainfall
and streamflow.
Out of the five sub-watersheds analyzed, the apparent land use change was found between
1993 and 1997 in Nam Khan, Nam Ou and Nam Suong watersheds, where shrub lands increased
and upland agriculture conversely decreased. Corresponding to this change, annual runoff ratio
increased by more than 10 points in Nam Khan and Nam Suong watersheds. On the other hand,none to slight changes in land use were found for Nam Lik and Nam Ngum watersheds, whichcorrespond to relatively constant or even decreasing runoff ratios. The seasonal Kendall test
revealed increasing trends of areal rainfall in May for four watersheds, and comparatively
strong increasing trend of streamflow in July was found for watersheds where drastic land usechange occurred in 1990s.

1.

INTRODUCTION

In the Mekong River basin, Lao PDR, where slash and burn agriculture has long been
managed, relocation of villages from highlands to riparian and roadside areas proceeded for
economical development and restricting expansion of shifting cultivation (Thongmanivong et al.,2006). In addition, governmental policy to restrict the slash and burn agriculture has been in
operation since the 1990s for the conservation of forests. As a consequence, the land use has
been reportedly changed, resulting in the shortened fallow periods and degraded fertility ofagricultural lands. However, no analysis clearly revealed possible hydrological consequences ofsuch a land use change. Thus, this study aims to analyze the impacts of land use changes on
streamflow to provide scientific information for national policy makers by looking into
meteorological and hydrological trends and rainfall-runoff relations for the tributary watershedsof the Mekong River basin using measurement data obtained in the past two decades.

1

2

STUDY AREA AND DATA
Nam Ou2.1 General characteristics ofstudy area
This study focuses on thehydrological impact of land use andland cover changes in uplandagricultural regions located in thenorthern Laos. Study areas are selectedbased on the data availability ofrainfall, streamflow and land usechange during a certain period of year.
Sub-watersheds of the Mekong Riverbasin selected for this study are Nam
Ou, Nam Suong, Nam Khan, Nam
Ngum and Nam Lik (Figure 1), whichhave catchment areas of 20,087km2,
6,578km2, 7,455km2, 8,430km2 andrespectively.
These
4,795km2,
watersheds are located in the altitude
ranging from 250m to 2,160m above
mean sea level (Figure 1).
2.2

Nam Suong
Nam
Khan
Nam
Lik

Nam
Ngum

Figure 1. Location of five sub-watersheds.

Data source and availability

Hydrological and meteorological
data such as daily streamflow andprecipitation has been measured since
1920s and is available from the
Mekong River Commission (MRC)
and the Department of Meteorology
and Hydrology of the LaoPDR (DMH),
but includes discontinuities andmissing data values (Table 1). Datameasured in recent two decades areused in this study even these data
includes missing values during acertain period and thus the number ofmeasurement sites suit for trend
analysis is limited. Figure 2 and 3
show the locations of streamflow andrainfall gauging sites, of which dataobtained at stations listed in Table 1 isused for analysis. Data availability issummarized in Table 1, in which thenumber of month with missing data is
specified. In addition, a gridded
rainfall data (Yatagai et al., 2008),
which was interpolated from multiplepoints rainfall data, is utilized toconsider spatial variability of rainfall

Figure 2. Location of gauging stations.
(Left: streamflow, right: rainfall)
Table 1. Number of month with missing data.
(up: streamflow, bottom: rainfall)
Station / Year85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06
0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 0 12 12
Ban Mixay
12 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ban Naluang
Ban Hin Heup 10 12 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 12
Ban Sibounhom 12 12 0 0 0 0 0 0 8 0 0 0 0 0 0 0 0 0 0 0 12 12
12 12 3 4 3 0 0 0 10 6 1 0 0 0 0 0 0 1 0 12 12 12
Muong Ngoy
Station / YearBan Hinheup
Vang Vieng
Sengkhalok
Luang Prabang
Ban Naluang
Xiengkhouang
Muong Ngoy
Oudomxay
Phongsaly

85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06
12 12 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 0 0 0 0 12
12 12 0 7 0 0 0 0 0 0 1 0 1 4 0 0 0 0 0 0 0 012 12 12 8 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0 12
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 012 12 12 12 12 12 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 012 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 012 12 12 12 12 12 12 12 0 12 0 12 0 0 0 0 0 0 0 0 0 012 12 12 12 12 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 12
12 12 12 0 12 0 0 0 8 0 1 4 0 0 0 0 0 0 0 0 0 12

2
Impact of land use change in the Mekong River basin

over large mountainous areas.
3

LAND USE CHANGE

In 1980s, the relocationof the upland population tolower elevations and roadside
areas
began
aimingat
restricting expansion of shifting
cultivation while extending
government services to ruralvillages (Thongmanivong et al.,2006). Since then, Lao PDR
hasundergonearapid
economictransformation
toward a market economy(Fujita and Phanvilay, 2008).
Providing secure resource andproperty rights particularly
became an important issue inthe early 1990s as a way topromoteinvestment
andefficient use of land, thus the<1993><1997>
Land and Forest Allocation
Figure 3. Land use distribution in five sub-watersheds.
(LFA) Policy was introduced in
the early 1990s as a means of legitimately recognizing the customary rights of local communities
to use and manage land and forest resources and it was proclaimed in 1996 (Fujita and Phanvilay,
2008). LFA policy regulated household access to upland swidden and fallow lands, by limiting
householders’ access to three or four plots, which resulted in shortening of the fallow period
from the traditional interval, which generally extends 7 to 15 years (Fujita and Phanvilay, 2008).
The substantial impact of LFA policy enforcement can be found in national statistics that showsa large area of upland agriculture has declined even during the short period of years between
1995 and 2000.
To investigate the hydrological impacts of recent land use changes in the Northern Laos,the land use and land cover status was analyzed for five sub-watersheds shown in Figure 1. Landuse data obtained from MRC, which is originally produced from Landsat ETM, was used.
Original land use types are reclassified after Thongmanivong and Fujita (2006) as shown in thelegend of Figure 3. It is clearly seen that the areas of upland agriculture significantly reduced andconversely turned into shrub lands, especially in the downstream area of Nam Suong and Nam
Khan watersheds, and the upstream area of Nam Ou watershed. The land use ratios in eachwatershed are summarized in Figure 4. The ratio of forest shows no substantial change between
1993 and 1997 for all watersheds, although its magnitude is quite different from each other. Nam
Suong and Nam Lik watersheds have the lowest and the highest forest ratios, respectively. The
ratio of Shrubs increased in Nam Ou, Nam Khan and Nam Suong watersheds by 18%, 17% and25%, respectively, while the ratio of upland agriculture decreased by almost the same amounts ineach watershed. The increase of shrubs and grassland occurred probably as a result of the
3

1.0

1.0

1.0

0.8

0.8

0.8
0.6

Nam Ou
0.4

0.4

0.2

0.2

0.0

Nam
Suong

0.4
0.2

0.0
1993

Year

1997

0.0
1993

1.0

1.0

0.8

0.8

Nam
Khan

Ratio

Ratio

0.6

Ratio

0.6

Year

1997

1993

Year

1997

Water
Built up land
Barren land or rock

Nam Lik
0.6

Permanent agriculture

Nam
Ngum

Ratio

Ratio

0.6
0.4

0.4

0.2

0.2

0.0

0.0

Upland agriculture
Grass
Shrub
Forest

1993

Year

1997

1993

Year

1997

Figure 4. Land-use change between 1993 and 1997.
succession of abandoned swidden areas to secondary forest due to the implementation of LFA
policy (Thongmanivong and Fujita, 2006). Opposed to extensively performed upland shifting
cultivation in those watersheds, Nam Ngum and Nam Lik watersheds show a little change ofratio in each land use type, probably due to relatively low land use ratio of the shifting
cultivation.

4

HYDROLOGICAL RESPONSE CHARACTERISTICS

4.1

Monthly rainfall and stream discharge

The mean monthly rainfalls measured at 9 gauging stations in recent years (1999 - 2005)
are shown in Figure 5. Monthly rainfall during the wet season (May to September) varies muchdepending on the location of gauging station. Vangvieng and Ban Naluang, where elevations are
below 300m, recorded larger magnitudes compared with other stations located in higher altitude
such as Xiengkhouang (1,060m) and Oudomxay (550m). Vangvieng and Ban Naluang are both
located at the outlet of valleys, which connect northern uplands and southern flat plains with anabrupt change in elevation. The reason of larger rainfall recorded at these stations would be thatthe vapor transported from the south is urged to converge and form the clouds over the areas. As
the streamflow in the watersheds of this study is emerged mainly from the rainfall during the wet
season, the spatial variability of the rainfall during the wet season poses great uncertainties inseparating the hydrological impact of land use change on streamflow.
To understand hydrological behaviors of watersheds under the circumstances of
meteorological variability and the land use change, the monthly areal rainfall (R) and monthly
4
Impact of land use change in the Mekong River basin

4.2

Runoff ratio

Rainf all and streamflow (mm)Rainf all and streamf low (mm)Monthly rainfall (mm)900
discharge (Q) are drawn in Figure 6
Ban Hin Heup
for three separate periods during
800
Luang Prabang
Phongsaly
1987 - 2002. Areal rainfall is700
Vangvien
calculated using a product called
600
Ban Naluang
Sengkhalok
APHRO_EA_V0804 (Yatagai et al.,500
Muong Ngoy2008) to average the spatial
Oudomxay
400
Xiengkhouang
variability. The mean areal rainfall
300
of Nam Suong watershed is less200
during 1997-2002 than that during100
1987-1992, but the mean monthly0
streamflow is higher in 1997-2002
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
than in 1987-1992. In contrast, mean Figure 5. Monthly rainfall for the period 1999 – 2005.
monthly streamflow at Ban Naluang
400
Basin: Nam Suonglocated in Nam Ngum watershed
R (1987-1992)
Rainf all: APHRODITER (1994-1996)
Streamf low: Ban
300
shows little difference between the
R (1997-2002)
Q (1987-1992)
same two periods, although the mean
Q (1994-1996)
200
areal rainfall is larger during 1997Q (1997-2002)
2002. The different behavior of two
100
watersheds in the rainfall-runoff
response is possibly explained by
0
Jan
Feb
Mar
Apr MayJun
Jul
Aug Sep
Oct
Nov Dec
land use changes enhanced by the600
LFA policy started in 1990s as well
Basin: Nam Ngum
Rainf all: APHRODITE
500
as the uncertainty in estimating theStreamf low: Ban Naluang
R (1987-1992)
R (1993-1996)
areal rainfall and other factors such
400
R (1997-2002)
as the soil condition and rainfall
Q (1987-1992)
300
Q (1993-1996)
intensity.
Q (1997-2002)
200
100
0

Jan
Feb
Mar
Apr MayJun
Jul
Aug Sep
Oct
Nov Dec
The rate of precipitation that
Figure6.
Monthlyrainfallanddischarge
fordifferent
emerged as runoff from a watershedperiods (up: Nam Suong, bottom: Nam Ngum).
in each year, namely the annual
runoff ratio, was quantified to extract
the impact of land use change in the five sub-watersheds (Figure 7). Two types of rainfall data
are used for each watershed, i.e., data obtained at a single gauging station and areal rainfall
estimated from APHRO_EA_V0804 (shown by APHRODITE in Figures 6 and 7). The runoff
ratio of Nam Suong watershed, when areal rainfall was applied, shows a strong increasing trend
over the studied period. Nam Khan and Nam Ou show slight to moderate increasing trends ofannual runoff ratio, but no distinct trend was observed for Nam Ngum watershed. Extremely
large runoff ratio is calculated for Nam Lik watershed when areal rainfall is applied. This isprobably due to the underestimation of areal rainfall caused by limited data availability.
Although it is uncertain if a single gauging station represents the areal rainfall magnitude, using
rainfall data observed at Vangvieng gives reasonable values of runoff ratio probably due to that
Nam Lik watershed is relatively small and most part of the watershed lies under the topographic
condition similar to Vangvieng. Mean annual runoff ratios in two separated periods are
summarized in Figure 8. It must be noted that the different averaging period is used in eachwatershed depending on the data availability of streamflow, and the mean runoff ratios for Nam

5

Lik are calculated using point rainfall at
Vangvieng. Figure 8 clearly shows that therunoff ratio increased in watersheds where asignificant land use change was detected(Figure 4).

0.7
Nam OuRunof f ratio

0.6
0.5
0.4
0.3
0.2

APHRODITE
Phongsaly

0.1
0.0

0.7

RAINFALL

0.6

AND
Runof f ratio

5
TREND OFSTREAMFLOW

Rainfall and streamflow are interrelated
by watershed-scale physical and biologicalprocesses such as evapo-transpiration,
infiltration and groundwater outflows. In
addition, land use change due to the restricted
shifting cultivation and more commercialized
agriculture would affect the interrelation byincreasing the surface runoff and reducing thewater storage in the surface soil layers. To
estimate the change of hydrological system
response incurred by the land use and land
cover change, a statistical trend analysis wasapplied. If a significant trend in streamflow isfound, that should be a composite impact ofsystem’s inputs, i.e., rainfall and land usechange in each watershed. Negative trend in
one input variable and positive trend in theother input variables can cancel out the trendof output. Thus, to understand the trend of
rainfall and streamflow and relate them to theland use change would give some information
about the possible change in the watershedscale hydrological system response.

Nam Suong

0.5
0.4
0.3
0.2

APHRODITE
Luang Prabang

0.1
0.0
1985

1990

1995

2000

2005

0.7
Nam Ngum

Runof f ratio

0.6
0.5
0.4
0.3
0.2

APHRODITE

0.1

Ban Naluang

0.0
1985

1990

1995

2000

2005

0.7
Nam Khan

0.6
Runof f ratio

0.5
0.4
0.3
0.2

APHRODITE

0.1

Luang Prabang

0.0
1985

1990

1995

1.2
Runof f ratio

2005

APHRODITE
Vang Vieng

Nam Lik

1.0

2000

0.8
0.6
0.4
0.2
0.0

Trend test

Trends of monthly rainfall andstreamflow are analyzed by the seasonal
Kendall Test (Hirsch et al., 1982). The null
hypothesis Ho is that the data (Xi, i=1,2, …, n)
are a sample of independent and identically
distributed random variables. The test statistic
S is defined with the mean E(S) and thevariance V(S) as follows.

1985

1990

1995

2000

2005

Figure 7. Runoff ratio derived using areal
rainfall (APHRODITE) and point rainfall.
0.5

～1992

1997～

Nam KhanNam Lik

0.4

Runoff ratio

5.1

0.3
0.2
0.1
0
Nam OuNam Suong

Nam Ngum

Figure 8. Mean runoff ratio in two periods.
6
Impact of land use change in the Mekong River basin

(1)i =1 j = i +1

⎧ 1 if θ > 0⎪sgn(θ ) = ⎨ 0 if θ = 0⎪− 1if θ < 0⎩
E (S ) = 0

(2)
(3)

n
⎧
⎫
V ( S ) = ⎨n(n − 1)(2n + 5) − ∑ t m m(m − 1)(2m + 5)⎬ 18
m =1
⎩
⎭

(4)

Rainfa ll (mm/month)nRainfall (mm/month)n −1

S = ∑ ∑ sgn( X j − X i )500

May & June

400
300

Nam NgumNam Lik200
100
085 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02

700
600
500
400
300
200
100
0

July & Aug.

Nam NgumNam Lik

85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02

standard normal
cumulative distribution function and thesignificance level, respectively.

Slope estimator B(mm/month/year)

Rainfall (mm/month)400
where tm is the number of ties of extent m. The
Nam Suong
May & June
300
standardized statistic Z follows the standard
Nam Khannormal distribution. In a two-sided test for trend,200
the hypothesis Ho100⎧ S −1shouldbe>0S0⎪85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02
accepted if |Z| ≦⎪ V (S )(5)
S =0
Figure 9. Monthly areal rainfall in two months.
where Z = ⎨ 0zα/2,⎪ S +120
FN(zα/2) = α/2, FN
S <0⎪
Nam Ouand α being the⎩ V (S )Nam Suong

15
10

Nam KhanNam Lik
Nam Ngum5
The Seasonal Kendall slope estimator
B was used to quantify the trend magnitude.
0
In addition, the normalized Seasonal
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Kendall slope estimator B’ was introduced
Figure 10. Seasonal Kendall slope estimator forto quantify the relative magnitude of trends
areal rainfall during 1987-2002.
against the monthly average of streamflow.
n −1

n

B=∑ ∑

k =1 j = k +1

X j − Xkj−k(6), B ′ = B / Q (7)where B is the Seasonal Kendall slope
estimator of each month and Q is the mean
monthly streamflow.
5.2 Trend of precipitation andstreamflow

Slope estimator B(mm/month/year)

40
30
20
10

Luang Prabang
Ban Hin Heup
Vang Vieng
Sengkhalok
Ban Hin Heup

0
-10

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

-20
-30

Figure 11. Seasonal Kendall slope estimator for
point rainfall during 1987-2002.

Figure 9 shows examples of areal
rainfall derived from APHRO_EA_V0804. During May and June, monthly rainfall is increasing
for both Nam Lik and Nam Ngum watersheds, while such a trend is not seen for Nam Khan and
Nam Suong watersheds. Part of the reason for the increase can be attributable to theunderestimation of areal rainfall in 1985 and 1986, when the gauging data is only available at
Luang Prabang (Table 1). For this reason, the seasonal Kendall Test of the monthly areal rainfall
7

Slope estimator B (mm/month/year)

12
Muon Ngoy (Nam Ou)
10

Ban Sibounhom (Nam Suong)
Ban Mixay (Nam Khan)

8

Ban Hin Heup (Nam Lik)Ban Na Luang (Nam Ngum)

6
4
2
0

Jan Feb Mar Apr May Jun

Jul Aug Sep Oct Nov Dec-2

Figure 12. Seasonal Kendall slope estimator formonthly flow depth during 1987-2002.
Streamflow (m3 /s)

800
600

Ban Hin Heup, July

400
200
0
1987

1989

1991

1993

1995

1997

1999

2001

1995

1997

1999

2001

800

Streamflow (m3 /s)

was applied to the five watersheds
during the period 1987 - 2002. The
slope estimator B for data representing
a trend with the significance level of
5% was shown in Figure 10. All thewatersheds except for Nam Ou
watershed showed increasing trends in
May with the significance level of 5%,
while Nam Ou and Nam Ngum
watersheds showed distinct trends inJuly and August, respectively (Figure10). The increasing trend in May isconsistent with the earlier onset of wet
season alleged from local people.
Trends of monthly point rainfalls werealso analyzed with the same
significance level for the same period(actual period of analysis depends onthe data availability shown in Table 1).
In this case, significant increasing
trend was found at Vang vieng for May
and June, and two other points also
showed positive trends in May. Trendsof monthly areal rainfall during the wet
season are likely due to a composite
result of point rainfall with different
trend characteristics.

600

Ban Sibounhom, July

400
200
0
1987

1989

1991

1993

Figure 13. Monthly mean streamflows of Nam Lik(Ban HinHeup) and Nam Suong (Ban Sibounhom)during 1987-2002.

Normalized slope estimator

The result of trend test for themonthly streamflow was shown in
15
Muon Ngoy (Nam Ou)
Ban Sibounhom (Nam Suong)
Figure 12, in which streamflow was
Ban Mixay (Nam Khan)
converted to the flow depth by
Ban Hin Heup (Nam Lik)
10
considering the catchment area of eachBan Na Luang (Nam Ngum)
watershed. In contrast to the areal
5
rainfall trends (Figure 10), a strong
increasing trend of the flow depth was
found for July, except for the Nam Lik0watershed. In principle, runoff is
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
generated with some delay due to the-5water storage in relatively dry
watersheds (Figure 6), thus the trend Figure 14. Normalized slope estimator for monthly
mean streamflow during 1987-2002.
detected for the streamflow in July ispossibly corresponds to the increasing
trends of rainfall in May. However, areal rainfall of Nam Suong and Nam Ou watersheds shows
smaller or even no trend in May, while the increasing trend of streamflow in July is larger for the
Nam Ou river (Muon Ngoy station) and the Nam Suong river (Ban Sibounhom station, see also
Figure 13). These results indicate that drastic land use changes due to the abandoned swidden
8Impact of land use change in the Mekong River basin

and increased shrub over the northern part of the Mekong basin can be related not only to theincreasing runoff ratio but also to the increasing trends of streamflow. These hydrologicalimpacts can be explained by some reasons such as reduced evapo-transpiration and soil
permeability. For Nam Lik watershed, where no trend of streamflow was found for July (Figure13), it is considered that the impact of increasing areal rainfall is alleviated by the forest thatcovers more than 40% of the watershed. It is interesting to note that the normalized slope
estimator shows increasing trends of streamflow even in the dry season (from October to April),especially for Ban Na Luang in Nam Ngum watershed (Figure 14). As indicated in Figure 9, astrong increasing trend of areal rainfall in May is followed by a moderate trend in August for
Nam Ngum watershed. This implies that the larger amount of rainfall during the wet season,
especially in May and August, contributed to the increased streamflow in the subsequent periods
including the dry season.

6

CONCLUSIONSThis study aimed to better understand the hydrological response of the land use and land
cover change in the upper Mekong River basin located in LaoPDR. Under limited hydrologicaland meteorological data availability, annual runoff ratio estimated for five sub-watersheds for theperiod since the middle of 1980s showed increases by more than 10 points in Nam Khan and
Nam Suong watersheds, where a drastic change in the land use and land cover was found. This is
likely due to the introduction of the National Land Allocation policy and the relocation ofvillages to the lowland areas. On the other hand, none to slight changes in land use were foundfor Nam Lik and Nam Ngum watersheds, which correspond to relatively constant or evendecreasing runoff ratios. The seasonal Kendall test showed increasing trends of areal rainfall in
May for four watersheds, which support alleged early onset of the wet season. Increasing trendsof Streamflow in July is partly due to the increased rainfall in May, but the streamflow trend wassignificant for watersheds where drastic land use change occurred in the 1990s.

7

REFERENCES

Fujita, Y. and Phanvilay, K., 2008. Land and Forest Allocation in Lao People’s Democratic Republic:
Comparison of case studies from community-based natural resource management research, Society
and Natural Resources 21:120–133, DOI: 10.1080/08941920701681490.
Hirsch, R. M., Slack, J. R. and Smith, R. A., 1982. Techniques of trend analysis for monthly water quality
data, Water Resources Research 18(1), 107–121, doi:10.1029/WR018i001p00107.
Thongmanivong, S. and Fujita, Y., 2006. Recent land use and livelihood transitions in northern Laos,
Mountain Research and Development Vol 26, No.3, 237–244.
Thongmanivong, S., Phanvilay, K., Fujita, Y. and Fox, J., 2006. Agrarian land-use transformation innorthern Laos, 2nd international conference on Sustainable Sloping Lands and Watershed
Management 190-199, Luang Prabang, Lao PDR.
Yatagai, A., Kawamoto, H. and Xie, P., 2008. Product and validation of GAME re-analyses and JRA-25:
Precipitation, Third WCRP International Conference on Reanalysis, Tokyo, Japan.

9