Generation Challenge Programme (GCP) project number: G3008.09
Project title: Breeding drought tolerance for rainfed lowland rice in the Mekong region
Location: Asia; Thailand, Laos, Cambodia and Australia
Lead institute, Principal Investigator: Boonrat Jongdee, BRRD, Thailand
Collaborators (institute[s], researcher[s]):
Phoumi Inthapanya, NAFRI, Laos
Ouk Makara, CARDI, Cambodia
Shu Fukai and Jaquie Mitchell, The University of Queensland, Australia
Grienggrai Pantuwan, BRRD, Thailand
Contact: Jaquie.mictell@uq.edu.au for further information or permission to utilise maps
This work has been the product of collaboration between at least 10 scientists and their support
staff working across 4 countries.
Thavone Inthavong, Phoumi Inthapanya and Sipaseuth (NAFRI, Laos); Boonrat Jongdee, Grissana
Lintawana and Grienggrai Pantuwan (BRRD, DOA Thailand); Veasna Touch and Makara Ouk
(CARDI, Cambodia) and Jaquie Mitchell and Shu Fukai (University of Queensland, Australia)
Simulation modelling for defining target drought environments
In order to determine drought environment characterization we utilised a water balance model
that incorporates deep percolation rate as a function of soil clay content. Full description of
the model is given in Inthavong et al. (2011). For determining the length of growing period
(LGP), start of growing period (SGP) was defined as the time when three continuous weeks
of field water storage within the surface layer was greater than field capacity, while end of
growing period (EGP) was defined as the time when the amount of water storage within the
surface layer was lower than wilting point. The LGP was then determined by the duration of
the period between SGP and EGP (Inthavong et al., 2012). Key input data for the model are
rainfall and soil clay and sand content. Key meteorological and soils data were compiled for
each country and maps generated based on model output. The maps generated for each
individual region or country utilised the rainfall from data available within or close (Laos
used a number of NE Thailand rainfall stations) to this region, while the maps generated
across region used all rainfall stations available across the region for interpolation. It would
now be useful given that all rainfall data has been compiled to re-run the models within
countries based on rainfall interpolation across the region and compare results, this could be
done in a future project.
Across Countries of the Mekong (Thailand, Laos and Cambodia)
The Mekong region is dominated by a monsoonal climate with a distinct wet (May to
October) and dry (November to April) season. Median annual rainfall decreases from highs
of 3600 mm in Laos and the northeast corner of Thailand to as low as 600 mm in southern
Cambodia and western provinces in NE Thailand (Figure 11a). As noted by Inthavong et al
(2011) 90% of annual rainfall is received during the wet season however variability in timing
and amount is high and can lead to intermittent drought through the season, early-season
drought occurring mid-June to mid-July or late- season drought occurring late-September to
October.
The simulated results of start, end and length of the growing period are indicated in Fig 11.
The start of the growing period varied from week 14 in parts of northern NE Thailand, with
most of Laos starting between week 18-20 to as late as week 32-36 which reflected the very
late on-set of wet season in parts of western NE Thailand and SE Cambodia. In general the
variation in end of growing season was less than the start of growing season. The growing
season finishes earliest in weeks 38-40 in parts of NE Thailand, to week 40-42 in Laos in
eastern Savannakhet while as late as weeks 50-51 marks the end of growing season in SE
Cambodia. The map of length of the growing period (Fig 11d) indicates that the shortest
growing seasons, as short as 14-16 weeks, are located in the western part of NE Thailand and
a large extent of rice growing areas in Cambodia. In general, the likelihood of severe drought
in rice fields is considerably higher in provinces of NE Thailand and Cambodia than Laos
where lengths of growing season ranged from 17-32 weeks. As noted by Inthavong et al
(2012) for Savannakhet rainfall has a large influence on field water stored however, short
LGP and an early finish of the growing season were also associated with low soil clay
content. The regions identified with short LGP in the Mekong were often associated with low
clay content.
a)
c)
b)
d)
Figure 11: a) Annual rainfall (median); b) start; c) end; and d) drought prone areas as
identified by length of growing period (weeks); for Mekong region (Thailand, Laos and
Cambodia) estimated from soil-water balance method using median weather data from 294
meteorological and hydrological stations.
Soil data:
Laos: The level of resolution varies across countries depending on data availability.
Inthavong et al (2012) collected over 300 soil samples from Savannakhet province and
consequently the model output in terms of standing water and hence length of growing season
estimates are well correlated to that observed in field trials (Inthavong et al. 2011; 2012).
Thailand: Input data for soils was extracted for 161 point-locations where rainfall data was
available from Thailand Land Development Department (LDD, 1996) digital soil map
database.
Cambodia: The 294 soil profiles consisted of 97 sites collected from the provinces around
Tonle Sap Lake including Banteay Meanchey, Kampong Thom, Kampong Chhnang, Pursat,
Battambang, and Siem Reap. Data was available for 28 sites from the plateau region of
Cambodia located in Steung Treng, and Kampong Speu. There were 35 sites across the three
provinces of Koh Kong, Phreah Sihanouk, and Kampot province all based in the coastal zone.
In the plain area there were 42 and 35 soil profiles positions collected in Kampong Cham and
Takeo province respectively. A further 57 points were distributed across Kandal, Svay Rieng,
and Prey Veng provinces; and Phnom Penh.
Rainfall:
Laos: Annual rainfall ranged from as high as 2200-3700 mm in Vientiane province to as low
as 1300-1900 mm in Savannakhet with parts of southwest Champassak only receiving
1500mm annually (Figure12a). However, a large portion of the rainfed rice paddies are found
in areas with above 2200 mm annually.
Thailand: The daily rainfall data from 136 rainfall stations and 25 meteorological stations
totalling 161-point locations were obtained for 10 years (1999-2008) courtesy of the Thailand
Meteorological Department (Figure 12b). The weekly rainfall and PET of the periods 19992008 of 161-point locations were utilised as input to the model to generate the weekly rainfall
surfaces at 5 km cell resolution (i.e. 52 weeks). Annual rainfall in NE Thailand ranged from
600 mm in south west corner (eg. Nakon Ratchassima), to as high as 2400 mm in far north
eastern province of Nong Khai.
Cambodia: The daily rainfall data are available from 88 rainfall stations. The number of years
was not consistent. Some stations had more than 10 years data such as Phnom Penh (CARDI
and Pochentong stations), or Kampong Cham. However, some stations like Battambang had
data which spans across 65 years but there were a lot of gaps over the years (eg 25 years of
discontinuous data). The annual rainfall stations used in this study were selected from stations
where the median annual rainfall data was greater than 640 mm (below this value was
considered to be potentially erroneous or missing data recording). In the coastal area, rainfall
ranged from 1,600-3,280 mm. However, the rainfall in the central area where the rainfed
lowland rice is predominantly grown ranged from only 640-1200 mm. The southern part of
the country was identified as very low rainfall especially Takeo, Kampong Speu, Kandal, and
some part of Prey Veng. The North-East part of Cambodia was also considered as drought
prone in Pailin and Banteay Meanchey province (Figure 12c).
a)
b)
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Khai
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Rainfall (mm)
Pr ovince
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Rain-Station
Ann-Rainfall (mm)
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d)
Figure 12. Median annual rainfall pattern for a) Laos; b) Northeast Thailand; c) Cambodia
median and d) Cambodia mean interpolated from 45 (Laos), 161 (Thailand), 88 (Cambodia)
rainfall sites respectively.
a)
b)
d)
e)
g)
h)
c)
f)
i)
Figure 13. a, d, g) Start; b, e, h) end and c, f, i) length of growing period for a, b, c)
Savannakhet; d, e, f) Champassak and g, h, i) Vientiane province, Laos, estimated from soilwater balance method
Figure 14. Drought prone areas in Laos as identified by length of growing period, estimated
by the soil-water balance method.
Growing period
Laos
The SGP was earliest on the western side of Savannakhet (SVK) starting week17-19 (Fig
13a), this was similar to SGP in Vientiane (VTN) while much of Champassak (CPK) began
in week 18-19.
The EGP was earliest in SVK in the northwest with EGP finishing W38-40 while CPK and
VTN finished between week 44-48, with a few districts finishing W40-42 in western CPK
and southern VTN.
As a consequence the LGP was shortest in western SVK with some areas having less than 21
weeks. The shortest duration in CPK was 21-24 weeks but this extended to an average of 2729 weeks. The majority of VTN province was as long as 27-29 weeks. Thus CPK and VTN
are more likely to be prone to intermittent drought stress, while SVK may tend to have late
season drought.
Thailand
The start of growing seasons (SGP) for Thailand starts from W17 to as late as W36 (MidApril-late August) beginning from the upper right corner, along the Mekong River, Nong
Khai, Sakonakorn and downwards Mukdahan Province and end of SGP towards Southwest
corner at Nakhon Ratchasim and Chaiyaphum Provinces (Figure 15a).
The end of growing period (EGP) occurs from W33-48 (Mid- August-late November),
occurring earlier in the upper right corner, Nong Khai, Sakonakorn and downwards
Mukdahan Province and later towards Southwest corner at Nakhon Ratchasim and
Chaiyaphum Province (Figure 15b).
As a result of SGP and EGP, length of rice growing period ranged from as short as 9 to 34
weeks (Figure 15c). Generally, the LGP in as many as 13 provinces in NE Thailand was less
than 14 weeks, thus extremely prone to drought. However, provinces near the Mekong River
tended to have lengths between 14 and 26 weeks, with these areas more prone to intermittent
drought.
a)
b)
Nong Khai
Loei
Udon Thani
End Growing Period
Kalasin
Mukdahan
Khon Kaen
Chaiyaphum
Umnat Charoen
Roi Et
Yasothon
Maha Sarakham
Ubon Ratchathani
Surin
Nakhon Ratchasim
Si Sa Ket
Buri Ram
N
W
Sakon Nakhon
Loei
Nakhon Phanom
Nong Bua Lamphu
Start Growing Period
Wtr-body-NE.shp
Wet Land-NE.shp
Province
SGP (Week)
16 - 18
18 - 20
20 - 22
22 - 24
24 - 26
26 - 28
28 - 30
30 - 32
32 - 34
34 - 36
No Data
Nong Khai
Sakon Nakhon
Wtr-body-NE.shp
Wet Land-NE.shp
Province
EGP (Week)
28 - 30
30 - 32
32 - 34
34 - 36
36 - 38
38 - 40
40 - 42
42 - 44
44 - 46
46 - 48
48 - 50
No Data
Udon Thani
Nakhon Phanom
Nong Bua Lamphu
Kalasin
Mukdahan
Khon Kaen
Chaiyaphum
Umnat Charoen
Roi Et
Yasothon
Maha Sarakham
Ubon Ratchathani
Surin
Nakhon Ratchasim
Si Sa Ket
Buri Ram
N
E
W
100
0
S
100 Kilometers
100
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S
0
100 Kilometers
c)
Nong Khai
Sakon Nakhon
Loei
Length Growing Period
Wtr-body-NE.shp
Wet Land-NE.shp
Province
LGP (No. Weeks)
8 - 10
10 - 12
12 - 14
14 - 16
16 - 18
18 - 20
20 - 22
22 - 24
24 - 26
26 - 28
28 - 30
30 - 32
No Data
Udon Thani
Nakhon Phanom
Nong Bua Lamphu
Kalasin
Mukdahan
Khon Kaen
Chaiyaphum
Umnat Charoen
Roi Et
Yasothon
Maha Sarakham
Ubon Ratchathani
Surin
Nakhon Ratchasim
Si Sa Ket
Buri Ram
N
W
100
E
S
0
100 Kilometers
Figure 15. a) Start; b) end and c) length of growing period for northeast Thailand estimated
from soil water balance method.
Cambodia
a)
b)
c)
Figure 16. a) start; b) end and c) length of growing rice growing period in Cambodia
estimated from soil-water balance method.
The estimated Start of Growing Period (SGP) from the simulation was overlayed on the rice
growing area map (Figure 16a). The early start of the growing season were found in some
parts of Siem Reap, Pursat, Kampong Thom, Kampong Chhnang, and Svay Rieng ranging
from week 17-23 which are April to June. In the plain zone of Svay Rieng, Takeo, Prey
Veng, Kampong Speu, Kandal, and the Tonle Sap zone such as some part of Pursat and
Battambang provinces were identified as starting growing season late ranged from week 3338 which is August to September.
The End of Growing Period (EGP) came early in some parts of Siem Reap, Pursat, Kampong
Chhnang, Kampong Speu, and Takeo from week 46-48 which is in November (Figure 16b).
The growing season finished later (week 50-51, December) in some parts of Prey Veng, Svay
Rieng, Takeo, Kandal, and Battambang. The Length of Growing Period (LGP) estimated for
some parts of Svay Rieng, Takeo, Kampong Speu, Prey Veng, and Banteay Meanchey were
short ranging from only 10-16 weeks (Figure 16c). The longest growing duration were found
in some parts of Banteay Meanchey, Siem Reap, Kampong Thom, Kampong Chhnang,
Kampong Cham, and Takeo province.