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Presented by Luna Bharati at the Global Water Systems Project: Water in the Anthropocene Conference May 21-24th in Bonn, Germany.
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Water for a food-secure world
Current and Future Variability in the Hydrological Regime of the Koshi Basin, Nepal
L. Bharati , P. Gurung and L. Maharjan
Basin Characteristics
Area considered in this study is the Koshi Basin upstream of Chatara in the mountainous region of eastern Nepal and southern Tibet (57,760 km2)
The average elevation of the basin is 3,800 m but varies from 110 m at Chatara to more than 8,000 m in the Great Himalayan Range
The basin can be divided into the Trans-mountain Region, Central Mountain Region, Eastern Mountain Region, Central Hill Region and Eastern Hill Region
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#*
#*
#*
#*
#*
#*
#*#*
#*
#*
#*
#*
#*
#*#*
4300
4000
2223
2222
2221
14191406
1404
1325
1324
1307
1303
13011220
1213
1212
1206
1115
1108
1103
1062
1022
1006
285885
695690
684
681
670652
650647
630
620
606
668.5
627.5
604.5
Ü
0 50 10025 km
Legend
#* Flow Station
!( Climate Station
Rivers
Koshi Basin Boundary
Country Boundary
INDIA
CHINA
NEPAL
INDIA
INDIA Ü
1
8
6
2
4
3
5
14
9
32
17
51
7
16
78 73
11
18
10
75
12
45
34
27
13
5762
65
58
56
15
38
5560
72
23
71
30
61
53
54
36
6967
44
66
42
35
59 64
40
74
70
19
47
43
4137
68
7679
28
77
29
20
31
48 5249
63
39
2225
50
33
46
2624
21
LEGEND
Country boarder
Subbasin
Trans-mountain region
Central mountain region
Eastern mountain region
Central hill region
Eastern hill region0 40 80 12020 km
Ü
Study Area: Koshi River Basin
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Water for a food-secure world
Projected Climate Data for Climate Change Study:
Downscaled using MarkSim Weather Generator (RCM)
(http://gismap.ciat.cgiar.org/MarkSimGCM/)
- Average of CNRM-CM3, CSIRO-Mk3.5, ECHam5, and MIROC3.2
- AR4-SRES: BL, A2 and B1
- Period: 2000s (1971-2000) for BL
2030s (2016-2045) for A2 and B1
2050s (2036-2065) for A2 and B1
- Variable: Rainfall, Temperature (Max & Min), Solar Radiation
Methods: Input Data
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Water for a food-secure world
Results: Spatial Distribution of Precipitation, Actual ET and Water Yield
•Average annual precipitation is highest in the Central Mountain (1775 mm) and Eastern Mountain Regions (1418 mm)
•The lowest rainfall during both the dry and wet season is the Trans-mountain region (mean precipitation was 113 mm during the dry season and 307mm during the wet season
1
8
6
2
4
3
5
14
9
32
17
51
7
16
78 73
11
18
10
75
12
45
34
27
13
5762
65
58
56
15
38
5560
72
23
71
30
61
53
54
36
6967
44
66
42
35
59 64
40
74
70
19
47
43
4137
68
31
7679
28
48
77
29
22
20
46 5249
63
39
25
50
33
2624
21
LEGEND
Precipitation (mm)
294 - 350
351 - 500
501 - 1000
1001 - 1500
1501 - 2000
2001 - 2500
2501 - 3000
3001 - 3500
3501 - 4000
4001 - 45000 50 10025 km
Ü(a)
1
8
6
2
4
3
5
14
9
32
17
51
7
16
78 73
11
18
10
75
12
45
34
27
13
5762
65
58
56
15
38
5560
72
23
71
30
61
53
54
36
6967
44
66
42
35
59 64
40
74
70
19
47
43
4137
68
31
7679
28
48
77
29
22
20
46 5249
63
39
25
50
33
2624
21
LEGEND
Actual ET (mm)
189 - 250
251 - 300
301 - 350
351 - 400
401 - 450
451 - 600
601 - 650
651 - 700
701 - 750
751 - 8170 50 10025 km
Ü(a)
1
8
6
2
4
3
5
14
9
32
17
51
7
16
78 73
11
18
10
75
12
45
34
27
13
5762
65
58
56
15
38
5560
72
23
71
30
61
53
54
36
6967
44
66
42
35
59 64
40
74
70
19
47
43
4137
68
31
7679
28
48
77
29
22
20
46 5249
63
39
25
50
33
2624
21
LEGEND
Net Water Yield (mm)
23 - 50
51 - 100
101 - 500
501 - 1000
1001 - 1500
1501 - 2000
2001 - 2500
2501 - 3000
3001 - 3500
3501 - 40000 50 10025 km
Ü(a)
• ET is mainly related to precipitation as
well as land cover
•During both the dry and wet seasons, average Actual ET is highest in the Central and Eastern mountain region and lowest in the Trans-mountain region
• Water yield is highest also in
the mountain region and lowest in the Trans-mountains
• Range is quite big with lowest of 5mm during the dry season in Trans mountain region to 1629 mm in the Central mountain zone
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Water for a food-secure world
Results: Simulated Seasonal Flow Contribution
Simulated seasonal flow contribution in annual flow under current and future climate
Under 2030s Projection
Under 2050s Projection
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Water for a food-secure world
Percent change in precipitation during the a)winter, b)pre-monsoon,
c)monsoon and d)post-monsoon seasons under the A2 climate
projections for the 2030’s
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Water for a food-secure world
Percent change in flow volume during the a)winter, b)pre-monsoon,
c)monsoon and d)post-monsoon seasons under the A2 climate
projections for the 2030’s
Change in Monsoon Rainfall
SRES Family – A1B
WRF-ECHAM5 WRF-GFDL-V2 WRF-HADCM3
PRECIS-HadCM3Q0 RegCM4-ECHAM5 WRF-CCSM3
Change in Monsoon Max. Temperature
WRF-ECHAM5 WRF-GFDL-V2 WRF-HADCM3
PRECIS-HadCM3Q0 RegCM4-ECHAM5 WRF-CCSM3
SRES Family – A1B
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Water for a food-secure world
Results: Minimum, maximum and mean precipitation in the Central mountain region
of the Koshi Basin for observed, baseline, A2 and B1 projections for the 2030’s and 2050’s
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Water for a food-secure world
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Water for a food-secure world
Summary of Results for the Koshi Basin
• (i) Higher maximum precipitation during monsoon and post-monsoon and lower maximum precipitation during winter (in A2 and B1 scenarios)
• (ii) Increase in precipitation and flows in the Trans Mountain region during all the seasons except for flows during the monsoon under the B1 scenario
• (iii) Increase in post-monsoon precipitation and routed flow volumes in the whole basin (under A2 and B1 scenarios)
• (iv) Decrease in winter precipitation and routed flow volumes in all the regions except the Trans Mountain
• (v) Increase in the frequency of high flow peaks and decrease in the base flow portion of runoff.
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Water for a food-secure world
• Understanding of and adapting to existing climate variability as well as the changes in variability is critical for adaptation to future climates
• There is still high level of uncertainty in future Climate Change projections
• Instead of planning for certain trends, adaptation strategies need to plan for future uncertainty…
– Will future climate lead to exposer that is outside the boundaries of past data ranges
– increased frequency of extreme events such as both high-flows and low-flows
– Investments in systems which reduce risk such as storage development, crop insurance schemes might be more effective
Conclusions
