Presented by Luna Bharati at the Global Water Systems Project: Water in the Anthropocene Conference May 21-24th in Bonn, Germany.

1. www.iwmi.org
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

2. 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
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
!(
#*
#*
#*
#*
#*
#*
#*
#*
#*
#*
#*
#*
#*
#*
#*
4300
4000
2223
2222
2221
1419
1406
1404
1325
1324
1307
1303
1301
1220
1213
1212
1206
1115
1108
1103
1062
1022
1006
285885
695
690
684
681
670
652
650
647
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
57
62
65
58
56
15
38
55
60
72
23
71
30
61
53
54
36
69
67
44
66
42
35
59 64
40
74
70
19
47
43
41
37
68
76
79
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 region
0 40 80 12020 km
Ü
Study Area: Koshi River Basin

3. www.iwmi.org
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

4. www.iwmi.org
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
57
62
65
58
56
15
38
55
60
72
23
71
30
61
53
54
36
69
67
44
66
42
35
59 64
40
74
70
19
47
43
41
37
68
31
76
79
28
48
77
29
22
20
46 52
49
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 - 450050 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
57
62
65
58
56
15
38
55
60
72
23
71
30
61
53
54
36
69
67
44
66
42
35
59 64
40
74
70
19
47
43
41
37
68
31
76
79
28
48
77
29
22
20
46 52
49
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
57
62
65
58
56
15
38
55
60
72
23
71
30
61
53
54
36
69
67
44
66
42
35
59 64
40
74
70
19
47
43
41
37
68
31
76
79
28
48
77
29
22
20
46 52
49
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

5. www.iwmi.org
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

6. www.iwmi.org
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

7. www.iwmi.org
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

8. Change in Monsoon Rainfall
SRES Family – A1B
WRF-ECHAM5 WRF-GFDL-V2 WRF-HADCM3
PRECIS-HadCM3Q0 RegCM4-ECHAM5 WRF-CCSM3

9. Change in Monsoon Max. Temperature
WRF-ECHAM5 WRF-GFDL-V2 WRF-HADCM3
PRECIS-HadCM3Q0 RegCM4-ECHAM5 WRF-CCSM3
SRES Family – A1B

10. www.iwmi.org
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

11. www.iwmi.org
Water for a food-secure world

12. www.iwmi.org
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.

13. www.iwmi.org
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