A comprehensive approach and methods for glacial lake outburst flood risk assessment, with examples from Nepal and the transboundary area

Figures & data

Figure 1 Step-by-step approach for glacial lake outburst flood risk assessment and management.

Table 1 Potentially dangerous lakes in Nepal, by priority.

Priority	Number	Lake ID (Lake name)
1	6	Kotak_gl_0009 (Tsho Rolpa), Koaru_gl_009 (Lower Barun), Kodud_gl_0184 (Imja Tsho), Kodud_gl_0036 (Lumding), Kodud_gl_0242 (West Chamjang), Ganmar_gl_0018 (Thulagi/Dona)
2	4	Kotam_gl_0133 (Nagma), Kodud_gl_0241 (Hungu), Kodud_gl_0193 (Tam Pokhari), Kodud_gl_0229 (Hungu)
3	11	Kotam_gl_0191, Gakal_gl_0004, Koaru_gl_0012 (Barun), Kodud_gl_0238, Gabud_gl_0009, Kodud_gl_0220, Koaru_gl_0016, Gakal_gl_0008, Kotam_gl_0111, Kodud_gl_0239, Gakal_gl_0022

Source: after ICIMOD (2011).

Figure 2 Locations of study area and lakes selected for detailed investigation.

Figure 3 Schematic diagram of the steps used in GLOF modelling and inundation mapping. Note: HEC-GeoHMS =  Hydrologic Engineering Center Geospatial Hydrologic Modeling System Extension; HEC-GeoRAS =  Hydrologic Engineering Center Geospatial River Analysis System; HEC-RAS =  Hydrologic Engineering Center River Analysis System; BOSS DAMBRK =  Boss International dam-break flow simulation model; NWS BREACH =  National Weather Service dam-breach flood forecasting model.

Figure 4 Maximum discharge and time for flood to reach selected downstream locations.

Figure 5 Maximum discharge and flood depth at selected downstream locations.

Table 2 Land, people, and houses potentially affected by glacial lake outburst floods.

Elements exposed	Imja (Dudhkoshi)	Tsho Rolpa (Tamakoshi)	Thulagi (Marsyangdi)	Lumuchimi (Bhotekoshi/ Sunkoshi)^a
Land (ha)
Total	1,010	833	1,133	944
Cultivated	314.3 (377.8)	26.8 (129.3)	32.6 (109.2)	36.2 (166.5)
People
Severely affected	5,784 (7,762)	1,985 (5,183)	953 (3,808)	5,782 (16,313)
Highly affected	96,767	141,911	165,068	101,397
Moderately affected	501,773	524,323	2,044,145	727,185
Houses	445 (808)	145 (330)	125 (298)	731 (2,113)

Note: Values for modelled GLOF scenario (values in brackets for maximum affected level).

a ¹Nepal part of watershed.

Table 3 Crops potentially exposed to glacial lake outburst floods (in tonnes).

Crops	Imja (Dudhkoshi)		Tsho Rolpa (Tamakoshi)		Thulagi (Marsyangdi)		Lumuchimi (Bhotekoshi/ Sunkoshi)
	Model	Max	Model	Max	Model	Max	Model	Max
Paddy	686.7	696.3	57.3	248	50.9	237	122.5	384.5
Wheat	138	252.4	6.4	52.1	0	0	23.8	94.5
Maize	469.2	478.5	27	179	85.1	334.6	72.9	258.5
Millet	74.2	82.6	1.8	120	0	10.6	13.8	82.4
Potato	43.9	277.9	15.6	54.8	105	157.5	1.5	53.2
Vegetables	3	13.6	6.1	13.2	64	64	166.3	586.8
Other	0	0	0	0	23.8	36.6	27.3	54.4
Total	1,415	1,801	114.2	666	328.8	840	428	1,514

Model =  modelled GLOF scenario. Max =  maximum affected level.

Table 4 Infrastructure potentially exposed to glacial lake outburst floods.

	Imja (Dudhkoshi)		Tsho Rolpa (Tamakoshi)		Thulagi (Marsyangdi)		Lumuchimi (Bhotekoshi/Sunkoshi)
	Model	Max	Model	Max	Model	Max	Model	Max
Schools	3	3	0	2	3	4	6	13
Office buildings	3	4	0	2	5	6	15	17
Temples	2	3	2	11	6	13	7	10
Trails (km)	65	74	18	41	4	8	1	20
Roads (km)	5	5	3	10	1	2	24	37
Embankments (km)	1	1	10	10	4	7	5	5
Bridges	25	25	23	23	35	35	17	30
Hydropower plants	1	1	0	0	6	6	3	3
Irrigation canals (km)	1	1	7	16	0	0	0	0
Water mills	5	5	0	1	4	6	4	11
Transmission lines (km)	5	7	1	3	4	6	14	25

Model =  modelled GLOF scenario. Max =  maximum affected level.

Table 5 Monetary value of elements potentially exposed to glacial lake outburst flood risk (USD thousands).

	Imja (Dudhkoshi)		Tsho Rolpa (Tamakoshi)		Thulagi (Marsyangdi)		Lumuchimi (Bhotekoshi/Sunkoshi)
	Model	Max	Model	Max	Model	Max	Model	Max
Real estate	8,917	31,729	1,411	6,524	2,036	6,685	15,889	40,606
Agriculture	932	1,680	117	330	234	519	246	996
Public infrastructure	2,037	2,084	319	1,928	335,784	339,469	98,845	109,446
Revenue	7	7	0	0	68,678	68,678	37,762	37,762
Total	11,894	35,501	1,847	8,781	406,731	415,351	152,741	188,810

Model =  modelled GLOF scenario. Max =  maximum affected level.

Figure 6 Share of different sectors in total value exposed to glacial lake outburst flood risk (a) under the modelled flood scenario and (b) under the maximum affected level.

Figure 7 Monetary value of property exposed to glacial lake outburst flood risk under the modelled flood scenario (left-side charts in each figure) and the maximum affected level (right-side charts).

Table 6 Percentage of households with different indicators of vulnerability in total households within areas susceptible to glacial lake outburst floods.

Indicator	Imja	Tsho Rolpa	Thulagi
Marginal and small farm households with less than 0.5 ha land	68	77	93
Food sufficiency from own production for less than 6 months per year	59	39	99
Annual household income less than approximately USD 1000	60	71	44