Hydrologic Modeling and Flood frequency analysis under climate change.pdf

Climate change impact on flood discharge

1. Hydrologicalmodelingandassessmentofflood
dischargeinafutureclimate:Acasestudyof
BagmatiRiverBasin,Nepal
Binaya Kumar Mishra
Professor, School of Engineering
Pokhara University, Nepal
June 24, 2024

2. Flood discharge under climate change
•Urban flooding is frequently reported as a result of anthropogenic
activities like climate change, unplanned growth and development in
floodplains
•Climate change is considered one of main reasons behind increasing
flood events in Kathmandu valley
•Hydrologic modeling set-up, flood discharge simulations and analysis for
current and future climate conditions are applied.
•Change in peak river flows, an important information for flood risk
measures, was analysed in Bagmati river basin which covers Kathmandu
valley, Nepal
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3. 3
Bagmati river basin upstream of Khokana;
Catchment area is 593 km
2
Study area

4. 4Hydrologic Model (HEC-HMS) set-up

5. 5
Sub-basins and river networks for HEC-HMS modeling

6. 6
Landcover maps of Bagmati river basin

7. 7
Hydrological soil groups (HSG) of Bagmati river basin
HSGindicates the amount of infiltration that
occurs in various types of soil. Broadly, there
are four hydrologic soil groups: A, B, C and D
with “A” soil representing high permeability
and little runoff production to “D” soil
representing low permeability rates and
produce much more runoff.

8. 8
Spatial variation of SCS-CN values over Bagmati
river basin

9. 9
Comparison of simulated and observed for 2002 flood discharge series
NSE: 0.7 and PBIAS: -2.8%

10. 10
Comparison of simulated and observed for 1998 flood discharge series
NSE: 0.6 and PBIAS: 18.3%

11. 11
Comparison of simulated and observed for 2011 flood discharge series
NSE: 0.7 and PBIAS: 1.5%

12. Climate projections (precipitation)
•NonHydrostaticRegionalClimateModel(NHRCM)
•Presentclimate(1981-2000);FutureClimate(2080-2099)
•ClimateChangeScenario:SSP5-8.5(2-kmspatialresolution)
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Domain

13. •Future RCM precipitation values were found with greater peaks over present RCM output.
•Precipitation with more than 100 mm were found of 7- and 16-days for present and future
RCM series respectively.
•Highest precipitation was found to be 198.5 and 245.9 for Present and future RCM series
respectively.
NHRCM precipitation for 1981-2000 and 2080-2099 period over Kathmandu
Airport station (#1030)

14. 14YearQ (m
3
/s)YearQ (m
3
/s)
19811350.12080 249.1
1982 479.1 20811131.7
1983 383.8 20821189.3
1984 716.6 2083 533.6
1985 455.6 20841294.2
1986 541.8 2085 410.4
1987 793.1 2086 800.4
1988 415.4 2087 510.5
19891362.12088 519.8
1990 663.2 2089 665.5
1991 379.6 2090 343.7
1992 656.7 2091 434.3
1993 460.4 2092 920.2
1994 469.2 20931818.4
1995 317.2 20941180.6
1996 462.7 20951140.1
1997 713.0 2096 439.4
1998 458.9 2097 426.0
1999 397.7 2098 511.2
2000 817.3 2099 402.0
Present climateFuture climate
Flood-frequency curves for current and future
climate conditionsPresent climateFuture climate
5 876 1120 27.9
10 1077 1408 30.7
25 1331 1771 33.1
50 1520 2041 34.3
100 1707 2308 35.2
Return
period, T
years
Discharge, m
3
/s
Increase (%)

15. Conclusive remarks
•Comparison of annual daily maximum discharge at Khokana revealed
rising flood risks in the Kathmandu Valley in future.
•The projected increase in flood risk underscores the imperative for re-
evaluating existing flood management systems in the capital city.
•Large uncertainties are often reported in the projections of GCMs and
SSPs. It is recommended to consider multiple GCMs and SSPs to obtain
more reliable impact studies on streamflow under climate change.
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16. Acknowledgments:
This work was conducted by Theme 4 of the Advanced Studies of Climate Change
Projection (SENTAN Program) Grant Number JPMXD0722678534 supported by the
Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
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Thank you.