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Phy, S.R.;  Sok, T.;  Try, S.;  Chan, R.;  Uk, S.;  Hen, C.;  Oeurng, C. Driving Factors on Flood in Cambodia. Encyclopedia. Available online: https://encyclopedia.pub/entry/34079 (accessed on 19 April 2024).
Phy SR,  Sok T,  Try S,  Chan R,  Uk S,  Hen C, et al. Driving Factors on Flood in Cambodia. Encyclopedia. Available at: https://encyclopedia.pub/entry/34079. Accessed April 19, 2024.
Phy, Sophea Rom, Ty Sok, Sophal Try, Ratboren Chan, Sovannara Uk, Chhordaneath Hen, Chantha Oeurng. "Driving Factors on Flood in Cambodia" Encyclopedia, https://encyclopedia.pub/entry/34079 (accessed April 19, 2024).
Phy, S.R.,  Sok, T.,  Try, S.,  Chan, R.,  Uk, S.,  Hen, C., & Oeurng, C. (2022, November 11). Driving Factors on Flood in Cambodia. In Encyclopedia. https://encyclopedia.pub/entry/34079
Phy, Sophea Rom, et al. "Driving Factors on Flood in Cambodia." Encyclopedia. Web. 11 November, 2022.
Driving Factors on Flood in Cambodia
Edit

Flooding in Cambodia, divided into riverine and flash floods, is subject to a multitude of common driving factors. As the MRC rightly noted, flooding in the country can be aggravated by numerous factors, including but not limited to climate change, infrastructure development, dam construction, land cover/use change, or land clearing.

flood hazard driving factors Cambodia

1. Climate Change

A growing number of researchers have been investigating the impacts of climate change on floods in major watersheds, that is, the MR and TSL basins. As strongly remarked by the Royal Government of Cambodia (RGC), this stems from the fact that Cambodia is highly susceptible to climate change, given the country’s low adaptive capacity, yet high dependence on climate-driven resources [1]. The mean annual temperature will rise from 1.4 to 4.3 °C which induces an upward trend in average annual rainfall, especially during the rainy season [2] as well as spurs the unpredictability of weather patterns [3]. This unequivocal phenomenon will increase the frequency, duration, and severity of flood inundation, as a result of rising peak discharges in most streams, thereby leading to a more pressing future of flooding in Cambodia [3].
Oeurng et al. [4] and Try et al. [5] corroborated the alteration in peak discharge and flood inundation in the TSL Basin under certain climate change scenarios whilst climate change will enlarge flood extent and increase water level [6]. Given that TSL is governed by the monsoonal flood pulse, major modifications in this basin have been anticipated along with its consequences on the whole ecosystem, including forests, wetlands, and aquatic ecosystems [7][8][9][10][11]. Other local watersheds are on course to deal with this climate change as flooding patterns diverge from the baseline and thus become more frequent and severe. For example, peak flows tend to rise dramatically in the 3S Basin by over 50% in the 2060s due to climate change [12]. Moreover, it is generally perceived that climate change triggers other factors such as failures of flood mitigation structures including dams and embankments, and more occurrences of extreme weather events [13].

2. Water Infrastructure Development

The construction of dams was cited to affect flood levels in the Cambodian lowland as well as the Mekong Delta in an insignificant way; the annual flood extent between 1996 and 2000 saw a mean decrease of only 3–5%, compared with the baseline area of 38,200 km2 [14]. In case of a dam collapse, flooding will turn into an unmanageable hazard, in which emergency response is of paramount importance, yet losses are woefully inevitable. The MRC also attested that should any dam failure occur along the MR, three provinces, namely Stung Treng, Kratie, and Kampong Cham, can be adversely threatened by flooding [13]. For instance, the major Xe Pian Xe Namnoy hydropower dam collapse in Laos in July 2018 left a devastating flash flood in the northeastern provinces of Cambodia along the MR by raising the water level in Stung Treng to 12 m, which is 0.5 m higher than the emergency level [15][16]. Thousands of Cambodians, over 100 km downstream, were displaced and forced to evacuate while rice crops were critically damaged [15][17]. Another study found that villagers in the 3S Basin incessantly suffered from floods of almost annual recurrence since 1996 due to water release in the wet season from dams in Vietnam and Laos [18]. The act is to keep dam levels below safe levels with respect to dam failure, especially during an extreme rainfall event [18].
Likewise, embankments were found to increase flooding depths as a result of the floodplain being replaced by those structures [14]. Notwithstanding flood risk management, which generally includes embankments, flooding is liable to occur as a result of floodplain loss. This is largely due to the capacity of flood water retention of the floodplain being depleted [19], which is otherwise crucial in maintaining hydrological regime and soil infiltration, reducing surface flow [20], and fostering a mosaic of ecological systems [21]. Rising water levels are inevitable when natural floodplain zones are substituted by such structures [19].

3. Weather Extremes

The unpredictability of future typhoons impacting Cambodia may be overlooked in the previous studies. This is largely because the country is never directly hit by typhoons and therefore, receives less severe effects from any typhoons that decay or transform into tropical storms, compared with the countries that are directly hit by typhoons. However, flash floods in over 14 provinces were logged as a result of decaying Typhoon Ketsana between the end of September and the beginning of October 2009 [22]. The aftermath left almost 4 dozen casualties, with other injuries and substantial property loss. 4 years later, two typhoons (Wutip on 26 September and Nari on 14 October) hitting the Lower Mekong Basin (LMB) transformed into significant tropical storms once they made landfall in Cambodia [23]. Almost 170 casualties were reported over the country as a result of flash floods due to these storms. That said, other than riverine flooding, flash flooding caused by tropical storms or typhoons is deemed perilous.
On top of that, the El Niño-Southern Oscillation (ENSO), comprising Neutral, La Niña, and El Niño phenomena, also plays an evident role in disproportionately affecting flooding situations globally, especially the duration of a flood event which was found to prolong [24]. Also, more intense precipitation and therefore extreme floods are attributed partially to La Niña [25]. In other words, above-average rainfall is usually expected during the La Niña period. However, some years are recorded as La Niña years or events while others are El Niño or Neutral years, both of which are of irregular occurrence, leading to another strain and uncertainty on climate variability over the region. Although La Niña often manifests as a factor in accruing flood risk, studies on these phenomena of flood inundation are not abundant enough in Cambodia [26]. Indeed, the years 2000 and 2011, during which two of the most severe flood events were well recorded in the LMB, were markedly influenced by the La Niña phase; Cambodia also underwent these two severest events, in which casualties and losses were insurmountable [27].

4. Land-Use Change

In addition to the above factors, flooding in Cambodian river basins is also attributed to land-use change, irrespective of any extent. The upstream part, usually occupied by forests, is central to regulating flow and averting flooding downstream. In other words, more land clearing in the upstream areas begets escalation of surface runoff, peak discharge, and flood magnitude [14]. Land-use change, usually from forests to agriculture and built-up area, brings about changes in surface roughness and a decrease in infiltration rates, which generally result in rising flood discharges [28]. The hydrological systems can be sustained unless major modifications of land cover in the highland take place. It is worth mentioning that this change is poised to continue in line with commonly known societal trends such as demographic transition, agricultural demand, and economic growth within the country. To illustrate, the transition from forest to agriculture and urban area is apparent in response to those aforementioned trends. For example, numerous forest types were transformed into agricultural and built-up areas at a rapid pace in the Stung Sangke catchment [29] and Battambang province [30]. The rates of such land conversion can be measured through in-situ and remotely sensed data, the RS and GIS approaches, and modeling to predict; however, the impact of those changes on hydrology and flooding remains to be uncovered. The uncertainty of hydrological response and flooding attributes becomes larger when the rapid land-use change is coupled with the aforementioned driving factors like climate change and infrastructure development.

References

  1. RGC. Cambodia Climate Change Strategic Plan 2014–2023; Royal Government of Cambodia: Phnom Penh, Cambodia, 2013; p. 62.
  2. MRC. Adaptation to Climate Change in the Countries of the Lower Mekong Basin: Regional Synthesis Report; MRC Technical Paper No. 24; Mekong River Commission: Vientiane, Laos, 2009; p. 89.
  3. RGC. Climate Change Action Plan 2016–2018; Royal Government of Cambodia: Phnom Penh, Cambodia, 2016.
  4. Oeurng, C.; Cochrane, T.A.; Chung, S.; Kondolf, M.G.; Piman, T.; Arias, M.E. Assessing Climate Change Impacts on River Flows in the Tonle Sap Lake Basin, Cambodia. Water 2019, 11, 618.
  5. Try, S.; Tanaka, S.; Tanaka, K.; Sayama, T.; Lee, G.; Oeurng, C. Assessing the Effects of Climate Change on Flood Inundation in the Lower Mekong Basin Using High-Resolution AGCM Outputs. Prog. Earth Planet Sci. 2020, 7, 34.
  6. Arias, M.E.; Cochrane, T.A.; Piman, T.; Kummu, M.; Caruso, B.S.; Killeen, T.J. Quantifying Changes in Flooding and Habitats in the Tonle Sap Lake (Cambodia) Caused by Water Infrastructure Development and Climate Change in the Mekong Basin. J. Environ. Manag. 2012, 112, 53–66.
  7. Uk, S.; Yoshimura, C.; Siev, S.; Try, S.; Yang, H.; Oeurng, C.; Li, S.; Hul, S. Tonle Sap Lake: Current Status and Important Research Directions for Environmental Management. Lakes Reserv. 2018, 23, 177–189.
  8. Siev, S.; Yang, H.; Sok, T.; Uk, S.; Song, L.; Kodikara, D.; Oeurng, C.; Hul, S.; Yoshimura, C. Sediment Dynamics in a Large Shallow Lake Characterized by Seasonal Flood Pulse in Southeast Asia. Sci. Total Environ. 2018, 631–632, 597–607.
  9. Uk, S.; Yang, H.; Vouchlay, T.; Ty, S.; Sokly, S.; Sophal, T.; Chantha, O.; Chihiro, Y. Dynamics of Phosphorus Fractions and Bioavailability in a Large Shallow Tropical Lake Characterized by Monotonal Flood Pulse in Southeast Asia. J. Great Lakes Res. 2022, 48, 944–960.
  10. WBG; ADB. Climate Risk Profile: Cambodia; The World Bank Group and Asian Development Bank: Mandaluyong, Philippines, 2021.
  11. Yang, H.; Siev, S.; Sovannara, U.; Yoshimura, C. Flood Pulse and Water Level. In Water and Life in Tonle Sap Lake; Yoshimura, C., Khanal, R., Sovannara, U., Eds.; Springer Nature: Singapore, 2022; pp. 101–109. ISBN 9789811666315.
  12. Shrestha, B.; Cochrane, T.A.; Caruso, B.S.; Arias, M.E.; Piman, T. Uncertainty in Flow and Sediment Projections Due to Future Climate Scenarios for the 3S Rivers in the Mekong Basin. J. Hydrol. 2016, 540, 1088–1104.
  13. ICEM. MRC Strategic Environmental Assessment (SEA) of Hydropower on the Mekong Mainstream: Summary of the Final Report; International Centre for Environmental Management: Hanoi, Vietnam, 2010.
  14. MRC. Working Paper 2011–2015: The Impact & Management of Floods & Droughts in the Lower Mekong Basin & the Implications of Possible Climate Change; Mekong River Commission: Vientiane, Laos, 2012.
  15. Kann, V. Thousands of Cambodians Displaced After Laos Dam Collapse. Available online: https://www.voacambodia.com/a/thousands-of-cambodians-displaced-after-laos-dam-collapse/4503890.html#:~:text=Thousands%20of%20residents%20in%20northern,Nam%20Noy%20Dam%20on%20Monday (accessed on 3 October 2021).
  16. Sok, S.; Chhinh, N.; Hor, S.; Nguonphan, P. Climate Change Impacts on Rice Cultivation: A Comparative Study of the Tonle Sap and Mekong River. Sustainability 2021, 13, 8979.
  17. Baird, I.G. Catastrophic and Slow Violence: Thinking about the Impacts of the Xe Pian Xe Namnoy Dam in Southern Laos. J. Peasant Stud. 2021, 48, 1167–1186.
  18. Sithirith, M. Downstream State and Water Security in the Mekong Region: A Case of Cambodia between Too Much and Too Little Water. Water 2021, 13, 802.
  19. Dang, T.; Cochrane, T.; Arias, M.E.; Van, T.P.D.; Vries, T.T.D. Analysis of Water Level Changes in the Mekong Floodplain Impacted by Flood Prevention System and Upstream Dams. In Proceedings of the 2015 International Association for Hydro-Environment Engineering and Research World Congress (IAHR), Hague, The Netherlands, 28 June–3 July 2015.
  20. Collentine, D.; Futter, M.N. Realising the Potential of Natural Water Retention Measures in Catchment Flood Management: Trade-Offs and Matching Interests: Realising the Potential of Natural Water Retention Measures. J. Flood Risk Manag. 2018, 11, 76–84.
  21. Thoms, M.C. Floodplain–River Ecosystems: Lateral Connections and the Implications of Human Interference. Geomorphology 2003, 56, 335–349.
  22. RGC. Cambodia–Post Ketsana Disaster Needs Assessment; National Committee for Disaster Management: Phnom Penh, Cambodia, 2010.
  23. MRC. Annual Mekong Flood Report 2011; Mekong River Commission: Vientiane, Laos, 2015; p. 72.
  24. Ward, P.J.; Kummu, M.; Lall, U. Flood Frequencies and Durations and Their Response to El Niño Southern Oscillation: Global Analysis. J. Hydrol. 2016, 539, 358–378.
  25. Kabeya, N.; Shimizu, A.; Shimizu, T.; Iida, S.; Tamai, K.; Miyamoto, A.; Chann, S.; Araki, M.; Ohnuki, Y. Long-Term Hydrological Observations in a Lowland Dry Evergreen Forest Catchment Area of the Lower Mekong River, Cambodia. Jpn. Agric. Res. Q. 2021, 55, 177–190.
  26. Sutton, W.R.; Srivastava, J.P.; Koo, J.; Vasileiou, I.; Pradesha, A. Striking a Balance: Managing El Niño and La Niña in Cambodia’s Agriculture; World Bank: Washington, DC, USA, 2019.
  27. Cosslett, T.L.; Cosslett, P.D. The Lower Mekong Basin: Rice Production, Climate Change, ENSO, and Mekong Dams. In Sustainable Development of Rice and Water Resources in Mainland Southeast Asia and Mekong River Basin; Springer: Singapore, 2018; pp. 85–114. ISBN 978-981-10-5612-3.
  28. Saghafian, B.; Farazjoo, H.; Bozorgy, B.; Yazdandoost, F. Flood Intensification Due to Changes in Land Use. Water Resour. Manage. 2008, 22, 1051–1067.
  29. Nut, N.; Mihara, M.; Jeong, J.; Ngo, B.; Sigua, G.; Prasad, P.V.V.; Reyes, M.R. Land Use and Land Cover Changes and Its Impact on Soil Erosion in Stung Sangkae Catchment of Cambodia. Sustainability 2021, 13, 9276.
  30. Sourn, T.; Pok, S.; Chou, P.; Nut, N.; Theng, D.; Rath, P.; Reyes, M.R.; Prasad, P.V.V. Evaluation of Land Use and Land Cover Change and Its Drivers in Battambang Province, Cambodia from 1998 to 2018. Sustainability 2021, 13, 11170.
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