Earth Science
Total Page：16
File Type：pdf, Size：1020Kb
Earth-Science Reviews 165 (2017) 81–109 Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev Invited review Design with nature: Causation and avoidance of catastrophic flooding, Myanmar G.R. Brakenridge a,⁎, J.P.M. Syvitski a,E.Niebuhrb,I.Overeema,S.A.Higginsa,A.J.Kettnera, L. Prades c a University of Colorado, United States b U.S. National Weather Service, United States c UN World Food Programme, Italy article info abstract Article history: Myanmar is among 15 nations that account for 80% of global population exposed to flooding. In 2008, the country Received 29 August 2016 suffered exceptional damage and human mortalities (N138,000) from tropical storm Nargis, which followed an Accepted 6 December 2016 unusual but not unprecedented storm track. In 2015, heavy monsoonal rains related to the tropical Madden– Available online 16 December 2016 Julian Oscillation plus a slow-moving tropical storm (Komen) together caused major flooding, ~130 fatalities, and very severe damage and losses. Both events triggered international food, medical, and other assistance, in- cluding efforts to design rebuilding with greater resilience to floods. Orbital remote sensing can be employed to characterize such damaging floods and quantify future flood risk; advanced lead-time flood prediction is also increasingly accurate and available. These capabilities must, however, be applied in a context of environmen- tal variables (climate, sea level, dams, and land cover) that are changing the hazard. In addition to the hydrome- teorology, distal causes for flood disasters include: high sediment loads carried by Myanmar rivers, locally rapid rates (N50–100 m/y) of channel migration, expansion of population into vulnerable locations, and anthropogenic modifications to floodplains, watersheds, and the coastal zone. Engineering projects can protect local communi- ties, but flood control structures will fail again unless the environmental changes that increase exposure to flood damage are also mitigated. Earth Science-based methods for long term reduction of societal exposure include floodplain reconnection, levee removal, controlled avulsions, and redirecting new housing and other economic development onto lands with less severe flood risk. © 2016 Elsevier B.V. All rights reserved. Contents 1. Introduction............................................................... 82 2. Sources of floodhazardinMyanmar.................................................... 82 2.1. Myanmarphysiographyandrivers.................................................. 82 2.2. Myanmar flood-producingprecipitationandrunoff.......................................... 83 2.3. Flow variability and the floodplain.................................................. 85 2.4. Effectsofhighsedimentload.................................................... 88 2.5. Effects of dams, reservoirs, and artificiallevees............................................ 89 3. Non-stationary floodriskinMyanmar................................................... 90 4. Remote sensing measurements of Myanmar floods.............................................. 91 4.1. Understanding floodhazard..................................................... 91 4.2. MODIS floodmappingforMyanmar................................................. 92 4.3. Informationfrompassivemicrowavesatellites............................................ 93 4.4. Myanmar floodhistoryobservedviamicrowave........................................... 94 5. Recent floodhistory............................................................ 97 5.1. Pre-1968 floods.......................................................... 97 5.2. 1968cycloneandstormsurge................................................... 100 5.3. The1970sthrough1990s..................................................... 100 ⁎ Corresponding author at: University of Colorado, 4001 Discovery Dr. Office N142, 80309 Boulder, CO, United States. E-mail address: [email protected] (G.R. Brakenridge). http://dx.doi.org/10.1016/j.earscirev.2016.12.009 0012-8252/© 2016 Elsevier B.V. All rights reserved. 82 G.R. Brakenridge et al. / Earth-Science Reviews 165 (2017) 81–109 5.4. 2003monsoonrainfallandcyclone................................................. 101 5.5. 2004cyclone........................................................... 101 5.6. 2006CycloneMalaand2010CycloneGiri.............................................. 102 5.7. Floodsin2011and2012..................................................... 102 6. The 2008 Cyclone Nargis storm surge and flood.............................................. 102 7. CausationandavoidanceofNargisevents................................................. 103 8. The 2015 Cyclone Komen and intense monsoon floods........................................... 104 9. CausationandavoidanceofKomenevents................................................. 105 10. Conclusion.............................................................. 106 Acknowledgements............................................................. 108 References.................................................................. 108 1. Introduction (The-World-Bank, 2011). In developing nations such as Myanmar, flood fatalities can be exceptional: entire communities have been Earth Science can help developing nations avoid the unwise water- drowned by coastal storm surges. Even in the 21st century, when related development pathways followed by other nations. Earlier mis- weather prediction has increased in accuracy (Webster, 2013), effective takes made since the Industrial Revolution are only recently being recti- warnings are not always accomplished. The locations of unusual South fied. For example, in North America and Europe, artificial levees Asian floods vary, but major damage occurs somewhere every year: blocking the connection of rivers to their floodplains are being removed thus begging the question as to whether it is the storms, or the failure (Galat, 1998). In the Mississippi delta, controlled flooding is being un- to prepare for them, that is the main cause for the losses (Ziegler et al., dertaken to restore the sediment influxes needed for landform stability 2012). (Day et al., 2016). Professional societies acknowledge the need for sur- Within the past 10 y, two exceptionally severe flood disasters oc- face process understanding to be communicated: “Geoscientists have curred in Myanmar. There were N138,000 fatalities in the Ayeyarwady a fundamental role in the engineering and architectural design, plan- delta in 2008, from storm surge and intense rain caused by tropical ning, construction, and maintenance of infrastructure systems with re- storm Nargis (Fritz et al., 2009). In 2015, tropical storm Komen and tor- spect to their relationship to local geology, hazards and the rential monsoonal rains inland caused 132 fatalities and another 1.6 environmental setting” (GSA, 2014). We review here a developing million affected while the flood wave made its way to the sea nation's experience with damaging floods, and describe from an Earth (Government-of-the-Union-of-Myanmar, 2015). We examine the cau- Science perspective the lessons for a safer recovery. The review presents sality and societal effects of these events, and within the relevant technologies now available for the rapid mapping of areas of flood risk, storm history. Satellite sensing is employed to investigate flood causa- and urges that they be applied in the context of modern science that has tion and evolution, and to demonstrate how space-based information invalidated certain widely-held assumptions (e.g. flood series statistical can be used in risk mapping. Also considered are the environmental stationarity). We consider that “designing with nature” using best- changes that are increasing the risk of catastrophic floods. These are available scientific knowledge is not only economically feasible, but nec- the changing variables that must be accommodated to foster greater essary (McHarg, 1969); otherwise even more catastrophic floods will “resilience” or a capacity to recover quickly from flood damage. certainly occur. Long term and effective disaster recovery requires understanding of 2. Sources of flood hazard in Myanmar why a particular event became exceptionally severe. In areas affected by the tropical monsoon, “flooding” is not unusual, but instead an annual Flood hazard can be usefully simplified to floodplain and coastal phenomenon. Inland river floodplains and coastal deltas are partially in- zone maps showing flood extent at different stages (river levels) or undated each summer; mountain snowmelt combined with heavy surge heights, and quantitative recurrence intervals/annual exceedance monsoonal rains fill river channels, and local tropical cyclones cause probabilities (Eychaner, 2015; Maidment, 1993). However, the hydro- coastal storm surges and intense precipitation inland. Important river- meteorological causes of flooding are diverse (Hirchboeck, 1988), and delta systems in the region include the Indus, Ganges-Brahmaputra- a region's unique suite of physiography, climate, and other environmen- Megna, Chao Phraya, Mekong, Red, Pearl, and, in Myanmar or Burma, tal variables such as river sediment load also exerts important controls the Ayeyarwady-Chindwin, Sittaung, and Salween. Many of the deltas over hazard. host large human populations: ~15 million out of Myanmar's 51 million presently reside on the Ayeyarwady delta. Residents and economies of 2.1. Myanmar physiography and rivers these deltas and the river floodplains