This book mainly focuses on the role of the Himalayas in the flooding process of Bangladesh. Although not mentioned explicitly, the three major objectives of this book are to: (1) determine if there are highland-lowland linkages in Bangladesh flooding that take into account the broad geographical area over which the major river basins are located; (2) understand the frequency of flooding in Bangladesh with the use of information from historical sources and long-term data; and (3) identify common or divergent key elements that lead to flooding by investigating different flood processes. These objectives have been analysed and discussed in the seven chapters in the book.
While reading the book I have found several issues that need careful examination. In Chapter 2 and in the remainder of the book, the authors describe the Ganges, Brahmaputra and Meghna (GBM) basins as a single basin. Yet each basin differs in origin, geology, topography and landscape, precipitation, discharge and flooding patterns, sediment transportation and sloping points from the rest. Promoting GBM basins as a single basin has significant far-reaching political implications for water sharing and its cooperative management in the eastern Himalayan region. The authors should have been more careful when including statements regarding exaggeration of the ‘inundation area’ in Bangladesh to attract foreign aid without any backup from peer-reviewed research (Chapter 2).
A large amount of hydro-meteorological and other data from India, Nepal and Bangladesh is presented in Chapter 3, yet with many missing values. To facilitate analyses, the authors applied two methods, namely interpolation and use of neighbouring stations to create complete data sets. There are dangers of using both methods without examining any changes in statistical properties in the data.
I am not sure whether the authors examined the goodness-of-fit of the flood data in Bangladesh when selecting linear regression for trend analysis (Chapter 4). I have found that a second order polynomial fits better than a straight line and shows an increasing trend instead of the decreasing trend shown. Another limitation to the chapter is the lack of parametric and non-parametric tests conducted on the data; they could have revealed any changes in the mean flooding in Bangladesh. Regarding impact of Farakka Barrage on peak flow in the Ganges River in Bangladesh, the authors could have consulted peer reviewed literature (for example Mirza Reference Mirza2004), where 13% and 58% increases in the mean and standard deviation, respectively, are shown to have occurred in the peak discharge of the Ganges in the post-Farakka period, instead of a single article published in a popular newsletter.
Chapter 5 is the core of the book and discusses Bangladesh floods in the context of highland-lowland linkages. Five methodological steps have been applied to explore the contribution of water from the different areas in the highlands and plains of the GBM basins to the hydrological system and to the flooding process in Bangladesh. These steps include: delimitation of sub-catchments, defining inter-annual time period, calculation of areal precipitation and its volume, calculation of potential run-off and the relevance of the potential run-off for Bangladesh. Following review of the chapter, the methodology contains five major problems. First, the scientific basis for delimitation of sub-catchments of the GBM basins is unclear. Although, entire GBM basins have been divided into 13 sub-catchments, these sub-catchments are significantly different from the already defined sub-catchments of these rivers (Rao Reference Rao1975). Second, when precipitation data is available (Chapter 3), it is not difficult to regionalize this with the use of principal components analysis (PCA). Third, the methodology of ‘discharge factor’ is unclear, as explanations on how topography, temperature, air humidity, vegetation cover, soil moisture content and ground water level have been taken into account are missing. Fourth, run-off from rains in the dry season seems to have been overestimated, as virtually no run-off occurs in the dry season in the Ganges Basin due to high potential evapotranspiration and sporadic rainfall. Fifth, data from very few stations (42 over a 1.75 million km2 area) have been used for the discharge calculations, with no data from Bhutan having been used.
Chapter 6 discusses the erosion and sedimentation processes in the Ganges and Brahmaputra basins in the context of highland-lowland linkages and is worth reading. However, information on sediment transportation from agriculture sources could have added value to this discussion. Chapter 7 focuses on the human dimensions of flood problems through the employment of field-level questionnaire surveys, and results are not very different from what is already known from the published literature.
The GBM basins are very complex in terms of physical, hydro-meteorological and human intervention settings, and so are its flooding processes. The authors have tried to reduce the role of the Himalayas in the flooding in Bangladesh, but for methodological reasons, further research on this issue is clearly necessary. While the graphics of the book are of high quality, the uses of more recent peer-reviewed literature would have sharpened the analysis and discussion.
