Indicators of Necessary Storages for Flood and Drought Management: Towards Global Maps
Other literature type
(issn: 1607-7938, eissn: 1607-7938)
Storage is the only means to smooth out the discharge variation necessary to control hazards and utilize water resources. Necessary storage depends on the levels of discharge variation, required flood control and water use. The main methodologies to calculate necessary storage include mass curve method and simulation. The use of flood duration curve (FDC) and drought duration curve (DDC) that this paper presents is an alternative way that has considerable advantages over the others. The diagram of FDC-DDC serves as the classification indicator of basin hydrology and the FDC-DDC based estimates of necessary storages can be used for reservoir operation. The FDC-DDC based necessary storages pay an attention to the finite term hydrological variation rather than the asymptotic infinite memory of variation that Range analysis focuses. On the other hand the FDC-DDC focus on spatial distribution of necessary storages and try to find spatial rules of hydrological heterogeneity in necessary storages. For a case study, the Ganges-Brahmaputra-Meghna basin was selected and its spatial distribution of the FDC–DDC based necessary storages was calculated based on the discharge dataset obtained by hydrological simulation of the MRI-AGCM3.2S projections using the hydrological model BTOPMC developed at University of Yamanashi and ICHARM. The spatial distribution of necessary storages indicate the relative difficulty of managing the temporal variation of river discharges for human use at respective locality. The climate change impacts on the necessary storages were analysed and found the increase in difficulty of managing high flows and the general ease of managing low flows. But local differences were rather large that indicates the need of careful study to respond unique spatial structure of local discharge variation. The relation to catchment area was also analysed and found such regional heterogeneity diminishes into a basin average slowly in several 10,000 km<sup>2</sup>. A representative elementary area of necessary storages for discharge smoothing is a new concept that deserves for further study. A creation of global maps would be a useful challenge for assessment of current state of water resources, climate change impact on water resources and for study of hydrological heterogeneity and its scale effect.