Articles | Volume 21, issue 9
Hydrol. Earth Syst. Sci., 21, 4495–4516, 2017

Special issue: Observations and modeling of land surface water and energy...

Hydrol. Earth Syst. Sci., 21, 4495–4516, 2017

Research article 11 Sep 2017

Research article | 11 Sep 2017

Necessary storage as a signature of discharge variability: towards global maps

Kuniyoshi Takeuchi1,a and Muhammad Masood2 Kuniyoshi Takeuchi and Muhammad Masood
  • 1International Centre for Water Hazard and Risk Management (ICHARM), Public Works Research Institute (PWRI), Tsukuba, 305-8516, Japan
  • 2Bangladesh Water Development Board (BWDB), Design Circle-1, Dhaka, Bangladesh
  • acurrently at: Iwakubo-cho 392-2, Kofu, Yamanashi 400-0013, Japan

Abstract. This paper proposes the use of necessary storage to smooth out discharge variability to meet a discharge target as a signature of discharge variability in time. Such a signature has a distinct advantage over other statistical indicators such as standard deviation (SD) or coefficient of variation (CV) as it expresses hydrological variability in human terms, which directly indicates the difficulty and ease of managing discharge variation for water resource management. The signature is presented in the form of geographical distribution, in terms of both necessary storage (km3) and normalized necessary storage (months), and is related to the basin characteristics of hydrological heterogeneity. The signature is analyzed in different basins considering the Hurst equation of range as a reference. The slope of such a relation and the scatter of departures from the average relation are analyzed in terms of their relationship with basin characteristics. As a method of calculating necessary storage, the flood duration curve (FDC) and drought duration curve (DDC) methods are employed in view of their relative advantage over other methods to repeat the analysis over many grid points. The Ganges–Brahmaputra–Meghna (GBM) basin is selected as the case study and the BTOPMC hydrological model with Water and Global Change (WATCH) Forcing Data (WFD) is used for estimating FDC and DDC. It is concluded that the necessary storage serves as a useful signature of discharge variability, and its analysis could be extended to the entire globe and in this way seek new insights into hydrological variability in the storage domain at a larger range of scales.

Short summary
There are many global maps of hydrology and water resources, but none on necessary storage to smooth out discharge variability. This paper provides a methodology to create such a map, taking the Ganges–Brahmaputra–Meghna basin as an example. Necessary storage is calculated by a new method, intensity–duration–frequency curves of flood and drought (FDC–DDC). Necessary storage serves as a signature of hydrological variability and its geographical distribution provides new insights for hydrology.