The authors proposed a methodology for estimating flow duration curves (FDC) for perennial and ephemeral catchments in islands using a disaggregated approach. The proposed method is approached statistically and uses no complex parameters in order to reduce uncertainty and retain simplicity. Firstly, the FDC was disaggregated into three parts (high, middle and low) and, for the purpose of this study, it focusses on the low flow section. Initially, the mean monthly flow was used for estimating runoff in both types of catchments. The results show the mean monthly flow provided proper estimates in the perennial catchments, but for the ephemeral catchments the estimates were substandard. Therefore, a different approach using climate indices such as aridity and a precipitation index was used in a generalized regression equation. The results show the majority of the ephemeral catchments responded properly to the climate indices indicating climate as a major controlling factor at the lower end of the FDC.

Many recent studies have argued that tropical cyclones will become severer in future warming climate and may cause various catastrophic damages to human life and economy. This study explores the impact of climate change on Typhoon Chanthu (2016) by performing a high-resolution (1 km) simulation for current and future climate. We focused on the typhoon intensity, size, heat fluxes, associated precipitation and wind speed over northern Japan under global warming with different initial times at 6-hour interval. We find that the typhoon tracks in the present and future climates remained similar, however with stronger intensity and heat fluxes in warming climate condition. In the landfall region of Hokkaido in future climate, the maximum wind speed and precipitation amount associated with the typhoon is significantly increased. The results imply that the damages associated with Typhoon Chanthu in future climate over northern Japan would be enhanced through strong wind, heavy rainfall and flooding.

Hydrological-hydraulic modeling is a core technique in assessing surface water dynamics of rivers, lakes, and floodplains. The local inertial model (LIM) as a physically simplified model of the shallow water equations is essential for efficient numerical simulator of surface water dynamics. In this paper, we point out that the conventional semi-implicit finite difference scheme for the friction slope terms, despite being convenient, is not consistent in the sense that it may lead to incorrect numerical solutions if the temporal resolution is not high. We propose an alternative discretization to resolve this issue, which is more accurate and stable, and has comparable computational efficiency. The new numerical scheme is implemented into a modern hydrological-hydraulic model, demonstrating reasonable accuracy. The new scheme is also compared with a recently-proposed implicit scheme, demonstrating comparable theoretical and computational performances. The results indicate that the proposed scheme potentially serves as a new central core for numerical simulation with the LIM.

A hydrological model, XAJMISO is adopted from the XinAnJiang (XAJ) model and modified by transforming the parametric routing system into a non-parametric system to reduce parameters and improve performance. The proposed model replaces routing components of the XAJ model with two linear systems: surface flow and subsurface flow, including interflow and baseflow. The discharge at the basin outlet is then calculated using response functions of surface and subsurface flow, which are derived by means of a multiple input single output (MISO) system. In contrast to other MISO studies, the present study defines the finite length for calculating response function coordinates based on time scales of all runoff components. The model is applied to six river basins of different data aridity indices in the United States and compared with our modified XAJ (mXAJ) model. The results reveal that the proposed model sufficiently represents the relationship between rainfall and runoff of relatively large basins and provides better and more stable performance. The proposed model also makes calibration much easier by reducing four sensitive parameters out of seven in mXAJ.