Dai Yamazaki

Abstract Spaceborne digital elevation models (DEMs) are a fundamental input for many geoscience studies, but they still include nonnegligible height errors. Here we introduce a high‐accuracy global DEM at 3″ resolution (~90 m at the equator) by eliminating major error components from existing DEMs. We separated absolute bias, stripe noise, speckle noise, and tree height bias using multiple satellite data sets and filtering techniques. After the error removal, land areas mapped with ±2 m or bette

Abstract High‐resolution raster hydrography maps are a fundamental data source for many geoscience applications. Here we introduce MERIT Hydro, a new global flow direction map at 3‐arc sec resolution (~90 m at the equator) derived from the latest elevation data (MERIT DEM) and water body data sets (G1WBM, Global Surface Water Occurrence, and OpenStreetMap). We developed a new algorithm to extract river networks near automatically by separating actual inland basins from dummy depressions caused b

Current global river routing models do not represent floodplain inundation dynamics realistically because the storage and movement of surface waters are regulated by small‐scale topography rather than the commonly used spatial resolution of global models. In this study, we propose a new global river routing model, CaMa‐Flood, which explicitly parameterizes the subgrid‐scale topography of a floodplain, thus describing floodplain inundation dynamics. The relationship between water storage, water l

Global river models are an essential tool for both earth system studies and water resources assessments. As advanced physical processes have been implemented in global river models, increasing computational cost has become problematic for executing ensemble or long‐term simulations. To improve computational efficiency, we here propose the use of a local inertial flow equation combined with a vector‐based river network map. A local inertial equation, a simplified formulation of the shallow water

Abstract River width is a fundamental parameter of river hydrodynamic simulations, but no global‐scale river width database based on observed water bodies has yet been developed. Here we present a new algorithm that automatically calculates river width from satellite‐based water masks and flow direction maps. The Global Width Database for Large Rivers (GWD‐LR) is developed by applying the algorithm to the SRTM Water Body Database and the HydroSHEDS flow direction map. Both bank‐to‐bank river wid

Abstract. This paper proposes an improved method for converting a fine-resolution flow direction map into a coarse-resolution river network map for use in global river routing models. The proposed method attempts to preserve the river network structure of an original fine-resolution map in the upscaling procedure, as this has not been achieved with previous upscaling methods. We describe an improved method in which a downstream cell can be flexibly located on any cell in the river network map. T

In this paper we show the importance of bifurcation channels for flow in river mega deltas through the use of a new computational scheme implemented in the global hydrodynamic model, CaMa-Flood (Catchment-based Macro-scale Floodplain model). First, we developed a new river network map based on SRTM3 DEM (Shuttle Radar Topography Mission 3 arc-second Digital Elevation Model) and HydroSHEDS (hydrological data and maps based on shuttle elevation derivatives at multiple scales) which includes bifurc

Water level dynamics in continental‐scale rivers is an important factor for surface water studies and flood hazard management. However, most continental‐scale river models have not focused on the reproduction of water level because the storage and movement of surface waters are regulated by smaller‐scale topography than their grid resolutions. Here we analyzed the water level dynamics simulated by a state‐of‐the‐art global river model, CaMa‐Flood, with subgrid representation of floodplain topogr

Abstract. Coastal river deltas are susceptible to flooding from pluvial, fluvial, and coastal flood drivers. Compound floods, which result from the co-occurrence of two or more of these drivers, typically exacerbate impacts compared to floods from a single driver. While several global flood models have been developed, these do not account for compound flooding. Local-scale compound flood models provide state-of-the-art analyses but are hard to scale to other regions as these typically are based

The existence of a primordial magnetic field (PMF) would affect both the temperature and polarization anisotropies of the cosmic microwave background (CMB). It also provides a plausible explanation for the possible disparity between observations and theoretical fits to the CMB power spectrum. Here we report on calculations of not only the numerical CMB power spectrum from the PMF, but also the correlations between the CMB power spectrum from the PMF and the primary curvature perturbations. We th

We present the newest statistical and numerical analysis of the matter and cosmic microwave background power spectrum with effects of the primordial magnetic field (PMF) included. New limits to the PMF strength and power spectral index are obtained based upon the accumulated data for both the matter and CMB power spectra on small angular scales. We find that a maximum develops in the probability distribution for a magnitude of the PMF of $|{B}_{\ensuremath{\lambda}}|=0.85\ifmmode\pm\else\textpm\