The current global water body maps have a resolution of approximately 30 m depending on the available remote sensing data. A water body map with higher spatial resolution is required to distinguish smaller rivers for advanced applications involving global carbon cycle and real-time flood predictions. Conventional water extraction methods use water indices that combine visible and infrared spectra. State-of-the-art remote sensing data including aerial photography, offers a few-meter spatial resolution but only contains the visible spectrum. Here, we established a water extraction method at 60-cm resolution via Bayesian inference, using aerial photography’s visible spectrum combining the Landsat-based Global 1-second Water Body Map and the Open Street Map (OSM). The Japan Flow Direction Map (J-FlwDir) was used to link the water bodies. Our method detected the main streams of the Tsurumi and Tama rivers and their tributaries, which were not resolved by the Landsat-based dataset. With our approach, rivers with widths >10 m were detected and water extent was obtained for 37% of small rivers, represented as lines on the OSM. These findings indicate that our method, solely based on visible spectra with hydrography data and existing water body maps, improves the spatial resolution of water mapping without requiring infrared.

In global hydrological models, river discharge is accumulated by following the river network, which presumes that there is one downstream destination for each grid. Implementing “diversions” where there are multiple downstream destinations, such as bifurcations and inter-basin water transfers, requires an extension of river routing algorithms. Previous global water resources models that implemented diversions typically used a semi-implicit numerical scheme where river discharge should be calculated in an upstream-to-downstream order. The major obstacle to flexible application to any river network with diversions was that ad-hoc modification of the model’s code was required because the river sequence map to specify calculation order was developed without considering diversions. To overcome this limitation, we developed two new river routing algorithms that can generally represent diversions. One is automatically updating river sequence considering diversions and the other is introducing the Forward Time Centered Space scheme. The former has the advantage of stability under longer time steps, while the latter’s strength lies in its easy implementation and applicability where backwater happens. We confirmed that both algorithms efficiently handle the complex canal network in the Indus River. These approaches allow us to flexibly implement diversions in river routing algorithms.

The tertiary irrigation system (TIS) was designed for the Muda Irrigation Scheme (MIS) to distribute irrigation water to farmers’ fields to ensure the reliability of water supply for cultivating rice paddies twice a year. Variability in farming practices, influenced by farmer autonomy along the tertiary canal adds complexity and uncertainty to adherence monitoring. Traditional on-site data collection methods are limited in scope and efficiency, whereas Earth observation (EO) enables continuous monitoring. In this study, we introduced a methodology that uses EO datasets to monitor individual field adherence to rice-planting schedules under TIS. These tools improve the monitoring of rice-planting schedule adherence by identifying non-adherent fields for further countermeasures. This study highlights the potential use of EO datasets and advanced data processing techniques for efficient agricultural monitoring.

In this study, overtopping-induced levee breach experiments were conducted to explore the effect of differences in levee structure on levee breach characteristics, considering the heterogeneity of the levee material and the flow outside the levee. A homogeneous levee composed of silica sand No. 7 and a heterogeneous levee composed of silica sand No. 5 and No. 7 overlapped by two levees were subjected to overtopping-induced levee breaches in the presence of flow outside the dike. Comparison of these processes revealed that the downstream progress of erosion is more plausible than the upstream side due to flow outside the levee. The shape of the breach opening was different during the levee breach process between the levee made of a heterogeneous structure and that made of a single material. Moreover, the rate of widening of the breach opening on the back slope increased at an earlier stage in the former case than in the latter, resulting in a larger overflow rate. To the best of our knowledge, few studies have simultaneously considered the heterogeneous structure of an actual levee and the flow outside the levee.

In this study, we use a long-term gridded dataset of daily precipitation and atmospheric fronts delineated on weather maps of Japan, the Northwestern Pacific, to identify rainfalls influenced by fronts within heavy rainfall periods occurring from June to August. We clarify the relationship between daily precipitation and the distance to fronts. The analytical targets are heavy rain events that occur for approximately four days each season. In the areas from Northwestern Kyushu to Western Tohoku, facing the Sea of Japan, the amount of precipitation from heavy rain events occurring within 500 km of fronts accounts for at least 80% of all heavy rain events. This is the same for the number of heavy rain events as well. Specifically, in Northwestern Kyushu, the amount of precipitation and the number of heavy rain events occurring within 200 km of fronts account for approximately 70% of all heavy rain events.

Estimates from 3 statistically downscaled General Circulation Models (GCMs) from version 6 of the Coupled Model Intercomparison Project, namely the EC Earth3, GFDL ESM4 and MPI ESM1 2 HR are used in the HBV hydrological model to estimate design streamflow projections with 20, 50, and 100-year return periods for the selected main basins of Costa Rica. The changes in these streamflows were computed between the baseline period (1985–2015) and the mid-century projection (2035–2065) for the SSP5-8.5 scenario. The novelty resides in being the first study that explores the magnitude of climate changes in design flows of Costa Rica, a tropical country. Although, calibration and validation statistics are generally good for most of the basins, only around one quarter of the simulations reproduce the observed distribution of the 3-day annual maximum flows. Results show that the MPI model presents lower sensitivity with changes of different sign depending on the basin studied and the other two models suggest only significant increases in the design flow in most of the basins. Results of the model’s ensemble suggests a great concern, as there is a general increase in the design flows, and the magnitudes of the changes are large, especially in the Pacific slope.

Irrigation reservoirs are vital for ensuring a stable water supply to nourish crops, but the environmental conditions that influence their geographical location have not been quantitatively determined on a global scale. This study applied a species distribution model (SDM) to predict the locations of irrigation reservoirs based on seven natural and social predictor variables. Under the assumption that the location of an irrigation reservoir reflects the conditions of the downstream beneficiary areas, new social predictor variables were generated to account for the beneficiary grid cells, and the predicted SDM performance was compared to the results of experiments that did not consider beneficiary grid cells. The consideration of beneficiary areas resulted in response curves that were more in accordance with the actual locations of irrigation reservoirs and improved the prediction accuracy of the SDM. The geographical locations of reservoirs were revealed to be most sensitive to social predictors, and the variable importance was improved by integrating information regarding the beneficiary grid cells. These findings highlight the significance of considering the environment surrounding the target grid cell when applying SDMs to water-related infrastructure.