•Streamflow and hydropower potential maps for small basins generated using ANNs.•Proposed ANNs showed high robustness for disinformative inputs and multicollinearity.•The proposed ANNs for Japan ...outperformed a previous strong global ANNs model.•Hydropower potential map corresponded to location and output of existing plants.•Hydropower potential map is consistent with the history of electric power in Japan.
Japan recently introduced a feed-in tariff for small-scale hydropower plants, promoting the development of run-of-river hydropower plants in small-sized basins; however, appropriate implementation requires gauging station streamflow data at substantial costs and time (i.e., more than several years). Thus, in this study, we generated streamflow maps for small-sized basins (∼10 km2) throughout Japan using artificial neural networks (ANNs). Modeled output streamflow characteristics relied upon the input variables obtained from 176 basin characteristics and consisted of mean annual streamflow (QMEAN), daily streamflow indices in a flow duration curve (QD), and a water volume index for run-of-river hydropower energy production (WD95). We preliminarily investigated the impacts of selecting the input variables obtained from 176 basin characteristics on performances of the ANNs, which indicated that the ANNs showed high robustness for disinformative input variables and multicollinearity between input variables. Although QMEAN, high QD, and WD95 performed well, low QD were inadequate, possibly due to snowmelt contributions and small catchment sizes obstructing the detection of geological impacts. To accurately estimate the streamflow characteristics throughout Japan, we emphasize the importance of developing robust methods for correcting wind-induced precipitation undercatch and a spatial interpolation for precipitation in high-montane areas. Nevertheless, the ANNs for Japan proposed herein significantly outperformed a previous study exhibiting excellent global-scale ability. A map expressing run-of-river hydropower potential in small-sized basins was generated and closely corresponded to the spatial distribution and electrical output of existing hydropower plants. Furthermore, we demonstrated that the hydropower potential map reproduces the hydropower developments corresponding to the history of the electric power systems in Japan, which reflects its high reliability. Therefore, the hydropower potential map can greatly aid the exploration of optimal sites for hydropower developments.
•GRFM and GRA were studied for p(Q) model parameterization for 57 Japanese basins.•GRFM suited for high precipitation basins, GRA suited for unconfined groundwater.•We discussed performance ...improvements by optimizing GRFM and GRA.•We found complementary relation between GRFM and GRA based on BFI.
The development of run-of-river hydropower requires the flow duration curve (FDC) to estimate the electricity production. As obtaining an FDC based on gauging station streamflow requires significant cost and time (i.e., more than several years), it is important to predict the FDC in the absence of streamflow data. An analytical probabilistic model of streamflow dynamics (p(Q) model) can calculate the FDC, which requires several rainfall and runoff recession parameters. To estimate the recession parameters in the absence of discharge data, we selected two approaches: the geomorphic recession flow model (GRFM) and geological recession approach (GRA). The GRFM and GRA associate the river network and geology, respectively, with runoff recession features. This study aims to comprehend the characteristics of the GRFM and GRA employed in the p(Q) model by targeting 57 basins throughout Japan. We found different performance trends between the GRFM and GRA that corresponded to specific basin characteristics. While the GRFM performed well in high precipitation basins, the GRA performed well in basins with abundant unconfined groundwater contributions. These results agree with the features in the derivations of the GRFM and GRA. In addition, we found a complementary relationship between the GRFM and GRA based on the baseflow index (BFI), which suggests that the complementary relationship is one method to improve the performance of the p(Q) model in the absence of streamflow data.
This study aimed to evaluate the impact of climate change on flood damage and the effects of mitigation measures and combinations of multiple adaptation measures in reducing flood damage. The ...inundation depth was calculated using a two-dimensional unsteady flow model. The flood damage cost was estimated from the unit evaluation value set for each land use and prefectures and the calculated inundation depth distribution. To estimate the flood damage in the near future and the late twenty-first century, five global climate models were used. These models provided daily precipitation, and the change of the extreme precipitation was calculated. In addition to the assessment of the impacts of climate change, certain adaptation measures (land-use control, piloti building, and improvement of flood control level) were discussed, and their effects on flood damage cost reduction were evaluated. In the case of the representative concentration pathway (RCP) 8.5 scenario, the damage cost in the late twenty-first century will increase to 57% of that in the late twentieth century. However, if mitigation measures were to be undertaken according to RCP2.6 standards, the increase of the flood damage cost will stop, and the increase of the flood damage cost will be 28% of that in the late twentieth century. By implementing adaptation measures in combination rather than individually, it is possible to keep the damage cost in the future period even below that in the late twentieth century. By implementing both mitigation and adaptation measures, it is possible to reduce the flood damage cost in the late twenty-first century to 69% of that in the late twentieth century.
This study performed flood analysis, considering the water storage of irrigation reservoirs, to realize flood control by reservoirs, which are traditional irrigation facilities. The effect on flood ...control was determined through flood analysis performed by varying the reservoir storage rates. Based on the flood analysis results, Japan’s flood damage costs were estimated. Using three Shared Socioeconomic Pathways (SSPs) (SSP1-2.6, SSP2-4.5, and SSP5-8.5), we evaluated the flood control potential of reservoirs under future climate conditions. When the reservoirs were empty, the damage cost reduction rate resulting from the use of reservoirs across Japan was small, ranging from 1.1% to 2.3%, but as the damage cost reduction rate did not change under all future scenarios, reductions in flood damage were not affected by changes in rainfall under future climate conditions. Moreover, some prefectures showed high damage cost reduction effects. In northern part of Japan and numerous prefectures in western Japan, the potential to reduce damage through flood control by irrigation reservoirs was high. Some prefectures experienced similar reduction levels as those under alternative adaptation strategies. In the Kanto region, flood control by irrigation reservoirs had low potential for reducing damages. Even among prefectures with low water storage capacities of irrigation reservoirs, the potential to mitigate the effect of damage was high.
Climate change places considerable stress on riverine ecosystems by altering flow regimes and increasing water temperature. This study evaluated how water temperature increases under climate change ...scenarios will affect stream invertebrates in pristine headwater streams. The studied headwater-stream sites were distributed within a temperate catchment of Japan and had similar hydraulic-geographical conditions, but were subject to varying temperature conditions due to altitudinal differences (100 to 850 m). We adopted eight general circulation models (GCMs) to project air temperature under conservative (RCP2.6), intermediate (RCP4.5), and extreme climate scenarios (RCP8.5) during the near (2031–2050) and far (2081–2100) future. Using the water temperature of headwater streams computed by a distributed hydrological-thermal model as a predictor variable, we projected the population density of stream invertebrates in the future scenarios based on generalized linear models. The mean decrease in the temporally averaged population density of Plecoptera was 61.3% among the GCMs, even under RCP2.6 in the near future, whereas density deteriorated even further (90.7%) under RCP8.5 in the far future. Trichoptera density was also projected to greatly deteriorate under RCP8.5 in the far future. We defined taxa that exhibited temperature-sensitive declines under climate change as cold stenotherms and found that most Plecoptera taxa were cold stenotherms in comparison to other orders. Specifically, the taxonomic families that only distribute in Palearctic realm (e.g., Megarcys ochracea and Scopura longa) were selectively assigned, suggesting that Plecoptera family with its restricted distribution in the Palearctic might be a sensitive indicator of climate change. Plecoptera and Trichoptera populations in the headwaters are expected/anticipated to decrease over the considerable geographical range of the catchment, even under the RCP2.6 in the near future. Given headwater invertebrates play important roles in streams, such as contributing to watershed productivity, our results provide useful information for managing streams at the catchment-level.
Display omitted
•Anticipated climate changes might alter the habitat of stream animals.•Hydrological and climate models were used to project future stream temperature.•Invertebrate density was projected by future stream temperature.•Spatial distribution of density reduction was projected in a catchment.•Partial taxa in Plecoptera family were sensitive indicator of climate change.
The Tohoku region, Northeast Japan, was hit by a gigantic earthquake which occurred in the Pacific close to Tohoku, and subsequently by a giant tsunami. These hazards have caused huge damage on the ...eastern coast Japan. The earthquake’s magnitude was 9.0, the strongest ever recorded in Japan. The tsunami was also historical as its run-up height reached over 39 m. As of early May, 2011, over 24 thousand people were reported as dead or missing. Moreover, serious accidents at the Fukushima Nuclear Power Plants No.1 were caused by the effects of the tsunami. Therefore, the damage faced by Japanese people can be seen as a giant composite disaster. Although Japan, and the northeast of Japan in particular, has over a long time period increased its preparedness against earthquakes and tsunamis, huge damage still occurred. This paper considers why this tragedy occurred, and what unrecognized factors contributed to the high vulnerability of the area. To assist in answering such questions, this paper presents a timely report of the features of the earthquake and tsunami, the damage they caused, and the early efforts for recovery and reconstruction.
•Climate change impact on irrigation cost is assessed using empirical models.•Groundwater level will decline by 0.45–2.71 m under climate change scenarios.•Groundwater-based irrigation cost will ...increase by 1.61–9.82 U$/hectare.•Changes in irrigation cost depends on climate change scenario and geologic setup.
The objective of the present study was to assess the impacts of climate change on irrigation cost in a groundwater dependent irrigated region in northwest Bangladesh. An ensemble of general circulation model (GCMs) were used for the projection of climate, an empirical hydrological model based on support vector machine (SVM) was used to simulate groundwater level from climatic variables, and a multiple-linear regression (MLR) model was used to estimate the irrigation cost due to the changes in groundwater level. The results revealed a declination of average groundwater level in the study area in the range of 0.45 – 01.19 m, 0.55–1.79 m, and 0.76–2.71 m under three representative concentration pathways (RCP) scenarios namely, RCP2.6, RCP4.5 and RCP8.5, respectively and therefore, an average increase in irrigation cost in the range of 1.61 to 9.82 USD/hectare at 95% confidence level. The maximum declination of groundwater level was projected in the northeast part of the study area in the range of 2.23–4.12 m by the GCM MIROC-ESM-CHEM which might cause an increase of irrigation cost in the range of 8.07 to 14.79 USD/hector. The study concludes that the impact of climate change-induced fluctuations in groundwater level on crop production cost is much less compared to other costs, but it may be significant in locations where groundwater level is declining fast.
•Multitemporal UAV observations were for the post-fire heavy rain-affected area.•Substantial geomorphological changes were related to landslides and stream shifting.•The change in the vertex normal ...vector effectively captured the shape of the change.•The logSPI was utilized to classify the geological characteristics roughly.•Both logged-burnt and unlogged-burnt areas were highly affected by heavy rain.
Unmanned aerial vehicles (UAVs) are widely utilized for surveying various sediment disasters, and the high-resolution imaging they provide reveals detailed topographic characteristics. However, the availability of multitemporal UAV observations, which reveal geomorphological changes before and after the disaster, is still limited. In this research, we performed multitemporal UAV observations for geomorphological changes before and after extreme postfire heavy rain in the Ozaki Peninsula wildfire area in Japan. Significant geomorphological changes were observed associated with eight landslides and stream shifting, with a spatial resolution of 0.30 cm obtained by structure from motion (SfM) processing. To extract the surface changes based on multitemporal UAV observations, in addition to elevation displacement, vertex normal vectors were calculated for each mesh. We found that the elevation displacement showed comprehensive alterations in the entire area and that the changes in vertex normal vectors effectively captured the shape of these alterations. Deterioration, deposition, and scarping were shown for landslides, and the dynamics of erosion and deposition in the cross-section were for stream shifting. In addition, the detected geomorphological changes were compared with the predisaster topographic characteristics. Landslides occurred with a catchment area of 500 to 2,000 m2 and a slope inclination of 30 to 40°, and stream shifting occurred with a catchment area of 10,000 m2 or more and a slope inclination of less than 20°. In both regions affected by landslides and stream shifting, the logarithmic stream power index (logSPI), a natural logarithmic representation of the conventional stream power index (SPI), could describe the characteristics roughly. A logSPI value of 4 to 5 represented landslides, and 5 and greater represented stream shifting, with the probability of landslides and stream shifting occurring in areas with these values exceeding 99.5% and 99.9%, respectively. Therefore, the logSPI was utilized to roughly classify the terrain and geomorphological condition and the points among the unburnt, unlogged-burnt, and logged-burnt areas were compared. Even when the logSPI was similar, the damage was much more severe in the burnt areas. On slopes with a logSPI of approximately 4, there were signs of erosion in the logged-burnt area, and the increase in fallen trees was significant in the unlogged-burnt area, while there were no substantial changes in the unburnt area. In valleys with a logSPI of 8 or greater, sediment and woody debris were significantly deposited in the burnt areas following the postfire rain, while there were few changes in the unburnt area.
This study develops a model to estimate the spatiotemporal distribution of stream algae on a basin scale by integrating an existing periphyton model into a distributed hydrothermal model to calculate ...the daily periphyton biomass throughout the Natori River basin. The influence of inorganic phosphorus on periphyton growth is incorporated into the periphyton model. The inorganic phosphorus concentration is simulated using the distributed pollute model depending on land use data to determine the phosphorus load. The model had a root mean square error (RMSE)=14.1mg/m2 for periphyton biomass in the entire basin. This model shows that periphyton biomass tends to increase in the summer season with high water temperature and to decrease in the spring season with high discharge. This model can be applied to understand large spatial and temporal areas of the environment in a temperate catchment.
Freshwater biodiversity undergoes degradation due to climate change. Researchers have inferred the effects of climate change on neutral genetic diversity, assuming the fixed spatial distributions of ...alleles. However, the adaptive genetic evolution of populations that may change the spatial distribution of allele frequencies along environmental gradients (i.e., evolutionary rescue) have largely been overlooked. We developed a modeling approach that projects the comparatively adaptive and neutral genetic diversities of four stream insects, using empirical neutral/ putative adaptive loci, ecological niche models (ENMs), and a distributed hydrological-thermal simulation at a temperate catchment under climate change. The hydrothermal model was used to generate hydraulic and thermal variables (e.g., annual current velocity and water temperature) at the present and the climatic change conditions, projected based on the eight general circulation models and the three representative concentration pathways scenarios for the two future periods (2031–2050, near future; 2081–2100, far future). The hydraulic and thermal variables were used for predictor variables of the ENMs and adaptive genetic modeling based on machine learning approaches. The increases in annual water temperature in the near- (+0.3–0.7 °C) and far-future (+0.4–3.2 °C) were projected. Of the studied species, with different ecologies and habitat ranges, Ephemera japonica (Ephemeroptera) was projected to lose rear-edge habitats (i.e., downstream) but retain the adaptive genetic diversity owing to evolutionary rescue. In contrast, the habitat range of the upstream-dwelling Hydropsyche albicephala (Trichoptera) was found to remarkably decline, resulting in decreases in the watershed genetic diversity. While the other two Trichoptera species expanded their habitat ranges, the genetic structures were homogenized over the watershed and experienced moderate decreases in gamma diversity. The findings emphasize the evolutionary rescue potential, depending on the extent of species-specific local adaptation.
Display omitted
•Adaptive process was considered to project genetic diversity under climate change.•A hydrologic model projected future increase in stream temperature up to 3.2 °C.•A mayfly species lost partial habitats but retained genetic diversity.•Caddisfly species gain new habitats but experienced genetic homogenization.•Considering adaptation potentials is central to safeguarding genetic diversity.
PDF
