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The impacts of climate change on snowfall have received great interest in cold regions for water resource and flood risk management. This study investigated the effects of rises in air and sea surface temperatures and sea ice on snowfall in Hokkaido, northern Japan, over the period from 1961 to 2020 (60 years). Climate data observed at the 22 weather stations operated by the Japan Meteorological Agency (JMA) were analyzed. Statistics describing the effects of climate change on snowfall were computed. The trend in these quantities was obtained using Sen’s slope estimator, and their statistical significance was evaluated by the Mann–Kendall test. The warming trends obtained at these stations were all positive and statistically significant. Annual snowfall increased at seven stations but decreased at two stations. The snowfall period decreased mainly on the southern coast. This is attributed to the fact that these sites are on the leeward side of the Eurasian monsoon, and that air temperatures on the coast and the surface temperature of the sea off Kushiro have risen sufficiently. The results suggest that the flood risk may increase in response to the acceleration of the increase in the level of a river due to early melting snow in spring (March and April). Although the weather stations on the east coast are also on the leeward side, the snowfall period has not shortened. The warming trends in April are very weak on the east coast. The correlation between the air temperature in March and April and the period of sea ice accumulation suggests that melting sea ice in spring plays an important role in preventing the winter period from shortening. Decrease in sea ice due to a rise in both air and sea surface temperatures may increase flood risk in early spring, and thus, some measures may need to be taken in the future.

Spatiotemporal change in precipitation induced by climate change can be a concern for riverine disasters. The relationship between precipitation and flow discharge in the 8 rivers from northeast to southwest of Japan (either mainstream or tributary) in which neither manmade dam nor reservoir is present was investigated based on observed data at the stream gauging stations managed by the Ministry of Land, Infrastructure, Transport and Tourism of the Japanese government. Observed data of air temperature, precipitation, etc. by the Japan Meteorological Agency vicinity of the gauging station in the 8 rivers basins were also used in the analyses. The precipitation concentration index (PCI) which is the Gini coefficient of precipitation during a year, and the Gini coefficient of flow discharge were computed for about half a century. The results reveal that annual maximum flow discharge can be related closely to the extreme rainfall events such as annual maximum daily or hourly precipitation. Obtained trends of the PCI were all positive and statistically significant at the 1% level, indicating that an in – equality in rainfall distribution during a year has been accelerated as the air temperature has risen in the basins. Whereas obtained trends of the Gini coefficient of the flow discharge were either positive or negative, and very weakly correlated with the trends in the PCI. Temporal precipitation distributions in a year have changed in the 8 rivers basin, i.e. light rain days (0 – 1 mm/day) have increased whereas rain days with 1 – 10 mm/day have decreased, while no such trend is seen in flow discharge in the 8 rivers. The interaction between surface and subsurface flows, and soil moisture may play important roles in moderating the effects of spatiotemporal change in precipitation. The flow discharge, however, can increase immediately in response to the precipitation when rainfall intensity is sufficiently strong.

Air temperature and precipitation data observed and recorded by the Japan Meteorological Agency (JMA) from 1906 to 2005 were analyzed. Observed trends and correlations at 16 weather stations in urban and rural areas over Japan from Nemuro in the north (43.3oN) to Ishigaki in the south (24.3 N) were identified and quantified. Average annual values were emphasized in a previous analysis (Higashino and Stefan 2014). Herein monthly values and extreme events at the daily and hourly timescale were extracted and interpreted. As shown in 2014, observed air temperature rises are much larger in urban than in rural areas and are statistically significant at all sites. Air temperature rises in Japan in the period 1906–2005 are strongest in spring (March, April, and May) and weakest in midsummer (July and August). Monthly air temperature rises have accelerated over time by a factor of about 3 from the period (1906–2005) to (1981–2005), except for a short period in August. In the period (1906–2005), daily minimum air temperature rises have occurred at all sites. Daily and yearly minimum air temperature trends are more than twice as strong as daily and yearly maximum temperature trends. The numbers of annual hot days and hot nights have also increased at most of the study sites in the period (1906–2005), but only the number of hot nights and the daily minimum air temperature are strongly correlated with annual average air temperature increases. The trends in the annual numbers of frost days and hot nights are well correlated with the annual average air temperature trend, one negative, the other positive, as to be expected. Trends in mean annual precipitation are very small, near zero for (1906–2005), mostly negative for 1956–2005, and mostly positive for 1981–2005. There is no correlation with trends in air temperature. Daily maximum precipitation for (1906–2005) and (1956–2005) shows only small and often non-statistically significant changes at the 16 study sites. In (1981–2005), trends have increased significantly but fluctuate significantly between positive and negative trends.

Saturated/unsaturated pore water flow induced by rainwater infiltration in a soil column composed of a mixture of Toyoura sand and a small amount of clay (kaolin minerals) and the rinsing rate (mass transfer) of dissolved NaCl accumulated in the pore system from previous road salt application were investigated by experiments and simulations. Experiments were conducted with variable kaolin minerals mass contents (mixing ratios) in the soil columns. Measured saturated hydraulic conductivity ( K s ) diminished with increased clay contents, i.e., K s =0.00771, 0.00560, 0.00536, 0.00519, and 0.00314 cm s −1 , for clay contents = 0.2, 0.5, 1, 2, and 5%, respectively. Experimental NaCl concentrations in the effluent from the bottom of the soil columns were about constant for times t ≈ 800, 1200, 1300, 1400, and 3400 s from the beginning of a rinsing experiment for the clay contents = 0.2, 0.5, 1, 2, and 5%, respectively. These NaCl concentrations then decreased with time quickly, and finally, approached zero. The presented model can reproduce experimental time variations of NaCl concentration in the effluent from the soil column reliably. Simulated salt mass left in the soil column with time also matches the experimental results for the clay contents = 0.2 and 0.5%. An inconsistency between simulated and experimental salt mass left in the soil columns becomes more significant as the clay content increases. These results suggest that the soil–water retention curve for the pure Toyoura sand can be applied to the soil column composed of kaolin minerals/Toyoura sand mixture when the clay content is small, i.e., less than 1%. Prediction of rinsing process becomes more difficult with increased clay content. However, the time required to remove saline water from the soil column to less than 1% of its initial value simulated by the model agrees closely with experimental results of 1000, 1500, 1700, 2100, and 5400 s, respectively.

Mallory−Weiss syndrome (MWS) is a common cause of gastroesophageal bleeding. Vomiting increases intra‐abdominal and intra‐esophageal pressures, causing hyperextension of the esophagogastric junction and laceration. Most affected patients respond well to conservative treatment; however, those with active bleeding require endoscopic intervention. Upon contacting blood, PuraStat gels and coats the bleeding point to achieve hemostasis. PuraStat is reportedly effective for non‐variceal bleeding and bleeding associated with endoscopic procedures. However, there have been no reports on the use of PuraStat in MWS. Here we report a case in which PuraStat was useful for achieving hemostasis in a patient with MWS and difficult‐to‐achieve hemostasis. The patient was a 67‐year‐old man who had undergone coronary artery bypass grafting 1 month earlier and was taking an antithrombotic drug. He visited our hospital with bloody vomiting and melena in the evening and was diagnosed with upper gastrointestinal bleeding for which he underwent endoscopy. MWS with active bleeding was observed in the lower esophagus extending to the esophagogastric junction. We treated the patient with clipping; however, the oozing did not stop because of the large laceration. We applied PuraStat to the bleeding site and confirmed that the oozing had resolved; therefore, the procedure was terminated. The endoscope was reinserted the next day and confirmed the hemostasis. The patient was discharged without further deterioration. In patients with MWS with active bleeding, endoscopic hemostasis is commonly achieved using clips or endoscopic band ligation. However, PuraStat can achieve complete hemostasis when these techniques fail.

Mass transport and residence time of saline water from road salt applications in soil columns composed of Toyoura sand and weathered granite sand were investigated by simulations and in laboratory experiments. Both are sands found in Japan, especially the weathered granite sand. The Toyoura sand has a fairly uniform particle size of 0.1 to 0.4 mm diameter, and a saturated hydraulic conductivity Ks = 0.0296 cm/s, while the weathered granite sand used consisted of 13% fine materials (silt and clay) and 87% coarse materials (sand and gravel) with a saturated hydraulic conductivity Ks = 0.00393 cm/s. A model was developed to simulate rinsing of brine from a soil column. Assuming a steady, homogeneous flow induced by rainwater infiltration into the soil column, the model was found to match the experimental results for Toyoura sand very well. The normalized salt concentration in the effluent from the 40 cm tall soil column remained constant until about t = 500 s; the concentration then decreased with time quickly and, finally, approached zero. For the weathered granite sand, however, the salt concentrations in the effluent simulated by the model with assumption of homogeneous flow are inconsistent with the experimental data collected. A substantial delay occurs in mass transport of salt from the column, which is different from the Toyoura sand. The delay is attributed to shifts in “active” and “inactive pores” created in the soil due to fine particles such as silt and clay. The proportion of “active pores” and “inactive pores” is not constant but variable with time due to physical and/or electrochemical processes such as pore-size distributions and salt depletion in the soil. A modified model presented, using a time-variable active pore parameter k(t), can reproduce the experimental results for salt mass left in the soil better.

The time point of the most precise predictor of hepatocellular carcinoma (HCC) development after viral eradication with direct-acting antiviral (DAA) therapy is unclear. In this study we developed a scoring system that can accurately predict the occurrence of HCC using data from the optimal time point. A total of 1683 chronic hepatitis C patients without HCC who achieved sustained virological response (SVR) with DAA therapy were split into a training set (999 patients) and a validation set (684 patients). The most accurate predictive scoring system to estimate HCC incidence was developed using each of the factors at baseline, end of treatment, and SVR at 12 weeks (SVR12). Multivariate analysis identified diabetes, the fibrosis-4 (FIB-4) index, and the α-fetoprotein level as independent factors at SVR12 that contributed to HCC development. A prediction model was constructed with these factors that ranged from 0 to 6 points. No HCC was observed in the low-risk group. Five-year cumulative incidence rates of HCC were 1.9% in the intermediate-risk group and 15.3% in the high-risk group. The prediction model at SVR12 most accurately predicted HCC development compared with other time points. This simple scoring system combining factors at SVR12 can accurately evaluate HCC risk after DAA treatment.

High optical absorptivity or a large absorption cross-section is necessary to fully utilize the irradiation of light for photothermal heating. Recently, titanium nitride (TiN) nanostructures have been demonstrated to be robust optical absorbers in the optical range owing to their nonradiative decay processes enhanced by broad plasmon resonances. Because the photothermally generated heat dissipates to the surroundings, suppressing heat transfer from TiN nanostructures is crucial for maximizing the photothermal temperature increase. In the current work, compared to the planar TiN film, high-aspect-ratio TiN nanostructures with subwavelength periodicities have been demonstrated to enhance the photothermal temperature increase by a 100-fold using nanotube samples. The reason is attributed to the extremely anisotropic effective thermal conductivities. Our work has revealed that high-aspect-ratio TiN nanostructures are effective in improving photothermal heating, and they can be used in various applications, such as solar heating, chemical reactions, and microfluidics.

Variability and change of precipitation were investigated in Kumamoto on Kyushu Island in southwestern Japan, to assess water resources and flooding risk. Annual precipitation, annual maximum daily precipitation, and annual maximum hourly precipitation have increased over the period from 1891 to 2018 (128 years). Trends are 26.2 mm per decade, 6.07 mm/day per decade, and 2.17 mm/h/decade, respectively. Precipitation in the rainy season (June and July) is on average 37% (ranging from 12 to 59%) of annual precipitation for the 128-year period. Maximum daily precipitation in a year occurred at Kumamoto in the rainy season in 92/128 (72%) of the years of observation from 1891 to 2018, in the typhoon (August to November) season in 23/128 (18%), and in the March to May season in 12/128 (10%). This indicates that the rainy monsoon season poses the largest daily flooding risk. A wavelet analysis revealed that from 1891 to 2018 annual precipitation and daily maximum precipitation fluctuate with 2 and 4 years periods, which may be related to the El Nino-Southern Oscillation (ENSO). It is likely that air temperature rises, ENSO and topographical characteristics contributed to an increase in precipitation in the period. The analysis also showed that typhoons hitting or approaching Kumamoto have significantly affected annual precipitation and annual maximum daily precipitation, while the interval between typhoons affecting Kumamoto has been getting longer since the 1970s.

The water temperature regime of the Oita River on Kyushu Island (33°N latitude) in southern Japan is illustrated and analyzed, and related to the river’s hydrology. The river is short (55 km) and steep (ave. slope = 0.088), and has a flashy flow regime. Precipitation is high (1653 mm year −1 ) and divided between a wet monsoon season, typhoons, and a dry season in winter. A base flow analysis showed that groundwater contributes about 50 % of the annual flow to the Oita River and controls the river’s heat budget. At a measured mean annual temperature of ~16 °C, groundwater (base flow) input causes unexpected cool (≤24 °C) river temperatures in summer and warm (≥8 °C) river temperatures in winter. The Oita River is typical of many Japanese rivers. Its hydraulic residence time is very short (0.5–1.5 days) and limits the heat exchange with the atmosphere so that a significant deficit remains between observed river water temperatures and equilibrium temperatures in mid-summer and mid-winter. Correlations of recorded stream temperatures with atmospheric temperatures (air, dew point and equilibrium temperatures) were strong. Weekly air and stream temperature data (averaged from 10-min measurements) were fitted by linear regressions with R 2  = 0.98 and RMSE = 0.83 °C. Daily data were only slightly less well correlated with R 2  = 0.96 and RMSE = 1.17 °C. The relationships were highly linear. The slope of the stream temperature vs. air temperature correlation was in the range from 0.63 (weekly) to 0.58 (daily) indicating that stream temperatures are dominated by groundwater input. Air and stream temperatures have a strong correlation in both wet (monsoon) and dry seasons, and geothermal heat input has no basin-wide effect; the 50 % groundwater (base flow) input raises the annual mean and reduces seasonal temperature amplitude in the Oita River and provides a cool-water stream. Water temperatures were gathered from a long-term monitoring database and by recent (2012–2013) high-resolution in-stream monitoring. Key drivers of stream temperature were identified. Linear regressions were used to relate air temperature, dew point temperature, and equilibrium temperature with stream temperature. Groundwater was identified as a key input of water consistently around 16 °C, moderating temperatures in the summer and winter due to very short water residence times in the steep and short river. This paper contributes to the body of knowledge about global stream temperatures, and clarifies specific questions for Japanese rivers.