Evapotranspiration is a critical factor that plays a pivotal role in irrigation and water resource planning. It is also a major influence with regard to global warming issues. Therefore, several studies have been performed on the estimation methods for evapotranspiration; however, the most prevalent method used over a long period to estimate evapotranspiration is the complementary relationship approach. Recently, this method was modified to improve its symmetry and accuracy. However, to achieve better performance, a different evapotranspiration estimation method using an inverse analysis of the Bowen ratio was proposed by us in an earlier study. In order to present a performance comparison of these different estimation methods, the reproducibility of three types of complementary relationship methods and inverse analysis methods was assessed in this study. Our study utilized data from FLUXNET2015 and evaluated the performance of the methods using regression analysis and root mean square error (RMSE) with data from 15 test sites, mainly located in the U.S.A., for a total period of 132 years. From the results, it was observed that the inverse analysis approach demonstrated a slightly better performance than the complementary relationship methods. This study provides a valuable direction for future research works on the estimation of evapotranspiration.

Drylands cover approximately 40% of the Earth's land surface and account for up to 44% of cultivated lands. Therefore, evapotranspiration in drylands is an essential indicator of global warming because net radiation is partitioned into sensible (H, warming) and latent (LE, cooling) heat flux. This study aimed to estimate H (Hest) and LE (LEest) in arid regions using an inverse analysis (IA) method. The observed sensible (Hobs) and latent energy fluxes (LEobs) were compared with Hest and LEest over four time scales to confirm the reliability of the method, demonstrating that Hest and LEest were highly similar to Hobs and LEobs. Estimation accuracy was evaluated by the root mean squared error (RMSE) at each time scale, indicating that Hest and LEest can be reasonably estimated using IA. The method is expected to contribute significantly to estimating evapotranspiration for global warming research by providing for estimating H and LE in drylands.

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Evapotranspiration (ET) is a critical concern for water management and hydrological cycle; thus, studies of ET have been performed to aid irrigation and water resource planning. Moreover, global warming-related studies are critical, as sensible heat contributes to warming, while the latent heat flux contributes to cooling. Recently, FLUXNET2015, a large energy flux dataset comprising climatic elements, was updated with a corrected heat balance relationship. In this study, we aim to applicability of the inverse analysis (IA) for estimating farmland ET. Practically, we evaluated the estimated ET (LEest) consistency using IA, which compared common climate data with observed data (LEobs) from US-Ne1 (irrigated), US-Ne2 (irrigated), and US-Ne3 (non-irrigated) land in FLUXNET2015. For an hourly time step, net radiation (Rn) and heat flux into the ground (G) were reasonably allocated into sensible (H) and latent (LE) heat fluxes, and LEobs was reasonably reproduced by LEest. For daily and monthly time steps, LEobs was reproduced well by LEest, with similar accuracies. For a yearly time step, LEobs was reproduced by LEest with an R2 of 0.933. Reasonability of the IA method also confirmed ET in crop growing season by comparing LEobs and LEest. A cooling effect under the canopy was observed on irrigated farmland in eight of the 22 analyzed years, whereas non-irrigated farmland did not exhibit a cooling effect. The maximum cooling effect was 4.26 degrees C of the monthly average. The results confirm that IA can be applied to nonirrigated and irrigated farmland if a cooling effect is not observed. IA can therefore be used to improve farmland water utilization because of accurate LEest and determining the capacities of irrigation facilities. The findings can be used to evaluate cooling effects on farmland, as well as reasonable allocations of Rn into H and LE, which promote the advancement of global warming issues.

Conventionally, the Bowen ratio method and eddy covariance are used to measure evapotranspiration (ET); however, they have limited accuracy. Inverse analysis (IA), a novel method presented here, can estimate evapotranspiration (ETa) using commonly measured climatic variables. However, because actual ET data are limited, the accuracy of IA remains uncertain. Recently, IA accuracy has been improved, thus, observed latent heat flux (lEobs) in FLUXNET2015 data, a global dataset, and estimated values can be compared. Herein, we aim to evaluate the accuracy of the IA method. Eight forest sites in the dataset during 2000-2014 were selected as test sites, and hourly, daily, monthly, and yearly comparisons of lEobs and ETa were conducted using regression analysis and root mean square error (RMSE) calculations. The results are as follows: (sic) Comparison of lEobs-hourly and ETa for all sites showed a similar pattern, with an average root mean square error (RMSE) of 0.0053 mm h(-1). (sic) Comparison of lEobs-daily and ETa showed high correlation coefficients, with slopes ranging from 1.016-0.717 and an average RMSE of 1.08 mm h(-1). (sic)Comparison of lEobs-monthly and ETa showed similar patterns, with slopes ranging from 1.042-0.811 and an average RMSE of 17.9 mm m(-1). (sic) The slope of lEobs-yearly and ETa was 0.988 and the average RMSE was 71.0 mm year(-1). (sic) The average of lEobs-yearly and ETa showed a strong relationship, with a slope of 0.992. (sic) The differences between the time steps of lEobs and ETa were evaluated qualitatively using RMSE/lEobs-yearly, with hourly-yearly differences of 8.4%, 70.2%, 40.4%, and 14.2%, respectively. The above results indicate that IA can be used for an accurate estimation of ET. The findings of this study contribute significantly to water management and a deeper understanding of the hydrologic cycle.

First, this paper proposes a definition of the abnormal data that occur as the Bowen ratio (B-0) approaches -1. The data are defined as a times of the heat flux supply (Rn-G), thus indicating the rejection range for the B-0. The method is applied to observed data. Second, we compare the results of the B-0 method with those of the inverse analysis of Bowen ratio method (IABM). The IABM can estimate the sensible and latent heat flux using temperature and humidity observed at a single height above the ground by optimization. Third, the estimation of the monthly evapotranspiration required for water resources and irrigation planning is adequate for alpha = 1(similar to)3 in the B-0 method and IABM, and the initial humidity for IABM is adequate for 80% of the observed humidity plus 20%. Fourth, the features of the analysis of both methods regarding the direction of latent heat flux (lE) and sensible heat flux (H) associated with temperature difference (Delta T) and vapor pressure (Delta e) clarified. And we found that the number of the rejected data in hourly and monthly is remarkably large in B-0 method than IABM. Based on above results, the IABM has almost the same performance compared with the B-0 method excluding initial value determination in the optimization process.

2014年10月に手取川上流で発生した大規模な土砂崩壊によって,平均で585度(カオリン),最大で4,012度(カ オリン)という高濃度の濁水が2015年灌漑期に観測された.この高濃度濁水が手取川扇状地内の地下水循環に影響を及ぼすことが懸念されているが,影響の実態は不明なままである.そこで,本研究では,高濃度濁水が手取川扇状地内の水田浸透量に与える影響について明らかにすることを試みた.濁水発生前の2014年,濁水発生後の2016年を対象として,45地区の水田で減水深調査を行い,水田浸透量の変化を分析した.その結果,2014年の水田浸透量の平均値は12.4 mm/dayであるのに対して,2016年は7.9 mm/dayであり,水田浸透量が有意に減少していることが明らかとなった.また,水田浸透量が減少した地区は,扇端部に多くみられ,これは粒径の細かい土砂が扇端部に多く供給されたためと考えられた.水田浸透量の観測結果に基づいて扇状地全体の地下水涵養量の変化を概算すると,水田からの涵養量(浸透量)は濁水発生前より36 %減少し,扇状地全体の地下水涵養量が濁水発生前より25 %減少したことが示された.

Recently severe damage of flooding by urbanization was frequently occurred. To prevent this damage, small reservoir was constructed in the urbanized residential area. This paper describes an effect of flood peak discharge control by a small reservoir (control reservoir) caused by rapidly developed urbanization. Although work for this purpose was conducted, research on the effects of the control reservoir was not conducted until now. This research, conducted by simulation, was a case study in the Kurabe River Basin in the Tedori River Alluvial Fan Area, Japan, based on the precise investigation of the reservoir in the actual field. The study was conducted to determine not only the actual control reservoir capacity for the newly developed residential area but also the ideal capacity for all present residential areas and the largest capacity allowable for a maximum rainfall event that recently occurred. The control reservoir effects between individual blocks and the entire basin area were compared by dividing the test basin into 15 blocks (sub-basins). The results showed that the effects on the capacity per unit area of the residential area in blocks have close relationship with the decreasing ratio of peak discharge in blocks. Consequently, the effects of control reservoir capacity and the limitation were clarified. In the future, control reservoirs should be constructed for all of the already developed residential areas, for example, by utilizing underground car parking lot. The results of this research can contribute to the design of the control reservoir for protection against flooding damage in urbanized areas.

Flood runoff models of urbanization from farmland based on the physical characteristics of a basin have been minimally used in previous research until today. Consequently, the runoff analysis has not been performed that is based on physical basis. Therefore, this research undertook flood discharge analysis from urbanization using the unit flood discharge concept that is enhanced the previous research. The study area was selected at the Kurabe River basin, which is 17.5 km2 in area having a very steep landscape. Twenty-one rainfall events at 10-minute intervals were selected, and five urbanized years were tested. From 1976 to 2009 during 35 years, the flood discharge increased approximately 2.0 times, in which residential areas increased from 23% to 48%; the maximum specific discharge was 21.7 m3·s-1·km-2 in a some block, which is a remarkably large amount. Furthermore, following issues investigated: changes in the hydrograph were associated with urbanization, the effect of a small reservoir aiming to cut down the peak discharge and the relationship between the unit discharge, and the relationship between our method and the discharge estimated by a “Rational Formula”. In particular, the effect of the small reservoir for flood control was found to be remarkably efficient. Finally, the validity of our method was confirmed at the study area in the observed discharge. This result is very useful for estimating runoff discharge changes by urbanization from farmland.

There is no word to describe the importance of evapotranspiration research for water resource utilization.We have already proposed a new method for the reciprocal estimation of the sensible (H) and latent heat fluxes (lE) by using a single height temperature (Tz) and humidity (rehz) based on the observed net radiation (Rn) and ground heat flux (G).This research is more advanced than the previous research because it uses a Ts observed by a radiometer and identifies the observed data satisfactorily heat balance relationship in every hour at nine sites.First, we confirmed that the estimated H and lE are very close reproductions of the identified H and lE.Second, by analyzing the relative ground surface temperature (Ts -T 0 ) [Ts: ground surface temperature, T 0 : observed temperature near the soil surface], the hourly and seasonal changes of (Ts -T 0 ) were clarified, resulting in a marked difference in the (Ts -T 0 ) from previous research in arid and semi-arid regions.Next, the estimation accuracy of H, lE and rehs (the humidity of the soil surface) was determined by observing the slope of the estimated and observed relationship, resulting in the reasonable accuracy (0.85 -1.15 times) of rehs at seven of the nine sites.Furthermore, the annual evapotranspiration was estimated by comparing the identified and estimated H and lE, resulting in a reasonable accuracy (0.85 -1.15) at five of the nine sites in the case of the application of constraint b.Moreover, the effect of the lag-time between the net radiation Rn and both Tz and Ts for the estimation accuracy on H and lE was tested, and no remarkable difference was found because the effect was included already in the original data.The above results will contribute greatly to the advance of water resource planning and hydrometeorology.This research was conducted using FLUXNET data.

Sensible and latent heat flux at semi-arid and arid region, i.e., evapotranspiration, has been researched for long time because it serves an important role for water resource issues. However, the issues have not solved completely yet. Accordingly, by applying the Bowen ratio concept on the soil surface, the sensible and latent heat fluxes are reciprocally estimated using single height temperature (Tz) and humidity (rehz) with the net radiation (Rn) and heat flux into the ground (G). The procedure proposed by authors initially estimates the soil surface temperature (Ts) and the relative humidity (rehs) using optimization techniques. The method is remarkably effective to expand for estimating evapotranspiration at various regions. The validity of the method is confirmed by the latent heat flux (lE) and sensible heat flux (H) observed by the eddy covariance method. The hourly change of the lE, H, Ts and rehs on the soil surface, yearly change of lE and H and relationship of estimated lE and H versus observed are clarified. Yearly change of evapotranspiration is also estimated. The analysis is performed by general method (1), conventional method and general method (2). Above results are very useful for water resources issue and irrigation planning. The research is conducted using hourly data at eight globally dispersed sites using FLUXNET.

Evapotranspiration in forests has been researched for a long time because it serves an important role in water resource issues and biomass production. By applying the reciprocal analysis based on the Bowen ratio concept to the canopy surface, the sum result of sensible and latent heat fluxes, i.e., actual evapotranspiration (ET), is estimated from engineering aspect using the net radiation (Rn) and heat flux into the ground (G). The new method uses air temperature and humidity at a single height by determining the relative humidity (rehs) using the canopy temperature (Ts). The validity of the method is confirmed by the latent heat flux (lE) and sensible heat flux (H) observed by mean of eddy covariance method. The heat imbalance is corrected by multiple regression analysis. The temporal change of lE and H at the canopy surface is clarified using hourly and yearly data. Furthermore, the observed and estimated monthly evapotranspiration of the sites are compared. The research is conducted using hourly data and the validation of the method is conducted using observed covariance at five sites in the world using FLUXNET.

We proposed unit flood discharge model that defined as the discharge into end-order (smallest) drainage canals. The discharge acts an important role for estimating regional flooding by big rainfall events which leading roughly estimation of flood discharge associated with land use changes as urbanization. In some areas of Japan, increased urbanization with insufficient drainage canal capacity has led to increasingly frequent flooding and flood damage. The aim of this study was to investigate the effect of urbanization on unit flood discharge using a runoff model for the Tedori River alluvial fan area, Japan. The discharge was studied as collecting runoff from paddy fields, upland crop fields, and residential lots. A runoff model for various land use types in the study area was developed using actual and physical properties of the runoff sites, and parameters for paddy fields. The model was tested using 54 big events and inputted those. The maximum total runoff ratio among different land use types was observed for residential lots, and the ratio remained relatively constant across different flood events. The minimum total runoff ratio was observed for irrigated paddy fields. There was a positive relationship between the total runoff ratio and total precipitation for all land use types. Whereas, the relationship between the peak runoff ratio and peak precipitation was variable. The runoff analysis was carried out using 60-min and 10-min precipitation data. For agricultural land, data for both intervals produced similar results.

Evapotranspiration acts an important role in hydrologic cycle and water resources planning. But the estimation issue still remains until nowadays. This research attempts to make clear this problem by the following way. In a humid region, by applying the Bowen ratio concept and optimum procedure on the soil surface, sensible and latent heat fluxes are estimated using net radiation (Rn) and heat flux into the ground (G). The method uses air temperature and humidity at a single height by reciprocally determining the soil surface temperature (Ts) and the relative humidity (rehs). This feature can be remarkably extended to the utilization. The validity of the method is confirmed by comparing of observed and estimated latent (lE) and sensible heat flux (H) using the eddy covariance method. The hourly change of the lE, H, Ts and rehs on the soil surface, yearly change of lE and H and relationship of estimated lE and H versus observed are clarified. Furthermore, monthly evapotranspiration is estimated from the lE. The research was conducted using hourly data of FLUXNET at a site of Japan, three sites of the United States and two sites of Europe in humid regions having over 1000 mm of annual precipitation.

本研究では積雪深の再現を主目的として，石川県林業試験場内の気象露場で観測された積雪深をはじめ，降水量，気温などの気象データに基づいて降雪・積雪・融雪モデルを構築し，その構造およびモデルパラメータについて検討を行った．本モデルは，降雨・降雪の判定，新雪および積雪層の密度計算，日気温法（Degree-day法）に準じた融雪計算から構成されている．降雨・降雪の判定には気温に加えて湿度を採用した．密度計算では新雪と積雪層それぞれのサブモデルを採用し，とくに積雪層の密度は気温と積載荷重により増加するものとした．融雪量は気温，純放射，地中熱伝達量の関数とした．その結果，モデルによる積雪深および積雪層密度の計算値は観測値と非常によく一致し，本モデルの有効性を検証することができた．また，モデルに含まれるパラメータの重要性について検討し，いくつかのパラメータについては省略したり既存の値を採用しても再現精度は低下しないが，融雪計算に気温のみを用いた場合には融雪期の積雪深変化や消雪日にかなり大きな違いが生ずることを明らかにした．

Snowpack accumulation and melting, including the role of the heat flux underground, were investigated by employing the bulk transfer method and setting roughness lengths of Z(O) = Z(T) = 0.005 m and Z(T) = 0.007 m. Heat balance data were recorded for a period of 4 years, from the fall of 2009 to the spring of 2013, at a forest experiment station in the Hokuriku region, which lies along the Japan Sea. The findings of the research are as follows: (1) The observed temporal changes in the snowpack depth were well reproduced by our model using observed and estimated densities. (2) The importance and roles of the heat balance components were clarified. The total heat input during the 4 years was 252.2 MJ/m(2) on average; 41.4% was provided by net radiation (R-n), 37.8% by sensible heat flux (H), and 13.2% by underground heat flux (G). The total output was 120.7 MJ/m(2), of which 56.2% was accounted for by R-n and 31.1% by latent heat flux (lE). (3) Of the total heat input, 45.2% was released as freezing energy from the surface side and 2.6% was released from the bottom. (4) In the very cold season (December-February), the total input energy was 115.8 MJ/m(2) on average; 75.0% was supplied by the surface and the remaining 25.0% from underground. In an anomalous year, 40.8% of the energy was supplied from underground. (C) 2014 Elsevier B.V. All rights reserved.

Return flow and repeated use of irrigation water for paddies is the most important issue in the Asian monsoon region, because sometimes this water is applied in greater quantity than that of evapotranspiration plus percolation. A new return flow analysis, the “replacement-in-order method”, which introduces a unique numbering system for very complicated irrigation and drainage networks, is proposed for the main canal with the dual purposes of irrigation and drainage. The method is applied to the Shichika irrigation district in the ordinal (season) irrigation period, resulting in a return flow ratio of 45 % for the entire area. Of this amount, 25 % is available for irrigation again. The remaining 20 % is unavailable, because the return flow discharged directly into a canal lacking a diversion weir in the drainage system, or into the Japan Sea. The return flow ratio is very different at the main canal location, from no return flow to 88 %. With the aid of the above method, theoretical analysis of return flow for paddy irrigation water can be done. This includes the deterministic return flow ratio inside and outside the irrigation area, plus precise information of return flow ratios at various main canal locations and routes of irrigation and drainage water.

Water balance in the Tedori River alluvial fan areas was analyzed for all components of the hydrological cycle based on exchange of the channel/soil surface and aquifer horizon fractions with river water. The results were summarized on an annual basis, as well as for the irrigation and non-irrigation periods. The study area received 6.28 mm/day of precipitation and had an outflow of 2.32 mm/day as direct runoff, resulting in 3.96 mm/day of water being supplied to the soil surface. The channel/soil horizon fraction received this 3.96 mm/day, as well as 9.12 mm/day intake water from the head works. Conversely, 2.74 and 2.85 mm/day were lost by evapotranspiration and percolation, respectively. Thus, surface runoff of 7.49 mm/day flowed from the study area to the Sea of Japan or drainage canals near the river mouth. In the aquifer horizon fraction, 2.85 mm/day of water was supplied from the channel/soil horizon fraction and 2.15 mm/day was supplied from the Tedori River, while 1.73 mm/day was extracted by groundwater. Thus, 3.27 mm/day of groundwater flowed out to the Sea of Japan or into downstream drainage canals. An outline of the water balance of the irrigation and non-irrigation period is also shown. Because various hydrological components are closely related to each other, planning and management of water resources for individual goals are not adequate, but require the integrated aspect of water balance for sustainable water use.

To evaluate the nitrogen pollution load in an aquifer, a water and nitrogen balance analysis was conducted over a thirty-five year period at five yearly intervals. First, we established a two-horizon model comprising a channel/soil horizon, and an aquifer horizon, with exchange of water between the aquifer and river. The nitrogen balance was estimated from the product of nitrogen concentration and water flow obtained from the water balance analysis. The aquifer nitrogen balance results were as follows: 1) In the aquifer horizon, the total nitrogen pollution load potential (NPLP) peaked in the period 1981-1990 at 1800 t·yr-1; following this the NPLP rapidly decreased to about 600 t·yr-1 in the period 2006-2010. The largest NPLP input component of 1000 t·yr-1 in the period 1976-1990 was from farmland. Subsequently, farmland NPLP decreased to only 400 t·yr-1 between 2006 and 2010. The second largest input component, 600 t·yr-1, was effluent from wastewater treatment works (WWTWs) in the period 1986-1990; this also decreased markedly to about 100 t·yr-1 between 2006 and 2010; 2) The difference between input and output in the aquifer horizon, used as an index of groundwater pollution, peaked in the period 1986-1990 at about 1200 t·yr-1. This gradually decreased to about 200 t·yr-1 by 2006-2010. 3) The temporal change in NPLP coincided with the nitrogen concentration of the rivers in the study area. In addition, nitrogen concentrations in two test wells were 1.0 mg·l-1 at a depth of 150 m and only 0.25 mg·l-1 at 50 m, suggesting gradual percolation of the nitrogen polluted water deeper in the aquifer.