Examining the patterns of spatial variability of runoff and sediment transport is necessary for understanding hydrologic and geomorphic processes in watersheds. Knowledge of water and sediment transport behaviors in various catchment areas can improve the process-based representation of numerical models. We reviewed the relations between drainage areas and various properties of runoff and sediment transport comprehensively, particularly addressing spatial-scale dependence and spatial heterogeneity. Results show that patterns of increases and decrease of water and sediment amounts occurred relative to the catchment area, although other properties showed no distinctive relation to catchment areas, partly because of a lack of measured data. Most earlier studies specifically examined either spatial-scale dependence or spatial heterogeneity. Properties such as peak specific discharge showing clear spatial-scale dependence should be controlled by mechanisms that change with the spatial scale. Properties such as specific discharge during base flow showed spatial heterogeneity. Results suggest that mechanisms controlling base flow did not change much with the spatial scale for the measured ranges of catchment areas. Heterogeneous properties of landscapes exerted strong effects on those properties.

　Findings for spatial patterns of runoff and sediment transport at selected observation sites were summarized to elucidate processes controlling scale dependence and spatial heterogeneity of their catchment areas. We selected Fudoji and Kiryu watersheds in Shiga for runoff generation and Tanzawa in Kanagawa and Saru watersheds in Hokkaido for sediment transport. Regarding runoff generation, variation of concentration of specific chemical species (i.e. silica) suggested various flow paths from weathered bedrock layer to soil layer in small catchments, although variation tapered with increased catchment area because of the mixing of several flow components. Sediment transport also varied spatially depending on the catchment characteristics. Variation tapered with increased catchment area. Moreover, increased storage components and decreased ratios of sediment source areas to the total catchment area for larger drainage areas decreased the sediment transport with catchment areas in some catchments. Landscape legacies of sediment supply, storage, and transport can contribute to increased sediment yields in larger catchments.

　We reviewed the treatment of spatial scales in numerical models of runoff and sediment transport to elucidate current problems and to identify avenues for future research. We specifically examined the following questions: (1) Which spatial scale is used in existing modeling and how was it decided? (2) What spatial information was used? (3) Do the governing equations differ with spatial scale? Results show that the smallest spatial scale in distributed models was determined by the spatial resolution of spatially distributed information used in modeling, although lumped models were applicable at any scale. Some physical parameters used in modeling, aside from elevation, land use and vegetation cover, were not based on field-based information. Results demonstrate that the governing equations differ depending on locations within the watershed (i.e., hillslopes and channels) presenting different processes for runoff and sediment transport. Nevertheless, no report of the relevant literature describes a study with changed governing equations along with the changes in spatial scales. We also reviewed modeling studies of how we should treat the effects of spatial scale in runoff modeling, which revealed that they had reported minimum and the maximum spatial scales for lumping runoff mechanisms and the relative importance of spatial data used as input and parameters, although no attempts have been reported for a change in governing equations with spatial scale. We were unable to find similar studies of sediment runoff modeling. In summary, we suggest improvement of these findings and their use for modeling rainfall runoff and sediment transport mechanisms for better hydrological science.

　Several economic, social, and environmental issues affect sustained operations of microhydropower generation (MHP) in economically developing countries. Nevertheless, few studies have conducted field investigations to clarify practical issues that MHP stakeholders face or have proposed ways of resolving such issues. This study investigated the current status of MHP in Ciptagelar village, West Java, Indonesia, to summarize and elucidate issues related to sustained MHP operations. Results revealed issues related to budgeting and techniques for maintaining and operating MHP in the village. We found the difficulty of the village in securing funds for repairing broken intake weirs and maintaining the MHP facility. We also found that the intake weirs were vulnerable to large floods, and no accomplished technician was available for properly operating MHP in the village.

　We investigated suspended sediments (SS) discharges before and during line thinning in a forested watershed located in a national forest in Ibaraki Prefecture, Japan. Line thinning was conducted at a thinning rate of 35 % across 17 % of the watershed area in 2012. Five spur roads were constructed along the streams. The lower slopes in the experimental watershed are covered with conifer plantation of Japanese cedar whereas the upper slopes are covered with deciduous trees. After stream water samples of about 1 L were collected hourly using an automatic water sampler, the water samples were filtered through glass fiber filters (0.5 μm) to measure the SS concentrations. Comparison within the same range of runoff showed that SS concentrations in flood flow during thinning (September-November in 2012) were higher than before thinning (June 2010 - August 2012). We calculated the SS discharges using runoff data (September-November in 2012) and the regression equations between the specific cumulative load of SS and the specific cumulative runoff before and during thinning. The SS discharges before and during thinning were 0.8 kg ha^-1 and 1.9 kg ha^-1, respectively. The SS discharge was 2.4 times greater during thinning than before thinning. Results show that both SS concentrations and SS discharges increased during thinning. The harvesting intensity was low, but results show that thinning influenced on the SS concentrations in stream water.

　In order to avoid underestimations by methods of measuring sap flux densities (SFD), previous studies have suggested that sensors are replaced every growing season and/or year. However, limited information is available showing how the underestimations can be detected. We validated the detections of underestimations based on the relationship between the vapor pressure deficit (VPD) and SFD for data measured in stands of Japanese cedar (Cryptomeria japonica D. Don) planted in the Tsukuba Experimental Watershed (TEW) located in the Kanto district, and the Nagasaka Experimental Watershed (NEW) located in the Tohoku district, in Japan. The detections were valid for the data measured with the Granier method, the heat ratio (HR) method, and the heat field deformation (HFD) method. Decrease in the water content of sapwood around the sensors was determined as the cause of the underestimations and implied the sap flow encircling the inserted sensors. The sensors, durations of available data of which were 365 days or less, were 62 % and 86 % of 52 Granier sensors in TEW and 64 sensors in NEW, respectively. For measurements taken year-round, we suggest that researchers accept the possibility of replacing sensors within a year after installation and consider designing the measurements accordingly.

　Snowmelt and meteorological observations were conducted at the opening and three cedar stands with different sky view factors. The sky view factors of cedar stands A, B, and C were, respectively, 17.8%, 5.2%, and 2.4%. Snow water equivalent (SWE) at the stands on 9 March decreased concomitantly with the decreasing sky view factor. SWE at each site on 12 April in order from smallest to largest was the opening, the cedar stands C, A, and B. Melt-off dates were the same order from earliest to latest. The degree-day factors k calculated based on the snowmelt measurements for 21 days were also the same order from largest to smallest. The values of k estimated using the daily average air temperature at the open site for the opening, the cedar stands A, B, and C were, respectively, 4.09 mm °C^-1 day^-1, 2.34 mm °C^-1 day^-1, 2.13 mm °C^-1 day^-1, and 2.38 mm °C^-1 day^-1, whereas k estimated based on the daily average air temperature measured at each site for stands A, B, and C were, respectively, 2.83 mm °C ^-1 day^-1, 2.70 mm °C^-1 day^-1, and 2.90 mm °C^-1 day^-1. Dates of melt-off at all sites were reproduced using values of k except for cedar stand A, where snow disappeared 4-5 days earlier than the estimation. Sky view factors were insufficient to elucidate the magnitude relation on k between stands B and C. Instead, the living branch height and the amount of litter might contribute to it.

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