Vegetation indices play an important role in monitoring variations in vegetation. The Enhanced Vegetation Index (EVI) proposed by the MODIS Land Discipline Group and the Normalized Difference Vegetation Index (NDVI) are both global-based vegetation indices aimed at providing consistent spatial and temporal information regarding global vegetation. However, many environmental factors such as atmospheric conditions and soil background may produce errors in these indices. The topographic effect is another very important factor, especially when the indices are used in areas of rough terrain. In this paper, we theoretically analyzed differences in the topographic effect on the EVI and the NDVI based on a non-Lambertian model and two airborne-based images acquired from a mountainous area covered by high-density Japanese cypress plantation were used as a case study. The results indicate that the soil adjustment factor “L” in the EVI makes it more sensitive to topographic conditions than is the NDVI. Based on these results, we strongly recommend that the topographic effect should be removed in the reflectance data before the EVI was calculated—as well as from other vegetation indices that similarly include a term without a band ratio format (e.g., the PVI and SAVI)—when these indices are used in the area of rough terrain, where the topographic effect on the vegetation indices having only a band ratio format (e.g., the NDVI) can usually be ignored.

[1] Both scaling effect and connectivity of overland flow were examined in steep hillslopes covered by (1) Japanese cypress (hinoki, Chamecyparis obtusa) plantations with sparse understory vegetation, (2) hinoki plantations with fern understory vegetation, and (3) deciduous forests. Two sizes of plots were installed for monitoring overland flow: small (0.5 Â 2 m) and large hillslope scale (8 Â 24-27 m). For all hillslopes, measurable amounts of overland flow occurred during storms. Runoff coefficients of large plots (0.1-3%) were consistently smaller than those of small plots (20-40%). Estimated runoff flow lengths at the hillslope scale were based on runoff coefficients from small plots and were used to calculate runoff volume from large plots. Then we compared the differences between observed and estimated runoff volumes of large plots. Estimated runoff from large plots was smaller than observed runoff in hinoki slopes with sparse understory vegetation. Greater amounts of observed compared to estimated overland flow suggest that more runoff occurred from hillslopes with sparse understory. In contrast, estimated overland flow was larger than observed runoff from the deciduous forest, implying greater opportunities for infiltration compared to hinoki hillslopes. Comparison of estimated versus observed overland flow for successive 5 min intervals during storms indicates that runoff networks expand upslope during short and intense precipitation periods. Our examination and comparison of storm runoff from small and large plots facilitate better understanding of runoff mechanisms, scaling effects in hillslopes, and connectivity of the overland flow network.

Abstract:The influence of bedrock subsurface flow on storm runoff generation was investigated in Japan in two regions in Japan underlain by three bedrock types. One region, with approximately 2500 m of relief, is located in the Japan Alps, central Japan (In a region), where six small forest-covered watersheds underlain by granite and Mesozoic shale were studied. Two of these watersheds were instrumented to monitor stream discharge and the other four are springs occurring at the bedrock exposure. The other study area is in northern Kyoto prefecture, western Japan (Oe region). Here, spring distribution and seasonal flow were monitored in two steep basins underlain by serpentinite rocks. Distinctly different runoff responses were observed: the granite watershed exhibited a large and rapid runoff peak that coincided with the rainfall peak (type 1); and the shale and serpentinite basins exhibited small initial runoff peaks followed by a maximum peak discharge five to ten times greater with a convex recession limb (type 2). Runoff response from bedrock springs had characteristics similar to type 1 hydrographs; however, discharge increased only when the antecedent precipitation index was large and the runoff peak was delayed between 10 h and 1 week after rain events. The specific discharge of the springs decreased with increase in altitude in the Oe region, especially in dry periods. This decline in discharge with elevation suggests that a deep subsurface flow system through bedrock fissures contributes to the storm water flow in serpentinate basins. When comparing runoff response and spring discharge, slow or double peak runoff response may be a good indicator of the influence of bedrock subsurface outflow on storm runoff generation in steep mountainous regions.

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Soil deposition density maps of gamma-ray emitting radioactive nuclides from the Fukushima Dai-ichi Nuclear Power Plant (NPP) accident were constructed on the basis of results from large-scale soil sampling. In total 10,915 soil samples were collected at 2168 locations. Gamma rays emitted from the samples were measured by Ge detectors and analyzed using a reliable unified method. The determined radioactivity was corrected to that of June 14, 2011 by considering the intrinsic decay constant of each nuclide. Finally the deposition maps were created for (134)Cs, (137)Cs, (131)I, (129m)Te and (110m)Ag. The radioactivity ratio of (134)Cs-(137)Cs was almost constant at 0.91 regardless of the locations of soil sampling. The radioactivity ratios of (131)I and (129m)Te-(137)Cs were relatively high in the regions south of the Fukushima NPP site. Effective doses for 50 y after the accident were evaluated for external and inhalation exposures due to the observed radioactive nuclides. The radiation doses from radioactive cesium were found to be much higher than those from the other radioactive nuclides.

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Until recently, there have been few attempts to link hillslope, headwater and meso-scale hydrology. However, the paper by Shaman et al. (2004, Hydrological Processes 18: 3195-3206) has proposed concepts that link headwater and meso-scale basins. Although their paper provides an excellent example of how we should make connections between small-and large-scale hydrology, the analysis still lacked sufficient consideration of the spatial variability of hydrological behaviour at the hillslope/headwater scale. Here, we extend the discussion of Shaman et al. to smaller sized catchments. We use detailed datasets of hydrometric and hydrochemical measurements collected at the hillslope and small catchment scale at the Fudoji and Ibi catchments in Japan. We show that: (1) large spatial variation in the hydrological responses is present at the hillslope scale and that these responses are strongly controlled by the contribution of water flow from the bedrock into the soil at baseflow; (2) the spatial variability of hydrological responses in headwaters is damped compared with that of the hillslope, and this damping is determined by the integration of the hillslope responses which largely occurs in the stream.