The average temperature of the earth has increased about 1°C during the last 130 years (IPCC, 2007). Changes in crop calendars are also to be expected under climate change. This study revealed changes in crop calendars and the area of winter wheat cultivation, the main crop on the North China Plain. Furthermore, this study clarified the reasons for changes in terms of climatic variation and water policy. The combination of NDVIs by Pathfinder AVHRR Land (PAL) and SPOT/VEGETATION supported long-term analyses of 1982-2012. The greening season after winter dormant period has come faster with increasing spring temperatures. The sowing season has been delayed because of higher autumn mean temperatures and precipitation. Policies such as charging for groundwater withdrawal corresponding to water shortages and abolition of taxes promoting agriculture have influenced changes in winter wheat cultivation areas. Therefore, the winter wheat farming calendar and changes in crop cultivation area were investigated from a comprehensive perspective.

 The Talbot formula R=at/(t+b) and the Sherman formula R=ctⁿ were fitted as a rainfall depth-duration formula to the relation between probable rainfall depth and duration (DD relation), where R and t respectively represent the probable rainfall depth and the duration: a, b, c and n are constants.

 Both value a/b in the Talbot formula and value c in the Sherman formula represent characteristics of short-duration heavy rainfall. The geographical distributions of the two values show large latitudinal differences. Both value b in the Talbot formula and value n in the Sherman formula represent the continuity of heavy rainfall. The geographical distributions of the two values are closely related to topography.

 The DD relation is convex upward on a log-log plot. Therefore, the relation has a characteristic duration. This duration is definable as the duration for which the curvature of the logarithmically transformed Talbot equation is at its maximum [(1+√5)b/2] and can thereby be regarded as a continuous duration of heavy rainfall.

 One-to-one correspondence between values b and n and between values b and a/c is provable analytically. Value a/c, as well as values b and n, represents the continuity of heavy rainfall.

 To clarify the hydro-biogeochemical processes of a riparian wetland upstream from a stone masonry check dam built in a stream channel about 100 years ago, observations were conducted in a forested catchment with granite bedrock. On the upstream side of the observation plot, sandy soil was deposited in all layers. By contrast, on the downstream side close to the check dam, muddy soil was deposited on the surface layer; sandy soil was deposited in the lower layer. The two sedimentation patterns produced different hydrological pathways: one through the underground layer consisting of permeable sandy soil and one with flow over the low-permeable muddy soil layer as surface flow. Reductive conditions resulting in the removal of NO₃⁻ by denitrification were maintained within the wetland. Moreover, depending on the amount of annual rainfall and the different hydrologic pathways, the strength of the reductive environment fluctuated spatiotemporally. Fluctuations in the chemistry of stream water passing through the wetland were also observed in accordance with the outflow route. Small riparian wetlands formed by check dams exist in many rivers. To evaluate the effects of such riparian wetlands on hydrobiogeochemical phenomena, it is necessary to consider the sedimentation patterns, distribution, scale, and fluctuation of the wetlands within the catchments in a global and continuous manner, and to make detailed observations.

 To clarify canopy evapotranspiration and photosynthesis during and immediately after rainfall, measurements of ecosystem CO₂/H₂O fluxes using enclosed-path eddy covariance method, sap flow velocity, and micrometeorological conditions were taken in a Japanese cypress forest in the Kiryu Experimental Watershed in southern Shiga Prefecture, Japan. An enclosed path gas analyzer is more suitable than open-path or closed-path gas analyzers to measure CO₂/H₂O fluxes during and immediately after rainfall. Results show that H₂O flux during and after rainfall in relation to the vapor pressure deficit was greater than those on other days. H₂O flux during and after rainfall under low sap flow velocity is regarded as interception evaporation. With radiation increasing after rainfall, the H₂O flux component is regarded as a transition from interception evaporation to transpiration because of increased sap flow velocity. However, CO₂ absorption occurred during and immediately after rainfall in response to solar radiation in the same manner as on rain-free days. Observation revealed that the abaxial side of leaf surface remained dry even during and immediately after rainfall, which explains why photosynthesis occurs immediately with increased solar radiation after a rain event.