The Kiryu Experimental Watershed: 50-years of rainfall-runoff data for a forest catchment in central Japan

The Kiryu Experimental Catchment (KEW) is a small (5.99 ha) forest catchment located in Shiga Prefecture, central Japan (34°58′ N, 136°00′ E; www.bluemoon.kais.kyoto-u.ac.jp/kiryu/contents.html ). Around this area, forest devastation occurred from ca. 1250 to ca. 150 years ago because of overuse of forest and timbers. Then, hillside forestation was carried out for more than 100 years to prevent soil erosion and support the timber industry, and consequently, most of this area is now covered with plantation forests mainly by Chamaecyparis obtusa Sieb. et Zucc. (Japanese cypress) planted around 1960's. This plantation forest is not actively managed. The KEW is one of the leading experimental forests with long-term monitoring data in Japan. Research in the KEW began in 1967 to elucidate the hydrological and biogeochemical processes in the forested catchment in relation to climate, geology, soil, and vegetation growth. Since then, the long-term hydrological data of precipitation, runoff and sediment transport are continuously monitoring. In this study, we provide the data and preliminarily discuss the rainfall–runoff patterns and sediment transport through 50 years in the KEW. The annual precipitation and the maximum daily rainfall have been greater than the average over the last decade. In response to the rainfall patterns, the ratio of annual direct runoff to precipitation was also larger in the last decade. The sediment transport in this decade was consequently larger than the preceding decades. Our data presented here suggest that a close relationship exists between the climate condition, rainfall–runoff response, sediment dynamics, as well as a slowly progressing change of forest condition.     

Preliminary evaluation of the runoff processes in a remote montane cloud forest basin using Mixing Model Analysis and Mean Transit Time

In this study, the Mean Transit Time and Mixing Model Analysis methods are combined to unravel the runoff generation process of the San Francisco River basin (73.5 km²) situated on the Amazonian side of the Cordillera Real in the southernmost Andes of Ecuador. The montane basin is covered with cloud forest, sub‐páramo, pasture and ferns. Nested sampling was applied for the collection of streamwater samples and discharge measurements in the main tributaries and outlet of the basin, and for the collection of soil and rock water samples. Weekly to biweekly water grab samples were taken at all stations in the period April 2007–November 2008. Hydrometric data, Mean Transit Time and Mixing Model Analysis allowed preliminary evaluation of the processes controlling the runoff in the San Francisco River basin. Results suggest that flow during dry conditions mainly consists of lateral flow through the C‐horizon and cracks in the top weathered bedrock layer, and that all subcatchments have an important contribution of this deep water to runoff, no matter whether pristine or deforested. During normal to low precipitation intensities, when antecedent soil moisture conditions favour water infiltration, vertical flow paths to deeper soil horizons with subsequent lateral subsurface flow contribute most to streamflow. Under wet conditions in forested catchments, streamflow is controlled by near surface lateral flow through the organic horizon. Exceptionally, saturation excess overland flow occurs. By absence of the litter layer in pasture, streamflow under wet conditions originates from the A horizon, and overland flow. Copyright © 2011 John Wiley & Sons, Ltd.     

Estimation of mean residence times of subsurface waters using seasonal variation in deuterium excess in a small headwater catchment in Japan

We measured deuterium excess (d = δD ? 8δ¹⁸O) in throughfall, groundwater, soil water, spring water, and stream water for 3 years in a small headwater catchment (Matsuzawa, 0·68 ha) in the Kiryu Experimental Watershed in Japan. The d value represents a kinetic effect produced when water evaporates. The d value of the throughfall showed a sinusoidal change (amplitude: 6·9‰ relative to Vienna standard mean ocean water (V‐SMOW)) derived from seasonal changes in the source of water vapour. The amplitude of this sinusoidal change was attenuated to 1·3–6·9‰ V‐SMOW in soil water, groundwater, spring water, and stream water. It is thought that these attenuations derive from hydrodynamic transport processes in the subsurface and mixing processes at an outflow point (stream or spring) or a well. The mean residence time (MRT) of water was estimated from d value variations using an exponential‐piston flow model and a dispersion model. MRTs for soil water were 0–5 months and were not necessarily proportional to the depth. This may imply the existence of bypass flow in the soil. Groundwater in the hillslope zone had short residence times, similar to those of the soil water. For groundwater in the saturated zone near the spring outflow point, the MRTs differed between shallow and deeper groundwater; shallow groundwater had a shorter residence time (5–8 months) than deeper groundwater (more than 9 months). The MRT of stream water (8–9 months) was between that of shallow groundwater near the spring and deeper groundwater near the spring. The seasonal variation in the d value of precipitation arises from changes in isotopic water vapour composition associated with seasonal activity of the Asian monsoon mechanism. The d value is probably an effective tracer for estimating the MRT of subsurface water not only in Japan, but also in other East Asian countries influenced by the Asian monsoon. Copyright © 2006 John Wiley & Sons, Ltd.     

Stream and bed temperature variability in a coastal headwater catchment: influences of surface‐subsurface interactions and partial‐retention forest harvesting

Stream temperature was recorded between 2002 and 2005 at four sites in a coastal headwater catchment in British Columbia, Canada. Shallow groundwater temperatures, along with bed temperature profiles at depths of 1 to 30 cm, were recorded at 10‐min intervals in two hydrologically distinct reaches beginning in 2003 or 2004, depending on the site. The lower reach had smaller discharge contributions via lateral inflow from the hillslopes and fewer areas with upwelling (UW) and/or neutral flow across the stream bed compared to the middle reach. Bed temperatures were greater than those of shallow groundwater during summer, with higher temperatures in areas of downwelling (DW) flow compared to areas of neutral and UW flow. A paired‐catchment analysis revealed that partial‐retention forest harvesting in autumn 2004 resulted in higher daily maximum stream and bed temperatures but smaller changes in daily minima. Changes in daily maximum stream temperature, averaged over July and August of the post‐harvest year, ranged from 1.6 to 3 °C at different locations within the cut block. Post‐harvest changes in bed temperature in the lower reach were smaller than the changes in stream temperature, greater at sites with DW flow, and decreased with depth at both UW and DW sites, dropping to about 1 °C at a depth of 30 cm. In the middle reach, changes in daily maximum bed temperature, averaged over July and August, were generally about 1 °C and did not vary significantly with depth. The pre‐harvest regression models for shallow groundwater were not suitable for applying the paired‐catchment analysis to estimate the effects of harvesting. However, shallow groundwater was warmer at the lower reach following harvesting, despite generally cooler weather compared to the pre‐harvest year. Copyright © 2012 John Wiley & Sons, Ltd.     

Estimation of mean water transit time on a steep hillslope in South Korea using soil moisture measurements and deuterium excess

A method for estimating daily mean transit time (DMTT) within a soil layer was proposed using field measurements of soil moisture. Vertical profiles of soil moisture time series were used for storage estimation. Water fluxes were evaluated through matrix and bypass flow. Variations in soil moisture and soil thickness were used to evaluate matrix flow. Exponential decay in depth of macropores was also used for bypass flow approximation. DMTT evaluation was compared to results obtained from a stable water isotope model using two years of data acquired on a steep granite hillslope in the Sulmachun watershed, South Korea. Various uncertainties in transit time evaluation such as model structure, non‐stationary assumption and data acquisition of existing approaches can be accounted for in the proposed methodology, and the flowpath contribution can be further configured in conjunction with hydrometric measurements. Probability density functions of isotope analyses were partially explained by transit time distributions that were based on soil moisture measurements. Supplementary sensitivity analyses for uncertainty configurations indicate that matrix flow is the primary process in determining transit time distribution while the impact of bypass flow is minor. The feasibility of a DMTT approach over isotope‐based methodologies highlights not only the strength of this proposed method, both in cost and time, but also its further application potential for existing soil moisture measurements. Copyright © 2013 John Wiley & Sons, Ltd.     

Estimation of canopy drying time after rainfall using sap flow measurements in an emergent tree in a lowland mixed‐dipterocarp forest in Sarawak,Malaysia

This study emphasizes the importance of canopy drying time (CDT) after rainfall in a lowland tropical rain forest. In this study, we estimate CDT using sap flow velocities measured by a heat‐pulse method in an emergent tree in a lowland mixed‐dipterocarp forest. Estimated CDT (ECDT) for each rain event has been defined as the time from rainfall cessation to the specific time derived from the difference between diurnal courses of sap flow velocities on a rainy day versus bright days. ECDT could be derived for 22 rain events that were grouped into two types, depending on whether rainfall ceased before or after noon. The ECDTs were distributed more widely and with greater values when rainfall ceased before noon (Type 1) than after noon (Type 2). The ECDTs of both Type 1 and Type 2 decreased with increases in net radiation (Rn) and vapour pressure deficit (VPD) after rainfall. This result shows that ECDT is determined mainly by post‐rainfall evaporation rates. The sap flow velocity as a detector of canopy wetness worked out well because of the specific rainfall characteristics at this site. The practical limitations of the method using sap flow velocities are discussed in relation to rainfall characteristics and time lags between transpirations and sap flow velocities. Copyright © 2005 John Wiley & Sons, Ltd.