Spatiotemporal relations between water budget components and soil water content in a forested tributary catchment

Abstract

We examined 3 years of measured daily values of all major water budget components (precipitation P, potential evapotranspiration PET, actual evapotranspiration ET, and runoff R) and volumetric soil water content h of a small, forested catchment located in the west of Germany. The spatial distribution of h was determined from a wireless sensor network of 109 points with 3 measurement depths each; ET was calculated from eddy-covariance tower measurements. The water budget was dominantly energy limited, with ET amounting to approximately 90% of PET, and a runoff ratio R/P of 56%. P, ET, and R closed the long-term water budget with a residual of 2% of precipitation. On the daily time scale, the residual of the water budget was larger than on the annual time scale, and explained to a moderate extent by h (R 2 5 0.40). Wavelet analysis revealed subweekly time scales, presumably dominated by unaccounted fast-turnover storage terms such as interception, as a major source of uncertainty in water balance closure. At weekly resolution, soil water content explained more than half (R 2 5 0.62) of the residual. By means of combined empirical orthogonal function and cluster analysis, two slightly different spatial patterns of h could be identified that were associated with mean h values below and above 0.35 cm 3 /cm 3 , respectively. The timing of these patterns as well as the varying coherence between PET, ET, and soil water content responded to changes in water availability, including a moderate response to the European drought in spring 2011.

Using Sap Flow Data to Parameterize the Feddes Water Stress Model for Norway Spruce

“…In our Slope plot simulations this ratio was 80% for the uncalibrated Feddes model, but 87% for the calibrated simulation run in the samestudy period (2010-2013). The runoff ratio (runoff/precipitation) observed by [40] was 56%, while that in our simulations ranged between 62% (Slope plot after calibration of the Feddes model) and 65% (Slope plot before calibration of the Feddes model). This result confirms: (1) the finding of [77] that a good fit between simulated and measured SWC does not necessarily imply that the simulated water fluxes are correct; and (2) the assumption of [78] that sap flow measurements can help improving root water uptake simulations.…”

“…Grass reference evapotranspiration ET 0 was calculated using the FAO-Penman-Monteith method [45] following [40], who first calculated hourly ET 0 values and then aggregated these to daily sums. The required input data were obtained from the TERENO weather station Schöneseiffen (3.4 km east of the Wüstebach site).…”

“…Also, mean daily sap flow and simulated actual transpiration showed high correlations (R 2 > 0.82). However, although the adaptation of the Feddes function had little impact on the general dynamic of the simulated fluxes, the adjustment of h 3, low significantly changed transpiration (p < 0.001) and drainage fluxes (p < 0.01) at the Slope plot (two-sided Mann-Whitney U-test; Table 3) and made it more realistic: Based on eddy-covariance measurements, [40] found the annual ET act in the Wüstebach catchment to cover approximately 90% of ET 0 . In our Slope plot simulations this ratio was 80% for the uncalibrated Feddes model, but 87% for the calibrated simulation run in the samestudy period (2010-2013).…”

The integrated water balance and soil data set of the Rollesbroich hydrological observatory

“…This residual is related to measurement uncertainty and soil water storage depletion. As presented by Graf et al (2014), soil water storage can be derived from the measured soil water content, θ , as follows:…”

“…TERENO aims to collect long-term time series of system states and fluxes using state-of-the-art monitoring technologies, e.g., to close the local water balance (Graf et al, 2014) and to investigate of the effects of deforestation on water, energy, and matter fluxes in an integrative manner . The Rollesbroich grassland experimental catchment is part of the TERENO observatory Eifel/Lower Rhine Valley.…”