Short-term dynamics of soil matrix potential, groundwater head, and discharge were studied using principal component analysis. About 19 % of the spatial variance of soil matrix potential in the soil in a mature spruce forest was ascribed to the effect of spatially varying root water uptake. In addition, the analysis illustrated the effect of increasing damping and delay of the input signal with increasing depth. That of the runoff at the catchment outlet ranged between that of soil matrix potential at 40 cm depth, pointing to near-surface runoff generation. This gives clear evidence for the respective flowpath during stormflow. Thus, input signals imposed by heavy rainstorms reach the catchment outlet within a few hours. In contrast, changes of evapotranspiration become visible at the catchment outlet only with a few years’ time delay via corresponding changes of groundwater recharge that are transferred through the aquifer.
In hydrological and groundwater models, usually little attention is paid to the mutual interplay between evapotranspiration and root water uptake on the one hand and hydrological processes, especially in shallow groundwater areas. Sound assessments of effects of land use and climate change, however, need to account for that in more detail.
The first author is indebted to Andreas Kolb and Christina Weyer who performed most of the hydrological installations, maintenance, and data processing in the Lehstenbach catchment even under harsh conditions. Funding for soil hydrological, groundwater head, and stream discharge measurements had been provided by the German Federal Ministry for Education, Science, Research, and Technology (BMBF, Grant No. PT BEO 51—0339476 A-D) and by the German Research Foundation (DFG) within the Research Group 562 (University of Bayreuth) “Dynamics of Soil Processes Under Extreme Meteorological Boundary Conditions” which is highly appreciated. Long-term measurements of evapotranspiration and precipitation were financed by the German Research Foundation (Fo 226/16-1, Fo 226/21-1) and the Oberfrankenstiftung (Grant. No. 01879).
Correspondence to Gunnar Lischeid .
