Commentary: What We Know About Stemflow's Infiltration Area

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Peak grain forecasts for the US High Plains amid withering waters

ACKNOWLEDGMENTS. This paper stems from discussions during the Ettersburg Ecohydrology Workshop in Germany (October 2018), with the corresponding manuscript preparation ensuing in subsequent months. The workshop was funded by the UNIDEL Foundation, Inc. and the University of Delaware. Accordingly, partial support for this paper derived from funding for the workshop. A.M. was supported by the US NSF (Grants NSF-AGS-1644382 and NSF-IOS-175489).Peer reviewedPublisher PD

Peak grain forecasts for the US High Plains amid withering waters

Irrigated agriculture contributes 40% of total global food production. In the US High Plains, which produces more than 50 million tons per year of grain, as much as 90% of irrigation originates from groundwater resources, including the Ogallala aquifer. In parts of the High Plains, groundwater resources are being depleted so rapidly that they are considered nonrenewable, compromising food security. When groundwater becomes scarce, groundwater withdrawals peak, causing a subsequent peak in crop production. Previous descriptions of finite natural resource depletion have utilized the Hubbert curve. By coupling the dynamics of groundwater pumping, recharge, and crop production, Hubbert-like curves emerge, responding to the linked variations in groundwater pumping and grain production. On a state level, this approach predicted when groundwater withdrawal and grain production peaked and the lag between them. The lags increased with the adoption of efficient irrigation practices and higher recharge rates. Results indicate that, in Texas, withdrawals peaked in 1966, followed by a peak in grain production 9 y later. After better irrigation technologies were adopted, the lag increased to 15 y from 1997 to 2012. In Kansas, where these technologies were employed concurrently with the rise of irrigated grain production, this lag was predicted to be 24 y starting in 1994. In Nebraska, grain production is projected to continue rising through 2050 because of high recharge rates. While Texas and Nebraska had equal irrigated output in 1975, by 2050, it is projected that Nebraska will have almost 10 times the groundwater-based production of Texas

A novel framework to study the effect of tree architectural traits on stemflow yield and its consequences for soil-water dynamics

International audienceA novel experimental approach and numerical framework are proposed to study the effect of tree architectural traits on stemflow yield and its effects on soil-water dynamics. The framework includes a data mining workflowemploying information from two experimental steps: (i) evaluation of the effect of tree aboveground architecture on stemflow yield and (ii) quantification of specific parameters for soil-water dynamics with and withoutstemflow. We studied double-funnelling (stemflow and root-induced preferential flow) under three sycamore (Acer pseudoplatanus L.) trees growing on a slope in Scotland during the summer season and measured architecturaltraits. Stemflow yield ranged from 1.3 to 3.8% of the incident rainfall, with funnelling ratios of between 2.2 ± 2.1 and 5.2 ± 3.9. Double-funnelling to a depth of up to 400 mm beneath the soil surface occurred as matrix flow and was significantly and positively correlated with the vertical root distribution. Soil-water dynamics were distinctly different with and without stemflow. Our framework revealed that the number of tree branches, their insertion angle, leaf number, and stem basal diameter influenced stemflow yield within rainfall thresholds of 1.1 and 3.5 mm d-1. The framework also showed that stemflow yield had a negative impact on soil matric suction, while air temperature was the most influential covariate affecting soil-water dynamics, likely due to its strong correlation to evapotranspiration during the summer season. In spite of the study limitations, such as small sample size and differences between individuals, we show that the proposed framework and experimental approach can contribute to our knowledge of how stemflow generated aboveground triggers major responses in soil-water dynamics belowgroun

Sampling procedures for throughfall monitoring: a simulation study

What is the most appropriate sampling scheme to estimate event-based average throughfall? A satisfactory answer to this seemingly simple question has yet to be found, a failure which we attribute to previous efforts' dependence on empirical studies. Here we try to answer this question by simulating stochastic throughfall fields based on parameters for statistical models of large monitoring data sets. We subsequently sampled these fields with different sampling designs and variable sample supports. We evaluated the performance of a particular sampling scheme with respect to the uncertainty of possible estimated means of throughfall volumes. Even for a relative error limit of 20%, an impractically large number of small, funnel-type collectors would be required to estimate mean throughfall, particularly for small events. While stratification of the target area is not superior to simple random sampling, cluster random sampling involves the risk of being less efficient. A larger sample support, e.g., the use of trough-type collectors, considerably reduces the necessary sample sizes and eliminates the sensitivity of the mean to outliers. Since the gain in time associated with the manual handling of troughs versus funnels depends on the local precipitation regime, the employment of automatically recording clusters of long troughs emerges as the most promising sampling scheme. Even so, a relative error of less than 5% appears out of reach for throughfall under heterogeneous canopies. We therefore suspect a considerable uncertainty of input parameters for interception models derived from measured throughfall, in particular, for those requiring data of small throughfall events

Throughfall spatiotemporal variability within two conifer stands of the Mayson Lake Hydrological Processes Study Area

Rainfall and throughfall were measured during the growing-season of 2007 in a mature and a juvenile coniferous stand of the Thompson Plateau in south-central British Columbia. For the 18 rainfall events sampled (cumulative depth of 111.4 mm) no significant difference (ƒ¿ = 0.05) in cumulative throughfall was found between the mature and juvenile stand with inputs of 77.5 } 11.1 mm (69.6 } 9.9 % of rainfall) and 82.7 } 8.1 mm (74.2 } 7.3 % of rainfall), respectively. Linear regression equations relating throughfall depth to rainfall depth for events that saturate the canopy and those that do not were derived for both stands. The 32 stationary throughfall gauges used in this study represented a sufficiently large enough sample to estimate mean stand-scale throughfall to within } 20% at the 95 % confidence level for rainfalls . 8.7 and . 3.1 mm in the mature and juvenile stand, respectively. Cumulative point throughfall was found to be a function of canopy cover in the mature stand, while in the juvenile stand point throughfall was found to be correlated with both canopy cover and the cumulative basal area of trees contained within a 4 m radius of the gauge

Precipitation partitioning by a northern hardwood stand, southern Ontario, Canada, processes and variability

grantor: University of TorontoMeasurements of gross precipitation, throughfall, stemflow and litter interception loss in a northern hardwood stand in Southern Ontario were made during the summer of 1995. Equations were derived for estimating the quantitative importance of each of the following water fluxes under summer canopy conditions: Throughfall, stemflow, canopy interception loss and total interception loss (canopy interception loss + litter interception loss) and net precipitation entering the soil. Gross precipitation depth and intensity had a significant effect (Ã = 0.05) on all water fluxes while event duration, proportion of canopy openings and wind velocity above the canopy did not. The importance of litter interception, which has been largely ignored in previous interception studies, was found to be significant. Interception loss from the litter layer was ~6% of gross precipitation and ~25% of total interception loss from the stand. Throughfall, stemflow and canopy interception loss variability was determined and possible factors influencing the variability of these fluxes are examined.M.Sc