Estimation of evapotranspiration using diurnal groundwater level fluctuations: Comparison of different approaches with groundwater lysimeter data

Abstract

[1] In wetlands or riparian areas, water withdrawal by plants with access to groundwater or the capillary fringe often causes diurnal groundwater fluctuations. Various approaches use the characteristics of these fluctuations for estimation of daily groundwater evapotranspiration rates. The objective of this paper was to review the available methods, compare them with measured evapotranspiration and assess their recharge assumptions. For this purpose, we employed data of 85 rain-free days of a weighable groundwater lysimeter situated at a grassland site in the Spreewald wetland in north-east Germany. Measurements of hourly recharge and daily evapotranspiration rates were used to assess the different approaches. Our results showed that a maximum of 50% of the day to day variance of the daily evapotranspiration rates could be explained by the approaches based on groundwater fluctuations. Simple and more complex methods performed similarly. For some of the approaches, there were indications that erroneous assumptions compensated each other (e.g., when overestimated recharge counteracted underestimated storage change). We found that the usage of longer time spans resulted in improved estimates of the daily recharge rates and that the estimates were further enhanced by including two night averages. When derived from fitting estimates of recharge or evapotranspiration with according measurements the specific yield, needed to convert changes in water level to water volumes, differed considerably among the methods (from 0.022 to 0.064). Thus, the specific yield can be seen as ''correction factor'' that compensates for inadequate process descriptions.

Groundwater-dependent ecosystems: recent insights from satellite and field-based studies

“…No model outperformed the others in each of these error benchmarks, thus illustrating that errors in the estimation of S y are compensated by errors in the estimation of recovery (Fahle and Dietrich, 2014). The methods that provided the best estimates for recovery of the groundwater used approaches to estimate sub-daily rates of ET g and recovery (Gribovszki et al, 2008;Loheide, 2008).…”

“…Several modifications to the White method were evaluated in a study by Fahle and Dietrich (2014), in which they compared errors in estimation of S y , recovery and ET g . No model outperformed the others in each of these error benchmarks, thus illustrating that errors in the estimation of S y are compensated by errors in the estimation of recovery (Fahle and Dietrich, 2014).…”

“…In both methods, recovery was estimated from the previous and following nights, although application to other methods might require site-specific parameterisation of the time period that is most representative for their study conditions (e.g. 18:00-06:00; Fahle and Dietrich, 2014). In the method of Gribovszki et al (2008), recovery was estimated from the time rate of change in depth-to-groundwater, and this important upgrade reduced the error of recovery estimates (Gribovszki et al, 2010;Fahle and Dietrich, 2014).…”

“…18:00-06:00; Fahle and Dietrich, 2014). In the method of Gribovszki et al (2008), recovery was estimated from the time rate of change in depth-to-groundwater, and this important upgrade reduced the error of recovery estimates (Gribovszki et al, 2010;Fahle and Dietrich, 2014).…”

A review on the quantification of soil water balance components as a basis for agricultural water management with a focus on weighing lysimeters and soil water sensors / Ein Überblick über die Ermittlung von Wasserhaushaltsgrößen als Basis für die landeskulturelle Wasserwirtschaft mit Fokus auf Lysimeter und Bodenwassersensoren

“…Similar data were also used to evaluate a water balance model for predicting crop water requirements (Muzikova et al, 2010). In general, applications of sophisticated lysimeter facilities are manifold, including simulations of groundwater fluctuations (Fahle and Dietrich, 2014;Dietrich et al, 2016) or validation of water flow models that focus on processes in the vadose zone (Durner et al, 2008;Schelle et al, 2012). An overview on different lysimeter types and their usage was recently presented by Meissner et al (2014).…”