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| Home > Publications database > Advancing the understanding of actual evapotranspiration and critical soil moisture thresholds using lysimeter networks |
| Book/Dissertation / PhD Thesis | FZJ-2026-04662 |
2026
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-69367-001-9 (E-Book), 978-3-69367-000-2 (Print)
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Please use a persistent id in citations: doi:10.34734/FZJ-2026-04662
Abstract: Climate change is expected to significantly alter water availability, intensifying the frequency and severity of extreme weather events and increasing the risk of drought. Actual evapotranspiration (ETa) is a key component in the terrestrial water cycle, linking the hydrosphere, atmosphere and biosphere by modulating a range of land surface and ecohydrological processes. ETa is limited either by atmospheric energy supply or soil moisture (θ) availability. The shift between the energy-limited and water-limited ETa regimes is dependent on θ and is often characterized by a threshold known as critical soil moisture (θcrit). A comprehensive understanding and accurate quantification of ETa and its regime classification marked by θcrit is essential for irrigation management, drought monitoring, evaluating drought impacts and improving future projections of climate and water resources, food production, especially in the context of climate change. Weighable lysimeters play a vital role in understanding the complex interactions within the soil-plant-atmosphere continuum and are regarded as the most precise in situ method for quantifying ETa, but only at pedon scale due to their limited surface area. Equipped with soil moisture sensors at multiple depths, lysimeters offer a unique opportunity to assess the role of both surface, and, importantly, root zone θ on the transition between water and energy limited ETa regimes. This thesis explores the potential of lysimeters in providing ETa that is representative at larger scales than their surface area, as well as the surface and root zone θcrit associated with ETa regimes shifts. The scope of this thesis expands progressively, from a limited number of lysimeters in selected regions of Germany to a national network and, ultimately, incorporates an international dataset spanning multiple continents. The first study assessed whether lysimeter ETa measurement, despite their small surface area, can provide representative information for larger areas, such as the plot scale, landscape scale and larger regional scale. To address this, we examined the spatial correlations between ETa measured at different locations by lysimeter (ET-LYS) and at different locations by eddy covariance (ET-EC). This was done for the period 2015 - 2020 and the analysis was made for different spatial (range: 0 to 500 km) and temporal scales (range: 1 day to 1 year) using 23 lysimeters and 4 eddy covariance towers in Germany. We found that ET-LYS is generally as representative as ET-EC with high correlations at the plot scale, and moderate to high correlations at the landscape and larger regional scale. Wavelet analysis further indicated weaker spatial correlations under drought conditions (in the year 2018) and the strongest temporal correlations at annual and sub-seasonal scales. Furthermore, combination of multiple ET-LYS from different sites improved the predictability of ET-LYS for another site, suggesting that ET-LYS can be predicted well using ET-LYS from different neighboring sites. Overall, lysimeter measurements can provide information at much larger scales compared to their small measurement area.
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