Terrestrial Water Loss at Night: Global Relevance from Observations and Climate Models

Abstract

Abstract. Nocturnal water loss (NWL) from the surface into the atmosphere is often overlooked because of the absence of solar radiation to drive evapotranspiration and the measuring difficulties involved. However, there is growing evidence that suggests NWL – and particularly nocturnal transpiration – represents a considerable fraction of the daily values. Here we provide a global overview of the characteristics of NWL based on latent heat flux estimates from the FLUXNET2015 dataset, as well as from simulations of global climate models. Eddy-covariance measurements at 99 sites indicate that on average NWL represents 6.3 % of total evapotranspiration. There are six sites where NWL is higher than 15 %; these are mountain forests with considerable NWL during winter related to snowy and windy conditions. Higher vapor pressure deficit, wind speed and soil moisture are related to higher NWL, although this is not consistent across all sites. On the other hand, the global multi-model mean of terrestrial NWL is 7.9 % of total evapotranspiration. The spread of the model ensemble, however, is greater than 20 % over 70 % of the land area. Finally, the multi-model mean of future projections indicates an increase of NWL everywhere by an average of 1.8 %, but the spread between models at individual locations is often twice as large at least. Overall, this study highlights the relevance of water loss during the night and opens the door to explore its influence on the water cycle and the climate system under present and future conditions.

Prediction of soil evaporation measured with weighable lysimeters using the FAO Penman–Monteith method in combination with Richards’ equation

“…Large differences were especially visible during nighttime, when E m is mainly driven by wind speed (Figure 8c); Groh, Pütz, Gerke, Vanderborght, & Vereecken, 2019). Recent investigations highlight that water losses during night are of relevance at the global scale (Padrón, Gudmundsson, Michel, & Seneviratne, 2020). Also, non‐rainfall water such as dew might play a role for larger E m , which can make up 2–7 mm per month of E on grassland lysimeters (Brunke, Groh, Vanderborght, Vereecken, & Pütz, 2019).…”

Comparison of Nighttime With Daytime Evapotranspiration Responses to Environmental Controls Across Temporal Scales Along a Climate Gradient

“…As one of the key components in terrestrial water cycles, actual evapotranspiration ( ET ) links water, energy, and carbon cycles via plant physiological activities (Fisher et al., 2017; Katul et al., 2012). Although ET is primarily composed of daytime ET ( ET D ), a growing body of observational and modeling evidence suggests that nighttime ET ( ET N ) is also important for various ecohydrological and physiological processes from local to global scales (Forster, 2014; Padrón et al., 2020; Whitley et al., 2013). Globally, Padrón et al.…”

Bridging the Flux Gap: Sap Flow Measurements Reveal Species‐Specific Patterns of Water Use in a Tallgrass Prairie

“…ET measurements are difficult to make at night using eddy covariance techniques, and consequently, few studies have made continuous estimates of nocturnal transpiration in herbaceous ecosystems (Irmak, ; Novick et al, ; Padrón et al, ). By using an alternative approach, we were able to detect continuous rates of nocturnal transpiration in multiple grassland species (Figures and S2).…”

“…While these large spatial scale and high temporal frequency data are invaluable for describing temporal flux dynamics across the landscape, eddy covariance measurements provide an integrated picture of Earth‐atmosphere exchanges and cannot fully describe the mechanistic processes driving these fluxes for individual species. Nocturnal ET measurements made with eddy covariance techniques are also generally unreliable due to low turbulence that occurs at night (Baldocchi, ; Goulden et al, ), which limits their utility in describing diel patterns of water loss (but see Irmak, , Novick et al, , and Padrón et al, ). Conversely, leaf‐level gas exchange measurements (e.g., instantaneous leaf photosynthetic and transpiration rates) are useful in describing the physiology of individual species across a heterogeneous landscape but only provide snapshots of temporally dynamic physiological processes.…”