Contrasting roles of interception and transpiration in the hydrological cycle – Part 1: Temporal characteristics over land

Abstract

Abstract. Moisture recycling, the contribution of terrestrial evaporation to precipitation, has important implications for both water and land management. Although terrestrial evaporation consists of different fluxes (i.e. transpiration, vegetation interception, floor interception, soil moisture evaporation, and open-water evaporation), moisture recycling (terrestrial evaporation-precipitation feedback) studies have up to now only analysed their combined total. This paper constitutes the first of two companion papers that investigate the characteristics and roles of different evaporation fluxes for land-atmosphere interactions. Here, we investigate the temporal characteristics of partitioned evaporation on land and present STEAM (Simple Terrestrial Evaporation to Atmosphere Model) -a hydrological land-surface model developed to provide inputs to moisture tracking. STEAM estimates a mean global terrestrial evaporation of 73 900 km 3 year −1 , of which 59 % is transpiration. Despite a relatively simple model structure, validation shows that STEAM produces realistic evaporative partitioning and hydrological fluxes that compare well with other global estimates over different locations, seasons, and land-use types. Using STEAM output, we show that the terrestrial residence timescale of transpiration (days to months) has larger inter-seasonal variation and is substantially longer than that of interception (hours). Most transpiration occurs several hours or days after a rain event, whereas interception is immediate. In agreement with previous research, our simulations suggest that the vegetation's ability to transpire by retaining and accessing soil moisture at greater depth is critical for sustained evaporation during the dry season. We conclude that the differences in temporal characteristics between evaporation fluxes are substantial and reasonably can cause differences in moisture recycling, which is investigated more in the companion paper (van der Ent et al., 2014, hereafter Part 2).

The WACMOS-ET project – Part 2: Evaluation of global terrestrial evaporation data sets

“…2); however, the contribution from these areas to the global volumes is rather marginal (< 5 % based on our analyses). For comparison, values typically found in the literature based on a broad variety of methodologies and forcings are 63.2 × 10 3 km 3 (Zhang et al, 2016), 65.0 × 10 3 km 3 (Jung et al, 2010), 65.5 × 10 3 km 3 (Oki and Kanae, 2006), 65.8 × 10 3 km 3 (Schlosser and Gao, 2010), 67.9 × 10 3 km 3 (Miralles et al, 2011a), 71 × 10 3 km 3 (Baumgartner and Reichel, 1975), 73.9 × 10 3 km 3 (Wang-Erlandsson et al, 2014), and 74.3 × 10 3 km 3 (Zhang et al, 2015). We note again that some of these studies considered the poles and desert regions, while others did not.…”

“…The global contribution of transpiration to total average evaporation has been extensively debated recently (Schlesinger and Jasechko, 2014;. Studies have reported values ranging between 35 and 90 %, based on isotopes (Jasechko et al, 2013;Coenders-Gerrits et al, 2015), sapflow measurements (Moran et al, 2009), satellite data (Miralles et al, 2011a;Mu et al, 2011;Zhang et al, 2016), and modelling (Wang-Erlandsson et al, 2014). Consequently, this large range of uncertainty is also expected in the relative contribution from other evaporation sources.…”

“…While the global contribution of transpiration has received much attention in the literature (Jasechko et al, 2013;Coenders-Gerrits et al, 2015), the flux of interception loss has seldom been explored globally (Miralles et al, 2010;Vinukollu et al, 2011b;Wang-Erlandsson et al, 2014). The physical process of interception loss differs from that of transpiration on its sensitivity to environmental and climatic variables: the rates and magnitude of interception are dictated by the aerodynamic properties of the vegetation stand and the occurrence and characteristics of rainfall (Horton, 1919).…”

Description and validation of the Simple, Efficient, Dynamic, Global, Ecological Simulator (SEDGES v.1.0)

“…A very similar zonal mean temporal pattern is found in transpiration in the STEAM (Simple Terrestrial Evaporation to Atmosphere Model) land surface model (Fig. 6 of Wang-Erlandsson et al, 2014). Because this model was evaluated using ERA-Interim forcing data, the high ET anomalies that we see in Fig.…”

“…This approximation is supported by the conservative nature of the ratio of mitochondrial respiration to gross photosynthesis and (hence) of the ratio of net photosynthesis to gross photosynthesis over a wide variety of conditions, on timescales of weeks or more (see the brief review in Van Oijen et al, 2010). Since each model time step in SEDGES is much shorter than this, it thus might seem incorrect to hold NPP / GPP fixed for each time step.…”