Evapotranspiration of tropical peat swamp forests

Abstract

In Southeast Asia, peatland is widely distributed and has accumulated a massive amount of soil carbon, coexisting with peat swamp forest (PSF). The peatland, however, has been rapidly degraded by deforestation, fires, and drainage for the last two decades. Such disturbances change hydrological conditions, typically groundwater level (GWL), and accelerate oxidative peat decomposition. Evapotranspiration (ET) is a major determinant of GWL, whereas information on the ET of PSF is limited. Therefore, we measured ET using the eddy covariance technique for 4-6 years between 2002 and 2009, including El Niño and La Niña events, at three sites in Central Kalimantan, Indonesia. The sites were different in disturbance degree: a PSF with little drainage (UF), a heavily drained PSF (DF), and a drained burnt ex-PSF (DB); GWL was significantly lowered at DF, especially in the dry season. The ET showed a clear seasonal variation with a peak in the mid-dry season and a large decrease in the late dry season, mainly following seasonal variation in net radiation (Rn ). The Rn drastically decreased with dense smoke from peat fires in the late dry season. Annual ET forced to close energy balance for 4 years was 1636 ± 53, 1553 ± 117, and 1374 ± 75 mm yr(-1) (mean ± 1 standard deviation), respectively, at UF, DF, and DB. The undrained PSF (UF) had high and rather stable annual ET, independently of El Niño and La Niña events, in comparison with other tropical rainforests. The minimum monthly-mean GWL explained 80% of interannual variation in ET for the forest sites (UF and DF); the positive relationship between ET and GWL indicates that drainage by a canal decreased ET at DF through lowering GWL. In addition, ET was decreased by 16% at DB in comparison with UF chiefly because of vegetation loss through fires.

Multi‐year energy balance and carbon dioxide fluxes over a residential neighbourhood in a tropical city

“…A comparison of the annual energy and carbon fluxes with those from nearby natural ecosystems which may have existed at the measurement site before urban development occurred, demonstrates how drastically anthropogenic land cover changes can affect the energy and mass exchange at the surface and hence the microclimate. Using long‐term energy totals, partitioning rates into Q H and Q E at the present site are about 0.53 and 0.39 compared to 0.15 and 0.7 over a peat swamp forest located in the same region (2°21′S) (Hirano et al , ). The ratio of evaporation to precipitation is only ∼0.21 over the dry and mostly sealed city surface compared to ∼0.76 in the case of a lowland mixed dipterocarp forest (2°58′N) (Takanashi et al , ).…”

Global variation of transpiration and soil evaporation and the role of their major climate drivers

“…However, the majority of land surface belongs to equitant or water‐limited climate regimes where there is some vegetation cover and therefore low LAI (Figures a and b), requiring regional understanding of how variance in ET a is contributed by T and E . In the humid tropics, there is limited understanding on how aerodynamic and radiative energy components contribute to ET a variance, and current knowledge is limited to site observations [ Fisher et al ., ; Hirano et al ., ; Holwerda et al ., ; Wohl et al ., ]. Our results highlight the importance of regional ecohydrological links [ Villegas et al ., ; Wang et al ., ].…”

“…It is well known that E dominates ET a in extreme dry climates such as Gobi and Sahara deserts where there is little vegetation covered and T dominates ET a in extreme wet climates such as humid tropical rainforests with high LAI [Lawrence et al, 2007;Zhang et al, 2016]. However, the majority of land surface belongs to equitant or water-limited climate regimes where there is some vegetation cover and therefore low LAI (Figures 2a and 2b), requiring regional understanding of how variance in ET a is contributed by T and E. In the humid tropics, there is limited understanding on how aerodynamic and radiative energy components contribute to ET a variance, and current knowledge is limited to site observations [Fisher et al, 2009;Hirano et al, 2015;Holwerda et al, 2016;Wohl et al, 2012]. Our results highlight the importance of regional ecohydrological links [Villegas et al, 2015;Wang et al, 2014].…”

Hysteresis loops between canopy conductance of grapevines and meteorological variables in an oasis ecosystem

“…Previous studies often use midday data to quantify and simulate the responses of g c to its influencing factors (Irvine et al, 2004;Herbst et al, 2008;Fernández et al, 2009;Kochendorfer et al, 2011;Zhang et al, 2012;Zhu et al, 2013;Hirano et al, 2014), morning and afternoon data were usually eliminated from their procedure due to low values in global radiation (R), vapor pressure deficit (D) or E c (Granier et al, 2000b). Most studies found that g c decreased with increasing D, and the relationship generally followed an exponential decay (Cienciala et al, 1992;Monteith and Unsworth, 1990;Oren et al, 1999;Motzer et al, 2005;Chang et al, 2006Chang et al, , 2014Tang et al, 2006).…”