Dynamics of nocturnal, daytime, and sum-of-hourly evapotranspiration and other surface energy fluxes over nonstressed maize canopy

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The magnitude and driving forces of nocturnal evaporative losses, ET cnight , and the interactions of other surface energy fluxes and microclimatic variables under various climatic, soil, and management conditions are not well understood. Such relationships are important for ecophysiological studies. This research attempts to investigate such relationships. Furthermore, ET cnight can be a sizable portion of the daily total evaporative losses. Most empirical equations, especially ones that use solar or net radiation to estimate daily evapotranspiration (ET), either ignore or poorly treat the contribution of ET cnight to the daily total ET. Neglecting ET cnight can lead to errors in determining the daily or the sum-of-hourly ET c (i.e., ET cSOH) and can also cause cumulative errors when making long-term water balance analyses. In this paper, the magnitudes, trends, and contribution to the nocturnal surface energy balance of various microclimatic variables (air temperature, T a; vapor pressure deficit, VPD; relative humidity, RH; and wind speed at 3 m, u 3) and surface energy fluxes (ET cnight; soil heat flux, G; sensible heat flux, H; and net radiation, R n); were quantified and interpreted for a nonstressed and subsurface-drip-irrigated maize canopy. The effect of microclimatic variables and surface energy flux components on the Bowen ratio energy balance system (BREBS)-measured ET cnight and daytime evaporative loss, ETcday , were investigated in the growing season of 2005 (i.e., April 22-September 30) and 2006 (May 12-September 27). The nighttime evaporative losses were high early in the season during partial canopy closure because of increased surface soil evaporation and were also high later in the season during and after leaf aging, physiological maturity, and leaf senescence. The seasonal average nighttime evaporative losses for 2005 and 2006 were 0.19 and 0:11 mm=night, respectively. Losses of 0.50 mm or more occurred in 2005 and 2006 on eight and seven nights, respectively. The seasonal total ETcnight , ET cday , and ET cSOH in 2005 were 31, 612, and 642 mm, respectively. The ET c values in 2006 were 16, 533, and 547 mm, respectively. In both years, the percent ratio of ET cday to ET cSOH usually was more than 80-85%. ET cnight was affected primarily by u 3, VPD, and T a. A strong relationship between ET cnight and nighttime sensible heat was observed. Some of the largest ratios of ET cnight to ET cSOH occurred on rainy nights with strong winds. Because of strong winds, the ET cnight was high owing to the clear coupling among all energy exchanges within and above the canopy as a result of the mixing of the lower boundary layer of the microclimate. The results of this study showed that the ET cnight can be up to 5% of the ET cSOH , even for a subsurface-drip-irrigated maize canopy in which the soil surface is usually dry, thus, less evaporative losses potential compared with the surface or sprinkler-irrigated surfaces in which ET cnight would be expected to be considerably higher because of wetter surface conditions. ET cnight needs to be quantified for different vegetation surfaces and management practices, surface wetting, and climatic conditions to better account for nighttime water losses and better understand nighttime energy balance mechanisms.

Original languageEnglish (US)
Pages (from-to)475-490
Number of pages16
JournalJournal of Irrigation and Drainage Engineering
Issue number8
StatePublished - Aug 3 2011

All Science Journal Classification (ASJC) codes

  • Civil and Structural Engineering
  • Water Science and Technology
  • Agricultural and Biological Sciences (miscellaneous)


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