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The aim of the study was to quantify the energy balance components and to estimate evapotranspiration (ET) from maize crops under in‐field rainwater harvesting with wide and narrow runoff strip length (RSL) treatments. Based on micrometeorological measurements, energy balance components were compared for selected days under dry and wet conditions. Diurnal changes and daily evaporation flux peaks around midday were analysed. The average fraction of available energy was used to evaluate the efficiency of converting available energy to latent heat flux (LE). The results indicated that LE was higher in wide compared to narrow RSL during dry and wet conditions. However, sensible heat showed lower values on wide RSL during wet conditions due to the advective effect of the runoff area. The wide RSL with a higher basin leaf area ratio (BLAR) of 2.43 had more ET and used more energy on evaporating water compared to narrow runoff with a lower BLAR of 1.42. Wide runoff strips converted the higher available energy more efficiently into a higher biomass production than the narrow RSL. During wet days, the wide RSL used more than 70% of the available energy, while the narrow RSL response to the available energy (63%) was stronger during dry compared to wet days. Copyright © 2012 John Wiley & Sons, Ltd.

Micrometeorological measurements were used to evaluate heat and water vapor to describe the transpiration (Ev) and soil evaporation (Es) processes for wide and narrow runoff strips under in-field rainwater harvesting (IRWH) system. The resulting sigmoidshaped water vapor (ea) in wide and narrow runoff strips varied in lower and upper parts of the maize canopy. In wide runoff strips, lapse conditions of ea extended from lowest measurement level (LP) to the upper middle section (MU) and inversion was apparent at the top of the canopy. The virtual potential temperature (θv) profile showed no difference in middle section, but the lower and upper portion (UP) had lower in narrow, compared to wide, strips, and LP-UP changes of 0.6 K and 1.2 K were observed, respectively. The Ev and Es within the canopy increased the ea concentration as determined by the wind order of magnitude. The ea concentration reached peak at about 1.6 kPa at a range of wind speed value of 1.4-1.8 m·s for wide and narrow treatments, respectively. The sparse maize canopy of the wide strips could supply more drying power of the air in response to atmospheric evaporative demand compared to narrow strips. This is due to the variation in air flow in wide and narrow runoff strips that change gradients in ea for evapotranspiration processes. OPEN ACCESSAtmosphere 2013, 4 429