Agricultural and Forest Meteorology 124 (2004) 31–49 Micrometeorology and water use of mixed crops in upland West Java, Indonesia Albert I.J.M. van Dijk ∗ , L.A. (Sampurno) Bruijnzeel, Jaap Schellekens Department of Hydrology and Geo-environmental Sciences, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands Received 6 October 2003; received in revised form 22 December 2003; accepted 20 January 2004 Abstract The scarcity of information on the micrometeorology and water use of rain-fed humid tropical crops leads to uncertainty about the effects of land cover change on streamflow and atmospheric circulation. We made micrometeorological measure- ments during five wet season months in a rain-fed cropping system with maize (Zea mays L.) and cassava (Manihot esculenta Crantz) on a bench-terraced hillside in upland West Java, Indonesia. Reflection coefficients varied between 0.07 for moist bare soil and 0.22 for mature cassava with surface mulching. Fluxes of heat and vapour were estimated by the temperature variance method from wet- and dry-bulb temperature fluctuations measured with fast-responding thermocouples. Sensible heat fluxes were 24% larger when determined from Bowen ratios rather than directly, but latent heat fluxes inferred from the two estimates agreed within 10%. The difference was largely attributed to the greater effect of high-frequency losses on directly calculated fluxes. The Penman–Monteith model with optimised values for surface conductance (12.7 mm s -1 ), roughness length (0.03 times crop height) and displacement length (0.64 times crop height) was used to estimate dry canopy evaporation (E t ) for a full year, allowing for the effect of reduced soil water availability during the dry season. Rainfall interception losses (E i ) were estimated with an adapted version of the Gash model calibrated with local measurements of throughfall and stemflow. Simulations with a soil–vegetation–atmosphere transfer model reported elsewhere demonstrated that modelled evaporation rates were consistent with soil hydrological measurements. Total water use was 1228 mm, divided between 1030 mm crop transpiration and soil evaporation and 198 mm rainfall interception losses. © 2004 Elsevier B.V. All rights reserved. Keywords: Evapotranspiration; Bowen ratio; Temperature variance method; Water balance; Crop water use; Humid tropics; Albedo 1. Introduction The rapid conversion of forest to other land uses (notably annual cropping and pasture) in the hu- ∗ Corresponding author. Present address: Integrated Catchment Management, CSIRO Land and Water, G.P.O. Box 1666, Canberra, ‘ACT 2601, Australia. Tel.: +61-2-6246-5780; fax: +61-2-6246-5845. E-mail addresses: albert.vandijk@csiro.au (A.I.J.M. van Dijk), sampurno.bruijnzeel@geo.falw.vu.nl (L.A. Bruijnzeel), jaap.schellekens@geo.falw.vu.nl (J. Schellekens). mid tropics has raised concerns about the potentially negative impacts on water resources (Hamilton and King, 1983; Jepma, 1995). Conversion of forest to shorter vegetation types has been observed to affect both amounts and timing of streamflow, reflecting the decrease in infiltration capacity that usually accompa- nies deforestation (Lal, 1987) as well as differences in vegetation water use (Bruijnzeel, 1989, 2004). In addition, changes in the surface energy balance can affect regional atmospheric circulation (Giambelluca, 1996; Lawton et al., 2001). Despite the considerable 0168-1923/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.agrformet.2004.01.006