Micrometeorology and water use of mixed crops in upland West Java, Indonesia.

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 measurements 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