Land use changes from perennial to annual crops and vice versa may affect water balances, in particular through changing evapotranspiration rates with great implications for modelling. Direct comparison of evapotranspiration rates published in the literature is hardly possible, since differences in soils and climate make data incomparable. This paper presents literature data on crop parameters and environmental conditions that determine transpiration for four crops (oil palm, cocoa, maize and rice) and evaporation. Transpiration at leaf scale and soil evaporation as well as evaporation of intercepted rainfall have been computed using these data and are scaled-up to canopy scale. The objective is to quantify evapotranspiration of the crops under identical environmental conditions at two temporal scales: daily and annual evapotranspiration. Variation among crops in transpiration at leaf scale owing to crop characteristics is levelled out in scaling up to canopy scale. Differences in annual evapotranspiration between perennial and annual crops mainly are due to the fact that perennial crops transpire during the dry season, although at low rates, but still considerably higher than evaporation rates of bare and dry soils. Apparently, the degree of soil cover with vegetation in space and in time is of major importance to evaluate differences in annual evapotranspiration caused by changes in land use.
Radersma, S., & de Ridder, N. (1996). Computed evapotranspiration of annual and perennial crops at different temporal and spatial scales using published parameter values. Agricultural Water Management, 31, 17-34. https://doi.org/10.1016/0378-3774(95)01235-4