Impact of documented land use changes on the surface albedo and evapotranspiration in a plain watershed

Agricultural land use series are investigated in a plain catchment area of the Tisza River, almost identically represented by six administrative count ies. Each county, commonly covering 34,000 km(2), is characterised by high percentage (70-80 %) of managed vegetation. Effects of area coverage variat ions between the different plants are computed for the period 1951-1993 by applying results of a literature-based syntheses, specified for Hungary. Th e latter studies estimate surface-albedo values and proportion between real and potential evapotranspiration for the great majority of the plants grow n in the region. Potential evapotranspiration and relative soil moisture co ntent are estimated from the monthly meteorological series of temperature, precipitation and atmospheric water vapour pressure. Product of these plant -specific characteristics and the relative area coverage yield in monthly s eries of surface albedo and real evapotranspiration, Furthermore, these val ues are related to the energy balance of the surface-atmosphere system by u sing a radiative-convective model adjusted for the given location. Two ques tions are investigated: i) Are there monotonous trends in the given terms of the energy and water b udget ii) Are these changes comparable to the effects caused by other external fo rcings? Our computations give positive answer to both questions. (C) 2001 Elsevier Science Ltd. All rights reserved.