Estimating evapotranspiration in the Padova Botanical Garden

In 1996, intensive building operations near the botanical garden of Padova, the oldest botanical garden in the world, altered a long-established equil ibrium between groundwater and plants and threatened the lives of some of t hem. To avoid water stress, an advanced irrigation system was installed. Fo r design purposes, better knowledge of the water cycle and the monthly aver age evapotranspiration (ET) in the area was needed. Due to the complex cano py stand of the site, ET was estimated using the water balance method, inte grating mathematical models with the Arc/Info Geographical Information Syst em. The water balance was estimated in 1997 and 1998, and results were used to derive an empirical mean crop coefficient of the botanical garden, to s imulate the long-term water requirements using the product of reference ET and the apparent crop coefficient to estimate ET from the garden. Two types of hydrological behaviour were identified: one in the central area of the garden, where reduced ground cover diminishes ET and increases runoff and p ercolation. In the external area, the ET was higher because of the presence of many trees. The empirical mean monthly crop coefficient ranged between 0.56 and 0.83, indicating that ET in the entire area is always less than gr ass reference ET.