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 equilibrium between groundwater and plants and threatened the lives of some of them. To avoid water stress, an advanced irrigation system was installed. For design purposes, better knowledge of the water cycle and the monthly average evapotranspiration in the area was needed. Due to the complex canopy stand of the site, evapotranspiration was estimated using the water balance method, integrating mathematical models with the Arc/Info Geographical Information System. 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 simulate the long-term water requirements using the product of reference evapotranspiration and the apparent crop coefficient to estimate evapotranspiration from the garden. Two types of hydrological behaviour were identified: one in the central area of the garden, where reduced ground cover diminishes evapotranspiration and increases runoff and percolation. In the external area, the evapotranspiration was higher because of the presence of many trees. The empirical mean monthly crop coefficient ranged between 0.56 and 0.83, indicating that evapotranspiration in the entire area is always less than grass reference evapotranspiration.