Generalized regionalization of hydrological model parameters across Greece and water balance analysis within the Budyko framework

Greece is characterized by complex geomorphological variations and pronounced spatial hydroclimatic variability, which makes the generalization of hydrological model parameters challenging. Moreover, the limited availability of hydrometric data in the country necessitates the use of simulation models and theoretical frameworks for understanding hydrological processes. This study aims to provide a physical interpretation of the processes that shape catchment behavior under different hydro – geomorphological conditions. Although several studies have been conducted internationally on the regionalization of parameters in lumped conceptual models and the application of the Budyko framework, few have focused on Greek catchments. In this thesis, monthly time series of precipitation, potential evapotranspiration, and observed streamflow from 35 catchments distributed across six River Basin Districts of Greece are utilized. Initially, the suitability of different versions of a lumped conceptual hydrological model is examined with respect to the number and physical interpretation of its parameters, aiming at the selection of the optimal model structure. Subsequently, the generalized model, defined by 20 parameters and based on four hydrological response units (HRUs), is calibrated using selected catchments representative of diverse physiographic and hydrological conditions, while validation is conducted on the remaining catchments to assess the transferability of parameters. Additionally, the water balance is analyzed within the Budyko framework as a function of the aridity index, to investigate the relationship between long-term averages of precipitation, potential evapotranspiration, and actual evapotranspiration, as well as to evaluate empirical approaches from the international literature. The results indicate that the proposed parameter regionalization provides satisfactory simulation of monthly streamflow, while the water analysis within the Budyko framework demonstrates that the catchments exhibit a stronger degree of water limitation than theoretically anticipated, attributable to the pronounced hydroclimatic variability.