Hydrologic processes simulation using the conceptual model Zygos: the example of Xynias drained Lake catchment (central Greece)

Abstract

In the catchment of Xynias drained Lake, hydrologic processes simulation took place using a lumped approach with the conceptual model Zygos. The model implements a conceptual soil moisture accounting scheme extended with a groundwater tank and the input data were the monthly time series of rainfall and the potential evapotranspiration. The automatic optimization procedure of the model was implemented using the evolutionary annealing-simplex algorithm for maximum 11,000 iterations, inserting an 18-month observed runoff time series. It showed that hydrologic balance factors had non-physical significance for the study area. The model’s manual calibration for a Nash coefficient of 0.85 revealed that actual evapotranspiration constitutes 62.5 % (389.7 mm), runoff 22.7 % (141.8 mm) and infiltration 14.8 % (92.2 mm) of precipitation, showing optimal adaptation of simulated to observed runoff. The model estimated the initial reserve of soil moisture related to the presence of organic matter which increases water retention, a residue of the former lake. It confirmed zero runoff values during the summer months and connected the occurrence of springs and the outflows to other catchments (59.8 mm) with the karstification degree of the study area. The error on the annual rainfall is 4.9 % and is considered acceptable.