Estimation of evapotranspiration rate by using the Penman-Monteith and Hargreaves formulas for the loess in Northeast Bulgaria complex with HYDRUS-1D

摘要

Loess and loess-like sediments cover approximately 13 of the Bulgarian territory,mainly within the Danubian plain.From the Danube River to the Fore-Balkan,the loess soils form a loess complex where its depth varies from 50-60 meters in the north to few meters in the south,respectively.Widespread loess sediments possess a specific feature: they typically form deep unsaturated zones.Quantification of the near surface water balance is extremely important for evaluating land-atmosphere interactions,and the impact of land-use change on the subsurface flow and the evapotranspiration rate is an essential term in this quantification.In the frames of a scientific project,an automatic weather station was installed in a typical plain terrain of the loess complex in Northeast Bulgaria,recording meteorological data from September 2015 to February 2017. This study provides a mathematical description of processes (i.e.,Penman-Monteith and Hargreaves Methods) used to estimate daily evapotranspiration rates implemented into the numerical model HYDRUS-1D,as well as a respective rate investigation of months with and without intensive rainfalls.Overall results indicate that using the Hargreaves formula for evaluation of the potential evapotranspiration leads to overestimation between 10 and 20,respectively for a "wet" and "dry" month.