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

Abstract

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.

Impact of the loess’ hydraulic characteristics on its degree of saturation for the purpose of radon index measurements (Northeast Bulgaria case study)

“…The terrain is flat, and the loess deposits are approximately 30 m thick. The exact specifications of the devices recorder the meteorological dataset and the dataset itself are described in details in Gerginov (2019) and in Gerginov and Antonov (2019). At the site, in area approximately 12 sq.…”

“…The initial condition is set equal to the examined in situ pressure head (Antonov et al, 2018). The bottom boundary condition is set to free drainage condition and the (Gerginov, Antonov, 2019). Three observation points (OP) were set at 55 cm, 80 cm and 105 cm depths in the models due to the field measurement of gas permeability of soils in connection with the radon index determination.…”

“…In Bulgaria, there are some attempts for investigation and evaluation of the unsaturated state of the (near)surface sediment deposits and especially that one of the loess complex based on either modelling approach or field observations (Mallants et al, 2007;Benderev et al, 2015;Antonov et al, 2018;Gerginov at al., , 2020Tsvetkova et al, 2019). In addition, in the recent years there are few models concerning particular parts of the hydraulic characteristics (parameters) of the loess in the vadose zone and the moisture dynamics due to precipitation rates in Northeastern Bulgaria (Gerginov, Antonov, 2019;Kolev, 2021). The current study is an attempt to evaluate the degree of saturation based on onedimensional model and four different sets of hydraulic parameters.…”

Dissecting the Mutual Response of Potential Evapotranspiration with Vegetation Cover/Land Use over Heilongjiang River Basin, China

“…In the corresponding application, scholars have combined the required meteorological data to obtain the Penman-Monteith PET (PM_PET) of several key transboundary catchments worldwide through spatial interpolation algorithms such as Kriging and inverse-distance weighting. The long-term time-series distribution of the value was obtained, and its correlation with various meteorological elements and their contribution degrees was analyzed [17][18][19][20].…”