Improving methods to calculate the monthly water budget for Lake Velence, Hungary

Abstract

In recent years the water levels of Lake Velence - Hungary's third-largest lake - have dropped significantly due to a series of climatic and anthropogenic phenomena. Water managers calculate the lake's water budget based on a methodology established almost 50 years ago. The calculation error is determined as the difference between the computed and observed lake levels. A previous study on the calculation errors of annual water budget computations has found several uncertainties that result in predominantly negative errors; underestimating inflows and, or overestimating outflows.This study focuses on monthly water budget computations to investigate the possible causes of the calculation errors. The monthly error distribution shows that negative calculation errors accumulate during the year's first five months. Based on this outcome, the methods for determining monthly precipitation, evapotranspiration and surface inflow are explored in more detail for the January – May period. Remote sensing data and numerical modelling were used to fill spatial and temporal data gaps.The research will result in an improved water budget calculation method, which enhances our understanding of the main processes governing lake water levels. The new approach will give water managers a clearer picture of the effectiveness and necessity of engineering interventions to restore lake water levels.The research is carried out within the framework of the Széchenyi Plan Plus program with the support of the RRF 2.3.1 21 2022. 00008 project.