Dynamic Analysis of Hydrological Drought using Constant Threshold Method and Vensim Software

Abstract

This study aimed to present a dynamic simulation of hydrological drought using Vensim and the constant threshold level method in the Dorud-Borujerd basin in the 1991-2019 period. First, the threshold levels were estimated, and then the drought duration and volume were quantified. Next, the frequency of the highest duration and volume values was analyzed to determine the return periods. While confirming the superiority of the systems thinking approach, the results showed that the highest drought duration figures were 229 and 123 days, respectively, at the 70 and 90% threshold levels of the flow duration curve in the Bitun station. Tire station recorded 21.320 and 38.47 MCM for 70% and 90% threshold levels, respectively, which were the largest figures for drought volume. The frequency analysis of these figures obtained from dynamic simulation showed that the drought duration and volume will have a return period of 25 and 8 years and 4 and 14 years, respectively, at 70% and 90% threshold levels. Moreover, 2012 and 2015 were very dry years in terms of both duration and volume. Therefore, drought episodes have been occurring in the Dorud-Borujerd basin for many years and will continue with more intensity in the future.

Keywords

• drought duration
• drought volume
• frequency analysis
• system thinking