Assessment of Hydrological Drought Index change over long period (1990–2020): The case of İskenderun Gönençay Stream, Türkiye

Abstract

Recently, due to changes in the global climate, there have been significant increases in flood and drought events. The changes in wet and dry periods can be examined by various methods using hydrometeorological data to analyze climate disasters. In this study, Gönençay Stream in the Asi River Basin was chosen as the study area, which contains abundant underground and surface water reserves in Türkiye. Within this region, not only are the agricultural activities intense, but also hydraulic structure applications such as dams and reservoirs draw attention. Previous studies stated that meteorological and agricultural droughts have started to be noticed in the basin. Therefore, temporal variation analyses can positively contribute to assessing possible hydrological droughts in the following years. In this context, wet and drought periods were determined using the Streamflow Drought Index method at 3, 6, 9, and 12-month time scales with monthly average flow data observed between 1990 and 2020. At the same time, the number and probabilities of drought categories on a 12-month time scale, the first expected transition times between classifications, and the expected residence times between categories were specified. The study revealed that the most severe dry period occurred between 2013 and 2014 and was classified as Extremely Drought. The wettest period was around 2018–2019 and was classified as Extremely Wet. The largest expected time residence among all classifications was calculated for the Extremely Drought category with nine months, means that if the Extremely Drought period ever occurs, it remains for approximately nine months. While the Moderately Drought period occurred within one month following the Extremely Drought duration, and a Near Normal Wet period was observed three months after the Extremely Wet period. The most seen drought category for monthly calculations was the Near Normal Wet category, and was seen over 200 times with a 52.8% probability. Considering the Gönençay region, it is possible that any Extreme drought classification eventually regresses to normal.