Determining Drought Years Using Standard Deviation at Tobruk Station in the Al-Butnan Plateau for the Period (1991-2020)

Abstract

This research examines the fluctuations in annual rainfall, specifically the temporal variability and deviation of rainfall amounts from the general average. It identifies drought years at the Tobruk station during the study period (1991-2020). Standard deviation, measures of dispersion, and the coefficient of variation were used to demonstrate the dispersion of values ​​from the general annual rainfall average.The fluctuation is defined as an increase or decrease in rainfall amounts. The study focused on the Tobruk station, utilizing rainfall data for a period of 30 years. The study employed descriptive, statistical, and analytical methodologies to achieve its objectives. The study area is influenced by a Mediterranean climate and experiences fluctuations in rainfall amounts, either exceeding or falling below the general average for the study station. It has witnessed significant oscillations between drought and wet periods in recent years, lacking a consistent long-term pattern. However, recurring drought periods can be observed every few years. The percentage of this fluctuation was calculated and analyzed. The study showed that there were twelve dry years, with rainfall below the average. Eighteen wet years, with rainfall slightly above the average, were also observed.