Drought Classification based on Standard Runoff Index at Different Time Scales in Sakarya Basin

Drought is one of the most important hydroclimatic disasters directly affecting the natural environmentand human life. It is of great importance to monitor and analyze droughts, which bring many negativeconsequences such as decreasing water resources, decreasing agricultural production, and damagingecosystems. In this study, monthly flow data of station D12A33 in Sakarya Basin between October 1990and November 2020 were used. For station D12A33, the Standard Streamflow Index (SDI) wascalculated for 1, 3, 6, 9, and 12-month scales, and drought analyses were performed. Droughts werecategorised at different time scales and extreme, severe and moderate drought periods were determined.The findings show that extreme drought events are not observed in 1 and 3-month scales, whereasextreme drought events occur in 6, 9 and 12-month scales. The extreme drought values in these threescales were found to be -2.39, -2.69 and -2.80, respectively. In the SDI-12 index, the drought in August2009 was recorded as the most severe drought with a severity of -2.80. In five different time scales,especially the period between 2008-2009 stands out as a period of the longest droughts, lasting 13months on average. Similarly, the average drought values in SDI-1 and SDI-3 drought indices were -1.40 and -1.34, while the average drought values in SDI-6, SDI-9 and SDI-12 drought indices were -1.39, -1.46 and -1.51. The total drought rate is low in the SDI-1 and SDI-3 drought indices (12.32% and14.93%), but slightly higher in the SDI-6, SDI-9 and SDI-12 drought indices at about 16%. As a resultof this study, SDI-6, SDI-9 and SDI-12 are riskier in terms of both duration and severity in droughtindices, pointing out the importance of long-term monitoring studies in the management of waterresources in the region. In addition, it was evaluated that drought frequency and severity may increasedue to the impact of climate change, and therefore, early warning systems should be strengthened. Thisstudy has shown that flow-based drought analysis using SDI is an effective method for water resourcesmanagement and disaster planning.Keywords: Standard Streamflow Index (SDI), Hydrological Drought, Türkiye