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Journals / Firat University Journal of Experimental and Computational Engineering / 2026 / Cilt: 5 Sayı: 3

SPI-Based Drought and Trend Analysis with Improved Seasonal Decomposition Approaches

Geliştirilmiş Mevsimsel Ayrıştırma Yaklaşımları ile SPI Temelli Kuraklık ve Eğilim Analizi

Ramazan Acar(MUNZUR ÜNİVERSİTESİ)0000-0001-5864-0076
Mustafa Turan(Çevre, Şehircilik ve İklim Değişikliği Bakanlığı)0000-0001-8663-1169
Pages
739–764
Publication Date
2026-10-25
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AI Summary & Key Takeaways

AI Insight
⚡ TL;DR(Too Long; Didn't Read)

Finally, it is suggested that using the STL, SATS Z-score, and SPI approaches together will offer a comparative perspective for drought assessment in the Upper Euphrates Basin.

📌 3 Key Takeaways

🎯
Objective & Hypothesis:Drought is one of the most significant hydro-climatic hazards impacting water resources, agricultural production and the sustainability of ecosystems, particularly in regions with high climatic variability.
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Key Findings & Data:In this context, reliable approaches are needed to better evaluate short- and long-term drought conditions in the Upper Euphrates Basin (UEB).
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Conclusion & Impact:Finally, it is suggested that using the STL, SATS Z-score, and SPI approaches together will offer a comparative perspective for drought assessment in the Upper Euphrates Basin.
🔬Design:Araştırma Makalesi
📍Scope:Comprehensive Sample
⚙️Variables:Mevsimsellik · SATS · STL

Abstract

Drought is one of the most significant hydro-climatic hazards impacting water resources, agricultural production and the sustainability of ecosystems, particularly in regions with high climatic variability. In this context, reliable approaches are needed to better evaluate short- and long-term drought conditions in the Upper Euphrates Basin (UEB). In this study, the performances of the Standardized Precipitation Index (SPI), the Seasonal-Trend Decomposition (STL), and the Seasonality-Adjusted Time Series (SATS) Z-score approaches were comparatively evaluated. These indices were systematically evaluated for five meteorological stations over time scales of 1, 3, 6, and 12 months. The analysis indicated that the STL and SATS Z-score approaches provide seasonality-adjusted perspectives for identifying drought variability at shorter time scales. In contrast, due to its reliance on raw precipitation data, the Standardized Precipitation Index (SPI) was observed to capture such extreme events more sharply within similar short-term periods. A high level of concordance was observed between the proposed methods and the SPI, particularly over a 12-month timescale. The coefficient of determination (R²) values between STL Z-score and SPI were found to be between 0.91 and 0.96 for the 12-month timescale at all stations. For SATS Z-score and SPI, this value was found to be between 0.98 and 0.99. MK and Şen-ITA trend analysis methods were used to analyze the results of the three approaches for all stations. The obtained trend results generally support the consistency observed between the methods. Finally, it is suggested that using the STL, SATS Z-score, and SPI approaches together will offer a comparative perspective for drought assessment in the Upper Euphrates Basin.

Özet

Kuraklık, özellikle iklimsel değişkenliğin yüksek olduğu bölgelerde su kaynaklarını, tarımsal üretimi ve ekosistemlerin sürdürülebilirliğini etkileyen en önemli hidroklimatik tehlikelerden biridir. Bu bağlamda, Yukarı Fırat Havzası’nda (UEB) kısa ve uzun vadeli kuraklık koşullarını daha iyi değerlendirmek için güvenilir yaklaşımlara ihtiyaç duyulmaktadır. Bu çalışmada, Standartlaştırılmış Yağış Endeksi (SPI), Mevsimsel Eğilim Ayrıştırması (STL) ve Mevsimselliğe Göre Düzeltilmiş Zaman Serisi (SATS) Z-skor yaklaşımlarının performansları karşılaştırmalı olarak değerlendirilmiştir. Bu endeksler, beş meteoroloji istasyonu için 1, 3, 6 ve 12 aylık zaman ölçeklerinde sistematik olarak değerlendirilmiştir. Analiz, STL ve SATS Z-skor yaklaşımlarının, daha kısa zaman ölçeklerinde kuraklık değişkenliğini belirlemek için mevsimsellikten arındırılmış bakış açıları sağladığını ortaya koymuştur. Buna karşılık, ham yağış verilerine dayanması nedeniyle, Standartlaştırılmış Yağış Endeksi’nin (SPI) benzer kısa vadeli dönemlerde bu tür aşırı olayları daha net bir şekilde yakaladığı gözlemlenmiştir. Önerilen yöntemler ile SPI arasında, özellikle 12 aylık zaman ölçeğinde yüksek düzeyde bir uyum gözlemlenmiştir. Tüm istasyonlarda 12 aylık zaman ölçeği için STL Z-skoru ile SPI arasındaki belirleme katsayısı (R²) değerlerinin 0,91 ile 0,96 arasında olduğu tespit edilmiştir. SATS Z-skoru ile SPI arasında ise bu değerin 0,98 ile 0,99 arasında olduğu saptanmıştır. Tüm istasyonlar için üç yaklaşımın sonuçlarını analiz etmek üzere MK ve Şen-ITA eğilim analizi yöntemleri kullanılmıştır. Elde edilen eğilim sonuçları, genel olarak yöntemler arasında gözlemlenen tutarlılığı desteklemektedir. Son olarak, STL, SATS Z-skoru ve SPI yaklaşımlarının birlikte kullanılmasıyla Yukarı Fırat Havzası’ndaki kuraklık değerlendirmesi için karşılaştırmalı bir bakış açısı sağlanacağı öne sürülmektedir.

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Cite This Article

Acar, R., Turan, M. (2026). SPI-Based Drought and Trend Analysis with Improved Seasonal Decomposition Approaches. Firat University Journal of Experimental and Computational Engineering, Cilt: 5 Sayı: 3, 739–764. https://doi.org/10.62520/fujece.1987849

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