Impact of Methodological Variations on the Standard Precipitation Index: A Focus on Rainfall-Deficient Scenarios

Petrit Zorba – Institute of Geoscience, Polytechnic University of Tirana, Albania

Elsuida Hoxha – Grove School of Engineering, The City College of New York, United States of America

Abstract: This study delves into the nuances of Standard Precipitation Index (SPI) calculations, especially under conditions where precipitation records for certain months within the dataset are absent. It’s crucial to highlight that these gaps in data are not attributed to observational omissions but are instances where no rainfall was actually documented. In such cases, the absent values are substituted with nominal figures, such as 0.1 mm or 0.01 mm, to maintain the continuity of the dataset. Utilizing well-established methodologies for SPI estimation and referencing various models employed in similar analyses, including “RDIT,” “SPI Generator,” “DrinC,” and one developed by our team named “SPI – Alb PZ,” we aim to explore the implications and errors arising from the replacement of missing values with 0.1 or 0.01. At first glance, these small values may seem insignificant and may not appear to alter climate assessments for the study area. However, contrary to suggestions from some authors advocating for such replacements in SPI calculation methodologies, our study results demonstrate that this type of modification cannot be recommended. Unfortunately, it leads to higher SPI values and, at times, significantly inflates drought estimations for those specific months when rain values are modified.

Keywords: Standard Precipitation Index; drought; data monitoring; meteorology, data modification, SPI error.

Full Text: PDF

DOI: https://doi.org/10.5281/zenodo.10884229

Publication Date: 26.03.2024

How to Cite: Zorba, P., & Hoxha, E. Impact of Methodological Variations on the Standard Precipitation Index: A Focus on Rainfall-Deficient Scenarios. Journal of Integrated Engineering and Applied Sciences, 2024; 2(1); 48–57.

References:

  1. Standardized Precipitation Index User Guide, WMO-No.1090 (2012). World Meteorological Organization, Geneva 2, Switzerland.
  2. Cornel S.N. Comparative study regarding performance of some software for the calculations of the standardized precipitation index (SPI)”, Analele Universităţii din Oradea, Fascicula Protecţia Mediului, 2014; 23; 779-788.
  3. Wu H., Hayes M.J., Wilhite D.A., and Svoboda M.D. The Effect of the Length of Record on the Standardized Precipitation Index Calculation”, International Journal of Climatology, 2014; 25; 505-520.
  4. Guide to Instruments and Methods of Observation Volume V – Quality Assurance and Management of Observing Systems, WMO-No. 8 (2018). World Meteorological Organization, Geneva, Switzerland.
  5. AGRIMETSOFT. Available at https://agrimetsoft.com/calculators/Index Accessed on 18 September 2023. 
  6. Zorba P. Estimation of the error in the measurement of atmospheric precipitation and the correction coefficient due to evaporation. Monthly Climate Bulletin, 2023; 7(79); 39-47.
  7. Zorba, P., Hoxha, E. A New Approach for Drought Evaluation by Using the SPI Methodology. Lecture Notes on Multidisciplinary Industrial Engineering. 2024, p. 304-316.
  8. DrinC. Available at https://drought-software.com Accessed on 18 September 2023.
  9. SPI Generator. Available at https://drought.unl.edu/monitoring/SPI/SPIProgram.aspx Accessed on 18 September 2023.
  10. Zorba P., Hoxha E. Comparative Analysis of SPI Errors Generated by Software Tools Using Data Series of Different Lengths for Meteorological Stations in Mediterranean and Humid Continental Climates. Monthly Climate Bulletin, 2023; 7(73); p. 24-30.
  11. Zorba P., Hoxha E. A novel model for Standardized Precipitation Index (SPI) analysis and the calculation of errors produced by various software programs using meteorological data from stations of diverse climate types. Monthly Climate Bulletin, 2023; 7(75); 22-31.
  12. Zorba P., Hoxha E. Drought SPI Index, highly impacted by precipitation measurement errors, especially in extreme weather event” Monthly Climate Bulletin, 2023; 7(81). 
  13. Arléry R., Grisollet H., Guilmet B. (1973). Climatologie – Méthodes et Pratiques. Gauthier-Vilars Éditeur, Paris – Bruxelles – Montréal.