Bivariate Risk Analysis of Droughts Using a Nonparametric Multivariate Standardized Drought Index and Copulas

Saeed Vazifehkhah*, Fatih Tosunoglu, Ercan Kahya

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Citations (Scopus)


The Nonparametric Multivariate Standardized Drought Index (NMSDI) based on precipitation and soil moisture data in conjunction with copula functions is of primary concern in this study. We are the first to investigate bivariate return periods of the NMSDI using the two typical drought characteristics (duration and severity) at 10 stations in Konya Closed Basin (KCB) in Turkey. As a result, lognormal and log-logistic distributions were identified as the most suitable distributions for drought duration and severity series according to five commonly used goodness of fit tests. Various types of copulas were considered in modeling the joint dependence between duration and severity series at each station. Our results from the five goodness of fit tests and tail dependence assessments showed that BB6, BB7, and BB8 copulas outperformed the joint modeling of duration and severity series in the KCB. The bivariate return period analysis revealed a high risk for southeastern and southwestern regions in the KCB for the 3-month NMSDI series while north to northwestern regions could be exposed to high risk for the 6-month series.

Original languageEnglish
Article number05019006
JournalJournal of Hydrologic Engineering - ASCE
Issue number5
Publication statusPublished - 1 May 2019

Bibliographical note

Publisher Copyright:
© 2019 American Society of Civil Engineers.


The authors thank the Editor(s) and anonymous reviewers of this paper for their thorough review and constructive comments, which have led to substantial improvements. This research was partially supported by the Scientific Research Projects Unit of Istanbul Technical University through the project (No. 39267). The authors would like to thank Turkish State Meteorological Service (TSMS) for providing the precipitation data. The upper tail dependence calculation was done by Vine copula R package by Schepsmeier et al. (2012). We also would like to appreciate NOAA/NCEP/ESRL PSD, Boulder, Colorado, USA, for making soil moisture data available for public. We finally thank Mr. Turhan Uludag, who is acting as an English instructor at The Preparatory School of Foreign Languages, ITU North Cyprus, for editing the manuscript entirely.

FundersFunder number
Istanbul Teknik Üniversitesi39267


    • Copula
    • Drought
    • Konya closed basin
    • Nonparametric Multivariate Standardized Drought Index (NMSDI)
    • Return period
    • Turkey


    Dive into the research topics of 'Bivariate Risk Analysis of Droughts Using a Nonparametric Multivariate Standardized Drought Index and Copulas'. Together they form a unique fingerprint.

    Cite this