A New Method for Joint Frequency Analysis of Modified Precipitation Anomaly Percentage and Streamflow Drought Index Base
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A New Method for Joint Frequency Analysis of Modified Precipitation Anomaly Percentage and Streamflow Drought Index Based on the Conditional Density of Copula Functions Mohammad Nazeri Tahroudi 1 & Yousef Ramezani 1 Rasoul Mirabbasi 3
2
& Carlo De Michele &
Received: 19 May 2020 / Accepted: 7 September 2020/ # Springer Nature B.V. 2020
Abstract
In this study, a new method was proposed to model the occurrence of related variables based on the conditional density of copula functions. The proposed method was adopted to investigate the dynamics of meteorological and hydrological droughts in the Zarinehroud basin, southeast of Lake Urmia, during the period 1994–2015. For this purpose, the modified precipitation anomaly percentage and streamflow drought indices were extracted. Finally, the joint frequency analysis of duration-duration and severityseverity characteristics of meteorological and hydrological droughts was analyzed. Analysis of 7 different copulas used to create the joint distribution in the Zarinehroud basin indicated that the Frank copula had the best performance in describing the relationship between the meteorological and hydrological drought severities and durations. By examining the results of the bivariate analysis of duration-duration of meteorological and hydrological droughts at different stations, the expected meteorological and hydrological drought durations were estimated in the years ahead. For example, at Chalkhmaz station, 4- to 7-month duration for the hydrological drought and 9- to 12-month duration for the meteorological drought is expected in the years ahead. The joint frequency analysis of drought characteristics allows to determine the meteorological and hydrological drought characteristics at a single station at the same time using joint probabilities. Also, the results indicated that by knowing the conditional density, the hydrological drought characteristics can be easily estimated for the given meteorological drought characteristics. This could provide users and researchers useful information about the probabilistic behavior of drought characteristics for optimal operation of surface water. Keywords Bivariate copula . Conditional density . Hydrological drought . Joint return period
* Yousef Ramezani [email protected] Extended author information available on the last page of the article
Tahroudi M.N. et al.
1 Introduction Drought can be characterized by its duration and severity. There are also several indices to describe the drought condition such as the precipitation anomaly percentage (PAP), precipitation concentration index (PCI), standardized precipitation index (SPI) and joint deficit index (JDI) for meteorological drought (Ahmadi et al. 2018; Zamani et al. 2018; Tahroudi et al. 2019b; Ramezani et al. 2019), Palmer hydrological drought index (PHDI) and streamflow drought index (SDI) for hydrological drought. To analyze the drought of each sub-basin, it is important to know the characteristics of the drought as well as the influence of other dependent variables. T
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