Low flow frequency analyses: A new approach integrating seasonality and multivariate characteristics of drought

In this paper, we propose a new approach for multivariate drought frequency analysis. It combines extreme value statistics of magnitude, duration and deficit volume of annual streamflow drought events. Drought magnitude is represented by the annual minimum flow. It is modeled by the mixed distribution approach of Laaha (2023a) based on annual summer and winter minimum series, where possible seasonal correlations are modeled by a copula approach (Laaha 2023b). Duration and deficit volume of annual drought events are estimated by Yevjevich’s threshold level approach, using a constant threshold level. To this end, the dependence structure of magnitude (M), duration (D) and deficit volume (V) with seasonality characteristics is evaluated. The joint probability of occurrence of multiple drought characteristics is modeled using a Vine copula approach, thereby extending bivariate drought frequency analysis of Mirabbasi et al. (2012). The multivariate frequency model allows marginal and total frequencies or return periods of drought events to be calculated. We anticipate that the multivariate low-flow frequency analysis is more comprehensive, and thus more effective in capturing drought severity compared to the univariate analyses. We suggest that the method can be used for drought monitoring in various hydrological settings including strongly seasonal climates.

References:

Laaha, G., 2023a. A mixed distribution approach for low-flow frequency analysis–Part 1: Concept, performance, and effect of seasonality. Hydrology and Earth System Sciences, 27(3), pp.689-701.

Laaha, G. 2023b. A mixed distribution approach for low-flow frequency analysis–Part 2: Comparative assessment of a mixed probability vs. copula-based dependence framework. Hydrology and Earth System Sciences, 27(10), 2019-2034.

Mirabbasi, R., Fakheri-Fard, A. and Dinpashoh, Y., 2012. Bivariate drought frequency analysis using the copula method. Theoretical and applied climatology, 108, pp.191-206.