MULTIYEAR DROUGHT SIMULATION¹

Abstract

Previous studies on multiyear droughts have often been limited to the analysis of historic annual flow series. A major disadvantage in this approach can be described as the unavailability of long historic flow records needed to obtain a significant number of drought events for the analysis. To overcome this difficulty, the present study proposes to use synthetically generated annual flow series. A methodology is presented to model annual flows based on an analysis of the harmonic and stochastic properties of the observed flows. Once the model is determined, it can be utilized to generate a flow series of desired length so as to include many hydrologic cycles within the process. The key parameter for a successful drought study is the truncation level used to distinguish low flows from high flows. In this paper, a concept of selecting the truncation level is also presented. The drought simulation procedure is illustrated by a case study of the Pequest watershed in New Jersey. For the above watershed, multiyear droughts were derived from both historic and generated flow series. Three important drought parameters, namely, the duration, severity, and magnitude, were determined for each drought event, and their probability distributions were studied. It was found that gamma and log normal probaility functions produce the best fit for the duration and severity, respectively. The derived probability curves from generated flows can be reliably used to predict the longest drought duration and the largest drought severity within a given return period.

Proneness of European Catchments to Multiyear Streamflow Droughts

“…So far, the proneness of catchments to multiyear events has not been assessed on a European scale. This might be related to the fact that observed discharge time series are usually too short to capture the natural long-term variability and accordingly assess the potential occurrence of multiyear droughts (Wijayaratne & Golub, 1991). Natural variability can generate events longer than seasonal droughts that have occurred in the observation period (Parsons et al, 2018).…”

Stochastic simulation of droughts. Part 2: regional droughts

“…The presence of multiple frequencies in a particular hydrologic series is evidence that the periodicity of the hydrologic cycle has been changed over time. On the other hand, a precipitation series with a single frequency can be assumed to be more stationary and be subject to less temporal variations (Wijayaratne and Golub, 1991). The average periodicity of the annual precipitation series of each station is obtained and the average periodicity of annual precipitation series over the entire region was obtained by averaging the average periodicity of all precipitation series in the region.…”

Simulation of the occurrence of drought events via copulas

“…Drought studies have been received attention from researchers around the world since they are indispensable tools for water resource planning and management. The theory of runs allowed several researchers to conduct univariate analyses of the main variables of the hydrological droughts (severities and durations), as can be seen in Yevjevich (1967), Millian & Yevjevich (1971), Dracup et al (1980b), Zelenhasic & Salvai (1987), Sen (1990), Chang (1990), Wijayaratne & Golub (1991), Mathier et al (1992), Sharma (1997), Cancelliere & Salas (2004), Tesfaye (2005), Yahiaoui et al (2009), Panu & Sharma (2009), Sharma & Panu (2010), Akyuz et al (2012) and Sharma & Panu (2014). These studies are considered as references for the univariate analysis of the severities and durations of the droughts.…”