Scaling of low flows in Czechia – an initial assessment

O Ledvinka

doi:10.5194/piahs-366-188-2015

Abstract

Fiala et al. (2010) performed a study focused on the evolution of dry spells at 144 water-gauging stations covering the entire territory of Czechia. They investigated several indicators such as series of 7-day low flows, and deficit volumes and durations (both delimited based on two quantiles, Q330 and Q355, under which the flows are commonly considered as low). Using the Mann-Kendall (MK) test and its reliable modification that accounts for short-term persistence (STP) in data, they evaluated trends in their series. However, as stated in Khaliq et al. (2008), low flow data may also reveal so-called long-term persistence (LTP) that may cause the MK test to detect trends falsely. Therefore, the current study aims to find out if LTP was present before Fiala et al. (2010) applied the MK test to the 7-day low flow series. This was done through the Hurst exponent estimation. Also, testing for a unit root was carried out, similar to Fatichi et al. (2009).

Highlights

Fiala et al (2010) performed a study focused on the evolution of dry spells at 144 water-gauging stations covering the entire territory of Czechia
Θ(B) are autoregressive and moving-average polynomials, respectively, and εt is a white noise. It sufficed to estimate only parameter d that is related to the Hurst exponent H according to: H = d + 0.5
At α = 0.05, the unit root tests revealed that possible non-stationarity of 38 annual and summer series and 17 winter series could not be explained by a deterministic trend

Summary

INTRODUCTION

Fiala et al (2010) performed a study focused on the evolution of dry spells at 144 water-gauging stations covering the entire territory of Czechia. They investigated several indicators such as series of 7-day low flows, and deficit volumes and durations (both delimited based on two quantiles, Q330 and Q355, under which the flows are commonly considered as low). The current study aims to find out if LTP was present before Fiala et al (2010) applied the MK test to the 7-day low flow series. Testing for a unit root was carried out, similar to Fatichi et al (2009)

DATA AND METHODS

RESULTS AND DISCUSSION

CONCLUSION