Analyzing the Impacts of Climatic and Physiographic Factors on Low Flow Distributions

Low flow distributions are derived using the derived distribution function approach while considering the variabilities in the dry spell and recession response time to explore the impacts of climatic and physiographic factors on low flow distributions. The low flow distributions are separately derived from the distributions of the dry spell and the recession ratio, i.e., the ratio of the dry spell to the recession response time, on the basis of the linear recession equation, and the dry spell and recession ratio are both assumed to follow normal, gamma, and lognormal distributions. The parameters of these low flow distributions are estimated from the moments of the dry spell and recession ratio series. Applications of these low flow distributions are exemplified in three basins with different hydrological and climatic conditions in China. The gamma distribution outperforms the other two distributions while describing the distributions of the dry spell and the recession ratio. The derived low flow distributions with parameters estimated from the moments of the recession ratio show good consistency with the low flow empirical distributions, and the derived distributions can be applied to estimate the flow quantiles when continuous records of the streamflow are not available. The relationships between the quantiles of the low flow distributions and the moments of climatic factors and watershed characteristic variables show that the recession ratio has the largest influence on the low flow quantiles regardless of the hydrological regime and that the second-largest influencing factor is the dry spell distribution. Meanwhile, the recession response time has a prominent influence on the low flow distributions in erratic hydrological regimes.