Global-scale analysis on future changes in flow regimes using Gini and Lorenz asymmetry coefficients

Abstract

By introducing two scalar quantities, namely, the Gini and Lorenz asymmetry coefficients, we examined their characteristics and applicability to the global analysis of changes in river flow regimes under future climate change. First, by applying these coefficients to river discharge data, we showed that various types of flow-duration curves can be interpreted quantitatively in terms of the seasonal inequality in the discharge (i.e., the unevenness of the temporal distribution of river discharge). Their statistical characteristics, based on five theoretical distribution functions frequently used in hydrological analysis, were also shown. Next we used these coefficients to evaluate the seasonal inequality of major global rivers using the global hydrological model H08 for four 30 year time spans (1960-1989, 2010-2039, 2040-2069, and 2070-2099) under four climate-change scenarios. We used ensembles of hydrological simulation results with five general circulation models. From the analysis of the Gini coefficient, future changes in seasonal inequality show a contrasting geographical pattern: a decreasing trend at high northern latitudes and an increasing trend in most other areas. The Lorenz asymmetry coefficient shows large changes at high northern latitudes, attributable to major shifts in the flow regime accompanied by different snow-melting properties under different future climate scenarios. Although a flow-duration curve is a pictorial representation of river discharge suitable for one specific site, by depicting the geographical distribution of these two coefficients along river channels, different characteristics of flow-duration curves at different sites can be detected, even within the same river basin.

Temperature and precipitation changes over the Loess Plateau between 1961 and 2011, based on high-density gauge observations

“…Recently, the concept has been applied to other research fields, such as inequalities in global water use (Seekell et al, 2011) and plant size and fecundity (Damgaard and Weiner, 2000), and temporal inequalities in catchment discharge (Jawitz and Mitchell, 2011;Masaki et al, 2014). Rajah et al (2014) used the Gini coefficient to analyze the distribution of precipitation and changes in precipitation.…”

Sensitivity of simulated global-scale freshwater fluxes and storages to input data, hydrological model structure, human water use and calibration

“…The quantification of global-scale freshwater fluxes, in particular river discharge, is essential to assess availability and scarcity of water resources for humans and the environment for both present (Hoekstra et al, 2012;Oki and Kanae, 2006;Prudhomme et al, 2014) and scenario conditions (Döll and Müller Schmied, 2012;Masaki et al, 2014;. Further examples are the estimation of amounts and spatial distribution of precipitation (Harris et al, 2014;Schneider et al, 2014) and evapotranspiration (Jasechko et al, 2013;Jung et al, 2010;Sterling et al, 2012).…”

Development of an Evaluation System for Sustaining Reservoir Functions—A Case Study of Shiwen Reservoir in Taiwan

“…The coefficient can be one of the effective indices employed to explore equity in water allocation strategies [28]. The Gini coefficient here was calculated based on research on the fairness of water allocation in South Africa [48], future changes on water discharge in the coming 30 years (e.g., Masaki et al [49]), and the inequality in water supply and demand from 1999 to 2006 in the Yellow River basin (e.g., Wang et al [50]). Wang et al [50] used the Gini coefficient in assessing equity in domestic water supply.…”

“…Wang et al [50] used the Gini coefficient in assessing equity in domestic water supply. Masaki et al [49] used the Gini and Lorenz-asymmetry coefficients to evaluate the characteristics and applicability in river flow regimes under future climate change. Rajah et al [51] applied a Gini index to evaluate the precipitation distributions for wet-day frequency and decreasing wet-day frequency.…”