A conceptual socio-hydrological model of the co-evolution of humans and water: case study of the Tarim River basin, western China

摘要

The complex interactions and feedbacks between humans and water arecritically important issues but remain poorly understood in the newlyproposed discipline of socio-hydrology (Sivapalan et al., 2012). Anexploratory model with the appropriate level of simplification can bevaluable for improving our understanding of the co-evolution andself-organization of socio-hydrological systems driven by interactions andfeedbacks operating at different scales. In this study, a simplifiedconceptual socio-hydrological model based on logistic growth curves isdeveloped for the Tarim River basin in western China and is used toillustrate the explanatory power of such a co-evolutionary model. The studyarea is the main stream of the Tarim River, which is divided into twomodeling units. The socio-hydrological system is composed of foursub-systems, i.e., the hydrological, ecological, economic, and socialsub-systems. In each modeling unit, the hydrological equation focusing onwater balance is coupled to the other three evolutionary equations torepresent the dynamics of the social sub-system (denoted by population), theeconomic sub-system (denoted by irrigated crop area ratio), and theecological sub-system (denoted by natural vegetation cover), each of whichis expressed in terms of a logistic growth curve. Four feedback loops areidentified to represent the complex interactions among different sub-systemsand different spatial units, of which two are inner loops occurring withineach separate unit and the other two are outer loops linking the twomodeling units. The feedback mechanisms are incorporated into theconstitutive relations for model parameters, i.e., the colonization andmortality rates in the logistic growth curves that are jointly determined bythe state variables of all sub-systems. The co-evolution of the Tarimsocio-hydrological system is then analyzed with this conceptual model togain insights into the overall system dynamics and its sensitivity to theexternal drivers and internal system variables. The results show a costlypendulum swing between a balanced distribution of socio-economic and naturalecologic resources among the upper and lower reaches and a highly skeweddistribution towards the upper reach. This evolution is principally drivenby the attitudinal changes occurring within water resources managementpolicies that reflect the evolving community awareness of society to concernsregarding the ecology and environment.