The co-evolution of people and water: modelling framework for coupled socio-hydrology systems and insights for water resource management

It is increasingly acknowledged that the challenge of sustainable freshwater management requires identification and characterization of the underlying components, interactions and co‐evolving dynamics inherent in the coupled human‐hydrology system. To this end, a broadly applicable conceptual framework is needed to guide the consistent formulation of catchment models that include adequate representation of socioeconomic systems – and the dynamic feedbacks between human and natural systems. To achieve this goal, this research is comprised of three parts.

Firstly, a generic conceptual socio‐hydrology framework applicable to agricultural catchments is presented, made up of six key components that combine to form the coupled system dynamics: namely, catchment hydrology, population, economics, environment, socioeconomic sensitivity and collective response. The conceptual framework posits two novel constructs (i) a composite socioeconomic driving variable, termed the Community Sensitivity state variable, which seeks to capture the perceived level of threat to a community’s quality of life, and acts as a key link tying together one of the fundamental feedback loops of the coupled system, and (ii) a Behavioural Response variable as the observable feedback mechanism, which reflects land and water management decisions relevant to the hydrological context. The framework makes a further contribution through the introduction of three macro‐scale parameters that enable it to normalise for differences in climate, socioeconomic and political gradients across study sites. In this way, the framework provides for both macro‐scale contextual parameters, which allow for comparative studies to be undertaken, and catchment‐specific conditions, by way of tailored “closure relationships”, in order to ensure that site‐specific and applicationspecific contexts of socio‐hydrologic problems can be accommodated.

The second component of the research involves the application of the framework to build a localised socio‐hydrology model that captures the dynamic water balance evolution and coupled human response within the Lake Toolibin catchment in West Australia's wheatbelt region. Two sub‐catchments in different parts of the landscape are selected to examine the key emergent properties of the coupled system over a 100 year period, by analysing the two‐way feedbacks of land‐use management (human system feedback) and land degradation (natural system feedback). Using a relatively simple parameterisation of Community Sensitivity to land degradation, the model was able to identify positive and negative feedbacks, the presence of threshold behaviour, timescale differences between fast and slow moving variables, differences in time lags resulting from disparate resistance levels of the natural system, and the degree of adaptive learning inherent in the human system. Specifically, the valley floor sub‐catchment demonstrated a threshold shift in the human feedback after 60 years, whilst the upslope sub‐catchment showed no sign of reaching a threshold shift in 100 years. The results demonstrate that the fully parameterised case‐study model is able to quantify coupled system dynamics and isolate the inherent two‐way feedbacks.

Finally, the research addresses two fundamental information gaps concerning the sensitivity of coupled system feedbacks to various endogenous system properties and exogenous societal contexts and the implications of socio‐hydrological models to water management. An idealised implementation of the model is used to explore the sensitivity of emergent dynamics resulting from bi‐directional feedbacks to assumptions regarding (a) internal system properties that control the internal dynamics of the coupled system and (b) the external socio‐political context, and results are interpreted within the context of water resource management decision making. The analysis investigates feedback behaviour in three ways, (a) via a global sensitivity analysis on key parameters and equilibrium analyses on model outputs, (b) through a comparative analysis based on hypothetical placement of the catchment along various points on an international sociopolitical gradient, and (c) by assessing the effects of various direct management intervention scenarios. Results indicate the presence of optimum windows that might offer the greatest positive impact per unit of management effort. Results further advocate management tools that encourage an adaptive learning, community‐based approach with respect to water management, which are found to enhance centralized policy measures.

Thus the research demonstrates that it is possible to use a place‐based socio‐hydrology model to make abstractions as to the dynamics of bi‐directional feedback behaviour, and provide insights as to the efficacy of competing and complimentary water management tools under different circumstances. As the conceptual framework proposed and implemented in this research is applied across international study sites and gradients in future, we will develop a deeper understanding of the fundamental interactions and feedbacks in such complex human‐hydrology systems, thereby allowing hydrologists to improve social‐ecological systems modelling through better representation of human feedbacks on hydrological processes, and water managers to improve long‐term policy and management strategies that take into account adaptive learning within the social system.