Thesis - Dissertation

English

Kuil, Linda Anita 

Blöschl, Günter 

Fürnkranz-Prskawetz, Alexia 

E222 - Institut für Wasserbau und Ingenieurhydrologie 

2018

125

water scarcity

eng: Water economies can increasingly be considered mature. The development of additional water supply is extremely costly and the available water supply is subject to intense competition among the many users. In some cases, when water cannot satisfy agricultural, industrial, energy or transport demands, the consequences are economic. In other instances, drought forces people to temporarily reduce dependency on local resources or to relocate to a different location. To mitigate the impacts of water scarcity, solutions progressively need to focus on reforming institutions, improvement of water-efficient technologies and the management of water usage. Thus, the question has become not only "How can we manage water?", but "(How) Can we manage ourselves?". In order to answer this question, understanding of societal behaviour is necessary in addition to hydrological insights. It requires reflecting on our historical and current behaviour, in order to draw lessons in regards to long-term future behaviour. By searching for general patterns across societies each characterized by their unique histories, cultures and norms and values, it is foreseen that decision-making regarding water scarcity, but also floods or water quality issues, is improved. The field of socio-hydrology has been proposed to tackle such complex water management issues. It is built on the premises that human and water systems are coupled and coevolve. Humans are partly responsible for and at the same time adapt to water security problems. Accordingly, these feedbacks should be identified and studied to help understand alternative water futures. It is against this background that the work presented in this PhD thesis has been carried out. By taking a co-evolutionary perspective, this research aimed to improve our understanding of complex, socio-hydrological phenomena in relation to water scarcity in an agricultural setting to improve the knowledge base upon which future water management decisions can be made. Literature research covering a wide range of disciplines formed the basis for the development of a general socio-hydrological model framework. Subsequently, two stylized system models were developed consisting of non-linear differential equations. With the first model, we focused on societal feedbacks that result in and are a consequence of increased water supply. With the second model, we aimed to capture the continuous adaptation process of farmers facing uncertain water supplies thereby focussing on crop choice and water allocation. For each of the models, we investigated its suitability to simulate plausible socio-hydrological dynamics for a relevant case study, after which we explored general model dynamics to advance our overall system understanding. The stylized model focusing on water supply dynamics was presented in Chapter 2. By taking food as a central element of the model, we were able to couple hydrology with demography. We showed that the stylized formulation gives sufficiently rich dynamics to simulate archaeologically deduced depopulation trajectories of the Ancient Maya, which were, albeit the complexity of the society, dependent on subsistence agriculture. We contributed to the scientific debate on the role of drought in the Maya's collapse, by showing that an 80 % decline of population is possible as a consequence of droughts prevalent during the heyday of the civilization, but also that the drought impact can be less severe resulting in a faster recovery of society. The model furthermore shows the dual nature of water storage. Reservoirs allowed the Maya people to sustain longer economic growth and reach higher population levels. However, reliance on reservoirs also resulted in bigger population drops when major droughts occurred. We further explored the relationship between drought and population dynamics in Chapter 3. We showed that the impact of drought on population increases abruptly as soon as a critical population density is exceeded. The position of the threshold depends on the intensity and duration of the drought and also on technological advances, such as the construction of reservoirs or transfer of virtual water embedded in food. Using a stochastic approach, we hypothetically exposed the Ancient Maya to a drier climate. The simulations show that for a society to be as secure post climate change as they are pre-climate change, strategies would have to be adopted to not only increase the region's capacity to provide sufficient resources for its growing population, but also to overcome the impact of a drier climate on productivity. In Chapter 4, we presented a stylized model based on cognitive and bounded rationality theory that focused on crop choice and water allocation of small scale farmers in relation to water availability. With our model framework, we captured the observation that among farmers who are part of community water projects in Kenya's Upper Ewaso Ng'iro basin the fraction of water demanding crops went down, the less water was available. We demonstrated that even though farmers were to make use of simple decision rules and have diverse perceptions on water availability, similar, near optimal crop patterns can emerge. This outcome is consistent with the theory of bounded rationality, which hypothesizes that humans who are assumed to have limited cognitive abilities and imperfect information will adopt 'satisficing' behaviour. By focusing on farmer decision making, it also captures the 'rebound effect', i.e. as additional water becomes available through the improvement of crop efficiencies it will be reallocated on the farm instead of flowing downstream, as a farmer will adjust his (her) water allocation and crop pattern to the new water conditions. Overall, this work has demonstrated that valuable insights with respect to sustainable water management can be obtained by focusing on two-way feedbacks. The results of the first model are relevant for modern society as it shows our vulnerability to water shortage and underlines the need for sustainable water consumption patterns. Especially, for societies having grown accustomed to the availability of water after several decades of water supply expansion, major socio-economic changes might be required to ensure water security. The model is also relevant for areas where high population growth corresponds with the occurrence of more severe or frequent droughts due to climate change, and migration may become a realistic adaptation strategy among other possibilities to reduce water dependency. The second model provides a benchmark to which actual farmer behaviour and perceptions can be compared. It provides an alternative to, for example, normative approaches in which humans are assumed to choose the optimal outcome considering all possible combinations based on perfect information. Both type of approaches are valuable in designing policy and management actions that aim to shift suboptimal trajectories of socio-hydrological systems towards more desirable directions. Future work may focus on the application of the presented model frameworks to comparable archaeological and or contemporary case studies to help explain the observed patterns. The models may be used as a tool to explore behavioural questions or test the robustness of policy interventions. They may also provide a basis to guide data collection aimed at further elucidating socio-hydrological feedbacks.