Socio-hydrology

Supply-demand cycle: water shortage

Evidence has shown that water supply leads to higher water demand, which can quickly offset the initial benefits of reservoirs. These cycles can be seen as a rebound effect, also known in environmental economics as Jevon's paradox: as more water is available, water consumption tends to increase. This can result in a vicious cycle: a new water shortage can be addressed by further expansion of reservoir storage to increase water availability, which enables more water consumption, which then can potentially lead to conditions of water scarcity. As such, the supply-demand cycle can trigger an accelerating spiral towards unsustainable exploitation of water resources and environmental degradation.[13]

Over-reliance on reservoirs can increase the potential damage caused by drought and water shortage. The expansion of reservoirs often reduces incentives for individuals preparedness and adaptive actions, thus increasing the negative impacts of water shortage. Moreover, extended periods of abundant water supply, supported by reservoirs, can generate higher dependence on water resources, which in turn increases social vulnerability and economic damage when water shortage eventually occurs.[12]

Attempts to increase water supply to cope with growing water demand, which is fuelled by the increase in supply, has been shown to be unsustainable. Drought occurrences can trigger temporary reductions of water availability, often leading to water shortage when water demand cannot be satisfied by the available water.[14]

In Athens, the Mornos Reservoir overflow of 1985 lead to a new law in 1987 which declared water as a "natural gift" and "undeniable right" for every citizen. Two years later, a severe drought occurred the system was pushed to its limits and government responses were slow due to lack of conservation measures undertaken.[15]

Lake Mead was built in the 1930s to provide water to California, Arizona and Nevada. At that time, Las Vegas was projected to grow up to 400,000 inhabitants by the end of the century. Yet, the population of Las Vegas grew much faster than what was expected and it was about four times more than expected by the end of the century. This unexpected population growth was enabled by increased water supply secured by more and more in-take structure from Lake Mead. In the 2000s, in response to severe droughts, the city got close to water shortage and as a result, yet another water in-take structure was constructed.[16]

In Melbourne, in response to severe droughts in the 80's, water supply was increased. Yet, these increases in water capacity have been shown to only prevent water shortage during minor droughts.[17] The increase in human water use in Melbourne in fact doubled the severity of streamflows during the Millennium Drought[17] and also had the effect of making the area more vulnerable to prolonged droughts due to increase dependency on reservoirs.

An earlier example is within the Maya civilisation. Here, additional storage of water initially brought many benefits and allowed agricultural growth under normal and minor drought conditions. Yet, this also created increased reliance on water resources which made the population more vulnerable to extreme drought conditions, and might have possibly contributed to the collapse of the Maya civilisation " [18]

Socio-hydrology can be related to integrated water resources management (IWRM). In particular, while IWRM aims at controlling the water system to get desired outcomes for the environment and society, socio-hydrology aims at observing, understanding, and predicting the dynamics of coupled human-water systems.[19] Socio-hydrology can therefore be seen as the fundamental science underpinning the practice of IWRM. Socio-hydrology can also be attractive to social scientists when its focus is given to broader topics such as sustainability, resilience, and adaptive governance. Socio-hydrologists will be benefited from the wider participation of social scientists to understand and incorporate complex social processes into hydrological models.[20]

Floods can be mild, severe, or catastrophic. Human societies cope with flooding with a combination of structural (e.g. levees) and non-structural measures (e.g. resettlements). Structural measures, such as levees, change the frequency and magnitude of flooding. In areas protected by levees, for example, the frequency of flooding is lower, but this often cause a false sense of safety, thereby increasing exposure and vulnerability to rare and catastrophic floods.[21]

In socio-hydrology, it is often assumed that societies build flood memory after extreme events. Flood memory is considered as a primary mechanism explaining the emergence of levee effects. It is hyphosised to be built after flooding and proportional to associated losses. Flood memory does decay over time. It is very difficult to observe, so proxy variable such as flood insurance coverage are used.[22]

Bottom-up modeling focuses on processes to develop system behavior, whilst top-down modeling focuses on system outcomes and try to look for correlations to determine system behavior.[23]

There can also be other differences between models. Models could be physics-based, data-based or conceptual. Another difference between models is if they are distributed or lumped, where lumped models include dynamics that vary only in time and distributed models include spatial and temporal heterogeneity.[23]