Hydrology
Water is so essential to life that it’s mere presence is a primary indication as to whether a planet can support life. One of earths most precious resources, the magnitude of its presence or absence can drastically alter the landscape and the choices made therein. Because it is a resource, there is a natural tendency for humans to manage it. This is accomplished via infrastructure (damming of rivers, irrigation techniques, construction of aqueducts and such), technology (weather forecasting, hydrologic modeling), and policy (water rights and environmental protections). Additionally, like many resources there is an intrinsic need to quantify its presence and reserves in order to best manage it. This effort is stymied by the sheer quantity of water on the planet, the ease at which it crosses physical and political boundaries, and its communal nature.
The study of water is known as hydrology. The study of modeling the flow of water over a surface is hydraulics. Together, these two fields represent the state of human knowledge over the domain of water. One of the most fundamental equations in hydrology, and a primary means of quantifying the amount of water in a watershed, is the water mass balance equation. This is build off the principle of conservation of mass, and can be stated as: precipitation into a watershed must equal the sum of the discharge out, the evapotranspiration, and the change in storage. Mathematically, this is expressed as: P = Q + eT + \vartriangle S Though conceptually simple, this equation summarizes a plethora of processes and assumptions. Furthermore, the measurements of these parameters are generally taken in an indirect manner. For example, rainfall amounts are derived from the reflectivity of a radar pulse, as opposed to measuring the actual volume of water that falls on an area. Additionally, the magnitude of these fluxes and the associated spatio-temporal scales of these variables can vary across more than 6 orders of magnitude (groundwater flow can be measured in centuries, precipitation intensities vary on the scales of minutes, and discharge is generally measured as flow past a point per second.
The intense variation of the geographic context of these variables adds additional uncertainty to the already significant uncertainties present in the measurement of these variables, and makes the accurate modeling of these systems tenuous at best. This complexity and the lack of interconnectedness across the disparate sciences that touch hydrology has resulted in a failure to “close the water balance” across the domain. This means that the conservation of mass, while applied to individual components or models, is not applied to the system and therefore the potential for errors compound. If we are to accurately manage this resource, we must first close the water balance. It is against this background that my broader research agenda sits.