From Scoresby to Nansen to Wegener: The Role of Polar History in Producing the Next Generation of High-Latitude Hydrologic and Cryospheric Scientists
Many scientists, like myself, were first attracted to the polar regions by tales of heroic explorers. These earlier explorers were also scientists, or more correctly, naturalists. They produced maps, sketches, and studies on atmospheric, cryospheric, biological, and sociological topics alike. For many of us, reading about polar history led directly to our interests in cryospheric and hydrological science. While the age of geographical exploration is long over, replaced by Google Earth, the stories from that by-gone era may still be one of the most powerful recruiting tools for producing passionate and committed polar scientists for the next generation. I would argue for an increased emphasis in teaching our students about the history of exploration and science. If we do so, at a minimum our students will better appreciate modern clothing, transportation, data loggers, communication equipment, and computers. More importantly, it will introduce to the next generation the idea of the naturalist, whose purview is all components of the natural system. Many of the high latitude issues facing us today require a system-science approach that can be difficult to learn or master in an era of disciplinary specialization. The early naturalist-explorers understood this approach and still have much to teach us if we take the time to listen to what went before.
Biological Controls on the Hydrologic Cycle
Unlike most other parts of hydrologic cycle, that part involving plants is strongly influenced by behaviors that fall outside the realm of simple physics, and are, therefore, difficult to model. Plants have the capacity to make "decisions" that profoundly affect the surface energy budget, boundary layer processes and atmospheric dynamics over the continents. These decisions of plants are apparently based on anatomical structures and physiological mechanisms that have been tuned by evolutionary processes to permit plants to address the central dilemma of their existence. To grow requires that they open their stomata to allow CO2 to diffuse into their leaves, but they must also permit water to escape to the dry atmosphere. This water must be used sparingly lest they exhaust soil water and die of dessication, but to forgo using it comes at the expense of growth and competitive advantage. Improvements in our understanding of the physiological and environmental constraints that frame this dilemma have led to improvements in our ability to predict and model the responses of plants in the hydrologic cycle. However, there is, yet, much room for improvement in our understanding of plant hydrology and how to measure and model it. I will touch on new insights into mechanisms that regulate stomatal conductance, applications of stable isotopes for calibrating conductance parameterizations and a new tracer for assessing conductance at regional scales.
Sustainable Water Management - Slogan or Practicable Concept?
A definition of sustainability is difficult. It is much easier to define what is not sustainable. In general a practice is non-sustainable, if on one hand there is no alternative to it and on the other hand it cannot go on indefinitely without running into a crisis. Translated to water resources, non-sustainability may show in the depletion of a finite resource, which cannot be substituted, the resource being water itself, or resources linked to it such as soil and ecosystems. It can also show in the accumulation of substances - such as salts - to harmful levels, build-up of conflict potential due to unfair water allocation or bad governance leading to failure of institutions. To judge whether a regional water resources management strategy is sustainable, one can model the situation and extrapolate to time infinity to determine whether the system has a solution which is acceptable in economic, social and environmental terms. An example from the arid west of China is given. The solution of such a modeling effort need not be steady state but could be quasi-periodic or even non-stationary. A difficulty in testing for sustainability is the fact that system parameters and boundary conditions are not constant in time. Population, climate and values keep changing and adaptivity to those changes should be provided for. Another difficulty stems from the fact that parameters and boundary conditions (especially those in the future) are subject to uncertainty. That requires conservatism and robustness of a strategy. It may well be that for a region no sustainable solution can be designed without a substantial change in system characteristics such as population, area of cultivated land, or trans-basin water transfer.
Isotope tracers in catchment hydrology: How far can we go?
The use of stable isotopes as tracers of water has fundamentally changed the way that we view catchment hydrology. Tracer-based mass balance mixing studies in the past decades have revealed that most of the water comprising the storm hydrograph (in humid areas) is dominated by pre-event water. Furthermore, using the convolution integral approach to long term isotopic time series, studies have revealed a wide range of streamwater residence times (focused mostly on baseflow), from months to decades, but with most on the order of 1-3 years. These findings have now matured to the point where such information is informing rainfall- runoff model testing. As a result, stable isotope tracers offer new and orthogonal data measures for rejecting model structures. Similarly, scaling relations detected in streamwater residence time data offer hope for a new pathway to understand and quantify multi-scale catchment response patterns. So how far can we go with stable isotope tracers in catchment hydrology? Here I offer some suggestions on new research avenues that capitalize on the use of laser spectrometers and how the resulting increased sample frequencies in time and space (with laser specs in the lab and in the field) may offer new hydrological insights. Examples are given that apply to ecohydrological studies in catchments to resolve how vegetation and streams appear to return different pools of water to the hydrosphere; virtual experiments with catchment models to assess the fundamental controls on catchment residence time distribution; multi-tracer approaches to streamwater residence time to reconcile the striking differences in residence time estimates between oxygen-18 and tritium; and labeled isotope additions at the plot, hillslope and catchment scale under controlled input conditions for resolving the age, origin and pathway of flow.