Photo 1. Vernal Fall in spring, 2001.

This is the chemistry component of the hydroclimate network described in Jessica Lundquist's NatureNotes article “Monitoring snow from the beach in San Diego: Automatic snow sensors in the Sierra”. Our efforts to link large-scale atmospheric circulation to snowpack and snowmelt–driven river discharge and riverine chemistry will ultimately contribute to the accuracy of climate change models and their ability to predict downstream effects on human use (Fig. 1).

Occasionally, examples will be given to indicate why we are working in YNP, and here is the first one. Yosemite National Park provides a relatively pristine hydroclimate setting that serves as a background for measuring/studying largely human-caused down stream changes. For example, the downstream loss of spring snowmelt discharge (SMD) stands out when plotted against the background of essentially no change in the Merced River discharge at Happy Isles, YNP (Fig. 2). If the YNP data did not exist, sorting out causes of the loss would be more difficult. Further, use of the Merced River in YNP as a measure of downstream change could be applied to river chemistry. In other words, understanding chemical processes in a relatively pristine system will help in defining a largely human-altered system.

Figure 2. The decadal spring snowmelt discharge near the mouth of the San Joaquin River (Vernalis) and the tributary Merced River (Happy Isles, Yosemite National Park).

The next point for background is probably the most important one. Ever since you were at your mother’s knee, you were told how watersheds are exceedingly complex. “Little of what you learn from one could be transferred to another”. This was especially true for river chemistry. Therefore, to better define the principles and processes of rivers, a brute force watershed-by-watershed effort lasting many decades was expected. If you look at us (Photo 2), 3 or 4 decades of fieldwork seems a bit unrealistic.

Photo 2. Steve Hager, Rich Smith and Dave Peterson. The Three Musketeers.

Fortunately, one of our first surprises in research was the discovery of the remarkable synchronicity between snowmelt-driven watersheds. SMD variability correlates strongly with air temperature variability and the air temperature variations are large scale. Therefore, SMD variability is large scale, explaining why the same or similar SMD signatures cut across many watersheds (Fig. 3). Yahoo, this cuts our complexity problem to a much more reasonable size! By the way we consider water quantity (river discharge, the amount of water per unit time) and quality (chemistry) as parts of the same problem.

Figure 3.

Hydroclimatology is a relatively new discipline that evolved when researchers appreciated how much both hydrology and climatology benefited from the strengths of the other (i.e., the whole is greater than the sum of the parts). We could provide a list detailing why studying alpine hydroclimatology in general and in YNP in particular is important. However, the relatively pristine environment and the large scale coherence gives sufficient background to begin our discussion on the river chemistry component of the Hydroclimate Monitoring Network (HMN).