Monitoring the timing of snowmelt and the initiation of streamflow using a distributed network of temperature/light sensors

The loss of snow cover and the initiation of streamflow are key triggers for both terrestrial and aquatic biota. Landscape-scale snowmelt and streamflow dynamics are difficult to estimate, however, because they integrate large spatial extents and can vary rapidly in time. Remotely sensed observations are often temporally discontinuous and point observations lack sufficient spatial density (e.g. point measures from data-logging piezometers). In this study, we employ inexpensive temperature/light sensors to monitor the distribution of snowmelt and headwater stream discharge as a proxy for hydrological state of the landscape with high spatial and temporal resolution. This study was conducted at the Redondo Peak, a large (local relief over 1100 m) resurgent dome within the caldera complex of the Valles Caldera National Preserve, 30 km west of Los Alamos, New Mexico, USA. The first-order streams that drain the Redondo Peak encompass the full spectrum of terrain aspects, resulting in significant variability in wind exposure, turbulent and radiative fluxes, snow cover duration, and vegetation structure. Complex interactions between these variables impact groundwater recharge through variations in sublimation, evaporation, and transpiration. To monitor the role this variation plays with respect to spatio-temporal dynamics of snowmelt and headwater stream discharge, we have installed 128 temperature/light sensors in eight different streambeds draining through unique aspects of the peak. The variation of daily temperature/light levels relative to seasonal change in mean temperature/light levels provides a metric of the spatial distribution of surface waters and snow cover. This metric correctly identified flowing lengths of headwater streams with 80% accuracy during an early summer period (10 May 2007) and 79% of the time in late summer period (2 October 2007). Between these two observation periods, the percentage length of headwater streams flowing decreased by 12%, indicating a general drying of the landscape. On the basis of a conceptual model of a groundwater 'mound' within the peak that roughly follows the shape of the land surface, such a metric relates directly to the amount of water in the landscape, providing insight to the complex ecohydrological interactions between snowmelt, rainfall, and vegetative uptake. This serves as a precursor to developing a broader ecohydrological perspective of the interrelationships between ecology and hydrological processes. Copyright (C) 2008 John Wiley & Sons, Ltd.