A Strategy for Global Snow Information for Nature and Society

The properties of snow vary dramatically in time and in space. Each year the snowpack transitions from the accumulation phase, when snowfall and snow redistribution are dominant processes; to a ripening phase, when the snow's temperature and energy balance are most critical to determining melt timing; to a melt phase, when the energy balance and snow disappearance best define snow's role on the landscape (Fig. 1). Beyond these temporal changes, snow varies drastically in different regions of the world. Considering two extremes (Fig. 1), dry tundra snow covers 16.5 million km 2 but is only 0.3-0.5 m deep, while wet maritime snow covers only 3.6 million km 2 but is much deeper (1.5-2.0 m)[Sturm et al. 1995]. These very different snow types, which require very different sensing approaches, contain a similar volume of total snow (5000-8000 km 3), and both are critical to global energy balance, water supplies …