Snow algae are generally present in the snow of the Pacific Northwest but only become visible when conditions are warm enough for them to grow between ice crystals in the snow. In these conditions, the red pigments in the algae (which protects them from the sun) make the snow appear red, or “watermelon” colored. Algal blooms are problematic because “watermelon snow” absorbs solar radiation while clean white snow reflects most of the incoming solar radiation. This means that watermelon snow absorbs more heat and causes faster snowmelt, which is the main source of freshwater that sustains downstream human and natural communities in the spring and through the dry months of summer.  

In a new study published in Communications Earth & Environment, Northwest CASC-supported researchers demonstrated that imagery from unmanned aerial vehicles (UAVs, or drones) can be used to map different snow algae bloom intensities on alpine glaciers in Washington’s North Cascades. As earth warms, snow algal blooms are expected to become more widespread. Reliably mapping snow algae in hard-to-reach locations will be critical for monitoring changes to the timing and amount of snowmelt in the Pacific Northwest and for developing strategies to manage water resources in the region.