For our Christmas episode, Linden speculates what Santa may see on his journey, such as changes in rivers as described in a recent study; and Cat crunches the numbers on how many houses Santa may need to visit, and how. Dongmei Feng, Colin J. Gleason ,More flow upstream and less flow downstream: The changing form and function of global rivers. Science 386,1305-1311(2024).DOI:10.1126/science.adl5728