<p>Falling snow often accumulates in dunes. These bedforms are found on up to 14&thinsp;% of the surface of Earth, and appear occasionally on other planets. They have been associated with increased heat fluxes and rapid sea ice melting (Petrich et al., 2012; Popović et al., 2018). Their formation, however, is poorly understood (Filhol and Sturm, 2015; Kochanski et al., 2019a; Sharma et al., 2019). Here, we use field observations to show that dune growth is controlled by snowfall rate and wind speed. We then use numerical experiments to generate simulated dune topographies under varied wind and snowfall conditions, and use those to quantify conductive and radiative heat fluxes through snow. Our results show that dune growth leads to decreased snow cover, more variable snow depth, and significant increases in surface energy fluxes. We provide quantitative results that will allow modelers to account for the impact of snow bedforms in snow, sea ice, and climate simulations. In addition, this work offers a starting point for process-based studies of one of the most widespread bedforms on Earth.</p>