In this paper, we study the problem of disaster relief inventory prepositioning under uncertainty. Specifically, we aim to determine where to open warehouses and how much relief item inventory to preposition in each, pre-disaster. During the post-disaster phase, prepositioned items are distributed to demand nodes, and additional items are procured and distributed as needed. There is uncertainty in the (1) disaster level, (2) locations of affected areas, (3) demand of relief items, (4) usable fraction of prepositioned items post-disaster, (5) procurement quantity, and (6) arc capacity.We propose and analyze two-stage distributionally robust optimization (DRO) and stochastic programming (SP) models, assuming unknown and known distributions of uncertainty, respectively.The first and second stages correspond to pre-and post-disaster phases, respectively. We propose a decomposition algorithm to solve the DRO model and a Monte Carlo Optimization procedure to solve the SP. To illustrate potential applications of our approach, we conduct extensive experiments using a hurricane season and an earthquake as case studies. Our results demonstrate the (1) superior post-disaster operational performance of the DRO decisions under various distributions compared to SP decisions, (2) trade-off between DRO pessimism and SP optimism, and (3) computational efficiency of our approaches.