Wireless sensor networks (WSN) have become increasingly popular in monitoring environments such as: disaster relief operations, seismic data collection, monitoring wildlife and military intelligence. The sensor typically consists of small, inexpensive, battery-powered sensing devices fitted with wireless transmitters, which can be spatially scattered to form an ad hoc hierarchically structured network. Recently, the global positioning system (GPS) facilities were embedded into the sensor node architecture to identify its location within the operating environment. This mechanism may be exploited to extend the WSN�s applications. To face with the security requirements and challenges in hierarchical WSNs, we propose a dynamic location-aware key management scheme based on the bivariate polynomial key pre-distribution, where the aggregation cluster nodes can easily find their best routing path to the base station, by containing the energy consumption, storage and computation demands in both the cluster nodes and the sensor nodes. This scheme is robust from the security point of view and able to work efficiently, despite the highly constrained nature of sensor nodes.