Resource allocation is a critical problem in business processes due to the simultaneous execution of tasks and resource sharing among them. The number of allocated resources affects both the execution cost and time of the process. In the context of runtime processes, a well-defined resource allocation strategy is essential for optimising waiting times and costs by mitigating delays and enhancing resource utilisation. This paper introduces a novel approach to dynamically adjust resource allocation during the execution of BPMN (Business Process Model and Notation) processes. The BPMN process is monitored in real-time, and the execution traces produced during its multiple executions are analysed. These execution traces are used to compute various properties or metrics of interest, including resource usage and average execution time. The approach then relies on predictive analytics to compute the future values of the aforementioned metrics. Based on these predicted results, strategies for the dynamic allocation of resources are defined, which anticipate changes in resource usage and thus dynamically update the number of resources in advance. This approach is fully automated using a toolchain and has been validated with multiple examples.