FEMA Disaster Preparedness Improvement Act This bill increases Federal Emergency Management Agency (FEMA) support for disaster preparedness and emergency response to states and U.S. territories. Specifically, the bill increases the federal cost share to 85% for (1) hazard mitigation measures with respect to a major disaster (currently, 75%); and (2) emergency management performance grants (currently, 50%). The bill makes special flood hazard areas that have suffered at least one severe repetitive loss or repetitive loss under the National Flood Insurance Program eligible for FEMA hazard mitigation grants. It also exempts the time it takes to complete environmental reviews from the 36-month deadline to complete FEMA-funded hazard mitigation projects. The Government Accountability Office must report on the challenges to states and U.S. territories in obtaining assistance under FEMA's public assistance program alternative procedures.