Monitoring changes in U.S. Weather and Climate Extremes

NOAA's Climate Extremes Index (CEI) is examined for statistically significant trends in six of its weather and climate extreme indicators (daily mean maximum temperature, daily mean minimum temperature, monthly soil moisture, daily heavy precipitation events, days with and without precipitation, hurricanes and tropical storm land intensity). The appropriateness of adding an indicator for tornadoes is examined. Monte Carlo simulations are used to generate sampling distributions for different periods that correspond to changing reporting practices for tornadoes. The analysis of the current CEI reveals statistically significant changes for all components of the CEI except hurricanes and tropical storms. Overall, the CEI has a positive trend since the late 1970s which means an increase in extremes. This increase is the result of a greater frequency and/or spatial extent of much above normal: daily maximum and minimum temperatures, wet conditions, daily heavy precipitation, and wet days. These events all contributed to the record number of 14 billion dollar disasters observed in 2011.