North America climate extremes monitoring system

The North America Climate Extremes Monitoring (NACEM) system has been developed as part of a trilateral effort between several organizations in the United States, Mexico and Canada to better understand historical and evolving trends and variability in extreme climate conditions across the continent. This system uses indices that are part of an effort by the WMO CCl/CLIVAR Expert Team on Climate Change Detection, Monitoring & Indices to develop improved indices that are ideally suited as indicators of extremes. These data provide for the analysis of trends in observational series of phenomena with a daily time scale and typical return period of less than one year. A combination of daily homogeneity adjusted and raw data from the three countries were used in producing the indices. Many of the indices that are part of this system are percentile based, including the number of cool days (daily maximum temperature below the 10th percentile) and warm spell duration indicator (based on the number of days when the maximum temperature exceeded the 90th percentile). Other indices are important indicators of climate change, while not necessarily extremes. Examples of this type of index include the number of ice days (days with maximum temperature below 0º C) and growing season length. A number of precipitation-based indices are also included in the NACEM system, such as the maximum 1- and 5-day precipitation amount and the number of consecutive wet and dry days. Analysis features of this system include options for studying time series of individual stations and the spatial distribution of trends from a regional to continent-scale basis. It is also possible to graph and analyze based on the statistical significance of trends as well as percent completeness of station records. The features of this system are discussed and results from several analyses of trends in temperature and precipitation extremes are included.