Century-scale variations and trends in heat stress metrics

Introduction to the Problem: It is well understood that stress on the human body from high temperatures is exacerbated by high humidity. The National Weather Service uses a familiar metric (the heat index) that incorporates temperature and humidity to quantify this effect. However, long-term U.S. monitoring of heat stress indicators relevant to human health has been limited to the period from around the middle of the 20th century to present because of a lack of digitally available humidity data prior to 1948. This omits some of the most important heat events in U.S. history; namely, those associated with the 1930s Dust Bowl. On the basis of temperature alone, the Dust Bowl era includes some of the most intense and frequently occurring events across much of the eastern two-thirds of the country over the last 120 years. Extending the availability of heat stress metrics that combine both temperature and humidity over the past century is critically important for providing historical context to current heat wave trends.

Rationale: There is an opportunity to remedy this critical data gap. The Climate Database Modernization Program (CDMP), which ran from 2000 to 2011 at the former National Climatic Data Center (now the National Centers for Environmental Information [NCEI]), funded the keying of early hourly weather observations going back to the late 19th century. This set of data has never been publicly available but is now being incorporated into the new Global Historical Climatology Network-hourly (GHCNh) of NCEI. This study will provide the scientific basis for new heat wave monitoring products by characterizing, for the first time, the features of heat
waves in the contiguous United States over a century-plus time frame that includes the 1930s Dust Bowl era and uses human health–relevant heat metrics that incorporate humidity.

Brief Summary of Work: Human heat stress metrics will be created (as time series) using the new hourly humidity station data. These station time series will then be aggregated to create regional and national indicators that will be used to characterize long-term trends, decadal-scale variability, and individual event features. The Twentieth Century Reanalysis version 3 (20CRv3) will be used to fill in missing data, supporting the computation of indicators back through 1895.
This will match the period of record of NCEI’s climate division dataset. Our project will address how early 20th-century heat waves, particularly those during the 1930s, compare to modern events with regard to human health stress metrics. The 20CRv3 will be used to characterize the synoptic-scale features of heat events, including regional lower-tropospheric wind flow patterns that affect heat and moisture advection and hemispheric patterns of mid-tropospheric geopotential height anomalies, including blocking high occurrences.

Competition: New Climate Monitoring Approaches and Products for Areas of Climate Risk

Broader Impacts and Relevance to Competition: This proposal will target the high-priority climate risk area of extreme heat using a dataset that was previously unavailable for climate analysis. It will provide a new monitoring indicator suite (heat index and related metrics and circulation features) extending back to 1895. The longer period of analysis, encompassing the epic 1930s heat waves, will advance understanding about recent trends in heat waves and the nature of multidecadal variability.