Jeremy L. Weiss

Distinguishing Pronounced Droughts in the Southwestern United States: Seasonality and Effects of Warmer Temperatures

Abstract Higher temperatures increase the moisture-holding capacity of the atmosphere and can lead to greater atmospheric demand for evapotranspiration, especially during warmer seasons of the year. Increases in precipitation or atmospheric humidity ameliorate this enhanced demand, whereas decreases exacerbate it. In the southwestern United States (Southwest), this means the greatest changes in evapotranspirational demand resulting from higher temperatures could occur during the hot–dry foresummer and hot–wet monsoon. Here seasonal differences in surface climate observations are examined to determine how temperature and moisture conditions affected evapotranspirational demand during the pronounced Southwest droughts of the 1950s and 2000s, the latter likely influenced by warmer temperatures now attributed mostly to the buildup of greenhouse gases. In the hot–dry foresummer during the 2000s drought, much of the Southwest experienced significantly warmer temperatures that largely drove greater evapotranspir...

Tidally adjusted estimates of topographic vulnerability to sea level rise and flooding for the contiguous United States

Because sea level could rise 1 m or more during the next century, it is important to understand what land, communities and assets may be most at risk from increased flooding and eventual submersion. Employing a recent high-resolution edition of the National Elevation Dataset and using VDatum, a newly available tidal model covering the contiguous US, together with data from the 2010 Census, we quantify low-lying coastal land, housing and population relative to local mean high tide levels, which range from 0 to 3 m in elevation (North American Vertical Datum of 1988). Previous work at regional to national scales has sometimes equated elevation with the amount of sea level rise, leading to underestimated risk anywhere where the mean high tide elevation exceeds 0 m, and compromising comparisons across regions with different tidal levels. Using our tidally adjusted approach, we estimate the contiguous US population living on land within 1 m of high tide to be 3.7 million. In 544 municipalities and 38 counties, we find that over 10% of the population lives below this line; all told, some 2150 towns and cities have some degree of exposure. At the state level, Florida, Louisiana, California, New York and New Jersey have the largest sub-meter populations. We assess topographic susceptibility of land, housing and population to sea level rise for all coastal states, counties and municipalities, from 0 to 6 m above mean high tide, and find important threat levels for widely distributed communities of every size. We estimate that over 22.9 million Americans live on land within 6 m of local mean high tide.

Projections of future sea level becoming more dire

Few of the possible impacts of future climate change have captured more public attention than sea-level rise. Globally, sea-level rise has accelerated since the 19th century, driven primarily by the expansion of warmer oceans and melting glaciers, along with a modest transfer of water into the ocean from the Earths polar ice sheets. The observed rate of sea-level rise has not been uniform around the globe because of regional factors, but there is no doubt that the average sea-level trend is upwards (1). Implications for the rates and magnitudes of future sea-level rise are less clear, and a new study in this issue of PNAS (2) provides useful insight into how sea level will change through this century and beyond.

Discerning “Flavors” of Drought Using Climate Extremes Indices

AbstractMonitoring drought conditions in arid and semiarid regions characterized by high levels of intra- and interannual hydroclimatic variability is a challenging task. Typical drought-monitoring indices that are based on monthly-scale data lack sufficient temporal resolution to detect hydroclimatic extremes and, when used operationally, may not provide adequate indication of drought status. In a case study focused on the Four Corners region of the southwestern United States, the authors used recently standardized World Meteorological Organization climate extremes indices to discern intra-annual hydroclimatic extremes and diagnose potential drought status in conjunction with the simple metric of annual total precipitation. By applying data-reduction methods to a suite of metrics calculated using daily data for 1950–2014, the authors identified five extremes indices that provided additional insight into interannual hydroclimatic variability. Annual time series of these indices revealed anomalous years ch...

Developing an Event Database for Cutoff Low Climatology over Southwestern North America

Cutoff lows (COLs) can impact southwestern North America with heavy rainfall that leads to flooding. Despite the societal challenges presented by this weather phenomenon, there has been no recent study of COLs focused on this region. This information need, in combination with the current availability of large, multivariate atmospheric datasets, offers a clear data mining and applied research opportunity. Here, we describe our method to produce an objective, physically based algorithm that identifies COLs in reanalysis data and apply this method to a known COL event. Results suggest that the initial algorithm is too selective for adequately identifying COLs and needs additional adjustments in order to resolve the different spatial scales of COLs and reanalysis data. We further discuss the attributes of information extracted through this data mining approach that will be used to populate an event database for COL climatology over southwestern North America, as well as the verification of individual COL events. Integration of our COL event database with other data mining approaches has great potential to expand our currently limited knowledge on this important weather phenomenon.