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Henry F. Diaz
and
Gregory J. McCabe

One of the most severe outbreaks of yellow fever, a viral disease transmitted by the Aedes aegypti mosquito, affected the southern United States in the summer of 1878. The economic and human toll was enormous, and the city of Memphis, Tennessee, was one of the most affected. The authors suggest that as a consequence of one of the strongest El Nino episodes on record—that which occurred in 1877–78—exceptional climate anomalies occurred in the United States (as well as in many other parts of the world), which may have been partly responsible for the widespread nature and severity of the 1878 yellow fever outbreak.

This study documents some of the extreme climate anomalies that were recorded in 1877 and 1878 in parts of the eastern United States, with particular emphasis on highlighting the evolution of these anomalies, as they might have contributed to the epidemic. Other years with major outbreaks of yellow fever in the eighteenth and nineteenth centuries also occurred during the course of El Niño episodes, a fact that appears not to have been noted before in the literature.

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Nicholas E. Graham
and
Henry F. Diaz

Using NCEP–NCAR reanalysis and in situ data, evidence of important changes in the winter (December–March) cyclone climatology of the North Pacific Ocean over the past 50 years is found. The frequency and intensity of extreme cyclones has increased markedly, with associated upward trends in extreme surface winds between 25° and 40°N and major changes in cyclone-related circulation patterns in the Gulf of Alaska. Related increases in extreme wave heights are inferred from wave measurements and wave-model hindcast results. The more vigorous cyclone activity has apparently resulted from increasing upper-tropospheric winds and vertical wind shear over the central North Pacific. Such changes, which create an environment more favorable for cyclone formation and intensification, may be related to the observed modulation of El Niño–related teleconnections at decadal and longer timescales. It is intriguing that this trend has been relatively steady rather than the sudden or stepwise shifts documented for other aspects of North Pacific climate change. Increasing sea surface temperatures in the western tropical Pacific are suggested as a plausible cause of the observed changes, though other underlying mechanisms may also contribute.

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José Fernández-Partagás
and
Henry F. Diaz

A historical revision of Atlantic tropical cyclones for the period 1851–90 is presented. This work was undertaken with the aim of improving knowledge of the tropical storms and hurricanes in the North Atlantic basin, which occurred during the latter half of the nineteenth century. Another aim of the study was to develop more reliable figures regarding cyclone frequency variations than those that were currently available. The 40-yr period covered by this study spans the 20 yr (1851–70) prior to the founding of a U.S. meteorological service as part of the U.S. Signal Service and the approximately 20 yr (1871–90) that military personnel of that service took care of the official meteorological affairs in the country, prior to the establishment of a civilian U.S. Weather Bureau within the U.S. Department of Agriculture. The period 1851–90 was found to be particularly attractive from a research standpoint because it covered the time elapsed from 1855, the last year included in the storm catalog prepared by Poey, which is used in the cyclone list shown by Tannehill, to 1878, the year the Signal Service began to systematically trace all West Indian hurricanes.

A comparison of hurricane activity, in terms of the total number of storms, is made between the 40-yr period of 1851–90, and the corresponding period in the twentieth century. Even after taking into account the large differences in the observational network during these two periods, a century apart, there is some suggestion that the earlier period was relatively less active.

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Henry F. Diaz
and
Thomas W. Swetnam

During the summer of 1910 large wildfires occurred throughout the western United States, and especially in the northern Rocky Mountains. The “Great Idaho Fires” of 1910 alone burned about three million acres (~1.2 Mha)— an area that is approximately the size of Connecticut. Multiple fires ignited and coalesced, burning in forests of northern Idaho and western Montana including parts of the Bitterroot, Cabinet, Clearwater, Coeur d'Alene, Flathead, Kaniksu, Kootenai, Lewis and Clark, Lolo, and St. Joe National Forests. The firestorm burned for days in late August of 1910 and killed 87 people, including 78 firefighters. It is believed to be the largest, although not the deadliest, wildfire complex in recorded U.S. history. Here we show that highly anomalous weather preceded the conflagration in much of the West, including the occurrence of the warmest March on record for the contiguous United States (except March 2012). While the occurrence of very high winds greatly contributed to the fast spread of the wildfire, the preceding highly anomalous warm and dry condition since the spring of 1910 likely also contributed to the magnitude of this event. Improved understanding of extreme wildfire outbreaks and climatological conditions associated with them is increasingly important, as such events are increasing in frequency as global and regional warming continues.

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William E. Riebsame
,
Henry F. Diaz
,
Todd Moses
, and
Martin Price

Socioeconomic vulnerabilities and impacts associated with weather and climate hazards in the United States are assessed. Trends in deaths and economic losses resulting from tornadoes, tropical storms and hurricanes, and floods (including flash floods) are presented in detail. To the extent possible, death statistics are normalized by the population at risk, and loss data are adjusted for inflation. The results suggest a significant decline in deaths attributed to tornadoes and hurricanes at the same time that property damages have increased. In contrast, both deaths and losses due to floods have increased substantially in the past few decades.

A qualitative assessment is made of the effects of socioeconomic trends (e.g., the aging population) on the nation's sensitivity to atmospheric hazards and on the need for better information about these hazards. While the tally shows mixed impacts on vulnerability (i.e., some trends may reduce vulnerability while others increase it), the impact on information needs is nearly uniformly greater. More emphasis should be given to the following activities as ways to decrease the overall social burden of atmospheric hazards: 1) improve the use of weather and climate information by emergency managers, 2) develop better impact-assessment methods, and 3) explore new ways to reduce future property losses.

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Henry F. Diaz
,
Ricardo Trigo
,
Malcolm K. Hughes
,
Michael E. Mann
,
Elena Xoplaki
, and
David Barriopedro

Developing accurate reconstructions of past climate regimes and enhancing our understanding of the causal factors that may have contributed to their occurrence is important for a number of reasons; these include improvements in the attribution of climate change to natural and anthropogenic forcing, gaining a better appreciation for the range and magnitude of low-frequency variability and previous climatic regimes in comparison with the modern instrumental period, and developing greater insights into the relationship between human society and climatic changes. This paper examine upto- date evidence regarding the characteristics of the climate in medieval times (A.D. ~950–1400). Long and high-resolution climate proxy records reported in the scientific literature, which form the basis for the climate reconstructions, have greatly expanded in the last few decades, with greater numbers of sites that now cover more areas of the globe. Some comparisons with the modern climate record and discussion of potential mechanisms associated with the patterns of medieval climate are presented here, but our main goal is to provide the reader with some appreciation of the richness of past natural climate variability in terms of its spatial and temporal characteristics.

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Alison D. Nugent
,
Ryan Longman
,
Clay Trauernicht
,
Matthew Lucas
,
Henry F. Diaz
, and
Thomas W. Giambelluca
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Xiao Luo
,
Abby G. Frazier
,
Henry F. Diaz
,
Ryan Longman
, and
Thomas W. Giambelluca

Abstract

The Hawaiian Islands have some of the most spatially diverse rainfall patterns on Earth, affected by prevailing trade winds, midlatitude disturbances, tropical cyclones, and complex island topography. However, it is the only state in the United States that does not have assigned climate divisions (boundaries defining climatically homogeneous areas), which excludes it from many national climate analyses. This study establishes, for the first time, official climate divisions for the state of Hawai‘i using cluster analysis applied to monthly gridded rainfall data from 1990 to 2019. Twelve climate divisions have been identified: two divisions were found each for the islands of Kaua‘i (Leeward Kaua‘i and Windward Kaua‘i), O‘ahu (Waianae and Ko‘olau), and Maui County (Leeward Maui Nui and Windward Maui Nui), and six divisions were identified for Hawai‘i Island (Leeward Kohala, Windward Kohala, Kona, Hawai‘i Mauka, Ka‘u, and Hilo). The climate divisions were validated using a statewide area-weighted division-average rainfall index which successfully captured the annual cycle and interannual rainfall variations in the statewide average rainfall series. Distinct rainfall seasonality features and interannual/decadal variability are found among the different divisions; Leeward Maui Nui, Leeward Kaua‘i, Kona, and Hawai‘i Mauka displayed the most significant rainfall seasonality. The western Hawai‘i Island divisions show the most significant long-term decreasing trends in annual rainfall during the past 100 years (ranging from −2.5% to −5.0% per decade). With these climate divisions now available, Hawai‘i will have access to numerous operational climate analyses that will greatly improve climatic research, monitoring, education, and outreach, as well as forecasting applications.

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Paul R. Epstein
,
Henry F. Diaz
,
Scott Elias
,
Georg Grabherr
,
Nicholas E. Graham
,
Willem J. M. Martens
,
Ellen MosIey-Thompson
, and
Joel Susskind

The Intergovernmental Panel on Climate Change concluded that there is “discernible evidence” that humans—through accelerating changes in multiple forcing factors—have begun to alter the earth's climate regime. Such conclusions are based primarily upon so-called “fingerprint” studies, namely the warming pattern in the midtroposphere in the Southern Hemisphere, the disproportionate rise in nighttime and winter temperatures, and the statistical increase in extreme weather events in many nations. All three aspects of climate change and climate variability have biological implications.

Detection of climate change has also drawn upon data from glacial records that indicate a general retreat of tropical summit glaciers. Here the authors examine biological (plant and insect) data, glacial findings, and temperature records taken at high-elevation, mountainous regions. It is concluded that, at high elevations, the overall trends regarding glaciers, plants, insect range, and shifting isotherms show remarkable internal consistency, and that there is consistency between model projections and the ongoing changes. There are implications for public health as well as for developing an interdisciplinary approach to the detection of climate change.

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Ricardo García Herrera
,
Rolando R. García
,
M. Rosario Prieto
,
Emiliano Hernández
,
Luis Gimeno
, and
Henry F. Díaz

Spanish historical archives contain a vast store of information about Spain and its former colonies in America and Asia. Some searches for climate-related information within these archives have been undertaken recently, but they have been by no means exhaustive. This paper discusses the principal archives and shows, by means of several examples, that they exhibit a high potential for inferring past climate over a wide range of timescales and geographical areas. Extraction of such information is often time consuming, and requires a combination of archival, historical, and climatological expertise, and the development of individualized methodologies to fit each situation and type of data. In spite of these difficulties, the archives can be particularly useful in many cases where there are no alternative sources of climate data. Thus, the complexities of the multidisciplinary effort required should not discourage other researchers from undertaking similar studies.

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