Historical documentary records contain valuable information on climate, weather, and their societal impacts during the pre-instrumental period, but it may be difficult to assess the objectivity and reliability of this information, particularly where the documentary record is incomplete or the reliability of the information it contains is uncertain. This article presents a comprehensive review of information relating to drought found in original written records concerning all early European expeditions (1510–1610 CE) into the present-day US and Canada, and compares this information with maps and time series of drought generated from the tree-ring-based North American Drought Atlas (NADA). The two sources mostly agree in the timing and location of droughts. This correspondence suggests that much of the information in these early colonial historical records is probably objective and reliable, and that tree-ring-based drought atlases can provide information relevant to local and regional human historical events, at least in locations where their reconstruction skill is particularly high. This review of drought information from written sources and tree-ring-based reconstructions also highlights the extraordinary challenges faced by early European explorers and colonists in North America due to climatic variability in an already unfamiliar and challenging environment.
Regional climatic variability before the instrumental period, including the frequency and severity of historical droughts, may be reconstructed through analysis of proxies preserved in natural archives (paleoclimatology) or of proxies and descriptions in written records (historical climatology). The latter approach has been employed with high reconstruction skill for regions and periods with abundant and consistent personal writings and official archives, including parts of Europe and China during the past six centuries. However, most historical regions and periods lack such abundant and consistent written records before the instrumental period. In these cases, historical observers tend to act as a “high-pass filter” recording mostly extreme events and/or as degraded archives preserving scattered periodic climate proxies and descriptions (Bradley, 2015). Nevertheless, these written records remain potentially valuable for climate history since they contain information unavailable from proxies in natural archives, including precisely located and dated climate and weather events from all seasons and their societal impacts (Brönniman et al., 2018).
The challenge of using information in historical written records becomes particularly acute in the case of early European overseas exploration and colonization, including overseas imperial exploration and invasion, early religious missions, merchant companies, and the slave trade. On the one hand, these activities left written records of major importance to climate and environmental history. For North America, Australia, and much of Africa and Latin America, they provide the earliest written records of any kind, including observations of climate and weather conditions as well as climatic impacts on indigenous societies and their adaptations. Early colonial observers were typically much more sensitive to climatic and environmental conditions than observers in their home countries and therefore more likely to record and disseminate information on these topics. On the other hand, these same observers were unfamiliar with their new colonial environments and climates and at first lacked institutions and activities that could systematically record climate proxies and descriptions. The resulting records are typically too inconsistent to produce independent verifiable reconstructions of climate parameters. Even in cases where colonial activities continued into later periods and began to leave consistent records appropriate for standard historical climatology analysis and reconstruction – e.g., indices – one cannot assume that observations made during the unique conditions of these first colonial experiences were equally reliable or as objective as those made in later years and could therefore be calibrated in the same manner for climate reconstruction purposes (Pfister et al., 2018; Dobrovolný, 2018).
An alternative approach to examining the accuracy of climatic and other environmental information in these early colonial records is to compare their information on a defined parameter with a high-resolution reconstruction of that parameter based on proxies in a natural archive. This approach is particular promising in the case of early colonial North America, here defined as the present-day United States and Canada (1510–1610 CE). Colonial activities during this period left a large, diverse, well-preserved, and accessible body of documentary evidence with considerable information on environmental and climatic conditions (Sect. 2.1). This information may be compared with the North American Drought Atlas (NADA): a highly spatially and temporally resolved gridded Palmer Drought Severity Index (PDSI) reconstruction covering the region and period under study (Sect. 2.2). Moreover, the NADA reconstruction indicates sharply contrasting wet and dry conditions during different colonial expeditions in this period, which should highlight (in)consistencies between information in the documentary record and the tree-ring-based reconstruction. As previous scholars have concluded, “the integration of the [NADA] PDSI reconstructions with historical information on environmental conditions and the activities of Euroamerican and Native American societies is a largely unexploited opportunity that promises significant new insight into American history and environmental change” (Stahle et al., 2007).
Thus, this study makes a systematic comparison of information concerning drought from the documentary record of early colonial America with the NADA PDSI reconstruction. The primary goal of this comparison is to examine the objectivity and reliability of climate and environmental information in early European colonial records and thus their potential use for historical climatology and environmental history. In addition, this study may assist the following goals: (1) to crosscheck the NADA reconstructions – including those for extreme events reconstructed during the 16th and early 17th centuries – and NADA's applicability to the scale of local human historical events; (2) to gain further insights into the seasonality and severity of droughts in early colonial North America by combining the information from natural and human archives; and (3) to better understand the human impacts of climate variability during this critical and vulnerable phase of North American exploration and colonization.
This study acknowledges three important limitations. First, NADA is primarily a reconstruction of soil moisture deficit (hydrological drought), while human observers mainly recorded deficits of rainfall (meteorological drought) and failures of crops attributed to lack of water (agricultural drought). Second, most written observations about climate and weather in early North American colonial records concern temperature and storms rather than drought. While it may be reasonable to infer that observations about drought were no more or less reliable and objective than observations about other climate and environmental conditions, there is no similarly robust and highly resolved proxy-based reconstruction of temperature or other parameters with which to make a similar comparison. Third, NADA cannot be regarded as a perfect reconstruction of drought conditions, and therefore discrepancy between NADA and the documentary record does not necessarily mean that one is “right” and the other “wrong.” Nevertheless, frequent disagreement between the documentary record and the NADA reconstruction should raise concerns about the reliability of the former or the precision of the latter, while consistent agreement should build confidence in both.
A recent review has identified North America as one of the least studied regions for the historical climatology of drought (Brázdil et al., 2018). Although there are abundant personal and official records dating back to the colonial period, many of the them containing information on weather and climate, few researchers have used them to reconstruct the frequency or severity of historical droughts (Mock, 2012; White, 2018). Archeologists have reviewed physical and written evidence for the impact of climate and extreme weather, including droughts, during the first century of European expeditions in several regional contexts, particularly the Chesapeake (Blanton, 2000, 2003, 2004; Rockman, 2010), the southeastern US (Burnett and Murray, 1993), Florida (Paar, 2009; Blanton, 2013), and New Mexico (van West et al., 2013). A few historians have begun to incorporate climatic perspectives into accounts of early North American exploration and colonies (Kupperman, 2007a; Grandjean, 2011; Wickman, 2015, 2018), and a 2017 monograph has provided a comprehensive narrative of the role of regional climate differences and climatic variability in early Spanish, French, and English exploration and colonization of the present-day US and Canada (White, 2017). These studies indicate that climatic factors, including drought, played a major role in the failure of several early colonial expeditions in North America and the discouragement or redirection of others, as well as conflict between European colonies and Native Americans. This article provides the first concise comprehensive overview of the evidence concerning drought from historical records and systematic comparison with the NADA drought reconstructions.
A search was made for all primary historical records surviving from or directly relevant to every documented European colonial expedition that spent time in the present-day US and Canada from 1510 to 1610 CE. This search resulted in several thousand documents contained in several hundred printed volumes, as well as electronic collections and unpublished archival series in the Archivo General de Indias (Spain) and National Archives (UK), mostly available online (see the Supplement). The author read each of these personally and, where possible, in their entirety. Some documents were consulted in English translations, but in those cases almost all descriptions of weather, climate, or climatic impacts were read again in their original languages (French, Spanish, German, Italian, Latin, and Dutch) to correct any mistranslations and to ensure accuracy. All dates were converted from the Julian calendar into modern calendar dates with the new year beginning on 1 January. Descriptions of weather, climate, and climatic impacts were not simply extracted from their context and compiled separately but always considered contextually, meaning that the study took into account (1) the description's context within the individual document and its larger corpus; (2) the conditions of the observation and of its recording and publication; (3) the background of the author or authors, including their subjective sense of “normal” weather or climate; and (4) the genre of writing in which any description appeared. (For a complete book-length account of the historical context of climate observations in the course of early exploration and colonies, see White, 2017.)
The exploration and colonization of North America proceeded in sporadic, uncoordinated ventures by Spanish, French, and English companies until 1610 CE, by which date enduring colonies were established at St. Augustine (Florida), Santa Fe (New Mexico), Jamestown (Virginia), and Quebec (Quebec). Written first-hand observations potentially capable of providing useful information concerning the presence, absence, or impacts of droughts were left by members of colonial expeditions for the following regions and years: the southeastern US and Gulf Coast, principally Florida (1526, 1528–1529, 1539–1543, 1559–1560, 1560, 1562–1610); the southwestern US, principally New Mexico (1530–1535, 1540–1541, 1581, 1583, 1590, 1598–1610); Virginia and North Carolina (1570, 1585–1588, 1607–1610); the California coast (1542, 1587, 1595, 1596, 1602–1603); the New England coast (1524, 1602–1605, 1607–1608); Nova Scotia (1606–1607); and Quebec (1600–1601, 1608–1610).
The relevant surviving records fall broadly into six genres: private correspondence, official correspondence and memoranda, correspondence of religious orders, pamphlets, travelogues, and finally chronicles and other second-hand compilations of information, which were used only to supplement first-hand information. Each of these genres has been used in historical climatology and each presents particular strengths and weaknesses as a source of weather, climate, and impact evidence (Pfister, 2018; Pfister and White, 2018). However, the unique conditions under which early colonial records were compiled endow them with peculiar advantages and disadvantages compared to other similar written records. On the one hand, events during the exploration of new lands and the colonization of new territories were unusually well recorded for the period, and their records have been carefully sought out, preserved, and analyzed by scholars concerned with the historical and environmental significance of colonization. Moreover, observers present in unfamiliar environments and concerned with prospects for resource extraction, trade, colonization, or missionization usually devoted more attention to environmental features, including weather and climate, than those at home (Taylor, 1993; White, 2015b; Zilberstein, 2016). Europeans on early colonial expeditions were often acutely vulnerable to climatic variability and extremes. On the other hand, the earliest colonial observations in each location necessarily predate the establishment of local institutions or practices that could produce regular records containing climate proxies, such as officially prescribed annual harvest dates. Furthermore, the novelty of colonial environments made it difficult for observers to determine what was normal weather or climate or to identify reliable phenological markers of variability or extremes. Adding to their confusion, early European explorers and colonists of North America expected climates to align with latitudes, overlooking the differences between Europe's predominately maritime climates and North America's predominately continental ones (Kupperman, 1982; Rockman, 2010). This study aims to evaluate whether the advantages of these sources outweigh their potential drawbacks when it comes to reconstructing past weather and climate.
This study identified four main types of evidence concerning drought for early colonial North America. (1) Phenological descriptions, including the growth of plants and conditions of rivers, provide the most objective indicators of drought, but they are not common in all sources. (2) Narrative descriptions, describing a lack of precipitation, are found more frequently but provide less certain indicators of the presence or absence of drought. (3) Societal impacts, particularly crop failures or famine attributed to drought, appear most frequently in the sources and may provide confirmation that conditions were unusually severe. However, these descriptions need to be considered in the context of societal vulnerabilities, which varied according to the colony or Native American society in question. Most of the populations discussed in this study relied heavily on crops of maize, which in turn depended on adequate summer rainfall and a lengthy frost-free growing season. (4) Rain-making ceremonies represent a peculiar but potentially valuable type of evidence for drought. Measuring the occurrence and scale of officially sanctioned rain prayers, known as rogation ceremonies, has been demonstrated as a reliable method of drought reconstruction in Spain and Spanish America (Domínguez Castro et al., 2008, 2018). Historians have identified similar ceremonies outside Spain in many different religious and cultural traditions, but these have not yet been tested in the same fashion. In the colonial North American context, many early European expeditions reported performing rain prayers, being asked by Native Americans to perform rain prayers, or observing indigenous communities performing rain-making ceremonies. Some historians have argued that such accounts could have been biased or even falsified by early European observers eager to present Native Americans as simple pagans ready to be won over to Christianity. However, a close review of the context and consistency of these accounts across sources has indicated that most were probably based on actual events (Kupperman, 2007b; White, 2015a).
Information concerning drought was sorted by each type of evidence. It was evaluated according to whether the information is based on a single observer, two or three observers, or many observers in agreement, and according to whether it provides a definite or indefinite impression of drought. For instance, an observation that it had not rained for a certain number of months was taken as a definite impression, whereas a general description of dry weather was taken as indefinite. Results and further information for specific expeditions are provided in Sect. 3.2.
Most high-resolution reconstructions of drought in North America for the
pre-instrumental period have relied on measures of the variation in the
width of growth rings in trees whose growth has been limited by soil
moisture during the growing season. NADA is a set of annual June–August
PDSI reconstructions based on 1845 tree-ring chronologies estimated on a
0.5
For the area between 30 and 50
This study systematically compared the NADA reconstruction to the
information in the documentary record of each expedition identified in
Sect. 2.1. Using the visualization tools at
Early colonial expeditions left no first-hand written records clearly
indicating droughts in any of the following regions: the California coast,
the New England coast, Quebec, or Nova Scotia, apart from an observation of
“fine weather all winter [1606–1607]” at Port Royal (Nova Scotia). The NADA
PDSI reconstruction indicates drought in New England (that is, PDSI between
Summary of written evidence. A capital letter “Y” denotes a definite impression of drought in either the winter or summer half year; a lowercase “y” denotes an indefinite impression. Letters in bold indicate many mutually supporting observations, letters in roman font indicate similar observations in two or three personal sources and/or information contained in an official report, and letters in italics indicate a single observer. A letter “N” indicates information in the documentary record indicating abundant precipitation or lack of drought. An explanation of sources and types of evidence is provided in Sect. 2.1; details for each expedition are given in Sect. 3.2.
Early colonial expeditions left first-hand written records indicating droughts in the following regions: the southeastern US, the southwestern US, and Virginia and North Carolina. Table 1 provides a summary of the type of information concerning drought from these expeditions.
The first Spanish colonial expeditions to the southeast, led by Juan Ponce
de León in 1513 and 1521 and Lucas Vázquez de Ayllón in 1526,
left no first-hand evidence concerning climatic conditions during their
expeditions. In 1528, Pánfilo de Narváez led an overland expedition
along the Gulf Coast from roughly Tampa Bay to the mouth of the Mississippi,
where its members, traveling on rafts, were swept by a storm to the Gulf
Coast of Texas. A few survivors remained in the region as captives of Native
Americans until 1534; their testimonies, recorded years later, described
cold and famine among the indigenous populations but left no definite
indications of drought during these years. The NADA reconstruction indicates
droughts (PDSI
During 1539–1543, a much better documented Spanish expedition led by Hernando
de Soto landed in northern Florida and traveled throughout the southeastern
United States before departing down the Mississippi River. No observers
described drought conditions in 1539–1540, during which NADA indicates a
positive hydroclimate anomaly. Multiple independent eye-witness accounts
describe a 1541 episode in which Native Americans in present-day Arkansas
asked Soto to pray for rain in order to end a drought and save their maize
crop. In early 1542, the expedition ventured into eastern Texas, where one
witness reported frequent wet weather; late that year, the expedition
returned to Arkansas, which another source described as experiencing
continued drought (specifically, it had not rained for the past month). The
NADA map for 1541 (Fig. 1a) indicates a drought (PDSI
In late summer 1559, Spanish conquistador Tristán de Luna y Arellano led
over 1500 soldiers and colonists to settle in Pensacola Bay, Florida, where
a hurricane soon destroyed most of their ships and supplies. Unable to live
off the land and facing famine, the colony retreated inland to central
Alabama, while a detachment explored the region of northeast Alabama and
northwestern Georgia, thought to be more promising for settlement. The
expedition's breakdown left ample official documentation, including many
complaints about the region's environment and climate. These mentioned the
frequency and unpredictability of rains – in contrast to those of
Mediterranean climates on the same latitude across the Atlantic – but not
drought. The NADA composite map of the area in 1559–1560 (Fig. 2a)
indicates slightly dry conditions (PDSI between 0 and
Between 1562 and 1565, French Huguenots attempted to establish colonies on
the coast between present-day South Carolina and northern Florida. These
were overrun in 1565 by Spanish soldiers, who established the permanent
colony of St. Augustine, Florida, as well as several outlying posts
including St. Elena, which lasted until 1587. The French colonies, as
described in several personal accounts by eye witnesses, suffered from
frequent shortages and sometimes famine blamed on poor supplies, shipwrecks,
and inability to obtain food from local indigenous communities. The Spanish
presence left a much more complete official record, principally letters from
the governor to the viceroy and the correspondence of Catholic missionaries.
The former describe droughts that led to failure of wheat and maize crops
during 1565–1566 in the region between South Carolina and northern Florida;
the latter describes Native Americans asking the colony's governor at St.
Augustine to pray for rain in 1566 to end a long drought. Official
correspondence also indicates that drought led to poor harvests at the St.
Augustine colony in 1583, 1588–1589, 1591, and 1598–1599; for instance, the
governor reported that 1588 was a “very great drought” (
During 1534–1535, the four survivors of the Pánfilo de Narváez expedition (see Sect. 3.2.1) ventured south into today's Tamaulipas (Mexico), then northwest near the Rio Grande valley. Their testimonies describe dry conditions in the Sierra Madre Oriental but only a single definite indication of drought: survivor Cabeza de Vaca reported that Native Americans in west Texas in late summer 1535 asked them to pray for rain because it had not rained enough to plant maize during the past year. A comparison with the NADA map of PDSI for that year (Fig. 4) indicates average to dry conditions in that region in 1535.
NADA JJA PDSI reconstruction for 1535, Cabeza de Vaca expedition.
During 1540 and 1541, a large expedition from Mexico led by governor Francisco Vázquez de Coronado occupied first the Zuni Pueblos of today's western New Mexico, then various Puebloan towns of the central Rio Grande valley. Of the many surviving official and personal accounts of the expedition, several mentioned heavy winter snow and none mentioned drought. The NADA composite map for New Mexico 1540–1541 (Fig. 5a) shows exceptionally moist conditions (PDSI between 2 and 3), as does the time series for the approximate location of the Spanish base camp, near present-day Bernalillo (Fig. 5b).
During 1581, 1583, and 1590–1591, three small unauthorized expeditions entered New Mexico from New Spain. Each traveled through the territory of the present-day state for only a few weeks or months, mainly along the Rio Grande, leaving no enduring colony; and each produced only two or three written testimonies by eye witnesses. A witness of the 1581 expedition described a “climate like that of Castile”: a possible indication of deficient summer rainstorms, since unlike Castile, most of New Mexico usually receives more precipitation in summer than winter. This witness also described a Puebloan rain-making ceremony, although it is not clear whether this was a normal seasonal ritual or a specific response to drought. A witness from the 1583 expedition described heavy snow early in the year but reported Puebloans refusing to share maize due to a “lack of rain” and poor harvest that summer. The 1590–1591 expedition traveled mainly during the winter months and left testimonies of exceptional cold and heavy snow but not drought. The NADA reconstructions indicate near-average conditions in 1581 (Fig. 6a) and negative PDSI anomalies across most of the present-day state in 1583 (Fig. 6b) and in 1591 (Fig. 6c).
A 1598 invasion led by Juan de Oñate occupied present-day New Mexico and subjugated the Pueblos of the region. In 1601, the expedition nearly collapsed when a large number of officers and settlers defected and Catholic missionaries protested the abuse of Pueblos. Narratives of Oñate's campaign, as well as disputes arising from the colony's near collapse, left a large body of personal and official evidence concerning conditions in New Mexico. The earliest indication of a drought in the documentary record occurs in a description of Pueblos asking colonists to pray for rain in 1598; however, this episode appears only in one contemporary source, which contains some fictionalized material. Colonists during 1599 and 1600 compared the climate in New Mexico to that of Castile, with predominately winter precipitation, possibly indicating deficient summer rainstorms. Colonists and missionaries left abundant official testimonies and personal letters describing extreme summer drought during 1600 and 1601, along with descriptions of starvation when the Pueblo maize crop failed and livestock died for want of pasture. However, descriptions also indicate that the winter of 1600–1601 was exceptionally snowy and icy, and that the colony's crop of irrigated winter wheat yielded well. For the years 1602–1610, there is no comparable indication of drought in the documentary record. The NADA composite map for New Mexico during 1598–1601 (Fig. 7a) shows a significant negative PDSI anomaly, particularly in the central and northern parts of the present-day state, where the Oñate expedition settled. The NADA time series for the location of Oñate's first colony at the present-day Okhay Owingeh Pueblo (Fig. 7b) indicates negative PDSI anomalies in 1598 and 1600–1601, although not as significant as those of the “megadrought” during the 1580s.
In 1570, a small group of Spanish Jesuit missionaries attempted to establish
an outpost along the lower James River in present-day Virginia. In the
scarce documentation that survives from the expedition, they reported that
the land had been “punished with six years of sterility and death” and was
“very parched (
Between 1585 and 1587, English investors led by Sir Walter Raleigh made several attempts to colonize Roanoke Island in the Carolina Outer Banks, before losing all contact with the final “lost colony.” A settler described how in 1586 the Native Americans' corn “began to whither by reason of a drought which happened extraordinarily” and reported being asked to pray for rain to end that drought. During the following year, the colony was unable to obtain maize from indigenous communities, who reported scarcity, and the colonists therefore suffered famine. The NADA composite map for 1585–1588 (Fig. 9) shows a major drought throughout eastern North Carolina, although not specifically for Roanoke Island, which is not covered by the atlas.
NADA JJA PDSI reconstruction for 1585–1588, eastern North Carolina.
The English colony at Jamestown, Virginia, suffered through multiple
environmental disasters and conflict with Native Americans from its founding
in 1607 through 1610, when it was rescued by a large infusion of new
settlers and supplies. Several contemporary personal letters, as well as
pamphlets and histories later written by eye witnesses, left indications of
exceptional summer drought throughout these first years at the colony. In
summer and autumn of 1607, saltwater apparently intruded into the James
River as far as Jamestown, where the water was described as “at flood very
salt, at low tide full of slime and filth”; this unusual occurrence may
have caused salt poisoning at the colony (Earle, 1979). Settlers' summer
grain crops failed repeatedly for unspecified reasons. Multiple colonists
also recorded complaints from Native Americans in villages throughout the region
during 1608–1610 that they had no maize to share with colonists or even for
their own consumption. Two sources reported that in 1608 or 1609 a leader of
a nearby indigenous community asked a colonist to “pray to his god for
rain, for his [own] god would not send him any”. During the summer of 1610,
sturgeon did not swim up the James River as usual, which may indicate high
salinity in that waterway. The NADA composite map for 1606–1610 (Fig. 10a)
indicates a moderate drought over southeastern Virginia. The NADA time
series of PDSI variation for 1600–1620 at the location of Jamestown (Fig. 10b) indicates a negative PDSI anomaly each summer during 1606–1612, with a
severe drought (PDSI of
Synthesis of comparison between drought information in the documentary record of early North American colonial expeditions and the NADA PDSI reconstruction. Green indicates droughts identified in both the documentary record and NADA reconstruction; blue indicates droughts identified in neither; red indicates droughts identified in the NADA reconstruction but not the documentary record; yellow indicates instances of partial or possible agreement between the documentary record and NADA, including instances where the documentary record identifies the impacts of a long drought but does not specify each year of its occurrence; dark grey indicates that there is no first-hand written evidence concerning climatic conditions.
Continued.
Table 2 presents a synthesis of the results described in Sect. 3.1 and 3.2. It indicates the years and regions where documented expeditions were present, and one of the following results: (1) droughts identified in both the documentary record and NADA reconstruction; (2) droughts identified in neither; (3) droughts identified in the NADA reconstruction but not the documentary record; (4) instances of partial or possible agreement between the documentary record and NADA, including instances where the documentary record identifies the impacts of a long drought but does not specify each year of its occurrence; (5) no first-hand written evidence concerning climatic conditions.
As indicated in Table 2, concurrence between the documentary record and the
NADA PDSI reconstruction on the timing of droughts is not complete but
clearly better than would be expected by chance. The documentary record
produced no false positives vis-à-vis the NADA reconstruction – that is,
the documentary record never provided a definite indication of a drought
where NADA indicated a positive hydroclimate anomaly (PDSI > 0) –
but observers did not leave written indications of all droughts (PDSI
The results of the comparison point to three main patterns. First, the documentary information and tree-ring-based reconstruction frequently disagree where the NADA spatial coverage or reconstruction skill is poorest, including the New England coast and Nova Scotia. Second, during multi-year droughts in Florida, observers did not necessarily record the occurrence or impacts of the drought each year but only at the beginning or end of the drought. A study comparing documentary information and tree-ring reconstructed hydroclimate variability has found a similar pattern for medieval Hungary (Kiss, 2017). Third, concurrence between the NADA reconstruction and the documentary record – and in this case, probably the reliability of climatic information in early colonial written sources – is highest when and where colonial observers were able to exchange information with local indigenous populations, thanks to presence of at least one translator and cultural intermediary, whether a Native American who had lived among Europeans, or vice versa. This was the case for expeditions and colonies in the southeast and Florida in 1539–1541 and 1565–1610; the southwest in 1534–1535 and 1598–1610; and North Carolina and Virginia in 1570, 1585–1587, and 1608–1610. This pattern suggests that early colonial observers obtained the most reliable indications of climatic variability and extremes from local populations and their impacts and reactions.
The results suggest no obvious differences in the reliability of different source types (official, personal, or ecclesiastical) or nationalities (Spanish, English, or French). In general, colonial observers were most likely to record droughts that had a direct impact on their own livelihoods. However, in this small sample, reports of rain prayers and indigenous societies afflicted by drought also turned out to be reliable indicators, even when there were no other mentions of drought.
Written descriptions of drought nearly all concern the spring and summer, probably because spring and summer rains were vital to North America's staple crop, maize. Descriptions of summer droughts in New Mexico, in particular, were often combined with descriptions of snowy winters, particularly during 1599–1601, suggesting that the reconstructed negative PDSI anomaly for these years reflected a summer precipitation deficit. However, a tree-ring-based reconstruction attempting to distinguish winter and summer precipitation signals using separate early- and latewood measurements has concluded that New Mexico's “megadrought” of 1580–1600 affected all seasons (Stahle et al., 2009). Most years of drought identified in the documentary record and NADA reconstruction were also described by observers as unusually cold (White, 2017). This coincidence suggests that deficits in growing season soil moisture appearing in the NADA reconstruction as negative PDSI anomalies should have been due to reduced precipitation rather than increased evapotranspiration, unless the cold had a confounding effect on tree-ring growth in local samples.
This study finds broad agreement between the evidence in written records and
the tree-ring-based NADA concerning the occurrence and severity of droughts
in North America during 1510–1610 CE. In years and locations where
substantial written observations were made and the NADA reconstruction skill
is high, the resulting documentary records did not indicate drought where
the NADA reconstruction indicated a positive hydroclimate anomaly (PDSI > 0)
and usually did indicate drought where NADA
reconstructed indicated a negative hydroclimate anomaly (PDSI
The results also suggest that the NADA reconstruction could be precise enough to help examine historical drought conditions and impacts at a local human scale, at least for periods and locations where the reconstruction skill of the drought atlas is particularly good (e.g., the southwestern US during the past five centuries). In this respect, NADA's exceptionally high density of samples covering much of the continent may enable types of detailed climate history studies not yet possible for other parts of the world. By contrast, the Old World Drought Atlas – based on 106 tree-ring chronologies and with lower average reconstruction skill for each grid point (median CVRE of 0.271; VRSQ of 0.198; VRE of 0.161; VCE of 0.146) – does not reproduce many local hydroclimate events described in written records (e.g., Collet, 2018) and may be more suited for identifying extensive multi-year events (Cook et al., 2015; Kiss, 2017).
This general concurrence between the early colonial documentary record and
the NADA reconstruction does not mean that such incomplete documentary
records are themselves capable of producing drought reconstructions.
However, the result does suggest how incomplete documentary records
demonstrating concurrence with high-resolution proxy-based reconstructions
might be combined with other sources in order to arrive at better estimates
for past climate conditions. One might estimate from comparisons with
proxy-based reconstructions that a type of documentary record has a high
probability of containing certain observations whenever a climate parameter
has certain values (
Finally, this study has implications for the role of climate in early North American colonial history. Although early colonial observers did not record climate conditions perfectly, neither apparently did they exaggerate the occurrence of drought. Therefore, historians should take seriously the descriptions in several early expeditions and colonies of drought-driven food shortages, famines, and resulting conflict with indigenous communities over scarce resources. This study generally supports previous research findings that drought substantially altered the outcome of several expeditions and therefore the outcome of competition between the Spanish, French, and English empires for North American territory. However, the results of this study may be even more significant for assessing the role of non-drought climatic factors in early colonial history. Descriptions of drought are less common in early colonial North American records than descriptions of destructive storms and exceptional winter cold, which were reported during many expeditions and may have had an even greater impact on their outcomes (e.g., White, 2014). Since storms and winter temperature are more difficult than drought to reconstruct from proxies in natural archives, it is especially important to establish the reliability and objectivity of information in the documentary record in order to assess the role of those climate factors in early colonial history.
Further explanation of the underlying documentary evidence for this study, including references to historical sources for particular events and observations, is provided in White (2017). Additional information is available upon request.
The supplement related to this article is available online at:
The author declares that there is no conflict of interest.
This article is part of the special issue “Droughts over centuries: what can documentary evidence tell us about drought variability, severity and human responses?”. It is not associated with a conference.
The author thanks Bill Keegan for assistance in the preparation of maps, and the PAGES-CRIAS working group.
This paper was edited by Andrea Kiss and reviewed by Stefan Grab and one anonymous referee.