Extraordinary heat during the 1930s US Dust Bowl and associated large-scale conditions

Unusually hot summer conditions occurred during the 1930s over the central United States and undoubtedly contributed to the severity of the Dust Bowl drought. We investigate local and large-scale conditions in association with the extraordinary heat and drought events, making use of novel datasets of observed climate extremes and climate reanalysis covering the past century. We show that the unprecedented summer heat during the Dust Bowl years was likely exacerbated by land-surface feedbacks associated with springtime precipitation deficits. The reanalysis results indicate that these deficits were associated with the coincidence of anomalously warm North Atlantic and Northeast Pacific surface waters and a shift in atmospheric pressure patterns leading to reduced flow of moist air into the central US. Thus, the combination of springtime ocean temperatures and atmospheric flow anomalies, leading to reduced precipitation, also holds potential for enhanced predictability of summer heat events. The results suggest that hot drought, more severe than experienced during the most recent 2011 and 2012 heat waves, is to be expected when ocean temperature anomalies like those observed in the 1930s occur in a world that has seen significant mean warming.     

基于SPEI的近百年天津地区气象干旱时空演变特征

基于1921—2016年天津地区降水、气温观测数据,对全球降水气候中心降水(GPCC-P)、东英吉利大学气候研究中心气温(CRU-T)进行适用性评估后发现GPCC-P和CRU-T均能较好地反映天津地区降水和气温的变化。在此基础上,进一步利用GPCC-P、CRU-T计算的标准化降水蒸散指数(SPEI)分析天津地区近百年干旱时空演变特征并判断其未来变化趋势。结果表明：(1)天津干旱主要发生于1940年代初期、1990年代末和2000年代初期,四季均以轻旱和中旱为主,干旱高频季节由秋、冬季逐渐转为春、夏季。(2)天津全区SPEI气候趋势在6个时期除秋季整体呈“升、降、升”分布特征外,春、夏、冬季均表现为“升、降”的分布特征,且夏季下降趋势最为显著,1961—2010年宁河每10 a下降0.30。(3)1921—1970、1931—1980、1941—1990年天津春、冬季湿润化趋势由降水主导,而夏、秋季则由气温和降水协同影响;1951—2000、1961—2010、1971—2016年春季干旱趋势主要受气温影响,夏、冬季则为气温和降水协同影响,随着全球变暖,气温升高对干旱的影响逐渐增强。(4...     

Atmospheric circulation anomalies during two persistent north american droughts: 1932�C1939 and 1948�C1957

We use an early twentieth century (1908?C1958) atmospheric reanalysis, based on assimilation of surface and sea level pressure observations, to contrast atmospheric circulation during two periods of persistent drought in North America: 1932?C1939 (the ??Dust Bowl??) and 1948?C1957. Primary forcing for both droughts is believed to come from anomalous sea surface temperatures (SSTs): a warm Atlantic and a cool eastern tropical Pacific. For boreal winter (October?CMarch) in the 1950s, a stationary wave pattern originating from the tropical Pacific is present, with positive centers over the north Pacific and north Atlantic ocean basins and a negative center positioned over northwest North America and the tropical/subtropical Pacific. This wave train is largely absent for the 1930s drought; boreal winter height anomalies are organized much more zonally, with positive heights extending across northern North America. For boreal summer (April?CSeptember) during the 1930s, a strong upper level ridge is centered over the Great Plains; this feature is absent during the 1950s and appears to be linked to a weakening of the Great Plains low-level jet (GPLLJ). Subsidence anomalies are co-located over the centers of each drought: in the central Great Plains for the 1930s and in a band extending from the southwest to the southeastern United States for the 1950s. The location and intensity of this subsidence during the 1948?C1957 drought is a typical response to a cold eastern tropical Pacific, but for 1932?C1939 deviates in terms of the expected intensity, location, and spatial extent. Overall, circulation anomalies during the 1950s drought appear consistent with the expected response to the observed SST forcing. This is not the case for the 1930s, implying some other causal factor may be needed to explain the Dust Bowl drought anomalies. In addition to SST forcing, the 1930s were also characterized by massive alterations to the land surface, including regional-scale devegetation from crop failures and intensive wind erosion and dust storms. Incorporation of these land surface factors into a general circulation model greatly improves the simulation of precipitation and subsidence anomalies during this drought, relative to simulations with SST forcing alone. Even with additional forcing from the land surface, however, the model still has difficulty reproducing some of the other circulation anomalies, including weakening of the GPLLJ and strengthening of the upper level ridge during AMJJAS. This may be due to either weaknesses in the model or uncertainties in the boundary condition estimates. Still, analysis of the circulation anomalies supports the conclusion of an earlier paper (Cook et?al. in Proc Natl Acad Sci 106:4997, 2009), demonstrating that land degradation factors are consistent with the anomalous nature of the Dust Bowl drought.     

Coping with food crises: Lessons from the American Dust Bowl on balancing local food,agro technology,social welfare,and government regulation agendas in food and farming systems

This paper examines four broad policy and public responses to the American Dust Bowl in the 1930s as a way of exploring how society today could address our own “food crisis”. More particularly, in the Dust Bowl some argued that solutions would be found by engineers and farmers who would develop new ways of watering dry fields. A second group believed that inappropriate political and economic incentives had led to bad farming practices prior to the drought and this contributed to wide-spread erosion. To this group, the best solutions included governmental regulation of farm practices. A third group focused on the welfare of individuals, arguing that creating a social safety net to protect marginalized families was the highest priority. Finally, there were commentators who advocated for a smaller scale, ecological, and holistic approach to farming. Today, the same four perspectives are present in debates about how to maintain global food security in light of population growth, high energy prices and climate change. Exploring the similarity of the discourses between today's food crisis and the one that hit American society 80 years ago reveals that advocates of the four different camps are motivated by very different principles. Briefly, proponents of technological solutions base many of their arguments on the assumption that human ingenuity is capable of producing extremely productive food systems. The managerial arguments, by contrast, are based on the idea that the natural environment can be rationally and efficiently managed using scientific principles. The social welfare narrative seeks to create a more equitable food system. Finally, the ecological and holistic narrative argues that diverse, small scale and local food systems are a prerequisite for long term sustainability. The primary contribution of this paper, therefore, is to expose these deeply held ontological tensions as a way of arguing that policy makers today must de-politicise arguments and use the principles embedded in all four narratives when designing programmes to ensure that the 21st century does not face a repeat of the crisis of the 1930s.     

华北冬小麦-夏玉米两熟区干旱特征分析

研究华北冬小麦一夏玉米主要生长季的干旱时空特征,可为全球气候变暖背景下制定抗旱减灾对策提供理论依据。利用华北5省（市）64个气象台站1961-2010年逐日降水资料,以降水负距平或降水量表征的干旱指标,通过经验正交分解法提取了冬小麦、夏玉米全生育期和关键生长阶段的特征向量和时间系数,分析了干旱频率、站次比及干旱强度的变化特征,并通过构建冬小麦-夏玉米轮作期综合干旱指数,探讨了华北地区农业干旱的总体状况。结果表明：EOF分解的前4个模态提取了60％以上作物干旱的主要时空分布信息,冬小麦主要生长季收敛效果优于夏玉米;冬小麦全生育期、苗期及拔节-抽穗期干旱的高强度中心主要分布在冀中南、豫北及鲁西北地区,而灌浆-成熟期干旱则以豫东为中心;夏玉米全生育期干旱的高强度中心主要位于冀南和鲁北地区,初夏旱以冀北大部为高强度区,而卡脖旱以豫西和鲁南为高强度区。从时间系数和区域干旱强度及站次比的时间变化趋势看,冬小麦全生育期干旱、灌浆-成熟期干旱及夏玉米初夏旱、卡脖旱均表现为递减趋势,但未通过显著性检验,而冬小麦播种期、拔节-抽穗期干旱,以及夏玉米全生育期干旱为不显著的递增趋势。整个冬小麦-夏玉米轮作期干旱威胁较高的地区主要位于京津局部、冀中南、豫北和鲁北等地区。     

Circulation indices over the Mediterranean and Europe and their relationship with rainfall conditions across the Mediterranean

Summary Circulation types were identified by means of zonal and meridional indices calculated separately over ten different regions of 20° × 20° over the Mediterranean and Europe. Seasonal and annual rainfall totals in four stations Lisbon, Luqa (Malta), Athens and Jerusalem, were compared with circulation types for the period 1873–1991. Correlation coefficients of circulation indices with precipitation, for each station in each season were calculated and mapped.An oscillation in the meridional index during the winter and the spring, between the western and eastern Mediterranean, was detected.Time series analysis of the circulation indices demonstrates a significant reduction in zonality and an increase in meridionality mainly in spring and in summer, over most of the study area.With 9 Figures     

Upper Yellowstone River Flow and Teleconnections with Pacific Basin Climate Variability during the Past Three Centuries

Climate variability, coupled with increasing demand is raising concerns about the sustainability of water resources in the western United States. Tree-ring reconstructions of stream flow that extend the observational record by several centuries provide critical information on the short-term variability and multi-decadal trends in water resources. In this study, precipitation sensitive Douglas-fir (Pseudotsuga menzeisii) tree ringrecords are used to reconstruct annual flow of the Yellowstone River back to A.D. 1706. Linkages between precipitation in the Greater Yellowstone Region and climate variability in the Pacific basin were incorporated into our model by including indices Pacific Ocean interannual and decadal-scale climatic variability, namely the Pacific Decadal Oscillation and the Southern Oscillation. The reconstruction indicates that 20th century streamflow is not representative of flow during the previous two centuries. With the exception of the 1930s, streamflow during the 20th century exceeded average flows during the previous 200 years. The drought of the 1930s resulted in the lowest flows during the last three centuries, however, this probably does not represent a worst-case scenario for the Yellowstone as other climate reconstructions indicate more extreme droughts prior to the 18th century.     

Accelerated climate change and its potential impact on Yak herding livelihoods in the eastern Tibetan plateau

The Tibetan Plateau has experienced rapid warming like most other alpine regions. Regional assessments show rates of warming comparable with the arctic region and decreasing Asian summer monsoons. We used meteorological station daily precipitation and daily maximum and minimum temperature data from 80 stations in the eastern Tibetan Plateau of southwest China to calculate local variation in the rates and seasonality of change over the last half century (1960–2008). Daily low temperatures during the growing season have increased greatly over the last 24 years (1984–2008). In sites of markedly increased warming (e.g., Deqin, Yunnan and Mangya, Qinghai), daily and growing season daily high temperatures have increased at a rate above 5 °C/100 years. In Deqin, precipitation prior to the 1980s fell as snow whereas in recent decades it has shifted to rain during March and April. These shifts to early spring rains are likely to affect plant communities. Animals like yaks adapted to cold climates are also expected to show impacts with these rising temperatures. This region deserves further investigation to determine how these shifts in climate are affecting local biodiversity and livelihoods.     

多时间尺度下黑龙江省1980—2014年干湿演变特征及主导因子分析

利用黑龙江省1980—2014年28个气象台站常规观测资料,计算得到全省的相对湿润度指数。运用ArcGIS反距离权重空间插值法、趋势系数及相关分析法对全省作物生长季及各个季节干旱分布、干湿发展趋势及主要影响因素进行具体分析。结果表明:就相对湿润度指数年际分布而言,生长季干旱主要集中在2000—2010年,夏季和秋季干旱主要集中在1995年之后,春季干旱则在全时段均有发生,其中重旱和特旱居多;就相对湿润度指数变化趋势而言,春季全省整体呈微湿润化的趋势,冬季呈显著地湿润化发展趋势,其余时段则呈现干旱化发展,但不同时段空间差异显著;分析降雨量、潜在蒸散量与相对湿润度指数的相关系数发现,降雨量始终是黑龙江省生长季及各个季节相对湿润度指数变化的主导因子,但夏季潜在蒸散量的影响有所增加。     

Climate changes in the Amur River basin in the last 115 years

Tendencies in climate change in the Amur River basin are generally synchronous to the global ones. During the last century, the annual mean temperature of surface air increased by 1.3°C, minimum warming being observed in the east part of the basin (0.6°C) and maximum one in the west part (1.7–2.5°C). The largest impact on the annual mean temperature growth comes from winter and spring temperature increase (2–4°C/100 years). During the last 30 years, the warming rate in the basin was 2–3 times higher than during the whole period of 1891–2004. Simultaneously with warming in the Amur River basin, annual and warm-season precipitation totals increased by 8 and 6%, respectively, during the 115-year period. The highest increase in precipitation totals occurs in cold season (29% during 115 years). During the last 30 years, together with intense warming in the Amur River basin, the annual precipitation totals are found to decrease by an average of 2.1%/10 years.     

Tree-ring reconstructed rainfall over the southeastern U.S.A. during the medieval warm period and little ice age

A 1053-year reconstruction of spring rainfall (March-June) was developed for the southeastern United States, based on three tree-ring reconstructions of statewide rainfall from North Carolina, South Carolina, and Georgia. This regional reconstruction is highly correlated with the instrumental record of spring rainfall (r = +0.80; 1887–1982), and accurately reproduces the decade-scale departures in spring rainfall amount and variance witnessed over the Southeast during the past century. No large-magnitude centuries-long trends in spring rainfall amounts were reconstructed over the past 1053 years, but large changes in the interannual variability of spring rainfall were reconstructed during portions of the Medieval Warm Period (MWP), Little Ice Age (LIA), and the 20th century. Dry conditions persisted at the end of the 12th century, but appear to have been exceeded by a reconstructed drought in the mid-18th century. High interannual variability, including five extremely wet years were reconstructed for a 20-yr period during the late 16th and early 17th centuries, and may reflect amplified atmospheric circulation over eastern North America during what appears to have been one of the most widespread cold episodes of the Little Ice Age.     

An assessment of the near real‐time rainfall network on Canada's eastern Prairies

Abstract

Bogusing errors associated with estimating rainfalls for ungauged points on Canada's eastern Prairies based on the near real‐time network have been determined for growing season totals, summer monthly amounts and summer daily values. The bogusing errors as a percentage of the concurrent area‐average amount or the coefficients of variation decreased as the measurement period increased. Growing season precipitation totals can be approximated to within 20%. The error associated with bogused summer monthly amounts was more than twice as large. The field of summer daily rainfall amounts cannot be estimated accurately. It can be concluded, therefore, that the precipitation network on the eastern Prairies is not sufficient for applications requiring the input of summer daily or monthly precipitation amounts from points other than the gauged locations. The network does, nevertheless, provide relatively accurate estimates of the growing season's precipitation field to assist in defining the climate.

Reductions in the magnitude of the bogusing errors associated with estimated precipitation amounts can be achieved by adding new stations to the network. While additional sites provide data at the newly gauged points, they do little to improve the network's representation of the rainfall field unless the new stations are added in fairly large numbers.     

临洮县春末夏初干旱气候分析

文中统计了临洮县 196 1～ 2 0 0 0年共 4 0年逐旬降水量资料 ,用谐波分析法分析诊断临洮县逐旬降水量多年平均值的年周期与半年周期 ,划分出气候干湿期时段 ,分析造成春末夏初旱的环流特征 ,为做好短期气候预测 ,指导农业生产提供服务     

Synergistic feedbacks between ocean and vegetation on mid- and high-latitude climates during the mid-Holocene

Simulations with the IPSL atmosphere–ocean model asynchronously coupled with the BIOME1 vegetation model show the impact of ocean and vegetation feedbacks, and their synergy, on mid- and high-latitude (>40°N) climate in response to orbitally-induced changes in mid-Holocene insolation. The atmospheric response to orbital forcing produces a +1.2 °C warming over the continents in summer and a cooling during the rest of the year. Ocean feedback reinforces the cooling in spring but counteracts the autumn and winter cooling. Vegetation feedback produces warming in all seasons, with largest changes (+1 °C) in spring. Synergy between ocean and vegetation feedbacks leads to further warming, which can be as large as the independent impact of these feedbacks. The combination of these effects causes the high northern latitudes to be warmer throughout the year in the ocean–atmosphere-vegetation simulation. Simulated vegetation changes resulting from this year-round warming are consistent with observed mid-Holocene vegetation patterns. Feedbacks also impact on precipitation. The atmospheric response to orbital-forcing reduces precipitation throughout the year; the most marked changes occur in the mid-latitudes in summer. Ocean feedback reduces aridity during autumn, winter and spring, but does not affect summer precipitation. Vegetation feedback increases spring precipitation but amplifies summer drying. Synergy between the feedbacks increases precipitation in autumn, winter and spring, and reduces precipitation in summer. The combined changes amplify the seasonal contrast in precipitation in the ocean–atmosphere-vegetation simulation. Enhanced summer drought produces an unrealistically large expansion of temperate grasslands, particularly in mid-latitude Eurasia.     

Reconstructed cool- and warm-season precipitation over the tribal lands of northeastern Arizona

For over a decade, the Hopi Tribe and Navajo Nation of northeastern Arizona have suffered the effects of persistent drought conditions. Severe dry spells have critically impacted natural ecosystems, water resources, and regional livelihoods including dryland farming and ranching. Drought planning and resource management efforts in the region are based largely on the instrumental climate record, which contains a limited number of severe, sustained droughts. In this study, a new network of moisture-sensitive tree-ring chronologies provides the basis for evaluating the longer-term temporal variability of precipitation in the Four Corners region. By analyzing the earlywood and latewood components within each annual tree ring, we are able to generate separate, centuries-long reconstructions of both cool- (October-April) and warm-season (July-August) precipitation. These proxy records offer new insights into seasonal drought characteristics and indicate that the instrumental record fails to adequately represent precipitation variability over the past 400 years. Through the use of two different analysis techniques, we identify multiyear and decadal-scale drought events more severe than any in the modern era. Furthermore, the reconstructions suggest that many of the historically significant droughts of the past (e.g., 17th century Puebloan drought) were not merely winter phenomena, but persisted through the summer season as well. By comparing these proxy records with historical documents, we are able to independently validate the reconstructions and better understand the socioeconomic and environmental significance of past climate anomalies on the tribal lands of northeastern Arizona.     

Temperature and precipitation trends in Canada during the 20th century

Abstract

Trends in Canadian temperature and precipitation during the 20th century are analyzed using recently updated and adjusted station data. Six elements, maximum, minimum and mean temperatures along with diurnal temperature range (DTR), precipitation totals and ratio of snowfall to total precipitation are investigated. Anomalies from the 1961–1990 reference period were first obtained at individual stations, and were then used to generate gridded datasets for subsequent trend analyses. Trends were computed for 1900–1998 for southern Canada (south of 60°N), and separately for 1950–1998 for the entire country, due to insufficient data in the high arctic prior to the 1950s.

From 1900–1998, the annual mean temperature has increased between 0.5 and 1.5°C in the south. The warming is greater in minimum temperature than in maximum temperature in the first half of the century, resulting in a decrease of DTR. The greatest warming occurred in the west, with statistically significant increases mostly seen during spring and summer periods. Annual precipitation has also increased from 5% to 35% in southern Canada over the same period. In general, the ratio of snowfall to total precipitation has been increasing due mostly to the increase in winter precipitation which generally falls as snow and an increase of ratio in autumn. Negative trends were identified in some southern regions during spring. From 1950–1998, the pattern of temperature change is distinct: warming in the south and west and cooling in the northeast, with similar magnitudes in both maximum and minimum temperatures. This pattern is mostly evident in winter and spring. Across Canada, precipitation has increased by 5% to 35%, with significant negative trends found in southern regions during winter. Overall, the ratio of snowfall to total precipitation has increased, with significant negative trends occurring mostly in southern Canada during spring.

Indices of abnormal climate conditions are also examined. These indices were defined as areas of Canada for 1950–1998, or southern Canada for 1900–1998, with temperature or precipitation anomalies above the 66th or below the 34th percentiles in their relevant time series. These confirmed the above findings and showed that climate has been becoming gradually wetter and warmer in southern Canada throughout the entire century, and in all of Canada during the latter half of the century.     

Observed spatiotemporal characteristics of drought on various time scales over the Czech Republic

This paper analyses the observed spatiotemporal characteristics of drought in the Czech Republic during the growing season (April to September) as quantified using the Standardised Precipitation Evapotranspiration Index (SPEI) on various time scales. The SPEI was calculated for various lags (1, 3, 6, 12, and 24 months) from monthly records of mean temperature and precipitation totals using a dense network of 184 climatological stations for the period 1961–2010. The characteristics of drought were analysed in terms of the temporal evolution of the SPEI, the frequency distribution and duration of drought at the country level, and for three regions delimited by station altitude. The driest and the wettest years during the growing season were identified. The frequency distribution of the SPEI values for seven drought category classes (in per cent) indicates that normal moisture conditions represent approximately 65 % of the total SPEI values for all time scales in all three regions, whereas moderate drought and moderate wet conditions are almost equally distributed around 10.5 %. Differences in extremely dry conditions (5 %) compared with extremely wet conditions (1.5 %) were observed with increasing SPEI time scales. The results of the non-parametric Mann–Kendall trend test applied to the SPEI series indicate prevailing negative trends (drought) at the majority of the stations. The percentage of stations displaying a significant negative trend for the 90, 95, 99, and 99.9 % confidence levels is approximately 40 %. An Empirical Orthogonal Functions (EOF) analysis was used to identify the principal patterns of variability of the SPEI during the growing season that accounted for the highest amount of statistical variance. The variance explained by the leading EOF range 66 to 56 %, whereas for EOF2 and EOF3, the value is between 7 and 11 % and between 4 and 7 %, respectively, for the SPEI is calculated for 1- to 24-month lags.     

近55年广西融水县降水气候特征分析

利用融水县气象站1959-2013年的降水资料,采用数理统计和线性倾向估计分析方法,分析了融水县降水分布特征及其变化规律。结果表明：融水县降水分配不均,主要集中在4-8月,6月最多,5月次之;年暴雨日数6.9d,暴雨持续时间多为1d,最长4d;近55年来融水县年降水量和汛期（4-9月）降水量均呈减少趋势,每10年分别减少16mm和6mm,而主汛期（5-8月）的降水量却呈增多趋势,每10年增加13mm,这预示着融水县未来降水可能更趋于集中在主汛期（5-8月）,发生洪涝灾害的几率可能增多。此外,一日最大降水量呈增多趋势,预示未来降雨强度可能增大;春、秋季的降水量呈减少趋势,提示未来发生春旱、秋旱的几率可能增多。     

Reconstructions of annual summer precipitation and temperature in north-central China since 1470 AD based on drought/flood index and tree-ring records

The understanding of the ongoing climate change needs high-resolution records of the past, which are difficult to obtain in north-central China. Historical documents are unique materials for high-resolution (up to season) climate change reconstruction. Here, we report an attempt of quantitative climate reconstruction covering the main part of north-central China, by combining historical drought/flood index and tree-ring data. The rigorous verification tests confirm the fidelity of transfer functions used in the reconstructions. The precipitation and temperature anomalies/intervals were then defined based on the reconstructions. Finally, the intensity of several big droughts recorded in historical documents was re-examined and the dominant and recessive patterns of heat/water changes within the study area were identified. We concluded that (1) the droughts, occurred during the years of 1484 AD, 1585–1587 AD, 1689–1691 AD, 1784–1786 AD and 1876–1878 AD, were the results of rainless and torrid combination; (2) the droughts, occurred during the years of 1560–1561 AD, 1599–1601 AD, 1609 AD, 1615–1617 AD, 1638–1641 AD and 1899–1901 AD, were first caused by rainless summer, and then controlled by low precipitation and/or high temperature; (3) the droughts, occurred during the years of 1527–1529 AD, 1720–1722 AD, 1813–1814 AD, 1856–1857 AD and 1926–1930 AD, were first caused by torrid summer, and then controlled by both low precipitation and high temperature; (4) the dominant climate pattern within the study area consisted of warm–dry and cold–wet alternations, and the recessive pattern consisted of cold–dry and warm–wet alternations. We also showed that the drought/flood index is a valuable climate proxy in quantitative reconstructions, especially in places where tree-ring data is not available.     

新疆博州地区气候生长季降水变化分析

摘 要：对新疆博州（博尔塔拉蒙古自治州）地区1958-2005年作物生长季降水资料的分析结果表明：博州地区作物生长季降水量存在显著增加趋势,特别是20世纪90年代以来降水偏多年略多于偏少年;降水存在5～7 a、16 a 和30 a 左右的周期变化;90年代以来,由于博河上游地区5月份降水偏少,而且博河中游地区第一场"透雨"日期又快速推后以及透雨次数减少等原因,造成河谷一带春夏干旱尤为突出;而在6-8月份,博河上游地区降水量与大雨日数的显著增加却极易诱发山区洪灾;秋季月降水量的普遍增加对作物的采收晾晒不利,但是山区秋季降水的增加有利于秋水转为春用。