scholarly journals A comparison of model simulations of Asian mega-droughts during the past millennium with proxy reconstructions

2014 ◽  
Vol 10 (3) ◽  
pp. 2685-2716 ◽  
Author(s):  
B. Fallah ◽  
U. Cubasch
Keyword(s):  
Asian Monsoon ◽  
Climate Model ◽  
Severity Index ◽  
Ice Age ◽  
Drought Severity ◽  
Model Simulations ◽  
The Past ◽  
Global Circulation Models ◽  
Proxy Reconstructions ◽  
Past Millennium

Abstract. Two PMIP3/CMIP5 climate model ensemble simulations of the past millennium have been analyzed to identify the occurrence of Asian mega-droughts. The Palmer Drought Severity Index (PDSI) is used as the key metric for the data comparison of hydro-climatological conditions. The model results are compared with the proxy data of the Monsoon Asia Drought Atlas (MADA). Our study shows that Global Circulation Models (GCMs) are capable to capture the majority of historically recorded Asian monsoon failures at the right time and with a comparable spatial distribution. The simulations indicate that ENSO-like events lead in most cases to these droughts. Both, model simulations and proxy reconstructions, point to less monsoon failures during the Little Ice Age. During historic mega-droughts of the past millennium, the monsoon convection tends to assume a preferred regime described as "break" event in Asian monsoon. This particular regime is coincident with a notable weakening in Pacific Trade winds and Somali Jet.

scholarly journals A comparison of model simulations of Asian mega-droughts during the past millennium with proxy reconstructions

2015 ◽  
Vol 11 (2) ◽  
pp. 253-263 ◽  
Author(s):  
B. Fallah ◽  
U. Cubasch
Keyword(s):  
Asian Monsoon ◽  
Climate Model ◽  
Severity Index ◽  
Ice Age ◽  
Drought Severity ◽  
Model Simulations ◽  
The Past ◽  
Global Circulation Models ◽  
Proxy Reconstructions ◽  
Past Millennium

Abstract. Two PMIP3/CMIP5 climate model ensemble simulations of the past millennium have been analysed to identify the occurrence of Asian mega-droughts. The Palmer drought severity index (PDSI) is used as the key metric for the data comparison of hydro-climatological conditions. The model results are compared with the proxy data of the Monsoon Asia Drought Atlas (MADA). Our study shows that global circulation models (GCMs) are capable of capturing the majority of historically recorded Asian monsoon failures at the right time and with a comparable spatial distribution. The simulations indicate that El Niño-like events lead, in most cases, to these droughts. Both model simulations and proxy reconstructions point to fewer monsoon failures during the Little Ice Age. The results suggest an influential impact of volcanic forcing on the atmosphere–ocean interactions throughout the past millennium. During historic mega-droughts of the past millennium, the monsoon convection tends to assume a preferred regime described as a "break" event in Asian monsoon. This particular regime is coincident with a notable weakening in the Pacific trade winds and Somali Jet.

scholarly journals Teleconnections and relationship between the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) in reconstructions and models over the past millennium

2020 ◽  
Vol 16 (2) ◽  
pp. 743-756 ◽  
Author(s):  
Christoph Dätwyler ◽  
Martin Grosjean ◽  
Nathan J. Steiger ◽  
Raphael Neukom
Keyword(s):  
Climate Model ◽  
El Nino ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Last Millennium ◽  
Annular Mode ◽  
Model Simulations ◽  
The Past ◽  
Climate Model Simulations ◽  
Past Millennium

Abstract. The climate of the Southern Hemisphere (SH) is strongly influenced by variations in the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Because of the limited length of instrumental records in most parts of the SH, very little is known about the relationship between these two key modes of variability over time. Using proxy-based reconstructions and last-millennium climate model simulations, we find that ENSO and SAM indices are mostly negatively correlated over the past millennium. Pseudo-proxy experiments indicate that currently available proxy records are able to reliably capture ENSO–SAM relationships back to at least 1600 CE. Palaeoclimate reconstructions show mostly negative correlations back to about 1400 CE. An ensemble of last-millennium climate model simulations confirms this negative correlation, showing a stable correlation of approximately −0.3. Despite this generally negative relationship we do find intermittent periods of positive ENSO–SAM correlations in individual model simulations and in the palaeoclimate reconstructions. We do not find evidence that these relationship fluctuations are caused by exogenous forcing nor by a consistent climate pattern. However, we do find evidence that strong negative correlations are associated with strong positive (negative) anomalies in the Interdecadal Pacific Oscillation and the Amundsen Sea Low during periods when SAM and ENSO indices are of opposite (equal) sign.

scholarly journals Moisture and Temperature Covariability over the Southeastern Tibetan Plateau during the Past Nine Centuries

2020 ◽  
Vol 33 (15) ◽  
pp. 6583-6598
Author(s):  
Jianglin Wang ◽  
Bao Yang ◽  
Fredrik Charpentier Ljungqvist
Keyword(s):  
Tibetan Plateau ◽  
Climate Model ◽  
Severity Index ◽  
Early Summer ◽  
Convective Precipitation ◽  
Drought Severity ◽  
The Tibetan Plateau ◽  
Low Frequencies ◽  
The Past ◽  
Spatial Coverage

AbstractAccurate projections of moisture variability across the Tibetan Plateau (TP) are crucial for managing regional water resources, ecosystems, and agriculture in densely populated downstream regions. Our understanding of how moisture conditions respond to increasing temperatures over the TP is still limited, due to the short length of instrumental data and the limited spatial coverage of high-resolution paleoclimate proxy records in this region. This study presents a new, early-summer (May–June) self-calibrating Palmer drought severity index (scPDSI) reconstruction for the southeastern TP (SETP) covering 1135–2010 CE using 14 tree-ring records based on 1669 individual width sample series. The new reconstruction reveals that the SETP experienced the longest period of pluvial conditions in 1154–75 CE, and the longest droughts during the periods 1262–80 and 1958–76 CE. The scPDSI reconstruction shows stable and significant in-phase relationships with temperature at both high and low frequencies throughout the past 900 years. This supports the hypothesis that climatic warming may increase moisture by enhancing moisture recycling and convective precipitation over the SETP; it is also consistent with climate model projections of wetter conditions by the late twenty-first century in response to global warming.

Variability of the Azores High and regional hydroclimate over the past millennium

2020 ◽  
Author(s):  
Caroline Ummenhofer ◽  
Nathaniel Cresswell-Clay ◽  
Diana Thatcher ◽  
Alan Wanamaker ◽  
Rhawn Denniston
Keyword(s):  
Climate Model ◽  
Hadley Circulation ◽  
Meridional Overturning Circulation ◽  
Ice Age ◽  
Last Millennium ◽  
Atlantic Sector ◽  
Model Simulations ◽  
The Past ◽  
Climate Model Simulations ◽  
Azores High

<p>The subtropical dry zones, including the broader Mediterranean region, are likely to experience considerable changes in hydroclimate in a warming climate. An expansion of the atmosphere’s meridional overturning circulation, the Hadley circulation, over recent decades has been reported, with implications for regional hydroclimate. Yet, there exists considerable disagreement in magnitude and even sign of these trends among different metrics that measure various aspects of the Hadley circulation, as well as discrepancies in trends between different analysis periods and reanalysis products during the 20<sup>th</sup> century. In light of these uncertainties, it is therefore of interest to explore variability and trends in subtropical hydroclimate and its dominant driver, the Hadley Circulation. We focus on the North Atlantic sector and explore variability in the Azores High, the manifestation of the Hadley Circulation’s downward branch, and hydroclimate across the Iberian Peninsula using a combination of observational/reanalysis products, state-of-the-art climate model simulations, and hydroclimatically-sensitive stalagmite records over the past 1200 yr. The Last Millennium Ensemble (LME) with the Community Earth System Model provides thirteen transient simulations covering the period 850 to 2005 A.D. with prescribed external forcing (e.g. greenhouse gas, solar, volcanic, land use, orbital, and aerosol) and smaller subsets with individual forcing only. The LME is shown to accurately simulate the variability and trends in the Azores High when compared to observational records from the 20<sup>th</sup> century. We evaluate variability in the Azores High (e.g., size, intensity, position) in relation to other key metrics that measure different aspects of the Hadley circulation throughout the course of the last millennium, as well as during key periods, such as the Little Ice Age or Medieval Climate Anomaly. The smaller subsets of LME simulations with individual forcing factors (e.g., solar, volcanic) allow for an attribution of past changes in regional hydroclimate to external drivers. Results from the climate model simulations are compared with hydroclimate reconstructed from stalagmites from Portuguese caves.</p>

scholarly journals Constraining the temperature history of the past millennium using early instrumental observations

2012 ◽  
Vol 8 (3) ◽  
pp. 1653-1685 ◽  
Author(s):  
P. Brohan ◽  
R. Allan ◽  
E. Freeman ◽  
D. Wheeler ◽  
C. Wilkinson ◽  
...  
Keyword(s):  
Temperature Change ◽  
Large Scale ◽  
Climate Model ◽  
Ice Cores ◽  
East India Company ◽  
Temperature History ◽  
British Library ◽  
Model Simulations ◽  
Climate Model Simulations ◽  
Proxy Reconstructions

Abstract. The current assessment that twentieth-century global temperature change is unusual in the context of the last thousand years relies on estimates of temperature changes from natural proxies (tree-rings, ice-cores etc.) and climate model simulations. Confidence in such estimates is limited by difficulties in calibrating the proxies and systematic differences between proxy reconstructions and model simulations. As the difference between the estimates extends into the relatively recent period of the early nineteenth century it is possible to compare them with a reliable instrumental estimate of the temperature change over that period, provided that enough early thermometer observations, covering a wide enough expanse of the world, can be collected. One organisation which systematically made observations and collected the results was the English East-India Company (EEIC), and their archives have been preserved in the British Library. Inspection of those archives revealed 900 log-books of EEIC ships containing daily instrumental measurements of temperature and pressure, and subjective estimates of wind speed and direction, from voyages across the Atlantic and Indian Oceans between 1789 and 1834. Those records have been extracted and digitised, providing 273 000 new weather records offering an unprecedentedly detailed view of the weather and climate of the late eighteenth and early nineteenth centuries. The new thermometer observations demonstrate that the large-scale temperature response to the Tambora eruption and the 1809 eruption was modest (perhaps 0.5 °C). This provides a powerful out-of-sample validation for the proxy reconstructions – supporting their use for longer-term climate reconstructions. However, some of the climate model simulations in the CMIP5 ensemble show much larger volcanic effects than this – such simulations are unlikely to be accurate in this respect.

Glacier fluctuations during the past millennium in Garibaldi Provincial Park, southern Coast Mountains, British Columbia

2007 ◽  
Vol 44 (9) ◽  
pp. 1215-1233 ◽  
Author(s):  
Johannes Koch ◽  
John J Clague ◽  
Gerald D Osborn
Keyword(s):  
British Columbia ◽  
Little Ice Age ◽  
Ice Age ◽  
Southern Coast ◽  
Coast Mountains ◽  
The Past ◽  
Glacier Fluctuations ◽  
Garibaldi Provincial Park ◽  
Provincial Park ◽  
Past Millennium

The Little Ice Age glacier history in Garibaldi Provincial Park (southern Coast Mountains, British Columbia) was reconstructed using geomorphic mapping, radiocarbon ages on fossil wood in glacier forefields, dendrochronology, and lichenometry. The Little Ice Age began in the 11th century. Glaciers reached their first maximum of the past millennium in the 12th century. They were only slightly more extensive than today in the 13th century, but advanced at least twice in the 14th and 15th centuries to near their maximum Little Ice Age positions. Glaciers probably fluctuated around these advanced positions from the 15th century to the beginning of the 18th century. They achieved their greatest extent between A.D. 1690 and 1720. Moraines were deposited at positions beyond present-day ice limits throughout the 19th and early 20th centuries. Glacier fluctuations appear to be synchronous throughout Garibaldi Park. This chronology agrees well with similar records from other mountain ranges and with reconstructed Northern Hemisphere temperature series, indicating global forcing of glacier fluctuations in the past millennium. It also corresponds with sunspot minima, indicating that solar irradiance plays an important role in late Holocene climate change.

scholarly journals Projected Spatiotemporal Dynamics of Drought under Global Warming in Central Asia

2019 ◽  
Vol 11 (16) ◽  
pp. 4421 ◽  
Author(s):  
Zhang ◽  
Zhao ◽  
Ma ◽  
Brindha ◽  
Han ◽  
...  
Keyword(s):  
Global Warming ◽  
Central Asia ◽  
Social Life ◽  
Climate Model ◽  
Severity Index ◽  
Drought Severity ◽  
Warming Scenario ◽  
Intercomparison Project ◽  
Marked Decline ◽  
Human Social Life

Drought, one of the most common natural disasters that have the greatest impact on human social life, has been extremely challenging to accurately assess and predict. With global warming, it has become more important to make accurate drought predictions and assessments. In this study, based on climate model data provided by the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP), we used the Palmer Drought Severity Index (PDSI) to analyze and project drought characteristics and their trends under two global warming scenarios—1.5 °C and 2.0 °C—in Central Asia. The results showed a marked decline in the PDSI in Central Asia under the influence of global warming, indicating that the drought situation in Central Asia would further worsen under both warming scenarios. Under the 1.5 °C warming scenario, the PDSI in Central Asia decreased first and then increased, and the change time was around 2080, while the PDSI values showed a continuous decline after 2025 in the 2.0 °C warming scenario. Under the two warming scenarios, the spatial characteristics of dry and wet areas in Central Asia are projected to change significantly in the future. In the 1.5 °C warming scenario, the frequency of drought and the proportion of arid areas in Central Asia were significantly higher than those under the 2.0 °C warming scenario. Using the Thornthwaite (TH) formula to calculate the PDSI produced an overestimation of drought, and the Penman–Monteith (PM) formula is therefore recommended to calculate the index.

scholarly journals Historical droughts in Mediterranean regions during the last 500 years: a data/model approach

2007 ◽  
Vol 3 (2) ◽  
pp. 355-366 ◽  
Author(s):  
S. Brewer ◽  
S. Alleaume ◽  
J. Guiot ◽  
A. Nicault
Keyword(s):  
Drought Stress ◽  
General Circulation ◽  
Distance Measure ◽  
Severity Index ◽  
General Circulation Models ◽  
Ice Age ◽  
Drought Severity ◽  
Atmospheric Circulation Patterns ◽  
Dry Conditions ◽  
Simulated Climate

Abstract. We present here a new method for comparing the output of General Circulation Models (GCMs) with proxy-based reconstructions, using time series of reconstructed and simulated climate parameters. The method uses k-means clustering to allow comparison between different periods that have similar spatial patterns, and a fuzzy logic-based distance measure in order to take reconstruction errors into account. The method has been used to test two coupled ocean-atmosphere GCMs over the Mediterranean region for the last 500 years, using an index of drought stress, the Palmer Drought Severity Index. The results showed that, whilst no model exactly simulated the reconstructed changes, all simulations were an improvement over using the mean climate, and a good match was found after 1650 with a model run that took into account changes in volcanic forcing, solar irradiance, and greenhouse gases. A more detailed investigation of the output of this model showed the existence of a set of atmospheric circulation patterns linked to the patterns of drought stress: 1) a blocking pattern over northern Europe linked to dry conditions in the south prior to the Little Ice Age (LIA) and during the 20th century; 2) a NAO-positive like pattern with increased westerlies during the LIA; 3) a NAO-negative like period shown in the model prior to the LIA, but that occurs most frequently in the data during the LIA. The results of the comparison show the improvement in simulated climate as various forcings are included and help to understand the atmospheric changes that are linked to the observed reconstructed climate changes.

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