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.

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

2006 ◽  
Vol 2 (5) ◽  
pp. 771-800 ◽  
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 ◽  
Mediterranean Regions ◽  
Dry Conditions

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 was able to exactly simulate the reconstructed changes, all simulations were an improvement over using the mean climate. Further, 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 this period. The results of the comparison emphasise the importance of the inclusion of the various forcings in the models and help to understand the atmospheric changes connected to reconstructed climate changes.

scholarly journals Twenty-First Century Drought Analysis Across China using CMIP6 Under Climate Change

2021 ◽  
Author(s):  
Gengxi Zhang ◽  
Thian Yew Gan ◽  
Xiaoling Su
Keyword(s):  
Soil Moisture ◽  
General Circulation ◽  
Coupled Model ◽  
Severity Index ◽  
General Circulation Models ◽  
Mitigation Strategies ◽  
Drought Indices ◽  
Drought Severity ◽  
Moisture Index ◽  
Arid Northwestern China

Abstract Under global warming, according to results obtained from offline drought indices driven by projections of general circulation models (GCMs), future droughts in China will worsen but the results are not consistent. We analyzed changes in droughts covering the entire hydrologic cycle using outputs of GCMs of the 6th Coupled Model Intercomparison Project (CMIP6) for SSP2-4.5 and SSP5-8.5 climate scenarios, and compared the results with that of popular, offline drought indices (the self-calibrating Palmer Drought Severity Index (scPDSI), Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Precipitation Actual Evapotranspiration Index (SPAEI)). Among meteorological, agricultural, and hydrological drought indices tested under both SSP scenarios, the results obtained from SPAEI and scPDSI agree better with univariate drought indices than SPEI. scPDSI generally agrees well with agricultural droughts (Standardized Soil Moisture Index with the surface soil moisture content; SSIS). Future droughts estimated using soil moisture analysis are more widespread than that from precipitation and runoff analysis in humid regions of South China by the end of the 21st century. In arid northwestern China and Inner Mongolia, drought areas and severity based on scPDSI and SSIS forced with the SSP scenarios show obvious decreasing trends, in contrast to increasing trends projected in humid regions. Trends projected using SPEI contradict those projected by other drought indices in non-humid regions. Therefore, selecting appropriate drought indices are crucial in project representative future droughts and meaningful information needed to achieve effective regional drought mitigation strategies under climate warming impact.

scholarly journals Northern Hemispheric Trends of Pressure Indices and Atmospheric Circulation Patterns in Observations, Reconstructions, and Coupled GCM Simulations

2005 ◽  
Vol 18 (19) ◽  
pp. 3968-3982 ◽  
Author(s):  
C. C. Raible ◽  
T. F. Stocker ◽  
M. Yoshimori ◽  
M. Renold ◽  
U. Beyerle ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
General Circulation ◽  
Southern Oscillation ◽  
Storm Track ◽  
General Circulation Models ◽  
Aleutian Low ◽  
Climate Conditions ◽  
Atmospheric Circulation Patterns ◽  
The North ◽  
Decadal Trend

Abstract The decadal trend behavior of the Northern Hemisphere atmospheric circulation is investigated utilizing long-term simulations with different state-of-the-art coupled general circulation models (GCMs) for present-day climate conditions (1990), reconstructions of the past 500 yr, and observations. The multimodel simulations show that strong positive winter North Atlantic Oscillation (NAO) trends are connected with the underlying sea surface temperature (SST) and exhibit an SST tripole trend pattern and a northward shift of the storm-track tail. Strong negative winter trends of the Aleutian low are associated with SST changes in the El Niño–Southern Oscillation (ENSO) region and a westward shift of the storm track in the North Pacific. The observed simultaneous appearance of strong positive NAO and negative Aleutian low trends is very unlikely to occur by chance in the unforced simulations and reconstructions. The positive winter NAO trend of the last 50 yr is not statistically different from the level of internal atmosphere–ocean variability. The unforced simulations also show a strong link between positive SST trends in the ENSO region and negative Aleutian low trends. With much larger observed SST trends in the ENSO region, this suggests that the observed negative Aleutian low trend is possibly influenced by external forcing, for example, global warming, volcanism, and/or solar activity change.

scholarly journals Plant responses to increasing CO2 reduce estimates of climate impacts on drought severity

2016 ◽  
Vol 113 (36) ◽  
pp. 10019-10024 ◽  
Author(s):  
Abigail L. S. Swann ◽  
Forrest M. Hoffman ◽  
Charles D. Koven ◽  
James T. Randerson
Keyword(s):  
Drought Stress ◽  
Impact Analysis ◽  
Water Flux ◽  
Central Africa ◽  
Severity Index ◽  
Climate Impacts ◽  
Drought Severity ◽  
Plant Responses ◽  
Future Assessment ◽  
Temperate Asia

Rising atmospheric CO2 will make Earth warmer, and many studies have inferred that this warming will cause droughts to become more widespread and severe. However, rising atmospheric CO2 also modifies stomatal conductance and plant water use, processes that are often are overlooked in impact analysis. We find that plant physiological responses to CO2 reduce predictions of future drought stress, and that this reduction is captured by using plant-centric rather than atmosphere-centric metrics from Earth system models (ESMs). The atmosphere-centric Palmer Drought Severity Index predicts future increases in drought stress for more than 70% of global land area. This area drops to 37% with the use of precipitation minus evapotranspiration (P-E), a measure that represents the water flux available to downstream ecosystems and humans. The two metrics yield consistent estimates of increasing stress in regions where precipitation decreases are more robust (southern North America, northeastern South America, and southern Europe). The metrics produce diverging estimates elsewhere, with P-E predicting decreasing stress across temperate Asia and central Africa. The differing sensitivity of drought metrics to radiative and physiological aspects of increasing CO2 partly explains the divergent estimates of future drought reported in recent studies. Further, use of ESM output in offline models may double-count plant feedbacks on relative humidity and other surface variables, leading to overestimates of future stress. The use of drought metrics that account for the response of plant transpiration to changing CO2, including direct use of P-E and soil moisture from ESMs, is needed to reduce uncertainties in future assessment.

scholarly journals ANALISIS KEKERINGAN DI KABUPATEN SRAGEN DENGAN METODE PALMER, THORNTHWAITE, DAN STANDARDIZED PRECIPITATION INDEX

2021 ◽  
Vol 17 (2) ◽  
pp. 111-124
Author(s):  
Safrudin Nor Aripbilah ◽  
Heri Suprapto
Keyword(s):  
Drought Index ◽  
Southern Oscillation ◽  
Standardized Precipitation Index ◽  
Severity Index ◽  
Precipitation Index ◽  
Suitable Method ◽  
Drought Severity ◽  
Severe Drought ◽  
Drought Hazard ◽  
Dry Conditions

El Nino and La Nina in Indonesia are one of the reasons that caused climate changes, which has possibility of drought and flood disasters. Sragen Regency wherethe dry season occurs, drought happened meanwhile other areas experience floods and landslides. A study on drought needs to be carried out so as to reduce the risk of losses due to the drought hazard. This study is to determine the drought index in Sragen Regency based on several methods and the correlation of each methods and its suitability to the Southern Oscillation Index (SOI) and rainfall. Drought was analyzed using several methods such as Palmer Drought Severity Index (PDSI), Thornthwaite-Matter, and Standardized Precipitation Index (SPI) then correlated with SOI to determine the most suitable method for SOI. The variables are applied in this method are rainfall, temperature, and evapotranspiration. The results showed that the drought potential of the Palmer method is only in Near Normal conditions, which is 1%, Severe drought conditions are 29% for the Thornthwaite-Matter method, and Extreme Dry conditions only reach 1,11% for the SPI method. The PDSI and SPI methods are inversely proportional to the Thornthwaite-Matter method and the most suitable method for SOI values or rainfall is the SPI method. These three methods can be identified the potential for drought with only a few variables so that they could be applied if they only have those data.Keywords: Drought, PDSI, Thornthwaite-Matter, SPI, SOI

Possible pathways to a Dansgaard-Oeschger (DO) PMIP protocol

2021 ◽  
Author(s):  
Irene Malmierca-Vallet ◽  
Louise C. Sime ◽  
Paul J. Valdes
Keyword(s):  
General Circulation ◽  
Climate Changes ◽  
General Circulation Models ◽  
Ice Age ◽  
Climate Change Projections ◽  
The Past ◽  
External Perturbations ◽  
Mis 3 ◽  
Last Ice Age ◽  
Earth System Models

<p>The DO events of the last ice age represent one of the best studied abrupt climate transitions, yet we still lack a comprehensive explanation for them. There is uncertainty whether current IPCC-relevant models can effectively represent the processes that cause DO events. Current Earth system models (ESMs) seem overly stable against external perturbations and incapable of reproducing most abrupt climate changes of the past (Valdes, 2011). If this holds true, this could noticeably influence their capability to predict future abrupt transitions, with significant consequences for the delivery of precise climate change projections.  In this task, the objectives of this study are (1) to cross compare existing simulations that show spontaneous DO-type oscillations using a common set of diagnostics so we can compare the mechanisms and the characteristics of the oscillations, and (2) to formulate possible pathways to a DO PMIP protocol that could help investigate cold-period instabilities through a range of insolation-, freshwater-, GHG-, and NH ice sheet-related forcings, as well as evaluating the possibility of spontaneous internal oscillations.</p><p>Although most abrupt DO events happened during MIS3, only few studies investigate DO events in coupled general circulation models under MIS 3 conditions (e.g., Kawamura et al., 2017; Zhang and Prange, 2020). Here, we thus propose that the MIS3 period could be the focus of such a DO-event modelling protocol. More specific sensitivity experiments performed under MIS 3 boundary conditions are needed in order to (1) better understand the mechanisms behind millennial-scale climate variability, (2) explore AMOC variability under intermediate glacial conditions, and (3) help answer the question: “are models too stable?”.</p>

Residual Mass Severity Index (RMSI) – a duration free method to characterise droughts

2020 ◽  
Author(s):  
Rounak Afroz ◽  
Ashish Sharma ◽  
Fiona Johnson
Keyword(s):  
Climate Change ◽  
General Circulation ◽  
Severity Index ◽  
General Circulation Models ◽  
Drought Indices ◽  
Severe Drought ◽  
Monthly Precipitation ◽  
Water Shortages ◽  
Simple Method ◽  
Residual Mass

<p>The complexity of representing droughts has led to many drought indices being developed. A common aspect for many of these indices, however, is the need to adopt a predefined time period, over which a drought is characterized. Therefore, to declare a catchment as drought-impacted, 6, 12 or 24-month SPI are required. Actual water allocations, however, are required at all times and are thus duration free; a concept well described by the well-known residual mass curve. Here we propose a new framework to characterize drought, termed as the Residual Mass Severity Index (RMSI). As the name suggests, the RMSI defines drought based on the magnitude of the residual mass in any location which is calculated by performing a water balance using a prescribed demand. Demand here is adopted as the median monthly precipitation for the region. Water shortages only become significant when there is a sustained deficit compared to this demand. The above described residual mass is standardized to formulate the RMSI across Australia. The new RMSI has been validated against established drought indices (such as the SPI) to highlight the advantages of a duration-free drought index.</p><p>RMSI provides a simple method of assessing sustained and severe drought anomalies which is important with expected increases in water scarcity due to anthropogenic climate change. We demonstrate that RMSI can be used as a tool to evaluate the performance of General Circulation Models (GMCs) in representing the sustainability of water resource systems as a product of resilience, reliability, and vulnerability (RRV) of the system. Future projections of drought from GCMs which perform well in representing RMSI in the RRV context in the historical climate are then compared to drought projections from the full CMIP5 ensemble.</p><p>Keywords: Drought, Residual Mass Curve, SPI, RRV, Climate Change, CMIP5 GCMs</p>

scholarly journals Unprecedented 21st century drought risk in the American Southwest and Central Plains

2015 ◽  
Vol 1 (1) ◽  
pp. e1400082 ◽  
Author(s):  
Benjamin I. Cook ◽  
Toby R. Ault ◽  
Jason E. Smerdon
Keyword(s):  
21St Century ◽  
General Circulation ◽  
General Circulation Models ◽  
American Southwest ◽  
Drought Severity ◽  
Historical Event ◽  
Drought Risk ◽  
Central Plains ◽  
Emissions Scenarios ◽  
Rcp 8.5

In the Southwest and Central Plains of Western North America, climate change is expected to increase drought severity in the coming decades. These regions nevertheless experienced extended Medieval-era droughts that were more persistent than any historical event, providing crucial targets in the paleoclimate record for benchmarking the severity of future drought risks. We use an empirical drought reconstruction and three soil moisture metrics from 17 state-of-the-art general circulation models to show that these models project significantly drier conditions in the later half of the 21st century compared to the 20th century and earlier paleoclimatic intervals. This desiccation is consistent across most of the models and moisture balance variables, indicating a coherent and robust drying response to warming despite the diversity of models and metrics analyzed. Notably, future drought risk will likely exceed even the driest centuries of the Medieval Climate Anomaly (1100–1300 CE) in both moderate (RCP 4.5) and high (RCP 8.5) future emissions scenarios, leading to unprecedented drought conditions during the last millennium.

Multidecadal Variability of North China Aridity and Its Relationship to PDO during 1900–2010

2014 ◽  
Vol 27 (3) ◽  
pp. 1210-1222 ◽  
Author(s):  
Cheng Qian ◽  
Tianjun Zhou
Keyword(s):  
North China ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Severity Index ◽  
Phase Changes ◽  
Drought Severity ◽  
Pressure System ◽  
Multidecadal Variability ◽  
Dry Conditions ◽  
Drying Trend

Abstract North China has undergone a severe drying trend since the 1950s, but whether this trend is natural variability or anthropogenic change remains unknown due to the short data length. This study extends the analysis of dry–wet changes in north China to 1900–2010 on the basis of self-calibrated Palmer drought severity index (PDSI) data. The ensemble empirical mode decomposition method is used to detect multidecadal variability. A transition from significant wetting to significant drying is detected around 1959/60. Approximately 70% of the drying trend during 1960–90 originates from 50–70-yr multidecadal variability related to Pacific decadal oscillation (PDO) phase changes. The PDSI in north China is significantly negatively correlated with the PDO index, particularly at the 50–70-yr time scale, and is also stable during 1900–2010. Composite differences between two positive PDO phases (1922–45 and 1977–2002) and one negative PDO phase (1946–76) for summer exhibit an anomalous Pacific–Japan/East Asian–Pacific patternlike teleconnection, which may develop locally in response to the PDO-associated warm sea surface temperature anomalies in the tropical Indo-Pacific Ocean and meridionally extends from the tropical western Pacific to north China along the East Asian coast. North China is dominated by an anomalous high pressure system at mid–low levels and an anticyclone at 850 hPa, which are favorable for dry conditions. In addition, a weakened land–sea thermal contrast in East Asia from a negative to a positive PDO phase also plays a role in the dry conditions in north China by weakening the East Asian summer monsoon.

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