scholarly journals The Forcing of Monthly Precipitation Variability over Southwest Asia during the Boreal Cold Season

2015 ◽  
Vol 28 (18) ◽  
pp. 7038-7056 ◽  
Author(s):  
Andrew Hoell ◽  
Shraddhanand Shukla ◽  
Mathew Barlow ◽  
Forest Cannon ◽  
Colin Kelley ◽  
...  
Keyword(s):  
Climate Variability ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
Cold Season ◽  
Precipitation Variability ◽  
Annual Rainfall ◽  
Monthly Precipitation ◽  
Southwest Asia

Abstract Southwest Asia, defined as the region containing the countries of Afghanistan, Iran, Iraq, and Pakistan, is water scarce and receives nearly 75% of its annual rainfall during the boreal cold season of November–April. The forcing of southwest Asia precipitation has been previously examined for the entire boreal cold season from the perspective of climate variability originating over the Atlantic and tropical Indo-Pacific Oceans. This study examines the intermonthly differences in precipitation variability over southwest Asia and the atmospheric conditions directly responsible in forcing monthly November–April precipitation. Seasonally averaged November–April precipitation over southwest Asia is significantly correlated with sea surface temperature (SST) patterns consistent with Pacific decadal variability (PDV), El Niño–Southern Oscillation (ENSO), and the long-term change of global SST (LT). In contrast, the precipitation variability during the individual months of November–April is unrelated and is correlated with SST signatures that include PDV, ENSO, and LT in different combinations. Despite strong intermonthly differences in precipitation variability during November–April over southwest Asia, similar atmospheric circulations, highlighted by a stationary equivalent barotropic Rossby wave centered over Iraq, force the monthly spatial distributions of precipitation. Tropospheric flow on the eastern side of the equivalent barotropic Rossby wave modifies the flux of moisture and advects the mean meridional temperature gradient, resulting in temperature advection that is balanced by vertical motions over southwest Asia. The forcing of monthly southwest Asia precipitation by equivalent barotropic Rossby waves is different from the forcing by baroclinic Rossby waves associated with tropically forced–only modes of climate variability.

scholarly journals Responses of groundwater to precipitation variability and ENSO in the Vietnamese Mekong Delta

2021 ◽  
Author(s):  
Phong V. V. Le ◽  
Hai V. Pham ◽  
Luyen K. Bui ◽  
Anh N. Tran ◽  
Chien V. Pham ◽  
...  
Keyword(s):  
Water Resources ◽  
Climate Variability ◽  
Time Scales ◽  
Groundwater Level ◽  
Southern Oscillation ◽  
Mekong Delta ◽  
Precipitation Variability ◽  
Annual Precipitation ◽  
Aquifer Recharge ◽  
Deep Aquifers

Abstract Groundwater is a critical component of water resources and has become the primary water supply for agricultural and domestic uses in the Vietnamese Mekong Delta (VMD). Widespread groundwater level declines have occurred in the VMD over recent decades, reflecting that extraction rates exceed aquifer recharge in the region. However, the impacts of climate variability on groundwater system dynamics in the VMD remain poorly understood. Here, we explore recent changes in groundwater levels in shallow and deep aquifers from observed wells in the VMD and investigate their relations to the annual precipitation variability and El Niño–Southern Oscillation (ENSO). We show that groundwater level responds to changes in annual precipitation at time scales of approximately 1 year. Moreover, shallow (deep) groundwater in the VMD appears to correlate with the ENSO over intra-annual (inter-annual) time scales. Our findings reveal a critical linkage between groundwater level changes and climate variability, suggesting the need to develop an understanding of the impacts of climate variability across time scales on water resources in the VMD.

scholarly journals Oceanic Origins of Historical Southwest Asia Precipitation During the Boreal Cold Season

2017 ◽  
Vol 30 (8) ◽  
pp. 2885-2903 ◽  
Author(s):  
Andrew Hoell ◽  
Mathew Barlow ◽  
Forest Cannon ◽  
Taiyi Xu
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Atmospheric Model ◽  
Cold Season ◽  
Southwest Asia ◽  
Regional Variability ◽  
Model Simulations ◽  
Dry Conditions

While a strong influence on cold season southwest Asia precipitation by Pacific sea surface temperatures (SSTs) has been previously established, the scarcity of southwest Asia precipitation observations prior to 1960 renders the region’s long-term precipitation history largely unknown. Here a large ensemble of atmospheric model simulations forced by observed time-varying boundary conditions for 1901–2012 is used to examine the long-term sensitivity of November–April southwest Asia precipitation to Pacific SSTs. It is first established that the models are able to reproduce the key features of regional variability during the best-observed 1960–2005 period and then the pre-1960 variability is investigated using the model simulations. During the 1960–2005 period, both the mean precipitation and the two leading modes of precipitation variability during November–April are reasonably simulated by the atmospheric models, which include the previously identified relationships with El Niño–Southern Oscillation (ENSO) and the multidecadal warming of Indo-Pacific SSTs. Over the full 1901–2012 period, there are notable variations in precipitation and in the strength of the SST influence. A long-term drying of the region is associated with the Indo-Pacific warming, with a nearly 10% reduction in westernmost southwest Asia precipitation during 1938–2012. The influence of ENSO on southwest Asia precipitation varied in strength throughout the period: strong prior to the 1950s, weak between 1950 and 1980, and strongest after the 1980s. These variations were not antisymmetric between ENSO phases. El Niño was persistently related with anomalously wet conditions throughout 1901–2012, whereas La Niña was not closely linked to precipitation anomalies prior to the 1970s but has been associated with exceptionally dry conditions thereafter.

Indian Ocean mediates the ENSO teleconnections to the Central Southwest Asia during the wet season 

2021 ◽  
Author(s):  
Muhammad Adnan Abid ◽  
Moetasim Ashfaq ◽  
Fred Kucharski ◽  
Katherine J. Evans ◽  
Mansour Almazroui
Keyword(s):  
Indian Ocean ◽  
Rossby Wave ◽  
Southern Oscillation ◽  
Intraseasonal Variability ◽  
Tropical Indian Ocean ◽  
Polar Regions ◽  
Southwest Asia ◽  
Wet Season ◽  
Enso Teleconnections ◽  
Hydroclimate Variability

<p>Central Southwest Asia (CSWA) is a region with the largest number of glaciers, outside the polar regions in its northeast and the Arabian desert to its southwest. The region receives precipitation from November to April period also known as the wet season, which contributes to the regional freshwater resources. Mainly, El Niño–Southern Oscillation (ENSO) modulates the wet season precipitation over CSWA, with a positive relationship. However, the intraseasonal characteristics of ENSO influence are largely unknown, which may be important to understand the regional sub-seasonal to seasonal hydroclimate variability. We noted that the ENSO‐CSWA teleconnection varies intraseasonally and is a combination of direct and indirect positive influences. The ENSO direct influence is through a Rossby wave‐like pattern in the tail months of the wet season, while the indirect influence is noted through an ENSO‐forced atmospheric dipole of diabatic heating anomalies in the tropical Indian Ocean (TIO), which also generates a Rossby wave‐like forcing and persists throughout the wet season. The stronger ENSO influence is found when both direct and indirect modes are in phase, while the relationship breaks down when the two modes are out of phase. Moreover, the idealized numerical simulations confirm and reproduce the observed circulation patterns. This suggests that improvements in sub-seasonal to seasonal scale predictability requires the better representation of intraseasonal variability of ENSO teleconnection, as well as the role of interbasin interactions in its propagation.</p>

scholarly journals Persistent decadal-scale rainfall variability in the tropical South Pacific Convergence Zone through the past six centuries

2014 ◽  
Vol 10 (4) ◽  
pp. 1319-1332 ◽  
Author(s):  
C. R. Maupin ◽  
J. W. Partin ◽  
C.-C. Shen ◽  
T. M. Quinn ◽  
K. Lin ◽  
...  
Keyword(s):  
Climate Variability ◽  
Decadal Variability ◽  
Solomon Islands ◽  
Rainfall Variability ◽  
South Pacific ◽  
Rainfall Amount ◽  
South Pacific Convergence Zone ◽  
Annual Rainfall ◽  
Convergence Zone ◽  
Decadal Scale

Abstract. Modern Pacific decadal variability (PDV) has global impacts; hence records of PDV from the pre-instrumental period are needed to better inform models that are used to project future climate variability. We focus here on reconstructing rainfall in the western tropical Pacific (Solomon Islands; ~ 9.5° S, ~160° E), a region directly influenced by PDV, using cave deposits (stalagmite). A relationship is developed between δ18O variations in the stalagmite and local rainfall amount to produce a 600 yr record of rainfall variability from the South Pacific Convergence Zone (SPCZ). We present evidence for large (~1.5 m), abrupt, and periodic changes in total annual rainfall amount on decadal to multidecadal timescales since 1423 ± 5 CE (Common Era) in the Solomon Islands. The timing of the decadal changes in rainfall inferred from the 20th century portion of the stalagmite δ18O record coincides with previously identified decadal shifts in PDV-related Pacific ocean–atmosphere behavior (Clement et al., 2011; Deser et al., 2004). The Solomons record of PDV is not associated with variations in external forcings, but rather results from internal climate variability. The 600 yr Solomon Islands stalagmite δ18O record indicates that decadal oscillations in rainfall are a persistent characteristic of SPCZ-related climate variability.

scholarly journals The Modulation of ENSO Variability in CCSM3 by Extratropical Rossby Waves

2009 ◽  
Vol 22 (22) ◽  
pp. 5839-5853 ◽  
Author(s):  
Shayne McGregor ◽  
Alex Sen Gupta ◽  
Neil J. Holbrook ◽  
Scott B. Power
Keyword(s):  
Pacific Ocean ◽  
Wind Stress ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Southern Oscillation ◽  
Interdecadal Variability ◽  
Western Boundary ◽  
Thermocline Depth ◽  
Enso Variability ◽  
Enso Events

Abstract Evidence suggests that the magnitude and frequency of the El Niño–Southern Oscillation (ENSO) changes on interdecadal time scales. This is manifest in a distinct shift in ENSO behavior during the late 1970s. This study investigates mechanisms that may force this interdecadal variability and, in particular, on modulations driven by extratropical Rossby waves. Results from oceanic shallow-water models show that the Rossby wave theory can explain small near-zonal changes in equatorial thermocline depth that can alter the amplitude of simulated ENSO events. However, questions remain over whether the same mechanism operates in more complex coupled general circulation models (CGCMs) and what the magnitude of the resulting change would be. Experiments carried out in a state-of-the-art z-coordinate primitive equation model confirm that the Rossby wave mechanism does indeed operate. The effects of these interactions are further investigated using a partial coupling (PC) technique. This allows for the isolation of the role of wind stress–forced oceanic exchanges between the extratropics and the tropics and the subsequent modulation of ENSO variability. It is found that changes in the background state of the equatorial Pacific thermocline depth, induced by a fixed off-equatorial wind stress anomaly, can significantly affect the probability of ENSO events occurring. This confirms the results obtained from simpler models and further validates theories that rely on oceanic wave dynamics to generate Pacific Ocean interdecadal variability. This indicates that an improved predictive capability for seasonal-to-interannual ENSO variability could be achieved through a better understanding of extratropical-to-tropical Pacific Ocean transfers and western boundary processes. Furthermore, such an understanding would provide a physical basis to enhance multiyear probabilistic predictions of ENSO indices.

scholarly journals Influence of large-scale circulation and interannual modes of climate variability on seasonal drought characteristics over Pakistan

2021 ◽  
Author(s):  
Irfan Ullah ◽  
Xieyao Ma ◽  
Jun Yin ◽  
Farhan Saleem ◽  
Sidra Syed ◽  
...  
Keyword(s):  
Climate Variability ◽  
Large Scale ◽  
Southern Oscillation ◽  
Statistical Significance ◽  
Influential Factors ◽  
Drought Severity ◽  
Monthly Precipitation ◽  
Large Scale Circulation ◽  
Drought Characteristics ◽  
Cropping Seasons

Abstract The long-term drought monitoring and its assessment are of great importance for meteorological disaster risk management. The recurrent spells of heatwaves and droughts have severely affected the environmental conditions worldwide, including Pakistan. The present work sought to investigate the spatiotemporal changes in drought characteristics over Pakistan during Rabi and Kharif cropping seasons. The role of large-scale circulation and interannual mode of climate variability is further explored to identify the physical mechanisms associated with droughts in the region. Monthly precipitation and temperature data (1983–2019) from 53 meteorological stations were used to study drought characteristics, using the standardized precipitation evapotranspiration index (SPEI). The non-parametric Mann-Kendall (MK), Sen’s Slope (SS), and Sequential Mann-Kendall (SQMK) tests were applied on the drought index to determine the statistical significance and magnitude of the historical trend. The state-of-the-art Bayesian Dynamic Linear (BDL) model was further used to analyze large scale climate drivers of droughts, analysis revealed an increase in drought severity mostly over arid to semi-arid regions for both cropping seasons. Temperature played a significant role in defining droughts over dry and hot seasons, while rainfall is influential over the western disturbances (WD) influenced region. The analysis of atmospheric circulation patterns revealed that large-scale changes in wind speed, air temperature, relative humidity and geopotential height anomalies are the likely drivers of droughts in the region. We found that Niño4, Sea Surface Temperature (SST), and multivariate El Niño-Southern Oscillation (ENSO4.0) Index are the most influential factors for seasonal droughts across Pakistan. Overall, the findings provide a better understanding of drought-prone areas in the region, and this information is of potential use for mitigating and managing drought risks.

scholarly journals Dominant Controls of Cold-Season Precipitation Variability Over the High Mountains of Asia

2021 ◽  
Author(s):  
Moetasim Ashfaq ◽  
Shahid Mehmood ◽  
Sarah Kapnick ◽  
Subimal Ghosh ◽  
Muhammad Adnan Abid ◽  
...  
Keyword(s):  
Climate Variability ◽  
Cold Season ◽  
Precipitation Variability ◽  
High Mountains ◽  
Precipitation Distribution ◽  
Natural Modes ◽  
Extratropical Forcing ◽  
Single Set ◽  
Modes Of Climate Variability

Abstract A robust understanding of the sub-seasonal cold season (November–March) precipitation variability over the High Mountains of Asia (HMA) is currently lacking. Here, we identify dynamic and thermodynamic pathways through which natural modes of climate variability establish their teleconnections over the HMA. First, we identify evaporative sources that contribute to the cold season precipitation over the HMA and surroundings areas. The predominant moisture contribution comes from the mid-latitude regions including Mediterranean/Caspian Seas and Mediterranean land. Second, we establish that several tropical and extratropical forcing display a sub-seasonally fluctuating influence on the cold season precipitation distribution over the region, and given that many of them varyingly interact with each other, their impacts cannot be explained exclusively or at seasonal timescales. Lastly, a single set of evaporative sources cannot always be identified as the only determinant in propagating a remote teleconnection, because nature of moisture anomalies and its sources depend on the pattern of sub-seasonally varying dynamical forcing in the atmosphere.

scholarly journals Climate reality - actual and expected

2003 ◽  
Vol 11 ◽  
pp. 13-18
Author(s):  
J. Salinger
Keyword(s):  
Global Warming ◽  
New Zealand ◽  
Climate Variability ◽  
East Coast ◽  
Climate Model ◽  
Potential Evapotranspiration ◽  
Southern Oscillation ◽  
Annual Rainfall ◽  
Climate Forecasting ◽  
Dryland Farming

New Zealand average surface temperatures have increased by 0.7 °C since 1871. In the last quarter of the 20th century, more prevalent west to southwest flows occurred, accompanying a higher incidence of El Niño events. This resulted in annual rainfall decreasing in eastern areas of the North Island. As well as the global warming signal, interannual to decadal climate variability is a strong feature of east coast dryland climates. The El Niño-Southern Oscillation, (ENSO), through El Niño/ and La Niña episodes, drives climate variability seasonally. The recently described Interdecadal Pacific Oscillation (IPO) shifts climate every one to three decades and changes precipitation averages in these areas. These features of the climate system leave east coast dryland farming open to considerable climate variability. Records of potential soil moisture deficit (PSMD) around Napier and Ashburton show that significant PSMD developed in these regions by 1 December, in 50 to 85% of years with severe deficits in 20 to 55% of years. These deficits build as summer progresses. El Niño events intensify, whilst La Niña episodes normally ameliorate these conditions on seasonal time scales. The IPO climate shifts significantly change the dryness of the soil of these areas, with the transition from negative to positive phases increasing PSMD by 35 to 50 mm. Climate change over the next few decades will be driven by the underlying trend of global warming. For New Zealand, this will be a warming of about 0.2 °C per decade. The latest scenarios and climate model results indicate that westerly circulation is likely to strengthen over New Zealand, with a drying of east coast climate in the order of 10% by 2080. These will cause an increase in PSMD in the order of 20 to 30%. ENSO and IPO variability will be a continuing feature of New Zealand climate in coming decades. East coast dryland farms experience substantial climate variability. As climate warming continues in the decades of the 21st century, these areas will become increasingly stressed as potential evapotranspiration (PET) rates increase, particularly when the IPO next changes phase and during El Niño events. Climate forecasting is an exciting new technology that will give farmers early warning and increase preparedness for dry seasons ahead, allowing them to make key strategic decisions. A mixture of new and traditional technologies will also assist, such as intercropping and use of seasonal climate forecasting. Despite this, dryland farming systems are likely to become increasingly limited owing to low rainfall and high potential evapotranspiration rates.

Multi-decadal climate variability, New South Wales, Australia

2004 ◽  
Vol 49 (7) ◽  
pp. 133-140 ◽  
Author(s):  
S.W. Franks
Keyword(s):  
Climate Variability ◽  
General Circulation ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
New South ◽  
New South Wales ◽  
General Circulation Models ◽  
Drought Risk ◽  
Decadal Climate Variability ◽  
South Wales

Traditional hydrological risk estimation has treated the observations of hydro-climatological extremes as being independent and identically distributed, implying a static climate risk. However, recent research has highlighted the persistence of multi-decadal epochs of distinct climate states across New South Wales (NSW), Australia. Climatological studies have also revealed multi-decadal variability in the magnitude and frequency of El Niño/Southern Oscillation (ENSO) impacts. In this paper, examples of multi-decadal variability are presented with regard to flood and drought risk. The causal mechanisms for the observed variability are then explored. Finally, it is argued that the insights into climate variability provide (a) useful lead time for forecasting seasonal hydrological risk, (b) a strong rationale for a new framework for hydrological design and (c) a strong example of natural climate variability for use in the testing of General Circulation Models of climate change.

Effects of Temperature and Precipitation Variability on Snowpack Trends in the Western United States*

2005 ◽  
Vol 18 (21) ◽  
pp. 4545-4561 ◽  
Author(s):  
Alan F. Hamlet ◽  
Philip W. Mote ◽  
Martyn P. Clark ◽  
Dennis P. Lettenmaier
Keyword(s):  
United States ◽  
Climate Variability ◽  
Snow Water Equivalent ◽  
Decadal Variability ◽  
Precipitation Variability ◽  
Hydrologic Model ◽  
Western United States ◽  
Infiltration Capacity ◽  
Temperature And Precipitation ◽  
Decadal Scale

Abstract Recent studies have shown substantial declines in snow water equivalent (SWE) over much of the western United States in the last half century, as well as trends toward earlier spring snowmelt and peak spring streamflows. These trends are influenced both by interannual and decadal-scale climate variability, and also by temperature trends at longer time scales that are generally consistent with observations of global warming over the twentieth century. In this study, the linear trends in 1 April SWE over the western United States are examined, as simulated by the Variable Infiltration Capacity hydrologic model implemented at 1/8° latitude–longitude spatial resolution, and driven by a carefully quality controlled gridded daily precipitation and temperature dataset for the period 1915–2003. The long simulations of snowpack are used as surrogates for observations and are the basis for an analysis of regional trends in snowpack over the western United States and southern British Columbia, Canada. By isolating the trends due to temperature and precipitation in separate simulations, the influence of temperature and precipitation variability on the overall trends in SWE is evaluated. Downward trends in 1 April SWE over the western United States from 1916 to 2003 and 1947 to 2003, and for a time series constructed using two warm Pacific decadal oscillation (PDO) epochs concatenated together, are shown to be primarily due to widespread warming. These temperature-related trends are not well explained by decadal climate variability associated with the PDO. Trends in SWE associated with precipitation trends, however, are very different in different time periods and are apparently largely controlled by decadal variability rather than longer-term trends in climate.

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