Freshwater transport from warm to cold ocean regions amplifying faster than all model estimates

Abstract Warming-induced global water cycle changes pose a significant challenge to global ecosystems and human society. The magnitude of historical water cycle change is uncertain due to a dearth of direct rainfall and evaporation observations, particularly over the ocean where 80% of global evaporation occurs. Air-sea fluxes of freshwater and river run-off imprint on ocean salinity at different temperatures, such that warmer regions tend to be saltier and cooler regions tend to be fresher. In this work, we track observed salinity trends in the warm, salty fraction of the ocean from 1970 to 2014, and infer the global poleward transport of freshwater over this period. Since 1970, 46 - 77 x10^12 m^3 of freshwater has been transported poleward from the warmest fraction of the ocean. No model in the current generation of climate models (the 6th Climate Model Intercomparison Project; CMIP6) replicates this transport, with the closest model underestimating transport by 2 - 4 times. We trace the climate model biases to a weaker than expected surface freshwater flux intensification, just 0 - 4% in CMIP6 models compared to an estimated 3 - 7.5% in observations.

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Transferability Intercomparison: An Opportunity for New Insight on the Global Water Cycle and Energy Budget

Bulletin of the American Meteorological Society ◽

10.1175/bams-88-3-375 ◽

2007 ◽

Vol 88 (3) ◽

pp. 375-384 ◽

Cited By ~ 39

Author(s):

E. S. Takle ◽

J. Roads ◽

B. Rockel ◽

W. J. Gutowski ◽

R. W. Arritt ◽

...

Keyword(s):

Energy Budget ◽

Climate Models ◽

Climate Model ◽

Water Cycle ◽

Regional Climate ◽

Climate Conditions ◽

Continental Scale ◽

Global Water Cycle ◽

Wide Range ◽

Global Water

A new approach, called transferability intercomparisons, is described for advancing both understanding and modeling of the global water cycle and energy budget. Under this approach, individual regional climate models perform simulations with all modeling parameters and parameterizations held constant over a specific period on several prescribed domains representing different climatic regions. The transferability framework goes beyond previous regional climate model intercomparisons to provide a global method for testing and improving model parameterizations by constraining the simulations within analyzed boundaries for several domains. Transferability intercomparisons expose the limits of our current regional modeling capacity by examining model accuracy on a wide range of climate conditions and realizations. Intercomparison of these individual model experiments provides a means for evaluating strengths and weaknesses of models outside their “home domains” (domain of development and testing). Reference sites that are conducting coordinated measurements under the continental-scale experiments under the Global Energy and Water Cycle Experiment (GEWEX) Hydrometeorology Panel provide data for evaluation of model abilities to simulate specific features of the water and energy cycles. A systematic intercomparison across models and domains more clearly exposes collective biases in the modeling process. By isolating particular regions and processes, regional model transferability intercomparisons can more effectively explore the spatial and temporal heterogeneity of predictability. A general improvement of model ability to simulate diverse climates will provide more confidence that models used for future climate scenarios might be able to simulate conditions on a particular domain that are beyond the range of previously observed climates.

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Historical changes in fresh water transport from sub-tropical to sub-polar oceans

10.5194/egusphere-egu21-9630 ◽

2021 ◽

Author(s):

Taimoor Sohail ◽

Jan Zika ◽

Damien Irving ◽

John Church

Keyword(s):

Fresh Water ◽

Climate Model ◽

Water Cycle ◽

Tropical Ocean ◽

Freshwater Transport ◽

Run Off ◽

Polar Oceans ◽

S Curve ◽

Polar Ocean ◽

Different Response

<p>Warming-induced global water cycle changes pose a significant threat to biodiversity and humanity. &#160;The atmosphere transports freshwater from the sub-tropical ocean to the tropics and poles in two distinct branches.&#160;The resulting air-sea fluxes of fresh water and river run-off imprint on ocean salinity (S) at different temperatures (T), creating a characteristic `T-S curve' of mean salinity as a function of temperature.&#160;Using a novel tracer-percentile framework, we quantify changes in the observed T-S curve from 1970 to 2014. &#160;The warming ocean has been characterised by freshening tropical and sub-polar oceans and salinifying sub-tropical oceans. Over the 44 year period investigated, a net poleward freshwater transport out of the sub-tropical ocean is quantified, implying an amplification of the net poleward atmospheric freshwater transport.&#160;Historical reconstructions from the 6th Climate Model Intercomparison Project (CMIP6) exhibit a different response, underestimating the peak salinification of the ocean by a factor of 4, and showing a weak freshwater transport <em>into</em> the sub-polar ocean.&#160;Results indicate this discrepancy between the observations and models may be attributed to consistently biased representations of evaporation and precipitation patterns, which lead to the the weaker amplification seen in CMIP6 models.</p>

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Evaluating the Uncertainty Induced by the Virtual Salt Flux Assumption in Climate Simulations and Future Projections

Journal of Climate ◽

10.1175/2009jcli3084.1 ◽

2010 ◽

Vol 23 (1) ◽

pp. 80-96 ◽

Cited By ~ 28

Author(s):

Jianjun Yin ◽

Ronald J. Stouffer ◽

Michael J. Spelman ◽

Stephen M. Griffies

Keyword(s):

Climate Models ◽

Climate Model ◽

Ocean Model ◽

Salt Flux ◽

Freshwater Flux ◽

Unexpected Result ◽

Geophysical Fluid Dynamics Laboratory ◽

External Forcing ◽

Future Evolution ◽

Near Term

Abstract The unphysical virtual salt flux (VSF) formulation widely used in the ocean component of climate models has the potential to cause systematic and significant biases in modeling the climate system and projecting its future evolution. Here a freshwater flux (FWF) and a virtual salt flux version of the Geophysical Fluid Dynamics Laboratory Climate Model version 2.1 (GFDL CM2.1) are used to evaluate and quantify the uncertainties induced by the VSF formulation. Both unforced and forced runs with the two model versions are performed and compared in detail. It is found that the differences between the two versions are generally small or statistically insignificant in the unforced control runs and in the runs with a small external forcing. In response to a large external forcing, however, some biases in the VSF version become significant, especially the responses of regional salinity and global sea level. However, many fundamental aspects of the responses differ only quantitatively between the two versions. An unexpected result is the distinctly different ENSO responses. Under a strong external freshwater forcing, the great enhancement of the ENSO variability simulated by the FWF version does not occur in the VSF version and is caused by the overexpansion of the top model layer. In summary, the principle assumption behind using virtual salt flux is not seriously violated and the VSF model has the ability to simulate the current climate and project near-term climate evolution. For some special studies such as a large hosing experiment, however, both the VSF formulation and the use of the FWF in the geopotential coordinate ocean model could have some deficiencies and one should be cautious to avoid them.

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Multiscale Convective Organization and the YOTC Virtual Global Field Campaign

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-11-00233.1 ◽

2012 ◽

Vol 93 (8) ◽

pp. 1171-1187 ◽

Cited By ~ 88

Author(s):

Mitchell W. Moncrieff ◽

Duane E. Waliser ◽

Martin J. Miller ◽

Melvyn A. Shapiro ◽

Ghassem R. Asrar ◽

...

Keyword(s):

Time Scales ◽

Climate Models ◽

Water Cycle ◽

Building Blocks ◽

Tropical Convection ◽

Global Water Cycle ◽

Weather And Climate ◽

Impact Phenomena ◽

Meteorological Systems ◽

The Tropics

The Year of Tropical Convection (YOTC) project recognizes that major improvements are needed in how the tropics are represented in climate models. Tropical convection is organized into multiscale precipitation systems with an underlying chaotic order. These organized systems act as building blocks for meteorological events at the intersection of weather and climate (time scales up to seasonal). These events affect a large percentage of the world's population. Much of the uncertainty associated with weather and climate derives from incomplete understanding of how meteorological systems on the mesoscale (~1–100 km), synoptic scale (~1,000 km), and planetary scale (~10,000 km) interact with each other. This uncertainty complicates attempts to predict high-impact phenomena associated with the tropical atmosphere, such as tropical cyclones, the Madden–Julian oscillation, convectively coupled tropical waves, and the monsoons. These and other phenomena influence the extratropics by migrating out of the tropics and by the remote effects of planetary waves, including those generated by the MJO. The diurnal and seasonal cycles modulate all of the above. It will be impossible to accurately predict climate on regional scales or to comprehend the variability of the global water cycle in a warmer world without comprehensively addressing tropical convection and its interactions across space and time scales.

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A general framework for understanding the response of the water cycle to global warming over land and ocean

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-10-15263-2013 ◽

2013 ◽

Vol 10 (12) ◽

pp. 15263-15294 ◽

Cited By ~ 1

Author(s):

M. L. Roderick ◽

F. Sun ◽

W. H. Lim ◽

G. D. Farquhar

Keyword(s):

Energy Balance ◽

Surface Energy ◽

Surface Energy Balance ◽

Climate Models ◽

Climate Model ◽

Water Cycle ◽

Specific Humidity ◽

Water Vapour Content ◽

Long Wave ◽

Small Change

Abstract. Climate models project increases in globally averaged atmospheric specific humidity at the Clausius–Clapeyron (CC) value of around 7% K−1 whilst projections for precipitation (P) and evaporation (E) are somewhat muted at around 2% K−1. Such global projections are useful summaries but do not provide guidance at local (grid box) scales where impacts occur. To bridge that gap in spatial scale, previous research has shown that the following relation, Δ(P − E) &propto; P − E, holds for zonal averages in climate model projections. In this paper we first test whether that relation holds at grid box scales over ocean and over land. We find that the zonally averaged relation does not hold at grid box scales. We further find that the zonally averaged relation does not hold over land – it is specific to zonal averages over the ocean. As an alternative we tested whether the long-standing Budyko framework of catchment hydrology could be used to synthesise climate model projections over land. We find that climate model projections of Δ(P − E) out to the year 2100 conform closely to the Budyko framework. The analysis also revealed that climate models project little change in the net irradiance at the surface. To understand that result we examined projections of the key surface energy balance terms. In terms of global averages, we find the climate model projections are dominated by changes in only three terms of the surface energy balance; an increase in the incoming longwave irradiance while the responses are (mostly) restricted to the outgoing longwave irradiance with a small change in the evaporative flux. Because the change in outgoing longwave irradiance is a function of the change in surface temperature, we show that the precipitation sensitivity (i.e. 2% K−1) is an accurate summary of the partitioning of the greenhouse-induced surface forcing. With that we demonstrate that the precipitation sensitivity (2% K−1) is less than the CC value (7% K−1) because most of the greenhouse-induced surface forcing is partitioned into outgoing longwave irradiance (instead of evaporation). In essence, the models respond to elevated [CO2] by an increase in atmospheric water vapour content that increases the incoming long-wave irradiance at the surface. The surface response is dominated by a near equal increase in outgoing long-wave irradiance with only minor changes in other terms of the surface energy balance.

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Inter-model variability and biases of the global water cycle in CMIP3 coupled climate models

Environmental Research Letters ◽

10.1088/1748-9326/7/1/014006 ◽

2012 ◽

Vol 7 (1) ◽

pp. 014006 ◽

Cited By ~ 56

Author(s):

Beate G Liepert ◽

Michael Previdi

Keyword(s):

Climate Models ◽

Water Cycle ◽

Global Water Cycle ◽

Coupled Climate Models ◽

Model Variability ◽

Global Water

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An Atlas on Global Water Cycle : Based on the IPCC AR4 Climate Models

10.26530/oapen_458809 ◽

2009 ◽

Cited By ~ 4

Author(s):

Wee Ho Lim ◽

Michael L. Roderick

Keyword(s):

Climate Models ◽

Water Cycle ◽

Global Water Cycle ◽

Ipcc Ar4 ◽

Global Water

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How uncertain are climate model projections of water availability indicators across the Middle East?

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2010.0174 ◽

2010 ◽

Vol 368 (1931) ◽

pp. 5117-5135 ◽

Cited By ~ 31

Author(s):

Debbie Hemming ◽

Carlo Buontempo ◽

Eleanor Burke ◽

Mat Collins ◽

Neil Kaye

Keyword(s):

Middle East ◽

Water Availability ◽

Large Scale ◽

Drought Index ◽

Climate Models ◽

Climate Model ◽

Regional Climate ◽

General Distribution ◽

The North ◽

Run Off

The projection of robust regional climate changes over the next 50 years presents a considerable challenge for the current generation of climate models. Water cycle changes are particularly difficult to model in this area because major uncertainties exist in the representation of processes such as large-scale and convective rainfall and their feedback with surface conditions. We present climate model projections and uncertainties in water availability indicators (precipitation, run-off and drought index) for the 1961–1990 and 2021–2050 periods. Ensembles from two global climate models (GCMs) and one regional climate model (RCM) are used to examine different elements of uncertainty. Although all three ensembles capture the general distribution of observed annual precipitation across the Middle East, the RCM is consistently wetter than observations, especially over the mountainous areas. All future projections show decreasing precipitation (ensemble median between −5 and −25%) in coastal Turkey and parts of Lebanon, Syria and Israel and consistent run-off and drought index changes. The Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) GCM ensemble exhibits drying across the north of the region, whereas the Met Office Hadley Centre work Quantifying Uncertainties in Model ProjectionsAtmospheric (QUMP-A) GCM and RCM ensembles show slight drying in the north and significant wetting in the south. RCM projections also show greater sensitivity (both wetter and drier) and a wider uncertainty range than QUMP-A. The nature of these uncertainties suggests that both large-scale circulation patterns, which influence region-wide drying/wetting patterns, and regional-scale processes, which affect localized water availability, are important sources of uncertainty in these projections. To reduce large uncertainties in water availability projections, it is suggested that efforts would be well placed to focus on the understanding and modelling of both large-scale processes and their teleconnections with Middle East climate and localized processes involved in orographic precipitation.

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