Increase In Precipitable Water Research Articles

Future Changes of Extreme Precipitation and Related Atmospheric Conditions in East Asia under Global Warming Projected in Large Ensemble Climate Prediction Data

Abstract Extreme precipitation is expected to pose a more severe threat to human society in the future. This work assessed the historical performance and future changes of extreme precipitation and related atmospheric conditions in a large ensemble climate prediction dataset, the database for Policy Decision-making for Future climate change (d4PDF), over East Asia. Compared with the TRMM and ERA5 datasets, the historical climate in d4PDF represents favorably the precipitation characteristics and the atmospheric conditions, although some differences are notable in the moisture, vertical motion, and cloud water fields. The future climate projection indicates that both the frequency and intensity of heavy precipitation events over East Asia increase compared with those in the present climate. However, when comparing the atmospheric conditions in the historical and future climates for the same precipitation intensity range, the future climate indicates smaller relatively humidity, weaker ascent, less cloud water content, and smaller temperature lapse rate, which negatively affect generating extreme precipitation events. The comparison of the precipitation intensity at the same amount of precipitable water between the historical and future climates indicates that extreme precipitation is weaker in the future, because of the more stabilized troposphere in the future. The general increase in extreme precipitation under future climate is primarily due to the enhanced increase in precipitable water in the higher temperature ranges, which counteracts the negative conditions of the stabilized troposphere.

Projected changes in extreme daily precipitation linked to changes in precipitable water and vertical velocity in CMIP6 models

Understanding the drivers of precipitation and their changes in a non-stationary climate is crucial for effective climate adaptation and water resource management, as it helps us anticipate and respond to shifting precipitation patterns and their impacts. Here, analysing simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) we show that the conditional probability of extreme daily precipitation given joint extremes of two drivers (precipitable water and vertical velocity) will be stable in a 3 °C warmer future. Consistent with earlier work, we find that the near-global increase in precipitable water (thermodynamic influence) is the baseline for changes in extreme precipitation, which are modulated by changes in vertical velocity (dynamic influence). Thus, in regions where vertical velocity increases, the effect of the two drivers is additive and their changes contribute to an increase in extreme precipitation. The changes of the two drivers are opposite where vertical velocity decreases, resulting in only small increases in extreme precipitation or even a decrease. Furthermore, we reveal that there are moderate changes in the dependence between the drivers, which are larger over the ocean than over landmasses, but they contribute only little to the overall changes in extreme precipitation. We conclude that the use of two very simple drivers that are readily available from climate models can be of great utility for evaluating precipitation extremes in models and understanding their projected changes.

Cenozoic stable isotope constraints on the Eurasian continental interior hydroclimate response to high CO2

The response of the terrestrial hydrologic cycle to higher atmospheric CO2 remains poorly constrained, largely due to difficulty in predicting how land surface processes may modify individual hydroclimate parameters such as precipitation (P), evapotranspiration (ET), and runoff (q). To interrogate how the terrestrial hydrologic cycle may change with warming and higher CO2, we utilize the Cenozoic geologic record of terrestrial stable oxygen isotopes (δ18O) as recorded in authigenic minerals, which reflect precipitation δ18O (δ18Op). Values of δ18Op are sensitive to changes in terrestrial hydroclimate, including to the ratio of P/ET and to precipitable water. In short, decreasing P/ET or higher precipitable water produces shallower δ18Op gradients inland, whereas increasing P/ET or lower precipitable water results in steeper δ18Op continental gradients. We compile nearly 15,000 samples of authigenic carbonate and tooth enamel across Eurasia—the largest continental landmass—that span the Cenozoic Era to reconstruct the past spatial distribution and zonal (i.e. east-to-west) gradients of δ18Op. We find that, in epochs with higher CO2, zonal δ18Op gradients increase, suggesting an increase in P/ET across Eurasia despite the expected increase in precipitable water in greenhouse climates. We compare these results to δ18Op gradients simulated by an isotope-enabled climate model (iCESM) forced with both pre-industrial (PI) and 4xPI CO2 mixing ratios. Simulated δ18Op gradients shallow as CO2 rises, in contrast to the reconstructed δ18Op gradients. This data-model mismatch suggests either that Earth system feedbacks not represented in our iCESM simulations, such as changes in Northern Hemisphere ice extent and vegetation, may have fundamentally changed Northern Hemisphere hydroclimate or that land-surface processes under high CO2 climates may be mis-represented in iCESM.

Future changes in extreme precipitation over the San Francisco Bay Area: Dependence on atmospheric river and extratropical cyclone events

Extreme precipitation poses a major challenge for local governments, including the City and County of San Francisco, California, as flooding can damage and destroy infrastructure and property. As the climate continues to warm, reliable future precipitation projections are needed to provide the best possible information to decision makers. However, future changes in the magnitude of extreme precipitation are uncertain, as current state-of-the-art global climate models are typically run at relatively coarse horizontal resolutions that require the use of convective parameterization and have difficulty simulating observed extreme rainfall rates. Here, we performed ensembles of convection-permitting regional climate model simulations to investigate how five historically impactful extreme precipitation events over the San Francisco Bay Area could change if similar events occurred in future climates. We found that changes in storm-total precipitation depend strongly on storm type. Precipitation associated with an atmospheric river (AR) accompanied by an extratropical cyclone (ETC) is projected to increase at a rate exceeding (by up to 1.5 times) the theoretical Clausius Clapeyron scaling of 6–7% per °C warming. On the other hand, future precipitation changes are weak or negative for events characterized by an AR only, despite increases in precipitable water and integrated vapor transport that are similar to those of the co-occurring AR and ETC events. The differences in the sign of future precipitation change between AR-only events and co-occurring AR and ETC events is instead linked with changes in mid-tropospheric vertical velocity. Given that the majority of observed ARs are associated with an ETC, this research has important implications for future precipitation impacts over the Bay Area, as it indicates that storm-total precipitation associated with the most common type of storm event may increase by up to 26–37% in 2100 relative to historical.

Explaining the Spatial Pattern of U.S. Extreme Daily Precipitation Change

AbstractObserved United States trends in the annual maximum 1-day precipitation (RX1day) over the last century consist of 15%–25% increases over the eastern United States (East) and 10% decreases over the far western United States (West). This heterogeneous trend pattern departs from comparatively uniform observed increases in precipitable water over the contiguous United States. Here we use an event attribution framework involving parallel sets of global atmospheric model experiments with and without climate change drivers to explain this spatially diverse pattern of extreme daily precipitation trends. We find that RX1day events in our model ensembles respond to observed historical climate change forcing differently across the United States with 5%–10% intensity increases over the East but no appreciable change over the West. This spatially diverse forced signal is broadly similar among three models used, and is positively correlated with the observed trend pattern. Our analysis of model and observations indicates the lack of appreciable RX1day signals over the West is likely due to dynamical effects of climate change forcing—via a wintertime atmospheric circulation anomaly that suppresses vertical motion over the West—largely cancelling thermodynamic effects of increased water vapor availability. The large magnitude of eastern U.S. RX1day increases is unlikely a symptom of a regional heightened sensitivity to climate change forcing. Instead, our ensemble simulations reveal considerable variability in RX1day trend magnitudes arising from internal atmospheric processes alone, and we argue that the remarkable observed increases over the East has most likely resulted from a superposition of strong internal variability with a moderate climate change signal. Implications for future changes in U.S. extreme daily precipitation are discussed.

Response of the Asian Summer Monsoon Precipitation to Global Warming in a High-Resolution Global Nonhydrostatic Model

AbstractThis study examined the responses of Asian monsoon precipitation to global warming on the regional scale, focusing on monsoon westerlies and monsoon trough. This is because the Asian monsoon precipitation is closely associated with tropical disturbances. To reproduce convective precipitation and tropical disturbances, this study used outputs of a high-resolution climate simulation. Two sets of approximately 30-yr simulations under present-day (control) and warmer climate conditions (global warming) were conducted by the 14-km Nonhydrostatic Icosahedral Atmospheric Model (NICAM) with explicitly calculated convection. For understanding the spatial pattern of future precipitation changes, a further set of a 5-yr simulation [sea surface temperature (SST) + 4 K] was also conducted. Overall, the Asian summer monsoon was well simulated by the model. Precipitation increased as a result of global warming along the monsoon trough, which was zonally elongated across northern India, the Indochina Peninsula, and the western North Pacific Ocean. This increased precipitation was likely due to an increase in precipitable water. The spatial pattern of the increased precipitation was associated with enhanced cyclonic circulations over a large area along the monsoon trough, although it was difficult to determine whether the large-scale monsoon westerly was enhanced. This enhancement can be explained by future changes in tropical disturbance activity, including weak tropical cyclones. However, over part of South Asia, circulation changes may not contribute to the increased precipitation, suggesting regional characteristics. The regional increase in precipitation along the monsoon trough was mostly explained by the uniform increase in SST, whereas SST spatial patterns are important over some regions.

Spatiotemporal variability of alpine precipitable water over arid northwestern China

AbstractFor a better understanding of the precipitable water in the arid northwestern China (NWC), we surveyed the water vapour variability on both sides of the alpine range crests based on the Tropical Rainfall Measuring Mission monthly precipitation data (TRMM 3B43). There were 12 target zones and 23 subzones in six mountain systems representatively selected according to alpine hydrogeomorphology. They were used for comparative analyses in time and space. Comparisons between the two sides of the range crests revealed that there is more precipitable water on the south slopes of the Qilian, Altun, Kunlun, and Altai Mountains, on the north slope of the Tian Mountains, and on the east slope of Helan Mountains. High correlations were detected between precipitable water for both sides of the range crests in target zones, while low correlations were found among precipitable water separately averaged in the Kunlun, Tian, and Qilian Mountains including both sides of the range crests. The proportion of precipitable water during the rainy season gradually increased from west to east along the mountains. Temporally, precipitation presented synchronous increases or decreases on the two sides of the range crests in most of the target zones during the time period from 1998 to 2016, and an overall increase in alpine annual precipitable water was found in the area, except for the decrease in the Altun and western Tian Mountains. The summer decay dominated the decrease in these two target zones, while strengthened conveyance was observed in other seasons, especially in spring and autumn, which compensated for, and led to, total increases in precipitable water in most of the target zones. All of the above findings were indicative of differences in vapour transport from outside areas into diverse alpine systems in the arid NWC, which could be schematically evidenced by the spatial patterns of monthly and annual water vapour conveyance retrieved from the TRMM precipitation data.

Dry and moist dynamics shape regional patterns of extreme precipitation sensitivity

Responses of extreme precipitation to global warming are of great importance to society and ecosystems. Although observations and climate projections indicate a general intensification of extreme precipitation with warming on global scale, there are significant variations on the regional scale, mainly due to changes in the vertical motion associated with extreme precipitation. Here, we apply quasigeostrophic diagnostics on climate-model simulations to understand the changes in vertical motion, quantifying the roles of dry (large-scale adiabatic flow) and moist (small-scale convection) dynamics in shaping the regional patterns of extreme precipitation sensitivity (EPS). The dry component weakens in the subtropics but strengthens in the middle and high latitudes; the moist component accounts for the positive centers of EPS in the low latitudes and also contributes to the negative centers in the subtropics. A theoretical model depicts a nonlinear relationship between the diabatic heating feedback (α) and precipitable water, indicating high sensitivity of α (thus, EPS) over climatological moist regions. The model also captures the change of α due to competing effects of increases in precipitable water and dry static stability under global warming. Thus, the dry/moist decomposition provides a quantitive and intuitive explanation of the main regional features of EPS.

Future Changes in East Asian Summer Monsoon Circulation and Precipitation Under 1.5 to 5 °C of Warming

AbstractUnderstanding the link between future changes in East Asian summer monsoon (EASM) and global warming levels is of great importance for regional climate change adaptation and mitigation in East Asia. Here, we analyze the projected changes in EASM circulation and precipitation under different warming levels from 1.5 to 5 °C above the preindustrial global mean temperature, using large‐ensemble simulations conducted with Canadian Earth System Model version 2. We find that the model projects enhanced monsoon circulation and precipitation with global warming. The 850‐hPa meridional winds, precipitation, and 500‐hPa vertical ascending motion will be enhanced nonlinearly, while the total column precipitable water will increase quasi‐linearly. The increase in precipitable water in the wet EASM region is only slightly greater than global average but the increase in precipitation is much greater than global one, with enhanced 500‐hPa vertical ascending motion contrary to global mean. The increased low‐level land‐sea thermal contrast leads to the enhanced EASM meridional circulation and thus bring a large amount of moisture into Eastern China, providing favorable conditions for additional increase in precipitation. A simplified moisture budget analysis shows that the dynamic component related to strengthening monsoon circulation plays dominant role in the increase in EASM precipitation when the global temperature increases by more than approximately 2 °C, while the thermodynamic component caused by increased water vapor is important when the warming is smaller.

Modification of Near‐Surface Temperature Over East Asia Associated With Local‐Scale Paddy Irrigation

AbstractThis study used two regional climate model experiments to assess the impact of paddy irrigation in the Sichuan Basin, China, on the near‐surface temperature across East Asia: a control experiment (CTL run), which was used to calculate soil moisture using an unmodified land surface scheme and a sensitivity experiment (SEN run) that incorporated an increase in soil moisture over the basin at the beginning of the rice‐growing season. Although the near‐surface temperature in the Sichuan Basin was higher in the CTL run than in the observations, it improved in the SEN run because of a change in the Bowen ratio associated with the increase in soil moisture. In the SEN run, the modification of local‐scale land surface wetness in the basin causes the decrease in the near‐surface temperature over northeastern China and its increase over southern China relative to that in the CTL run because of a change in the cloud convection associated with precipitation, which, in turn, modifies the solar and net radiation at the surface and the partitioning into the sensible and latent heat fluxes. The greenhouse effect associated with an increase in precipitable water in the SEN run also influences near‐surface warming over southeastern China and the ocean north of southwestern Japan, where the impacts of radiation processes and surface heat fluxes on the near‐surface temperature are small. Consequently, these results suggest that local‐scale modifications to land surface wetness in the Sichuan Basin result in changes in the spatial distribution of near‐surface temperatures over a part of East Asia.

Impacts of Wintertime Extratropical Cyclones on Temperature and Precipitation Over Northeastern China During 1979–2016

AbstractThis study examines the synoptic impacts of wintertime extratropical cyclones on northeastern China. The 181 analyzed cyclones mainly originate from eastern Mongolia and dissipate over the North Pacific Ocean. Precursor negative geopotential height anomalies for these cyclones emerge over continental areas near the Barents and Kara Seas. Baroclinic instability and midlatitude westerly winds are the dominant factors driving the development and movement of these cyclones from their precursor signals. Owing to the southeastward migration of the cyclones, temperature over northeastern China first increases and then decreases, resulting in a significant increase in the frequency of extreme weather. These cyclones contribute about 70.6% of the extreme precipitation days over northeastern China. Relative moisture contributions from the East China Sea, the Sea of Japan, and East Asia are all anomalously large during cyclones associated with extreme precipitation days, with moisture from these regions entering northeastern China mainly through its southern and western boundaries. Temperature variations over northeastern China play a critical role in the accumulation of moisture for extreme precipitation and the timing of that precipitation. Moisture transport initially contributes to an increase in precipitable water due to warm temperature anomalies. The added precipitable water is then released as extreme precipitation when the atmosphere over northeastern China starts to cool.

The More Extreme Nature of North American Monsoon Precipitation in the Southwestern United States as Revealed by a Historical Climatology of Simulated Severe Weather Events

AbstractLong-term changes in North American monsoon (NAM) precipitation intensity in the southwestern United States are evaluated through the use of convective-permitting model simulations of objectively identified severe weather events during “historical past” (1950–70) and “present day” (1991–2010) periods. Severe weather events are the days on which the highest atmospheric instability and moisture occur within a long-term regional climate simulation. Simulations of severe weather event days are performed with convective-permitting (2.5 km) grid spacing, and these simulations are compared with available observed precipitation data to evaluate the model performance and to verify any statistically significant model-simulated trends in precipitation. Statistical evaluation of precipitation extremes is performed using a peaks-over-threshold approach with a generalized Pareto distribution. A statistically significant long-term increase in atmospheric moisture and instability is associated with an increase in extreme monsoon precipitation in observations and simulations of severe weather events, corresponding to similar behavior in station-based precipitation observations in the Southwest. Precipitation is becoming more intense within the context of the diurnal cycle of convection. The largest modeled increases in extreme-event precipitation occur in central and southwestern Arizona, where mesoscale convective systems account for a majority of monsoon precipitation and where relatively large modeled increases in precipitable water occur. Therefore, it is concluded that a more favorable thermodynamic environment in the southwestern United States is facilitating stronger organized monsoon convection during at least the last 20 years.

Synoptic and quantitative attributions of the extreme precipitation leading to the August 2016 Louisiana flood

AbstractThe catastrophic August 2016 flood in the U.S. state of Louisiana was a result of intense precipitation produced by a slow‐moving tropical low‐pressure system interacting with an eastward traveling baroclinic trough to the north. While tropical‐midlatitude interactions of this nature are rare, they are not unprecedented. Analyses presented point toward the tendency for more and perhaps stronger upper level troughs propagating out of the western U.S. in summer; these then have an increasing potential to cross paths with low‐pressure systems that form around the Gulf Coast. Combined with the projected increase in precipitable water, resulting precipitation magnitude would increase. Large‐ensemble modeling indicates that the prospect of future tropical‐midlatitude interactions is a scenario that Louisiana will face in the future, while regional simulations estimate that the climate warming since 1985 may have increased the event precipitation (11–14 August 2016) on the order of 20%, all of which allude to a conceivable forecast of nonhurricane‐related, warm season extreme precipitation in the Gulf Coast states.

Atmospheric Moisture Transport to the Arctic: Assessment of Reanalyses and Analysis of Transport Components

Abstract The atmospheric water cycle of the Arctic is evaluated via seven global reanalyses and in radiosonde observations covering the 1979–2013 period. In the regional moisture budget, evaporation and precipitation are the least consistent terms among different datasets. Despite the assimilation of radiosoundings, the reanalyses present a tendency to overestimate the moisture transport. Aside from this overestimation, the reanalyses exhibit a remarkable agreement with the radiosondes in terms of spatial and temporal patterns. The northern North Atlantic, subpolar North Pacific, and Labrador Sea stand out as the main gateways for moisture to the Arctic in all reanalyses. Because these regions correspond to the end of the storm tracks, the link between moisture transports and extratropical cyclones is further investigated by decomposing the moisture fluxes in the mean flow and transient eddy parts. In all reanalyses, the former term tends to cancel out when averaged over a latitude circle, leaving the latter to provide the bulk of the midlatitude moisture imports (89%–94% at 70°N). Although the Arctic warms faster than the rest of the world, the impact of these changes on its water cycle remains ambiguous. In most datasets, evaporation, precipitation, and precipitable water increase in line with what is expected from a warming signal. At the same time, the moisture transports have decreased in all the reanalyses but not in the radiosonde observations, though none of these trends is statistically significant. The fluxes do not scale with the Clausius–Clapeyron relation because the increasing humidity is not correlated with the meridional wind, particularly near the surface.

Precipitation recycling and soil-precipitation interaction across the arid and semi-arid regions of China

Dynamic recycling model (DRM) and reanalysis data were used to study the interaction between the land surface and atmosphere during the warm season from 1979 to 2010 across the arid and semi-arid regions of China. The nonlinear trends common to the key land–atmosphere interaction variables were extracted. For the whole study region, the precipitation recycling ratio showed an increasing trend, especially in the period before the 1990s. Simultaneously, increasing trends were also found in variables regionally related to precipitation, such as soil moisture, evaporation, precipitation efficiency, low-level cloud and precipitable water. However, the moisture transport due to westerly moisture flux showed a remarkable weakening throughout the whole study region. Based on significantly positive correlation between the precipitation efficiency and precipitation recycling ratio under relatively low moisture advection, it was concluded that the precipitation recycling process should not been ignored, for both direct and indirect precipitation processes, in the study region. The spatial patterns of nonlinear trends in land–atmosphere interaction variables indicated reverse tendencies in two sub-regions divided by the meridional boundary at approximately 110°E. For the western sub-region, although decreasing westerly moisture flow was found, the strengthening southerly moisture flux mainly resulted in an increase of precipitable water. Positive relationships among precipitable water, low cloud, precipitation, soil moisture, evaporation and the precipitation recycling ratio were also found. The soil becoming wetter and the precipitation recycling process becoming enhanced suggested the existence of positive land–atmosphere interaction in the western sub-region. However, the opposite tendencies were found in the eastern sub-region, where a weakening of advected moisture convergence was caused by decreases in both westerly and southerly moisture transport. Furthermore, less evaporation and warming temperatures suggested the climate in the eastern sub-region shifted towards relatively warmer and drier conditions throughout the course of the study period.

Moistening Processes before the Convective Initiation of Madden–Julian Oscillation Events during the CINDY2011/DYNAMO Period

Abstract Convective initiation processes in the Madden–Julian oscillation (MJO) events that occurred during the Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (CINDY2011)/Dynamics of the Madden–Julian Oscillation (DYNAMO) intensive observation period (IOP) were investigated. Two episodes that were initiated in mid-October (MJO1) and mid-November (MJO2) 2011 were analyzed using European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis and satellite data. Moisture budgets in the equatorial Indian Ocean (IO) domain (10°S–10°N, 60°–90°E) were analyzed in detail by separating each variable into basic-state (>80 day), intraseasonal (20–80 day), and high-frequency (<20 day) variations. The quality of the ECMWF reanalysis was also evaluated against the sounding data collected during the field campaign. In both MJO events, the increase in precipitable water started 8–9 days prior to the convective initiation. Moisture advection decomposition revealed that advection of basic moisture by intraseasonal easterly anomalies and of intraseasonal moisture anomalies by the basic zonal wind were pronounced in these two events. The nonlinear high-frequency terms in the meridional moisture advection were the same order of magnitude as the primary term in the middle troposphere, implying systematic upscale transport of moisture. As a possible mechanism of the acceleration of easterly anomalies, amplification of off-equatorial Rossby wave trains that intruded into the equatorial zone was detected during the preconditioning periods in both MJO events.

Downscaling of Climate Change in the Hawaii Region Using CMIP5 Results: On the Choice of the Forcing Fields*

AbstractThe Weather Research and Forecasting (WRF) model has been configured as a regional climate model for the Hawaii region (HRCM) to assess the uncertainties associated with the pseudo–global warming (PGW) downscaling method using different warming increments from phase 5 of the Coupled Model Intercomparison Project (CMIP5) model experiments. Results from 15-km downscaling experiments using warming increments from 10 individual CMIP5 models for the two warming scenarios representative concentration pathway 4.5 (RCP4.5) and 8.5 (RCP8.5) are compared with experiments using multimodel mean warming increments. The results show that changes in 2-m temperatures, 10-m wind speed, rainfall, water vapor path, and trade wind inversion vary significantly among the individual model experiments. This translates into large uncertainties when picking one particular CMIP5 model to provide the warming increments for dynamical downscaling in the Hawaii region. The simulations also show that, despite the large interexperiment spread, a single downscaling experiment using multimodel mean warming increments gives very similar results to the ensemble mean of downscaling experiments using warming increments obtained from 10 individual CMIP5 models. Robust changes of the projected climate by the end of the twenty-first century in the Hawaii region shown by most downscaling experiments include increasing 2-m temperatures with stronger warming at higher elevations, a large increase in precipitable water, and an increase in the number of days with a trade wind inversion (TWI). Furthermore, most experiments agree on a reduction in TWI height and an increase in the TWI strength. Uncertainties in the projected changes in rainfall and 10-m wind speed are large and there is little consensus among the individual downscaling experiments.

Convective‐scale responses of a large‐domain, modelled tropical environment to surface warming

AbstractThis article explores the response of convective‐scale atmospheric characteristics to surface temperature through the lens of large‐domain, cloud‐system‐resolving model experiments run at radiative convective equilibrium. We note several features reminiscent of the response to surface warming in atmospheric general circulation models. These include an increase in the rain rate that is smaller than the modelled increase in precipitable water, a systematic decrease in sensible heating and an increase in clear‐sky cooling. However, in contrast to climate models, we note that tropospheric relative humidity increases and column‐integrated water vapour increases at the rate anticipated from the Clausius–Clapeyron relationship, but only when compared with the troposphere mean temperature rather than surface temperature. Also shown are results elucidating the changes in the vertically integrated water budget and the distribution of high precipitation rates shifting toward higher rates. Moist static energy distributions are analyzed and, from these, clouds are implicated in effecting the final equilibrium state of the atmosphere. The results indicate that, while there are aspects of the tropical equilibrium that are represented realistically in current general circulation model climate‐change experiments, there are potentially influential local interactions that are sufficiently important as to alter the mean response of the tropical water and energy balance to changes in sea‐surface temperature. Convection is shown to dictate the equilibrium state across all scales, including those unresolved in climate models, rather than only responding to surface‐induced changes.

ENSO Impacts on Lomas Formation in South Coastal Peru: Implications for the Pliocene?

Lomas formations in southern Peru are related to moisture availability due to frequent incursions of fog in austral winter. Due to warming of coastal waters of southern Peru during El Niño, lomas formations are enhanced via greater moisture availability for fog and drizzle. Our study evaluates the modern climatological record in austral winter to determine if there are differences in moisture availability between El Niño and La Niña for fog formation. Our results show anomalous northwesterly onshore flow, warmer than normal sea-surface temperatures, and an increase in precipitable water in El Niño, favoring lomas formations due to advection fog with higher moisture content. On the other hand, La Niña also favors frequent advection fog, with less moisture content due to strong onshore flow over relatively cool SSTs. Since lomas may represent fragments of a continuous vegetation belt that existed during the Pliocene, a permanent El Niño favoring vigorous vegetation production along the south Peruvian coast due to incursions of fog with high precipitable water may have occurred in this period. However, the possibility of normal El Niño variability superimposed on a warmer climatology producing fog with higher moisture content in both El Niño and La Niña conditions cannot be discounted.

Thermodynamic Causes for Future Trends in Heavy Precipitation over Europe Based on an Ensemble of Regional Climate Model Simulations

An extreme-value analysis of projected changes in heavy precipitation is carried out for an ensemble of eight high-resolution regional climate model simulations over the European domain. The consideration of several regional climate models that are forced by different global models allows for an assessment of the robustness of the results in terms of intersimulation agreement. The extreme-value statistical method is based on a model that includes time-dependent parameters. Summer and winter are examined separately. This allows for identifying and sharpening the understanding of physical processes inducing the changes in precipitation characteristics. Thermodynamic aspects of changes in heavy precipitation are discussed. Variables that are related to the process of precipitation formation, such as precipitable water and cloud liquid water, are examined. In this context, the scaling of changes in heavy precipitation and other thermodynamic quantities with changes in temperature is explored. The validity of a Clausius–Clapeyron scaling of heavy precipitation is assessed on regional scales. Significant regional and seasonal differences in trends of heavy precipitation and only a limited validity of the Clausius–Clapeyron scaling are found. In winter, enhanced moisture transport and storm-track intensity lead to an increase in heavy precipitation, especially over the northern parts of the European continent. In summer, the increase of precipitable water is less than that required to maintain the same probability for saturation over southern Europe, which results in negative trends of heavy precipitation in these regions.