Clausius Clapeyron Scaling Research Articles

The sensitivity of oceanic precipitation to sea surface temperature

Abstract. Our study forms the oceanic counterpart to numerous observational studies over land concerning the sensitivity of extreme precipitation to a change in air temperature. We explore the sensitivity of oceanic precipitation to changing sea surface temperature (SST) by exploiting two novel datasets at high resolution. First, we use the Ocean Rainfall And Ice-phase precipitation measurement Network (OceanRAIN) as an observational along-track shipboard dataset at 1 min resolution. Second, we exploit the most recent European Reanalysis version 5 (ERA5) at hourly resolution on a 31 km grid. Matched with each other, ERA5 vertical velocity allows the constraint of the OceanRAIN precipitation. Despite the inhomogeneous sampling along ship tracks, OceanRAIN agrees with ERA5 on the average latitudinal distribution of precipitation with fairly good seasonal sampling. However, the 99th percentile of OceanRAIN precipitation follows a super Clausius–Clapeyron scaling with a SST that exceeds 8.5 % K−1 while ERA5 precipitation scales with 4.5 % K−1. The sensitivity decreases towards lower precipitation percentiles, while OceanRAIN keeps an almost constant offset to ERA5 due to higher spatial resolution and temporal sampling. Unlike over land, we find no evidence for a decreasing precipitation event duration with increasing SST. ERA5 precipitation reaches a local minimum at about 26 ∘C that vanishes when constraining vertical velocity to strongly rising motion and excluding areas of weak correlation between precipitation and vertical velocity. This indicates that instead of moisture limitations as over land, circulation dynamics rather limit precipitation formation over the ocean. For the strongest rising motion, precipitation scaling converges to a constant value at all precipitation percentiles. Overall, high resolutions in observations and climate models are key to understanding and predicting the sensitivity of oceanic precipitation extremes to a change in SST.

Extratropical Transition of Hurricane Irene (2011) in a Changing Climate

Abstract Tropical cyclones (TCs) undergoing strong extratropical transition (ET) can produce adverse societal impacts in areas that rarely experience direct TC impacts. This, in conjunction with projected environmental changes in climatological ET regions, motivates the investigation of possible future changes in ET characteristics. We utilize a small ensemble of numerical model simulations to examine how warming affects the ET of Hurricane Irene. To assess the effects of climate change, we use the pseudo-global warming method in which thermodynamic changes, derived from an ensemble of 20 CMIP5 GCMs, are applied to analyzed initial and lateral boundary conditions of model simulations. We find increased storm intensity in the future simulations, both in reduced minimum sea level pressure and strengthened 10-m wind speed. Storm-centered composites indicate a strengthening of tropospheric potential vorticity near the center of Irene, consistent with enhanced latent heat release. The results also demonstrate that Irene’s precipitation in the warmed simulations increases at a rate that exceeds Clausius–Clapeyron scaling, owing to enhanced moisture flux convergence and an additional contribution from increased surface evaporation. The duration of the transition process increased in the warmed simulations due to a weakened midtropospheric trough and reduced vertical wind shear and meridional SST gradient with a slower northward translation. These results suggest that transitioning storms may exhibit an increased ability to extend TC-like conditions poleward, and motivates additional research.

Estimation of probable maximum precipitation at three provinces in Northeast Vietnam using historical data and future climate change scenarios

Study regionIn this study, three provinces in Northeast Vietnam including Bac Kan, Thai Nguyen, and Tuyen Quang are examined to determine the precipitation variation characteristics. Study focusThe average yearly temperature during the last two decades in Northeast Vietnam has increased by 0.72 °C when compared to the period 1962–1990. The Clausius Clapeyron (CC) relation indicates that a warmer atmosphere can result in higher moisture-holding capacity; hence, there is the possibility of increased extreme rainfall with respect to the rise in temperature. We evaluate the relationship between the average 24-hour temperature and rainfall extremes using the binning method. The estimation of the 24-hour probable maximum precipitation (PMP) is then implemented based on the moisture maximization and Hershfield statistical methods. New hydrological insights for the regionThe 99.9th percentiles of 24-hour precipitation are close to the super CC scaling up to peak points of 22.6–25.6 °C and decrease at higher temperatures. The Hershfield method produces 24-hour PMP results ranging from 232 mm to 895 mm. PMP outputs using the moisture maximization method based on the 100-year dew point are higher than those results generated from the statistical method except for Chiem Hoa station. Considering possible changes in future relative humidity under a warming climate from GCMs and RCM projections for two RCP scenarios, RCP 8.5 indicates the possible rise in probable extreme precipitation.

On the relationship of daily rainfall extremes and local mean temperature

Extreme rainfall is the most common cause of flooding and likelihood of such events is found to increase in recent studies. Large scale natural variability, human induced global warming and local atmospheric warming are important drivers of extreme rainfall. Understanding the association of these drivers with extreme rainfall and finding out the most significant physical driver will provide a foundation for risk assessment. This study presents a methodology to investigate the association of extreme rainfall events with physical drivers and to model their dependence structure. The methodology is demonstrated with application to Mahanadi River basin, India. Non-stationary extreme value models with multivariate ENSO index, global average temperature anomalies and local mean temperature anomalies as covariates are fitted at non-stationary rainfall grids of the basin. Statistical modelling confirms localized temperature to be the main driver influencing rainfall extremes. Clausius-Clapeyron (CC) scaling curves relating daily rainfall extremes and local mean temperature are developed at all the grids to obtain insights into warming induced changes in rainfall extremes. Significant deviations from the expected CC scaling behaviour are observed. Daily rainfall extremes show peaks at low (25 °C) to medium (30 °C) range of temperature, but exhibit a decrease at high temperatures for most of the grids. No change in this pattern of relationship is observed when the extreme rainfall is lagged by 1–9 days with temperature. This time lag is selected based on the concept of residence time of water in the atmosphere. The Copula theory is applied to capture the dependence of annual maximum daily rainfall and temperature extremes. Conditional probabilities of extreme rainfall are estimated by conditioning on local mean temperature values of strongest extreme rainfall events. Comparison of conditional probabilities suggests that stronger rainfall events are occurring at 30 °C. This study emphasizes the necessity of understanding the dependence structure of extreme rainfall and local mean temperature.

The Dependence of Daily and Hourly Precipitation Extremes on Temperature and Atmospheric Humidity over China

Precipitation extremes are expected to increase by 7% per degree of warming according to the Clausius–Clapeyron (CC) relation. However, this scaling behavior is inappropriate for high temperatures and short-duration precipitation extremes. Here, daily data from 702 stations during 1951–2014 and hourly data from 8 stations during 2000–15 are used to examine and explain this behavior in China. Both daily and hourly precipitation extremes exhibit an increase in temperature dependency at lower temperatures. The CC scaling transitions from positive to negative rates with temperatures greater than 25°C. Unlike the increase in daily data, which is similar to single-CC (1CC) scaling, the increase in hourly data resembles super-CC (2CC) scaling for temperatures greater than 13°C. Results show that the precipitation extremes are controlled by water vapor for a given temperature. At lower temperatures, precipitation extremes exhibit a positive linear dependence on daily actual vapor pressure whose value is almost equal to the saturated vapor pressure at a given temperature. At higher temperatures, actual vapor pressure has difficulty maintaining a consistent increasing rate because of the exponential increasing of the saturated vapor pressure. Higher temperatures result in larger vapor pressure deficits, which lead to sharp decreases in precipitation extremes. Similar scaling behaviors are obtained in 10 river basins over China, where the breaking point temperature increases from 17°C along the northwest inland area to 25°C along the southeast coast. These behaviors demonstrate that precipitation extremes are firmly linked to temperature when there is sufficient moisture at lower temperatures and limited by insufficient moisture at higher temperatures. Overall, precipitation extreme events require more attention in a warming climate.

Large increase in global storm runoff extremes driven by climate and anthropogenic changes

Weather extremes have widespread harmful impacts on ecosystems and human communities with more deaths and economic losses from flash floods than any other severe weather-related hazards. Flash floods attributed to storm runoff extremes are projected to become more frequent and damaging globally due to a warming climate and anthropogenic changes, but previous studies have not examined the response of these storm runoff extremes to naturally and anthropogenically driven changes in surface temperature and atmospheric moisture content. Here we show that storm runoff extremes increase in most regions at rates higher than suggested by Clausius-Clapeyron scaling, which are systematically close to or exceed those of precipitation extremes over most regions of the globe, accompanied by large spatial and decadal variability. These results suggest that current projected response of storm runoff extremes to climate and anthropogenic changes may be underestimated, posing large threats for ecosystem and community resilience under future warming conditions.

Projection of Landfalling–Tropical Cyclone Rainfall in the Eastern United States under Anthropogenic Warming

AbstractLandfalling–tropical cyclone (TC) rainfall is an important element of inland flood hazards in the eastern United States. The projection of landfalling-TC rainfall under anthropogenic warming provides insight into future flood risks. This study examines the frequency of landfalling TCs and associated rainfall using the GFDL Forecast-Oriented Low Ocean Resolution (FLOR) climate model through comparisons with observed TC track and rainfall over the July–November 1979–2005 seasons. The projection of landfalling-TC frequency and rainfall under the representative concentration pathway (RCP) 4.5 scenario for the late twenty-first century is explored, including an assessment of the impacts of extratropical transition (ET). In most regions of the southeastern United States, competition between increased storm rain rate and decreased storm frequency dominates the change of annual TC rainfall, and rainfall from ET and non-ET storms. In the northeastern United States, a prominent feature is the striking increase of ET-storm frequency but with tropical characteristics (i.e., prior to the ET phase), a key element of increased rainfall. The storm-centered rainfall composite analyses show the greatest increase at a radius of a few hundred kilometers from the storm centers. Over both ocean and land, the increase of rainfall within 500 km from the storm center exceeds the Clausius–Clapeyron scaling for TC-phase storms. Similar results are found in the front-left quadrant of ET-phase storms. Future work involving explorations of multiple models (e.g., higher atmospheric resolution version of the FLOR model) for TC-rainfall projection is expected to add more robustness to projection results.

Detection of continental-scale intensification of hourly rainfall extremes

Temperature scaling studies suggest that hourly rainfall magnitudes might increase beyond thermodynamic expectations with global warming1–3; that is, above the Clausius–Clapeyron (CC) rate of ~6.5% °C−1. However, there is limited evidence of such increases in long-term observations. Here, we calculate continental-average changes in the magnitude and frequency of extreme hourly and daily rainfall observations from Australia over the years 1990–2013 and 1966–1989. Observed changes are compared with the uncertainty from natural variability and expected changes from CC scaling as a result of global mean surface temperature change. We show that increases in daily rainfall extremes are consistent with CC scaling, but are within the range of natural variability. In contrast, changes in the magnitude of hourly rainfall extremes are close to or exceed double the expected CC scaling, and are above the range of natural variability, exceeding CC × 3 in the tropical region (north of 23° S). These continental-scale changes in extreme rainfall are not explained by changes in the El Nino–Southern Oscillation or changes in the seasonality of extremes. Our results indicate that CC scaling on temperature provides a severe underestimate of observed changes in hourly rainfall extremes in Australia, with implications for assessing the impacts of extreme rainfall. Theory predicts that hourly rainfall extremes may increase with anthropogenic warming. Observations from Australia suggest changes two to three times above the Clausius–Clapeyron rate, above that expected from natural variability.

Changing seasonality of moderate and extreme precipitation events in the Alps

Abstract. The intensity of precipitation events is expected to increase in the future. The rate of increase depends on the strength or rarity of the events; very strong and rare events tend to follow the Clausius–Clapeyron relation, whereas weaker events or precipitation averages increase at a smaller rate than expected from the Clausius–Clapeyron relation. An often overlooked aspect is seasonal occurrence of such events, which might change in the future. To address the impact of seasonality, we use a large ensemble of regional and global climate model simulations, comprising tens of thousands of model years of daily temperature and precipitation for the past, present, and future. In order to make the data comparable, they are quantile mapped to observation-based time series representative of the Aare catchment in Switzerland. Model simulations show no increase in annual maximum 1-day precipitation events (Rx1day) over the last 400 years and an increase of 10 %–20 % until the end of the century for a strong (RCP8.5) forcing scenario. This fits with a Clausius–Clapeyron scaling of temperature at the event day, which increases less than annual mean temperature. An important reason for this is a shift in seasonality. Rx1day events become less frequent in late summer and more frequent in early summer and early autumn, when it is cooler. The seasonality shift is shown to be related to summer drying. Models with decreasing annual mean or summer mean precipitation show this behaviour more strongly. The highest Rx1day per decade, in contrast, shows no change in seasonality in the future. This discrepancy implies that decadal-scale extremes are thermodynamically limited; conditions conducive to strong events still occur during the hottest time of the year on a decadal scale. In contrast, Rx1day events are also limited by other factors. Conducive conditions are not reached every summer in the present, and even less so in the future. Results suggest that changes in the seasonal cycle need to be accounted for when preparing for moderately extreme precipitation events and assessing their socio-economic impacts.

How intermittency affects the rate at which rainfall extremes respond to changes in temperature

Abstract. A detailed analysis of how intermittency (i.e., the alternation of dry and rainy periods) modulates the rate at which sub-daily rainfall extremes depend on temperature is presented. Results show that hourly extremes tend to be predominantly controlled by peak intensity, increasing at a rate of approximately 7 % per degree in agreement with the Clausius–Clapeyron equation. However, a rapid increase in intermittency upward of 20–25 °C is shown to produce local deviations from this theoretical scaling, resulting in lower scaling rates. On the other hand, rapidly decreasing intermittency with temperature between 10 and 20° can result in higher net scaling rates than expected, potentially exceeding Clausius–Clapeyron. In general, the importance of intermittency in controlling the scaling rates of precipitation with temperature grows as we progress from hourly to daily aggregation timescales and beyond. Thermodynamic effects still play an important role in controlling the maximum water-holding capacity of the atmosphere and therefore peak rainfall intensity, but the observational evidence shows that, beyond a few hours, storm totals become increasingly dominated by dynamical factors. The conclusion is that Clausius–Clapeyron scaling alone cannot be used to reliably predict the net effective changes in rainfall extremes with temperature beyond a few hours. A more general scaling model that takes into account simultaneous changes in intermittency and peak intensity with temperature is proposed to help better disentangle these two phenomena (e.g., peak intensity and intermittency). The new model is applied to a large number of high-resolution rain gauge time series in the United States, and results show that it greatly improves the representation of rainfall extremes with temperature, producing a much more consistent and reliable picture of extremes across scales than using Clausius–Clapeyron only.

Comparison of the Theoretical Clausius–Clapeyron Scaling and IDF_CC Tool for Updating Intensity-Duration-Frequency Curves under Changing Climatic Conditions in Canada

AbstractChanges in climatic conditions are expected to affect the hydrological cycle with intensification of extreme rainfall events caused by the disturbance in temperature and other atmospheric v...

Diagnosing Human-Induced Dynamic and Thermodynamic Drivers of Extreme Rainfall

Abstract Factors responsible for extreme monthly rainfall over Texas and Oklahoma during May 2015 are assessed. The event had a return period of at least 400 years, in contrast to the prior record, which was roughly a 100-yr event. The event challenges attribution science to disentangle factors because it occurred during a strong El Niño, a natural pattern of variability that affects the region’s springtime rains, and during the warmest global mean temperatures since 1880. Effects of each factor are diagnosed, as is the interplay between El Niño dynamics and human-induced climate change. Analysis of historical climate simulations reveals that El Niño was a necessary condition for monthly rains to occur having the severity of May 2015. The model results herein further reveal that a 2015 magnitude event, whether conditioned on El Niño or not, was made neither more intense nor more likely to be due to human-induced climate change over the past century. The intensity of extreme May rainfall over Texas and Oklahoma , analogous to the 2015 event, increases by roughly 5% by the latter half of the twenty-first century. No material changes occur in either El Niño–related teleconnections or in overall atmospheric dynamics during extreme May rainfall over the twenty-first century. The increased severity of Texas/Oklahoma May rainfall events in the future is principally due to thermodynamic driving, although much less than implied by simple Clausius–Clapeyron scaling arguments given a projected 23% increase in atmospheric precipitable water vapor. Other thermodynamic factors are identified that act in opposition to the increase in atmospheric water vapor, thereby reducing the effectiveness of overall thermodynamic driving of extreme May rainfall changes over Texas and Oklahoma.

Attribution of extreme rainfall from Hurricane Harvey, August 2017

During August 25–30, 2017, Hurricane Harvey stalled over Texas and caused extreme precipitation, particularly over Houston and the surrounding area on August 26–28. This resulted in extensive flooding with over 80 fatalities and large economic costs. It was an extremely rare event: the return period of the highest observed three-day precipitation amount, 1043.4 mm 3dy−1 at Baytown, is more than 9000 years (97.5% one-sided confidence interval) and return periods exceeded 1000 yr (750 mm 3dy−1) over a large area in the current climate. Observations since 1880 over the region show a clear positive trend in the intensity of extreme precipitation of between 12% and 22%, roughly two times the increase of the moisture holding capacity of the atmosphere expected for 1 °C warming according to the Clausius–Clapeyron (CC) relation. This would indicate that the moisture flux was increased by both the moisture content and stronger winds or updrafts driven by the heat of condensation of the moisture. We also analysed extreme rainfall in the Houston area in three ensembles of 25 km resolution models. The first also shows 2 × CC scaling, the second 1 × CC scaling and the third did not have a realistic representation of extreme rainfall on the Gulf Coast. Extrapolating these results to the 2017 event, we conclude that global warming made the precipitation about 15% (8%–19%) more intense, or equivalently made such an event three (1.5–5) times more likely. This analysis makes clear that extreme rainfall events along the Gulf Coast are on the rise. And while fortifying Houston to fully withstand the impact of an event as extreme as Hurricane Harvey may not be economically feasible, it is critical that information regarding the increasing risk of extreme rainfall events in general should be part of the discussion about future improvements to Houston’s flood protection system.

Changes in Temperature and Precipitation Extremes in Superparameterized CAM in Response to Warmer SSTs

Subdaily temperature and precipitation extremes in response to warmer SSTs are investigated on a global scale using the superparameterized (SP) Community Atmosphere Model (CAM), in which a cloud-resolving model is embedded in each CAM grid column to simulate convection explicitly. Two 10-yr simulations have been performed using present climatological sea surface temperature (SST) and perturbed SST climatology derived from the representative concentration pathway 8.5 (RCP8.5) scenario. Compared with the conventional CAM, SP-CAM simulates colder temperatures and more realistic intensity distribution of precipitation, especially for heavy precipitation. The temperature and precipitation extremes have been defined by the 99th percentile of the 3-hourly data. For temperature, the changes in the warm and cold extremes are generally consistent between CAM and SP-CAM, with larger changes in warm extremes at low latitudes and larger changes in cold extremes at mid-to-high latitudes. For precipitation, CAM predicts a uniform increase of frequency of precipitation extremes regardless of the rain rate, while SP-CAM predicts a monotonic increase of frequency with increasing rain rate and larger change of intensity for heavier precipitation. The changes in 3-hourly and daily temperature extremes are found to be similar; however, the 3-hourly precipitation extremes have a significantly larger change than daily extremes. The Clausius–Clapeyron scaling is found to be a relatively good predictor of zonally averaged changes in precipitation extremes over midlatitudes but not as good over the tropics and subtropics. The changes in precipitable water and large-scale vertical velocity are equally important to explain the changes in precipitation extremes.

Effects of sample size on estimation of rainfall extremes at high temperatures

Abstract. High precipitation quantiles tend to rise with temperature, following the so-called Clausius–Clapeyron (CC) scaling. It is often reported that the CC-scaling relation breaks down and even reverts for very high temperatures. In our study, we investigate this reversal using observational climate data from 142 stations across Germany. One of the suggested meteorological explanations for the breakdown is limited moisture supply. Here we argue that, instead, it could simply originate from undersampling. As rainfall frequency generally decreases with higher temperatures, rainfall intensities as dictated by CC scaling are less likely to be recorded than for moderate temperatures. Empirical quantiles are conventionally estimated from order statistics via various forms of plotting position formulas. They have in common that their largest representable return period is given by the sample size. In small samples, high quantiles are underestimated accordingly. The small-sample effect is weaker, or disappears completely, when using parametric quantile estimates from a generalized Pareto distribution (GPD) fitted with L moments. For those, we obtain quantiles of rainfall intensities that continue to rise with temperature.

Distributions of Tropical Precipitation Cluster Power and Their Changes under Global Warming. Part I: Observational Baseline and Comparison to a High-Resolution Atmospheric Model

Abstract The total amount of precipitation integrated across a precipitation feature (contiguous precipitating grid cells exceeding a minimum rain rate) is a useful measure of the aggregate size of the disturbance, expressed as the rate of water mass lost or latent heat released (i.e., the power of the disturbance). The probability distribution of cluster power is examined over the tropics using Tropical Rainfall Measuring Mission (TRMM) 3B42 satellite-retrieved rain rates and global climate model output. Observed distributions are scale-free from the smallest clusters up to a cutoff scale at high cluster power, after which the probability drops rapidly. After establishing an observational baseline, precipitation from the High Resolution Atmospheric Model (HiRAM) at two horizontal grid spacings (roughly 0.5° and 0.25°) is compared. When low rain rates are excluded by choosing a minimum rain-rate threshold in defining clusters, the model accurately reproduces observed cluster power statistics at both resolutions. Middle and end-of-century cluster power distributions are investigated in HiRAM in simulations with prescribed sea surface temperatures and greenhouse gas concentrations from a “business as usual” global warming scenario. The probability of high cluster power events increases strongly by end of century, exceeding a factor of 10 for the highest power events for which statistics can be computed. Clausius–Clapeyron scaling accounts for only a fraction of the increased probability of high cluster power events.

Clausius–Clapeyron Scaling of Peak CAPE in Continental Convective Storm Environments

AbstractA thermodynamic constraint on convective available potential energy (CAPE) in continental environments is established using an idealized one-dimensional model. This theoretical model simplifies the synoptic-scale preconditioning framework for continental severe convection by considering a dry adiabatic column that comes into contact with a moist land surface. A system of equations is derived to describe the evolution of the ensuing surface boundary layer. From these, the maximum value of transient CAPE in the column can be found for any particular combination of surface temperature and moisture. It is demonstrated that, for a given range of surface temperatures, the value of peak CAPE scales with the Clausius–Clapeyron relation.

The spatial extent of rainfall events and its relation to precipitation scaling

AbstractObservations show that subdaily precipitation extremes increase with dew point temperature at a rate exceeding the Clausius‐Clapeyron (CC) relation. The understanding of this so‐called super CC scaling is still incomplete, and observations of convective cell properties could provide important information. Here the size and intensity of rain cells are investigated by using a tracking of rainfall events in high‐resolution radar data. Higher intensities are accompanied by larger rainfall areas. However, whereas small rain cells mainly follow CC scaling, larger cells display super CC behavior. Even more, for dew point exceeding 15°C, the rain cell size has to increase in order to sustain super CC scaling and a remarked increase in rain cell area is found. Our results imply that the source area of moisture, the cloud size, and the degree of mesoscale organization play key roles in the context of a warming climate.

Changes in intensity of high temporal resolution precipitation extremes in Romania: implications for Clausius-Clapeyron scaling

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 72:239-249 (2017) - DOI: https://doi.org/10.3354/cr01469 Changes in intensity of high temporal resolution precipitation extremes in Romania: implications for Clausius-Clapeyron scaling Aristita Busuioc*, Madalina Baciu, Traian Breza, Alexandru Dumitrescu, Cerasela Stoica, Nina Baghina 1National Meteorological Administration, Sos. Bucuresti-Ploiesti 97, Sect.1, Bucharest 013686, Romania *Corresponding author: busuioc@meteoromania.ro ABSTRACT: We propose a new index for quantifying the maximum rain intensity (IMAX) within a rainfall event. The goal of this paper is 2-fold: first, to analyse the characteristics of variability (trends, change points) for maximum values of this index calculated for spring (April-May), summer (June-August) and autumn (September-October) in comparison with other 2 precipitation indices (daily maximum and total amount). Secondly, to investigate the scaling of the IMAX high percentiles with temperature and compare the results to hourly precipitation extremes. The analysis was carried out at 6 Romanian stations over the period 1966-2007, extended over 1902-2007 for one station. Our results revealed a statistically significant increase of IMAX over the 20th century (intensified over the second half), in contrast with no significant trends in the other 2 precipitation indices. On the other hand, an opposite phase between IMAX variability and its corresponding duration (e.g. shorter durations correspond to higher intensities) was noted. Regarding the scaling behaviour of the IMAX percentiles, there was a difference between summer and spring/autumn. In summer, the 90th and 99th percentiles showed a Clausius-Clapeyron (CC) scaling for temperatures between 14 and 26°C and then a decrease, while the 99.9th percentile showed a super-CC scaling for temperatures lower than 18°C and then a decrease. The spring and autumn 90th and 99th percentiles showed an approximate 2CC scaling for temperatures ranging from 8-20°C. The 99.9th percentile exhibited a scaling close to the 2CC relationship for a temperatures range of 12-18°C (spring) and then a decrease, while the autumn 99.9th percentile exhibited a dependence close to 2CC scaling for temperatures <18°C and then a scaling close to CC. Comparing these results with those referring to hourly and daily precipitation extremes, we conclude that the magnitude of the CC scaling in Romania is mainly dependent on the temporal scale of the extreme precipitation event, storm intensity and season. The proposed index (IMAX) is more sensitive to temperature increases than the hourly and daily extremes, and therefore it is more appropriate to quantifying the climate signal related to intense precipitation events in a warmer climate. KEY WORDS: Extreme precipitation index · Temperature · Scaling · Clausius-Clapeyron relation · Trends · Romania Full text in pdf format Supplementary material PreviousNextCite this article as: Busuioc A, Baciu M, Breza T, Dumitrescu A, Stoica C, Baghina N (2017) Changes in intensity of high temporal resolution precipitation extremes in Romania: implications for Clausius-Clapeyron scaling. Clim Res 72:239-249. https://doi.org/10.3354/cr01469 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 72, No. 3. Online publication date: July 12, 2017 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2017 Inter-Research.

Thermodynamic and dynamic responses of the hydrological cycle to solar dimming

Abstract. The fundamental role of the hydrological cycle in the global climate system motivates a thorough evaluation of its responses to climate change and mitigation. The Geoengineering Model Intercomparison Project (GeoMIP) is a coordinated international effort to assess the climate impacts of solar geoengineering, a proposal to counteract global warming with a reduction in incoming solar radiation. We assess the mechanisms underlying the rainfall response to a simplified simulation of such solar dimming (G1) in the suite of GeoMIP models and identify robust features. While solar geoengineering nearly restores preindustrial temperatures, the global hydrology is altered. Tropical precipitation changes dominate the response across the model suite, and these are driven primarily by shifts of the Hadley circulation cells. We report a damping of the seasonal migration of the Intertropical Convergence Zone (ITCZ) in G1, associated with preferential cooling of the summer hemisphere, and annual mean ITCZ shifts in some models that are correlated with the warming of one hemisphere relative to the other. Dynamical changes better explain the varying tropical rainfall anomalies between models than changes in relative humidity or the Clausius–Clapeyron scaling of precipitation minus evaporation (P − E), given that the relative humidity and temperature responses are robust across the suite. Strong reductions in relative humidity over vegetated land regions are likely related to the CO2 physiological response in plants. The uncertainty in the spatial distribution of tropical P − E changes highlights the need for cautious consideration and continued study before any implementation of solar geoengineering.