Atlantic influence on spring snowfall over the Alps in the past 150 years

Global warming is believed to be responsible for the reduction of snow amount and duration over the Alps. In fact, a rapid shortening of the snowy season has been measured and perceived by ecosystems and society in the past 30 years, despite the large year-to-year variability. This trend is projected to continue during the 21st century in the climate change scenarios with increasing greenhouse gas concentrations. Superimposed on the long-term trend, however, there is a low-frequency variability of snowfall associated with multi-decadal changes in the large-scale circulation. The amplitude of this natural low-frequency variation might be relatively large, determining rapid and substantial changes of snowfall, as recently observed. This is already known for winter snowfall over the Alps in connection with the recent tendency toward the positive phase of the North Atlantic Oscillation. In this study, we show that the low-frequency variability of Alpine spring snowfall in the past 150 years is affected by the Atlantic Multi-decadal Oscillation (AMO), which is a natural periodic fluctuation of Northern Atlantic sea surface temperature. Therefore, the recently observed spring snowfall reduction might be, at least in part, explained by the shift toward a positive AMO phase that happened in the 1990s

The Tropical Composite Cyclones: the integrated effect of hurricanes on the ocean-­‐atmosphere coupled system

In recent years increasing interest has been put on the role that intense Tropical Cyclones (hurricanes and typhoons) can play in modulating the climate system. Here we present a new approach to highlight strong Tropical Cyclones (TCs) fingerprint on the mean climate. Their composite effect on the surface winds is manifested through a wide cyclonic perturbation that affect a large portion of the Pacific and Atlantic tropical Oceans, as revealed by the ERA-Interim reanalysis dataset. The relationship between the resulting Tropical Composite Cyclones and the Northern hemispheric Ocean Heat Transport (OHT) is then investigated through a fully coupled atmosphere-ocean-seaice coupled global model, with high-resolution in the atmosphere (T159). The TCs activity increases significantly the poleward OHT out of the tropics, but also increases the heat transport into the deep tropics on the time scale of weeks. This effect, investigated looking at the 100 most intense Northern hemisphere TCs, is strongly correlated to the TC-induced momentum flux at the surface of the ocean: the winds associated to the TCs significantly weaken the Trade Winds in the 5-18oN latitude belt and reinforce them in the 18-30oN band. A comparison between two simulations with and without TCs effect on the wind stress over the ocean is also performed in order to better understand the role of TCs on the annually averaged OHT. The effect of the TCs induced OHT does not significantly change during the whole 1950-2069 (following 20C3M and A1B scenario) simulated period

TROPICAL CYCLONE ACTIVITY IN A WARMER CLIMATE AS SIMULATED BY A HIGH RESOLUTION COUPLED GENERAL CIRCULATION MODEL:CHANGES IN FREQUENCY AND AIR-SEA INTERACTION

This study investigates the possible changes that the greenhouse global warming might generate in the character- istics of the tropical cyclones (TCs). The analysis has been performed using climate scenario simulations carried out with a fully coupled high–resolution global general circulation model (INGV-SXG) with a T106 atmospheric resolution. The capability of the model to reproduce a reasonably realistic TC climatology has been assessed by comparing the model results from a simulation of the XX Century with observations. The model appears to be able to simulate tropical cyclone-like vortices with many features similar to the observed TCs. The simulated TC activity exhibits realistic geographical distribution, seasonal modulation and interannual variability, suggesting that the model is able to reproduce the major basic mechanisms that link the TC occurrence with the large scale circulation. The results from the climate scenarios reveal a substantial general reduction of the TC frequency when the atmospheric CO2 concentration is doubled and quadrupled. The reduction appears particularly evident for the tropical north west Pacific (NWP) and north Atlantic (ATL). In the NWP the weaker TC activity seems to be associated with a reduced amount of convective instabilities. In the ATL region the weaker TC activity seems to be due to both the increased stability of the atmosphere and a stronger vertical wind shear. Despite the generally reduced TC activity, there is evidence of increased rainfall associated with the simulated cyclones. Using the new fully coupled CMCC model (CMCC_MED), with a T159 atmospheric resolution, we found a significant modulation of the Ocean Heat Transport (OHT) induced by the TC activity. Thus the possible changes that greenhouse induced global warming during 21st century might generate in the characteristics of the TC-induced OHT have been analyzed

Tropical Cyclones -­‐ Ocean feedbacks: Effects on the Ocean Heat Transport as simulated by a High Resolution Coupled General Circulation Model

Tropical cyclones (TCs) activity and their relationship with the Northern hemispheric Ocean Heat Transport (OHT) is investigated with a focus on the Western North Pacific. The analysis has been performed using 20C3M (20th Century) and A1B (21st Century) IPCC scenario climate simulations obtained running a fully coupled atmosphere-ocean-seaice coupled global model, with high- resolution in the atmosphere (T159). The model is able to simulate tropical cyclone-like vortices with many features similar to the observed TCs. The simulated TC activity exhibits realistic structure, geographical distribution and interannual variability, indicating that the model is able to reproduce the major basic mechanisms that link the TC activity with the large scale circulation. The TC-induced ocean cooling is well represented and the TCs activity increases significantly the poleward OHT out of the tropics, but also increases the heat transport into the deep tropics on the time scale of weeks. This effect, investigated looking at the 100 most intense Northern hemisphere TCs, is strongly correlated to the TC-induced momentum flux at the surface of the ocean: the winds associated to the TCs significantly weaken the Trade Winds in the 5-18oN latitude belt and reinforce them in the 18-30oN band. A comparison between two simulation with and without TCs effect on the wind stress over the ocean will be also done in order to better understand the role of TCs on the annually averaged OHT. TCs frequency and intensity appear to be substantially stationary through the whole 1950-2069 period. Also the effect of the TCs induced OHT (TCiOHT) does not significantly change during the simulated period

Present and future climate simulation of Mediterranean cyclones with a high resolution AOGCMs

Preliminary results are presented of a study aiming at producing a climatology of Mediterranean cyclones making use of a global AOGCM coupled with an interactive high-resolution model of the Mediterranean Sea. Cyclones are analyzed with both the lagrangian and the eulerian approaches, applied to three different simulations: a control one (present climate conditions) and two IPCC scenarios (A1B and A2). Both the North Atlantic stormtrack and cyclone track and genesis density statistics from the control dataset are analyzed compared to ERA40 reanalysis. Cyclones are grouped according to their genesis location and the corresponding lysis regions are identified. Partic- ular attention is devoted to the effects of sea-surface fields (temperature gradients and heat fluxes). The wet season (October–March) is examined in relation to the decrease in the intensity of cyclogenesis events in the region and trends are investigated

Potential impact of climate change on length of ignition danger season in Mediterranean shrubland of North Sardinia

The main aim of this work is to identify useful tools to forecast impacts of expected climate change on live fuel moisture content (Live FMC) in Mediterranean shrublands

Annual green water resources and vegetation resilience indicators: Definitions, mutual relationships, and future climate projections

Satellites offer a privileged view on terrestrial ecosystems and a unique possibility to evaluate their status, their resilience and the reliability of the services they provide. In this study, we introduce two indicators for estimating the resilience of terrestrial ecosystems from the local to the global levels. We use the Normalized Differential Vegetation Index (NDVI) time series to estimate annual vegetation primary production resilience. We use annual precipitation time series to estimate annual green water resource resilience. Resilience estimation is achieved through the annual production resilience indicator, originally developed in agricultural science, which is formally derived from the original ecological definition of resilience i.e., the largest stress that the system can absorb without losing its function. Interestingly, we find coherent relationships between annual green water resource resilience and vegetation primary production resilience over a wide range of world biomes, suggesting that green water resource resilience contributes to determining vegetation primary production resilience. Finally, we estimate the changes of green water resource resilience due to climate change using results from the sixth phase of the Coupled Model Inter-comparison Project (CMIP6) and discuss the potential consequences of global warming for ecosystem service reliability.Fil: Zampieri, Matteo. Joint Research Centre; ItaliaFil: Grizzetti, Bruna. Joint Research Centre; ItaliaFil: Meroni, Michele. Joint Research Centre; ItaliaFil: Scoccimarro, Enrico. No especifíca;Fil: Vrieling, Anton. No especifíca;Fil: Naumann, Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Toreti, Andrea. Joint Research Centre; Itali

Projected changes in intense precipitation over Europe at the daily and subdaily time scales.

Abstract Heavy precipitation is a major hazard over Europe. It is well established that climate model projections indicate a tendency toward more extreme daily rainfall events. It is still uncertain, however, how this changing intensity translates at the subdaily time scales. The main goal of the present study is to examine possible differences in projected changes in intense precipitation events over Europe at the daily and subdaily (3-hourly) time scales using a state-of-the-science climate model. The focus will be on one representative concentration pathway (RCP8.5), considered as illustrative of a high rate of increase in greenhouse gas concentrations over this century. There are statistically significant differences in intense precipitation projections (up to 40%) when comparing the results at the daily and subdaily time scales. Over northeastern Europe, projected precipitation intensification at the 3-hourly scale is lower than at the daily scale. On the other hand, Spain and the western seaboard exhibit an opposite behavior, with stronger intensification at the 3-hourly scale rather than the daily scale. While the mean properties of the precipitation distributions are independent of the analyzed frequency, projected precipitation intensification exhibits regional differences. This finding has implications for the extrapolation of impacts of intense precipitation events, given the daily time scale at which the analyses are usually performed

Extreme events representation in CMCC-CM2 standard and high-resolution general circulation models

The recent advancements in climate modeling partially build on the improvement of horizontal resolution in different components of the simulating system. A higher resolution is expected to provide a better representation of the climate variability, and in this work we are particularly interested in the potential improvements in representing extreme events of high temperature and precipitation. The two versions of the Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC-CM2) model used here adopt the highest horizontal resolutions available within the last family of the global coupled climate models developed at CMCC to participate in the Coupled Model Intercomparison Projects, Phase 6 (CMIP6) effort. The main aim of this study is to document the ability of the CMCC-CM2 models to represent the spatial distribution of extreme events of temperature and precipitation, under the historical period, comparing model results to observations, the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5), multi-source weighted-ensemble precipitation (MSWEP) and Climate Hazards Group infrared precipitation with station data (CHIRPS) observations. For a more detailed evaluation we use both 6-hourly and daily time series, to compute indices representative of intense and extreme conditions. In terms of mean climate, the two models are able to realistically reproduce the main patterns of temperature and precipitation. The high resolution version ( ∘ horizontal resolution) of the atmospheric model provides better results than the standard resolution one (1°), not only in terms of means but also in terms of intense and extreme events of temperature defined at daily and 6-hourly frequencies. This is also the case of average and intense precipitation. On the other hand the extreme precipitation is not improved by the adoption of a higher horizontal resolution

Extreme events in high resolution CMCC regional and global climate models

Within the framework of the FUME EU project a set of climate projections covering the period 1970-2100 has been performed using a global General Circulation model (CMCC-Med) and a Regional Climate model (CMCC-CLM). Simulation outputs have been post-processed in order to investigate extreme events based on three principal weather parameters: precipitation, surface temperature and 10 metre wind. Using these parameters, several indexes for extreme event characterizations have been computed on daily time basis over 4 seasons. Trends and variability have been computed and examined both for the global and regional model