Patricio Velasquez Alvarez


Last Name

Velasquez Alvarez

First Name

Patricio

ORCID

0000-0002-7835-9094

Organisational unit

09762 - Barrage, Lint / Barrage, Lint

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2022 - 20256
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Publications 1 - 6 of 6
  • High-resolution LGM climate of Europe and the Alpine region using the regional climate model WRF
    Item type: Journal Article
    Russo, Emmanuele; Buzan, Jonathan; Lienert, Sebastian; et al. (2024)
    Climate of the Past
    In this study we present a series of sensitivity experiments conducted for the Last Glacial Maximum (LGM, 1/42 ka) over Europe using the regional climate Weather Research and Forecasting model (WRF). Using a four-step two-way nesting approach, we are able to reach a convection-permitting horizontal resolution over the inner part of the study area, covering central Europe and the Alpine region. The main objective of the paper is to evaluate a model version including a series of new developments better suitable for the simulation of paleo-glacial time slices with respect to the ones employed in former studies. The evaluation of the model is conducted against newly available pollen-based reconstructions of the LGM European climate and takes into account the effect of two main sources of model uncertainty: a different height of continental glaciers at higher latitudes of the Northern Hemisphere and different land cover. Model results are in good agreement with evidence from the proxies, in particular for temperatures. Importantly, the consideration of different ensemble members for characterizing model uncertainty allows for increasing the agreement of the model against the proxy reconstructions that would be obtained when considering a single model realization. The spread of the produced ensemble is relatively small for temperature, besides areas surrounding glaciers in summer. On the other hand, differences between the different ensemble members are very pronounced for precipitation, in particular in winter over areas highly affected by moisture advection from the Atlantic. This highlights the importance of the considered sources of uncertainty for the study of European LGM climate and allows for determining where the results of a regional climate model (RCM) are more likely to be uncertain for the considered case study. Finally, the results are also used to assess the effect of convection-permitting resolutions, at both local and regional scales, under glacial conditions.
  • The role of ice-sheet topography in the Alpine hydro-climate at glacial times
    Item type: Journal Article
    Velasquez Alvarez, Patricio; Messmer, Martina; Raible, Christoph C. (2022)
    Climate of the Past
    In this study, we investigate the sensitivity of the glacial Alpine hydro-climate to northern hemispheric and local ice-sheet changes. Bridging the scale gap by using a chain of global and regional climate models, we perform sensitivity simulations of up to 2 km horizontal resolution over the Alps for the Last Glacial Maximum (LGM) and the Marine Isotope Stage 4 (MIS4). In winter, we find wetter conditions in the southern part of the Alps during LGM compared to present day, to which dynamical processes, i.e. changes in the wind speed and direction, contribute substantially. During summer, we find the expected drier conditions in most of the Alpine region during LGM, as thermodynamics suggests drier conditions under lower temperatures. The MIS4 climate shows enhanced winter precipitation compared to the LGM, which is explained by its warmer climate compared to the LGM - thus, again explained by thermodynamics. The sensitivity simulations of the northern hemispheric ice-sheet changes show that an increase of the ice-sheet thickness leads to a significant intensification of glacial Alpine hydro-climate conditions, which is mainly explained by dynamical processes. Changing only the Fennoscandian ice sheet is less influential on the Alpine precipitation, whereas modifications in the local Alpine ice-sheet topography significantly alter the Alpine precipitation; in particular, we find a reduction of summer precipitation at the southern face of the Alps when lowering the Alpine ice sheet. The findings demonstrate that the northern hemispheric and local ice-sheet topography play an important role in regulating the Alpine hydro-climate and thus permits a better understanding of the precipitation patterns in the complex Alpine terrain at glacial times.
  • The Effect of 3°C Global Warming on Hail Over Europe
    Item type: Journal Article
    Thurnherr, Iris; Cui, Ruoyi; Velasquez Alvarez, Patricio; et al. (2025)
    Geophysical Research Letters
    Hail severely impacts humans, crops, and infrastructure. Quantifying future hail trends is extremely challenging due to the complex dynamic, thermodynamic, and microphysical processes behind severe convective storms. Here, we combine a km‐scale convection‐permitting regional climate model and an online hail diagnostic to quantitatively assess changes in hail frequency in Europe imposed by a C global warming level. Results show increases in summer hail frequency in northeastern Europe and decreases to the southwest for intense and severe hail days, related to changes in low‐tropospheric water vapor content, convective available potential energy and convective inhibition. Small hail days generally decline across continental Europe, due to increased melting of hailstones with higher melting level height. The physical‐based simulation approach captures convection and hail processes consistently, providing a solid basis for assessing the socioeconomic implications of hail and its trends with global warming.
  • Projections of Heavy Precipitation Characteristics Over the Greater Alpine Region Using a Kilometer-Scale Climate Model Ensemble
    Item type: Journal Article
    Estermann, Rebekka; Rajczak, Jan; Velasquez Alvarez, Patricio; et al. (2025)
    Journal of Geophysical Research: Atmospheres
    This study presents a detailed analysis of the CORDEX-FPS multi-model ensemble of convection-permitting climate simulations over the greater Alpine region. These simulations cover 10-year time slices and were obtained by downscaling global climate model (GCM) projections, using regional climate models (RCMs) and kilometer-scale convection-permitting models (CPMs). Our analysis over the Alpine area agrees with previous studies in terms of projected summer precipitation changes for the end of the century, in particular regarding a decrease in mean precipitation and increases in hourly precipitation intensities. In addition, we assess projected changes over different subregions, provide analyses at monthly and seasonal basis for temporal aggregations ranging from 1 hr to 5 days, address different extreme precipitation indices, and present validation against an Alpine-scale daily precipitation data set and an hourly precipitation product based on 3 Doppler radars. The evaluation reveals that CPMs show a refinement of spatial patterns, reduce the overestimation of precipitation frequency, and better capture intense precipitation characteristics. The improvements are especially apparent on the sub-daily scale and in the summer season. Convection-Permitting Model climate projections show an increase in precipitation intensity for all seasons and across all temporal aggregations in all regions, except for the Mediterranean in summer. The projections from different CPMs qualitatively agree, despite significant differences in the GCMs circulation changes, suggesting that the increase in heavy events is primarily due to thermodynamic effects. We also present a hypothesis explaining why projections of relative changes in hourly precipitation percentiles are similar between CPMs and RCMs, despite large biases in RCMs.
  • Simulating Hail and Lightning Over the Alpine Adriatic Region—A Model Intercomparison Study
    Item type: Journal Article
    Malečić, Barbara; Cui, Ruoyi; Demory, Marie-Estelle; et al. (2023)
    Journal of Geophysical Research: Atmospheres
    Hail is a significant convective weather hazard, often causing considerable crop and property damage across the world. Although extremely damaging, hail still remains a challenging phenomenon to model and forecast, given the limited computational resolution and the gaps in understanding the processes involved in hail formation. Here, eight hailstorms occurring over the Alpine-Adriatic region are analyzed using simulations with the Weather Research and Forecasting (WRF) and the Consortium for Small Scale Modeling (COSMO) models, with embedded HAILCAST and Lightning Potential Index (LPI) diagnostics at kilometer-scale grid spacing (∼2.2 km). In addition, a systematic model intercomparison study is performed to investigate the ability of the different modeling systems in reproducing such convective extremes, and to further assess the uncertainties associated with simulations of such localized phenomena. The results are verified by hailpad observations over Croatia, radar estimates of hail over Switzerland, and lightning measurements from the LINET network. The analysis reveals that both HAILCAST and LPI are able to reproduce the affected area and intensities of hail and lightning. Moreover, hail and lightning fields produced by both models are similar, although a slight tendency of WRF to produce smaller hail swaths with larger hailstones and higher LPI compared to COSMO is visible. It is found that these differences can be explained by systematic differences in vertical profiles of microphysical properties and updraft strength between the models. Overall, results are promising and indicate that both HAILCAST and LPI could be valuable tools for real-time forecasting and climatological assessment of hail and lightning in current and changing climate.
  • A European Hail and Lightning Climatology From an 11-Year Kilometer-Scale Regional Climate Simulation
    Item type: Journal Article
    Cui, Ruoyi; Thurnherr, Iris; Velasquez Alvarez, Patricio; et al. (2025)
    Journal of Geophysical Research: Atmospheres
    Hail and lightning, associated with severe convective storms, can cause extensive damage to infrastructure, agriculture, and ecosystems. Because of the small scale of these storms and the complexity of the involved processes, observing and modeling convective storms is challenging. The potential of online diagnostics in convection-permitting models to simulate hail and lightning, especially over climatic time scales and extended regions, has not yet been fully exploited. To address this gap, we present a European-wide hail and lightning climatology (2011–2021) using the Consortium for Small Scale Modeling (COSMO) regional climate model with a horizontal grid spacing of 2.2 km, coupled with a hail growth model (HAILCAST) and the lightning potential index (LPI) diagnostics. We further developed a new European-wide hail product based on the Operational Program for the Exchange of Weather Radar Information (OPERA) composite. Model validation against observations demonstrates an overall good performance in simulating hail and lightning on spatial, seasonal, and diurnal scales. The highest hail frequencies occur during summer along the slopes of high mountain ridges, such as the Alps, Pyrenees, and the Carpathians, aligning with observed lightning hotspots in Europe. In autumn, hail and lightning occur predominantly over the Mediterranean and along the Adriatic coast. Severe hail events with a maximum hail diameter larger than 20 mm mainly occur in the Po Valley, western Spain, and Eastern Europe. This 11-year simulation provides a European-wide data set of severe convective storms and their properties, serving as a basis for further studies of convective events and their impacts.
Publications 1 - 6 of 6