Towards the intensification of convective rain events with rising temperatures in Germany

Extreme convective precipitation events are among the most severe hazards in central Europe and are expected to intensify under global warming. However, the degree of intensification and the underlying processes are still uncertain. In this thesis, recent advances in continuous, radar-based precipitation monitoring and convection-permitting climate modeling are used to investigate Lagrangian properties of convective rain cells such as precipitation intensity, cell area, and precipitation sum and their relationship to large-scale, environmental conditions. Firstly, convective precipitation objects are tracked in a gauge-adjusted radar-data set and the properties of these cells are related to large-scale environmental variables to investigate the observed super-Clausius-Clapeyron (CC) scaling of convective extreme precipitation. The Lagrangian precipitation sum of convective cells increases with dew point temperature at rates well above the CC-rate with increasing rates for higher dew point temperatures. These varying, high rates are caused by a covarying increase of CAPE with dew point temperature as well as the effect of high vertical wind shear causing an increase in cell area and thus precipitation sum. At the same time, cells move faster at high vertical wind shear so that Eulerian scaling rates are lower than Lagrangian but still above the CC-rate. The results show that wind shear and static instability need to be taken into account when transferring precipitation scaling under current climate conditions to future conditions. Secondly, the representation of convective cell properties in the convection-permitting climate model COSMO-CLM is evaluated. The model can simulate the observed frequency distributions of cell properties such as lifetime, area, mean and maximum intensity, and precipitation sum. The increase of area and intensity with lifetime is also well captured despite an underestimation of the intensity of the most severe cells. Furthermore, the model can represent the temperature scaling of intensity, area, and precipitation sum but fails to simulate the observed increase of lifetime. Thus, the model is suitable to study climatologies of convective storms in Germany. Thirdly, two COSMO-CLM projections at the end of the century under emission scenario RCP8.5 were investigated. While the number of convective cells and their lifetime remain approximately constant compared to present conditions, intensity and area increase strongly. The relative increase of intensity and area is largest for the highest percentiles meaning that extreme events intensify the most. The characteristic afternoon maximum of convective precipitation is damped, and shifted to later times of day which leads to an increase of nighttime precipitation in the future. Scaling rates of cell properties with dew point temperature are nearly identical in present and future in the simulation driven by the EC-Earth model which means that the upper limit of cell properties like intensity, area, and precipitation sum could be predicted from near-surface dew point temperature. However, this result could not be reproduced by the simulation driven by MIROC5 and needs further investigation.Konvektive Starkregenereignisse gehören zu den verheerendsten Naturkatastrophen in Mitteleuropa und werden im Zuge des anthropogenen Klimawandels voraussichtlich an Intensität zunehmen. Die Höhe dieser Zunahme und die zugrundeliegenden physikalischen Prozesse sind allerdings noch sehr unsicher. Durch technischen Fortschritt stehen mittlerweile Fernerkundungstechniken zur Verfügung, die eine kontinuierliche Beobachtung konvektiver Stürme erlauben. Außerdem können Klimasimulationen seit einigen Jahren hochreichende Konvektion direkt simulieren. Auf Basis eines Zellverfolgungsalgorithmus wurden in dieser Arbeit sowohl beobachtungs- als auch modellbasierte Klimatologien von Eigenschaften konvektiver Zellen für Gegenwart und Zukunft analysiert. Mithilfe eines an ortsfeste Niederschlagsmessungen angeeichten Radardatensatzes wurde untersucht, wie großskalige atmosphärische Variablen die Eigenschaften konvektiver Stürme beeinflussen und welche Prozesse für das beobachtete super-Clausius-Clapeyron (CC) Scaling von konvektiven Niederschlägen verantwortlich sein könnten. Die Niederschlagssumme konvektiver Zellen steigt mit der Taupunkttemperatur weit über der CCRate an, wobei der Anstieg mit steigender Taupunkttemperatur zunimmt. Dieser starke Anstieg wird durch eine Zunahme von CAPE mit der Taupunkttemperatur verursacht, sowie durch den Effekt, dass vertikale Windscherung die Fläche der konvektiven Zellen und somit auch die Niederschlagssumme erhöht. Gleichzeitig sorgt hohe vertikale Windscherung dafür, dass die konvektiven Zellen sich schneller verlagern, sodass die ortsfesten Skalierungsraten unter denen der mitbewegten Niederschlagssumme, aber immer noch über der CC-Rate liegen. Diese Ergebnisse zeigen, dass das gegenwärtige Scaling nicht ohne Weiteres in die Zukunft übertragen werden kann, sondern Windscherung und die atmosphärische Schichtung berücksichtigt werden müssen. Es wurde evaluiert, inwieweit das regionale Klimamodell COSMO-CLM die Eigenschaften konvektiver Zellen abbilden kann. Hierzu wurden Simulationen, die mit Reanalysen angetrieben wurden, mit Beobachtungsdaten verglichen. Das Modell kann sowohl die beobachteten Häufigkeitsverteilungen der Zelleigenschaften ‚Lebensdauer‘, ‚mittlere und maximale Intensität‘, ‚Fläche‘ und ‚Niederschlagssumme‘ gut wiedergeben, als auch den Anstieg von Intensität und Fläche mit der Lebensdauer. Allerdings wird die Intensität und Fläche der extremsten Zellen unterschätzt. Des Weiteren kann die Simulation den Anstieg der hohen Perzentile von Intensität, Fläche und Niederschlagssumme mit der Temperatur wiedergeben, aber nicht den Anstieg der Lebensdauer. Somit ist das Model geeignet, die Klimatologien konvektiver Stürme in Deutschland zu untersuchen. Für die Zukunft (2071-2100) wurden zwei COSMO-CLM Simulationen, angetrieben von verschiedenen Globalmodellen unter dem repräsentativen Konzentrationspfad RCP8.5, untersucht. Die Intensität und Fläche der konvektiven Zellen steigt im Vergleich zur Gegenwart (1976-2005) in beiden Simulationen stark an, wohingegen Anzahl und Lebenszeit der Zellen gleich bleiben. Der relative Anstieg von Intensität und Fläche ist am größten für die hohen Perzentile, was bedeutet, dass sich extreme konvektive Ereignisse am stärksten intensivieren. Der typische Tagesgang des konvektiven Niederschlags ist in der Zukunft gedämpft. Während am Nachmittag weniger konvektiver Niederschlag fällt, nimmt er in der Nacht zu. Die Skalierungsraten der Zelleigenschaften mit dem Taupunkt sind in Gegenwart und Zukunft in der Simulation, die vom EC-Earth Modell angetrieben wird, nahezu identisch. Das bedeutet, dass die bodennahe Taupunkttemperatur einen guten Prädiktor für die Obergrenze von Intensität, Fläche, und Niederschlagssumme konvektiver Zellen darstellt. Dieses Ergebnis konnte allerdings nicht für die zweite, von MIROC5 angetriebene Simulation reproduziert werden, und bedarf daher weiterer Untersuchung

Convective shower characteristics simulated with the convection-permitting climate model COSMO-CLM

This paper evaluates convective precipitation as simulated by the convection-permitting climate model (CPM) Consortium for Small-Scale Modeling in climate mode (COSMO-CLM) (with 2.8 km grid-spacing) over Germany in the period 2001–2015. Characteristics of simulated convective precipitation objects like lifetime, area, mean intensity, and total precipitation are compared to characteristics observed by weather radar. For this purpose, a tracking algorithm was applied to simulated and observed precipitation with 5-min temporal resolution. The total amount of convective precipitation is well simulated, with a small overestimation of 2%. However, the simulation underestimates convective activity, represented by the number of convective objects, by 33%. This underestimation is especially pronounced in the lowlands of Northern Germany, whereas the simulation matches observations well in the mountainous areas of Southern Germany. The underestimation of activity is compensated by an overestimation of the simulated lifetime of convective objects. The observed mean intensity, maximum intensity, and area of precipitation objects increase with their lifetime showing the spectrum of convective storms ranging from short-living single-cell storms to long-living organized convection like supercells or squall lines. The CPM is capable of reproducing the lifetime dependence of these characteristics but shows a weaker increase in mean intensity with lifetime resulting in an especially pronounced underestimation (up to 25%) of mean precipitation intensity of long-living, extreme events. This limitation of the CPM is not identifiable by classical evaluation techniques using rain gauges. The simulation can reproduce the general increase of the highest percentiles of cell area, total precipitation, and mean intensity with temperature but fails to reproduce the increase of lifetime. The scaling rates of mean intensity and total precipitation resemble observed rates only in parts of the temperature range. The results suggest that the evaluation of coarse-grained (e.g., hourly) precipitation fields is insufficient for revealing challenges in convection-permitting simulations

Convective rain cell characteristics and scaling in climate projections for Germany

Extreme convective precipitation is expected to increase with global warming. However, the rate of increase and the understanding of contributing processes remain highly uncertain. We investigated characteristics of convective rain cells like area, intensity, and lifetime as simulated by a convection‐permitting climate model in the area of Germany under historical (1976–2005) and future (end‐of‐century, RCP8.5 scenario) conditions. To this end, a tracking algorithm was applied to 5‐min precipitation output. While the number of convective cells is virtually similar under historical and future conditions, there are more intense and larger cells in the future. This yields an increase in hourly precipitation extremes, although mean precipitation decreases. The relative change in the frequency distributions of area, intensity, and precipitation sum per cell is highest for the most extreme percentiles, suggesting that extreme events intensify the most. Furthermore, we investigated the temperature and moisture scaling of cell characteristics. The temperature scaling drops off at high temperatures, with a shift in drop‐off towards higher temperatures in the future, allowing for higher peak values. In contrast, dew point temperature scaling shows consistent rates across the whole dew point range. Cell characteristics scale at varying rates, either below (mean intensity), at about (maximum intensity and area), or above (precipitation sum) the Clausius–Clapeyron rate. Thus, the widely investigated extreme precipitation scaling at fixed locations is a complex product of the scaling of different cell characteristics. The dew point scaling rates and absolute values of the scaling curves in historical and future conditions are closest for the highest percentiles. Therefore, near‐surface humidity provides a good predictor for the upper limit of for example, maximum intensity and total precipitation of individual convective cells. However, the frequency distribution of the number of cells depending on dew point temperature changes in the future, preventing statistical inference of extreme precipitation from near‐surface humidity.We investigated characteristics of convective rain cells under historical and future conditions in convection‐permitting climate simulations using a tracking algorithm. There are more intense and larger cells in the future yielding an increase in hourly precipitation extremes. The temperature scaling curves of cell characteristics shift towards higher peak values at higher temperatures in the future. In contrast, cell characteristics scale consistently with dew point temperature. Therefore, near‐surface humidity provides a good predictor for the upper limit of for example, maximum intensity, and total precipitation of convective cells

Convective rain cell properties and the resulting precipitation scaling in a warm-temperate climate

Convective precipitation events have been shown to intensify at rates exceeding the Clausius–Clapeyron rate (CC rate) of ca. 7% K−1 under current climate conditions. In this study, we relate atmospheric variables (low-level dew point temperature, convective available potential energy, and vertical wind shear), which are regarded as ingredients for severe deep convection, to properties of convective rain cells (cell area, maximum precipitation intensity, lifetime, precipitation sum, and cell speed). The rain cell properties are obtained from a rain gauge-adjusted radar dataset in a mid-latitude region, which is characterized by a temperate climate with warm summers (Germany). Different Lagrangian cell properties scale with dew point temperature at varying rates. While the maximum precipitation intensity of cells scales consistently at the CC rate, the area and precipitation sum per cell scale at varying rates above the CC rate. We show that this super-CC scaling is caused by a covarying increase of convective available potential energy with dew point temperature. Wind shear increases the precipitation sum per cell mainly by increasing the spatial cell extent. From a Eulerian point of view, this increase is partly compensated by a higher cell velocity, which leads to Eulerian precipitation scaling rates close to and slightly above the CC rate. Thus, Eulerian scaling rates of convective precipitation are modulated by convective available potential energy and vertical wind shear, making it unlikely that present scaling rates can be applied to future climate conditions. Furthermore, we show that cells that cause heavy precipitation at fixed locations occur at low vertical wind shear and, thus, move relatively slowly compared to typical cells

Contrasting lightning projection using the lightning potential index adapted in a convection-permitting regional climate model

Lightning climate change projections show large uncertainties caused by limited empirical knowledge and strong assumptions inherent to coarse-grid climate modeling. This study addresses the latter issue by implementing and applying the lightning potential index parameterization (LPI) into a fine-grid convection-permitting regional climate model (CPM). This setup takes advantage of the explicit representation of deep convection in CPMs and allows for process-oriented LPI inputs such as vertical velocity within convective cells and coexistence of microphysical hydrometeor types, which are known to contribute to charge separation mechanisms. The LPI output is compared to output from a simpler flash rate parameterization, namely the CAPE [Formula: see text] PREC parameterization, applied in a non-CPM on a coarser grid. The LPI’s implementation into the regional climate model COSMO-CLM successfully reproduces the observed lightning climatology, including its latitudinal gradient, its daily and hourly probability distributions, and its diurnal and annual cycles. Besides, the simulated temperature dependence of lightning reflects the observed dependency. The LPI outperforms the CAPE [Formula: see text] PREC parameterization in all applied diagnostics. Based on this satisfactory evaluation, we used the LPI to a climate change projection under the RCP8.5 scenario. For the domain under investigation centered over Germany, the LPI projects a decrease of [Formula: see text] in flash rate by the end of the century, in opposition to a projected increase of [Formula: see text] as projected using the CAPE [Formula: see text] PREC parameterization. The future decrease of LPI occurs mostly during the summer afternoons and is related to (i) a change in convection occurrence and (ii) changes in the microphysical mixing. The two parameterizations differ because of different convection occurrences in the CPM and non-CPM and because of changes in the microphysical mixing, which is only represented in the LPI lightning parameterization

Technical specification for single point of access and process model (NFDI4Earth Deliverable D1.3.12)

This deliverable is a specification that outlines the process for managing the life cycle of education and training materials and services, including submitting, reviewing, publishing, revising, versioning, and using them, through a single point of access for the NFDI4Earth project. It starts by introducing the input used to develop the specification, including a comparison of learning management systems and their capabilities. The second part of the specification describes the process model for the life cycle of the open educational resources to be hosted on the platform, including the initial implementation and the long-term vision for the platform. The report also includes an initial version of the metadata specification to make the resources findable and integrate them into the NFDI4Earth knowledge graph.This work has been funded by the German Research Foundation (DFG) through the project NFDI4Earth (DFG project no.460036893, https://www.nfdi4earth.de/) within the German National Research Data Infrastructure (NFDI, https://www.nfdi.de/)

Analysis of Outcomes in Ischemic vs Nonischemic Cardiomyopathy in Patients With Atrial Fibrillation A Report From the GARFIELD-AF Registry

IMPORTANCE Congestive heart failure (CHF) is commonly associated with nonvalvular atrial fibrillation (AF), and their combination may affect treatment strategies and outcomes