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I. Keggenhoff
Justus Liebig University Giessen, Department of Geography, Giessen, Germany

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Preprint content
Published: 09 November 2015 in Earth System Dynamics Discussions
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During the last 50 years Georgia experienced a rising number of severe summer heat waves causing increasing heat-health impacts. In this study, the 10 most severe heat waves between 1961 and 2010 and recent changes in heat wave characteristics have been detected from 22 homogenized temperature minimum and maximum series using the Excess Heat Factor (EHF). A composite and Canonical Correlation Analysis (CCA) have been performed to study summer heat wave patterns and their relationships to the selected predictors: mean Sea Level Pressure (SLP), Geopotential Height at 500 mb (Z500), Sea Surface Temperature (SST), Zonal (u-wind500) and Meridional Wind at 500 mb (v-wind500), Vertical Velocity at 500 mb (O500), Outgoing Longwave Radiation (OLR), Relative Humidity (RH500), Precipitation (RR) and Soil Moisture (SM). Most severe heat events during the last 50 years are identified in 2007, 2006 and 1998. Largest significant trend magnitudes for the number, intensity and duration of low and high-impact heat waves have been found during the last 30 years. Significant changes in the heat wave predictors reveal that all relevant surface and atmospheric patterns contributing to heat waves have been intensified between 1961 and 2010. Composite anomalies and CCA patterns provide evidence of a large anticyclonic blocking pattern over the southern Ural Mountains, which attracts warm air masses from the Southwest, enhances subsidence and surface heating, shifts the African Intertropical Convergence Zone (ITCZ) northwards, and causes a northward shift of the subtropical jet. Moreover, pronounced precipitation and soil moisture deficiency throughout Georgia contribute to the heat wave formation and persistence over Georgia. Due to different large- to mesoscale circulation patterns and the local terrain, heat wave effects over Eastern Georgia are dominated by subsidence and surface heating, while convective rainfall and cooling are observed in the West.

ACS Style

I. Keggenhoff; M. Elizbarashvili; L. King. Severe summer heat waves over Georgia: trends, patterns and driving forces. Earth System Dynamics Discussions 2015, 6, 2273 -2322.

AMA Style

I. Keggenhoff, M. Elizbarashvili, L. King. Severe summer heat waves over Georgia: trends, patterns and driving forces. Earth System Dynamics Discussions. 2015; 6 (2):2273-2322.

Chicago/Turabian Style

I. Keggenhoff; M. Elizbarashvili; L. King. 2015. "Severe summer heat waves over Georgia: trends, patterns and driving forces." Earth System Dynamics Discussions 6, no. 2: 2273-2322.

Journal article
Published: 16 April 2015 in Climate
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The Caucasus Region has been affected by an increasing number of heat waves during the last decades, which have had serious impacts on human health, agriculture and natural ecosystems. A dataset of 22 homogenized, daily maximum (Tmax) and minimum (Tmin) air temperature series is developed to quantify climatology and summer heat wave changes for Georgia and Tbilisi station between 1961 and 2010 using the extreme heat factor (EHF) as heat wave index. The EHF is studied with respect to eight heat wave aspects: event number, duration, participating heat wave days, peak and mean magnitude, number of heat wave days, severe and extreme heat wave days. A severity threshold for each station was determined by the climatological distribution of heat wave intensity. Moreover, heat wave series of two indices focusing on the 90th percentile of daily minimum temperature (CTN90p) and the 90th percentile of daily maximum temperature (CTX90p) were compared. The spatial distribution of heat wave characteristics over Georgia showed a concentration of high heat wave amplitudes and mean magnitudes in the Southwest. The longest and most frequently occurring heat wave events were observed in the Southeast of Georgia. Most severe heat wave events were found in both regions. Regarding the monthly distribution of heat waves, the largest proportion of severe events and highest intensities are measured during May. Trends for all Georgia-averaged heat wave aspects demonstrate significant increases in the number, intensity and duration of low- and high-intensity heat waves. However, for the heat wave mean magnitude no change was observed. Heat wave trend magnitudes for Tbilisi mainly exceed the Georgia-averages and its surrounding stations, implying urban heat island (UHI) effects and synergistic interactions between heat waves and UHIs. Comparing heat wave aspects for CTN90p and CTX90p, all trend magnitudes for CTN90p were larger, while the correlation between the annual time-series was very high among all heat wave indices analyzed. This finding reflects the importance of integrating the most suitable heat wave index into a sector-specific impact analysis.

ACS Style

Ina Keggenhoff; Mariam Elizbarashvili; Lorenz King. Heat Wave Events over Georgia Since 1961: Climatology, Changes and Severity. Climate 2015, 3, 308 -328.

AMA Style

Ina Keggenhoff, Mariam Elizbarashvili, Lorenz King. Heat Wave Events over Georgia Since 1961: Climatology, Changes and Severity. Climate. 2015; 3 (2):308-328.

Chicago/Turabian Style

Ina Keggenhoff; Mariam Elizbarashvili; Lorenz King. 2015. "Heat Wave Events over Georgia Since 1961: Climatology, Changes and Severity." Climate 3, no. 2: 308-328.

Journal article
Published: 07 January 2015 in Weather and Climate Extremes
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Sixteen temperature minimum and maximum series are used to quantify annual and seasonal changes in temperature means and extremes over Georgia (Southern Caucasus) during the period 1961 and 2010. Along with trends in mean minimum and maximum temperature, eight indices are selected from the list of climate extreme indices as defined by the Expert Team on Climate Change Detection and Indices (ETCCDI) of the Commission for Climatology of the World Meteorological Organization (WMO), for studying trends in temperature extremes. Between the analysis periods 1961–2010, 1971–2010 and 1981–2010 pronounced warming trends are determined for all Georgia-averaged trends in temperature means and extremes, while all magnitudes of trends increase towards the most recent period. During 1981 and 2010, significant warming trends for annual minimum and maximum temperature at a rate of 0.39 °C (0.47 °C) days/decade and particularly for the warm temperature extremes, summer days, warm days and nights and the warm spell duration index are evident, whereas warm extremes show larger trends than cold extremes. The most pronounced trends are determined for summer days 6.2 days/decade, while the warm spell duration index indicates an increase in the occurrence of warm spells by 5.4 days/decade during 1981 and 2010. In the comparison of seasonal changes in temperature means and extremes, the largest magnitudes of warming trends can be observed for temperature maximum in summer and temperature minimum in fall. Between 1981 and 2010, summer maximum temperature shows a significant warming at a rate of 0.84 °C/decade, increasing almost twice as fast as its annual trend (0.47 °C/decade). The Georgia-averaged trends for temperature minimum in fall increase by 0.59 °C/decade. Strongest significant trends in temperature extremes are identified during 1981 and 2010 for warm nights (4.6 days/decade) in summer and fall as well as for warm days (5.6 days/decade) in summer. Analyses demonstrate that there have been increasing warming trends since the 1960s, particularly for warm extremes during summer and fall season, accompanied by a constant warming of temperature means in Georgia.

ACS Style

I. Keggenhoff; M. Elizbarashvili; L. King. Recent changes in Georgia׳s temperature means and extremes: Annual and seasonal trends between 1961 and 2010. Weather and Climate Extremes 2015, 8, 34 -45.

AMA Style

I. Keggenhoff, M. Elizbarashvili, L. King. Recent changes in Georgia׳s temperature means and extremes: Annual and seasonal trends between 1961 and 2010. Weather and Climate Extremes. 2015; 8 ():34-45.

Chicago/Turabian Style

I. Keggenhoff; M. Elizbarashvili; L. King. 2015. "Recent changes in Georgia׳s temperature means and extremes: Annual and seasonal trends between 1961 and 2010." Weather and Climate Extremes 8, no. : 34-45.

Journal article
Published: 10 May 2014 in Weather and Climate Extremes
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Annual changes to climate extreme indices in Georgia (Southern Caucasus) from 1971 to 2010 are studied using homogenized daily minimum and maximum temperature and precipitation series. Fourteen extreme temperature and 11 extreme precipitation indices are selected from the list of core climate extreme indices recommended by the World Meteorological Organization – Commission for Climatology (WMO-CCL) and the research project on Climate Variability and Predictability (CLIVAR) of the World Climate Research Programme (WCRP). Trends in the extreme indices are studied for 10 minimum and 11 maximum temperature and 24 precipitation series for the period 1971–2010. Between 1971 and 2010 most of the temperature extremes show significant warming trends. In 2010 there are 13.3 fewer frost days than in 1971. Within the same time frame there are 13.6 more summer days and 7.0 more tropical nights. A large number of stations show significant warming trends for monthly minimum and maximum temperature as well as for cold and warm days and nights throughout the study area, whereas warm extremes and night-time based temperature indices show greater trends than cold extremes and daytime indices. Additionally, the warm spell duration indicator indicates a significant increase in the frequency of warm spells between 1971 and 2010. Cold spells show an insignificant increase with low spatial coherence. Maximum 1-day and 5-day precipitation, the number of very heavy precipitation days, very wet and extremely wet days as well as the simple daily intensity index all show an increase in Georgia, although all trends manifest a low spatial coherence. The contribution of very heavy and extremely heavy precipitation to total precipitation increased between 1971 and 2010, whereas the number of wet days decreases.

ACS Style

I. Keggenhoff; M. Elizbarashvili; A. Amiri-Farahani; L. King. Trends in daily temperature and precipitation extremes over Georgia, 1971–2010. Weather and Climate Extremes 2014, 4, 75 -85.

AMA Style

I. Keggenhoff, M. Elizbarashvili, A. Amiri-Farahani, L. King. Trends in daily temperature and precipitation extremes over Georgia, 1971–2010. Weather and Climate Extremes. 2014; 4 ():75-85.

Chicago/Turabian Style

I. Keggenhoff; M. Elizbarashvili; A. Amiri-Farahani; L. King. 2014. "Trends in daily temperature and precipitation extremes over Georgia, 1971–2010." Weather and Climate Extremes 4, no. : 75-85.