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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 2:33 |
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Conference: Bucharest University Faculty of Physics 2013 Meeting
Section: Atmosphere and Earth Science; Environment Protection
Title:
Spatial and temporal variability of the thermal stress indices in Romania
Authors:
Andreea Dobrinescu (1,2), Aristita Busuioc (1), Marius-Victor Birsan (1), Sabina Stefan (2), Alina Orzan (1)
Affiliation:
(1) National Meteorological Administration, 97 Sos. Bucuresti-Ploiesti, Sect. 1, Bucharest 013686, Romania
(2) University of Bucharest, Faculty of Physics, P.O.BOX MG-11, Magurele, Bucharest, Romania
E-mail
andreea.dobrinescu@meteoromania.ro
Keywords:
thermal stress index, Mann-Kendall, Pettitt, Empirical Orthogonal Functions
Abstract:
Changes in the frequency and intensity of extreme climate events due to anthropogenic induced climate change have been documented in many scientific papers. The climate extremes usually analysed until now are those related to heavy precipitation, droughts, high temperatures expressed by various indices. It is known that, especially during summer, extreme weather conditions when high temperatures are associated to high relative humidity contribute to a high human discomfort. The index linking the two climate variables (air temperature and relative humidity) is commonly called thermal stress index, temperature-humidity (ITU), which has been less analysed, at least for Romania. Likewise, a cooling index (IR) was defined for the winter season linking the air temperature and wind speed.
This study presents the characteristics of spatial and temporal variability of monthly/seasonal ITU and IR values over the period 1961-2010. The monthly averages for May-September and summer averages (June-August) for 87 stations with complete observations, were considered for ITU, while for IR (December-February) only 61 stations with full data records were available. The statistical significance of linear trends and shifts in the mean (given by the Mann Kendall and Pettitt tests, respectively) as well as spatial mode of variability (using EOF analysis) are performed. The summer frequency of ITU values exceeding 80 units and winter frequency of IR values bellow -20 units (thresholds considered to be responsible for high impact on human health) has been also analysed using the same statistical techniques.
The results reveal statistically significant increasing trends (5% level) for the monthly ITU averages for May to August over the entire country. The highest trends were identified for July (3.12 units/50 years) and August (3.25 units/50 years). An increasing trend was also identified for the summer frequency of ITU values exceeding 80 units with highest values over the extra-Carpathian regions, reaching 16-25 days/50 years in the South of Romania (Danube Plain). A strong increase shift was identified around 1987 year, which is in agreement with the shift in the extreme temperature indices in Romania (presented in other study). The IR (winter mean) reveals also a statistically significant increasing trends (5% level) over the almost entire country with higher values over the eastern and western regions in agreement with the winter mean temperature trends (only for eastern areas).
The EOF analysis reveals that EOF1 pattern, showing same sign over the entire country for both indices, explaing 89% (ITU) and 78% (IR) from the total observed variance. This result shows that a large-scale mechanism is responsible for the summer ITU and winter IR variability. The correlation between the time series associated to EOF1 (PC1) of the summer ITU and PC1 of the T850 (large-scale temperature at 850 hPa) was performed, showing a significant strong correlation (0.91), as found for the extreme temperatures. This result shows a possible physical explanation of the ITU increasing trend. Similar correlation will be also calculated for IR. This study was funded by the Executive Agency for Higher Education, Research, Development and Innovation Funding (UEFISCDI) through the research project CLIMHYDEX « Changes in climate extremes and associated impact in hydrological events in Romania », cod PNII-ID-2011-2-0073.
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