HEAT STRESS IN SOUTH ROMANIA IN CONNECTION TO

LARGE-SCALE CIRCULATION PATTERNS

Simona Andrei(1), Dana Magdalena Micu(2), Nicu Barbu(3,4), Carmen Sofia Dragotă(2)

(1) National R&D Institute for Optoelectronics INOE2000; (2) Institute of Geography, Romanian Academy; (3) National Meteorological Administration; (4) Faculty of Physics, University of Bucharest

(e-mails: simona.andrei@inoe.ro; micudanamagdalena@gmail.com)

CONTEXT AND RESEARCH OBJECTIVES

The climate of Romania is on an ongoing and significant warming, visibly intensified since the mid 1980s. The southern and southeastern regions are highly exposed to hot extremes and heat stress, under both present and future climate (Busuioc et al., 2010, Fischer and Schär, 2010; Bojariu et al., 2015; Dobrinescu et al., 2015). Heat waves became increasingly frequent and persistent under the recent warming trends in most regions of the country, particularly in the southern plain and tableland regions (Georgescu et al., 2013; Barbu et al., 2014). Yet these extreme events have become not common enough to allow societal adaptation to extreme heat stress.

With this study we aim to:

(1) Investigate the changes in heat waves characteristics (1961-1990 vs. 1984-2013); (2) Examine the heat stress related to the occurrence of consecutive high day- and nigh-time temperatures; (3) Identify the large-scale circulation patterns associated to heat stress conditions.

ACKNOWLEDGEMENTS This work has been supported by grants of the STAR–ESA Program Project

No.55/2013 - CARESSE. Climhydex project (PNII-ID-2011-2-0073).

DATA

Datasets: Heat wave events occurred in southern Romania during 1961-2013, were identified and analyzed using daily data from ROCADA gridded database, 0.1° spatial resolution (Dumitrescu and Bîrsan, 2015); large-scale circulation patterns associated to heat wave occurrences were analyzed using NCEP/NCAR reanalysis daily data (Kalnay et. al, 1996)

Variables: Daily mean Tmax, Tmin, RH% were extracted for 31 weather sites from the corresponding ROCADA grid cells; daily mean sea level pressure, 925 and 500 hPa geopotential height, 700 hPa wind, and columnar precipitable water content were used to build circulation types within the area comprised between 5° to 35° E lon., and 35° to 55° N lat.

METHODS

Heat wave events (HW): Sequences of at least two consecutive hot days (Tmax≥35°C) followed by tropical nights (Tmin≥20°C), during the extended summer season (May-September interval).

Heat Stress: Apparent Temperature Index (ATI) (NOAA, Fischer and Schär, 2010, Tmax°C), Temperature-Humidity Index (THI) (Teodoreanu and Bunescu, 1987; Dobrinescu et al., 2015).

Circulation classification catalogues (COST733): GWT with 18 types and WLKC733 with 40 types (Philipp et al., 2010).

Trend analysis: Mann-Kendall non-parametric test (two-tail test), 5% significance level. RESULTS

2. Heat stress

3. Large scale circulation patterns associated to heat stress conditions

CONCLUSIONS • Spatially consistent upward trends of HW frequency and duration (especially in R2 and R1), after 1985-1987. Increasing frequency of severe HW both during the day (>40°C) and night (>25°C). Less significant changes in HW characteristics in R4 (the water bodies influence). • Significant increase of heat stress exposure and health risk all over the region (2010, 2012). • General synoptic context that characterizes heat wave events are mainly related to the presence of an anticyclonic regime. • According to GWT catalogue, dominant directions of circulation are eastern (E[A]), north-eastern (NE[A]) and to a less extent south-western (SW[A](not shown here)) that correspond to the extension of Azores/North African High over Central, South-Eastern and North-Eastern Europe. • The intrusion of Saharan hot air is also emphasized on WLKC733 catalogue (Undef[AAW], and Undef[CAW]) supporting prolonged heat wave episodes with more that 5 consecutive days.

STUDY AREA

Frequency of circulation patterns during the heat wave events (1961-1990 vs. 1984- 2013)

18th - 26th of July 1987

16th - 25th of July 2007

04th - 16th of July 2012

2012 - the year of maximum HW frequency in most of the regions 14 (R1), 64 (R2), 12 (R3); 2007 - only in R4

+17…19% more persistent HWs in the 1984-2013 period (R1-R3), and +4% (R4) vs. 1961-2013 mean; shifting years: 1985-1987.

2007 (47%), 2000 (37%) Increase of HW>40°C in the 1984-2013 interval (R2)

2007 (47%), 2000 and 2012 (13% each); increase of HW>25°C since the mid 1980s (R3 and R4)

1. Changes in heat wave characteristics

Changes in the frequency of heat stress Changes in health risk (days with ATI>41 ) (%/decade)

Peak heat stress years: 2010, 2012 (R2-R3) 2010 (R4) 2012 (R1)

THI>80 during HW in all regions

Most significant circulation patterns during the heat wave events (up) GWT catalogue and (down) WLKC733 catalogue

Top 3 of prolonged heat wave events in south Romania (1961 – 2013)

Averaged values of Tmax (left), Tmin (centre) and RH %(right) .