ALBERT

Description: This paper analyses the temporal and spatial variability of droughts in Romania, over the last five decades, based on a high-resolution data set developed at country level, namely ROCADA. Droughts are analyzed by means of the Standardized Precipitation Index (SPI) for 3-, 6- and 12-month time scales. The time period 1979–1995 was identified as the period with the highest number of months affected by moderate, severe as well as extreme drought conditions. The 2000–2001 episode was identified as the major drought event, concerning the severity and the spatial extent, with an area of 60 % of the country affected by extreme drought for more than 10 consecutive months. The results of the trend analysis emphasize an inhomogeneous spatial aspect of the dryness/wetness trends. Statistically significant positive trends (wetter conditions) over small areas distributed inhomogeneous around the country like the southernmost corner as well as the northeastern part and some small areas in the western part of the country have been identified. Statistically significant negative (drier conditions) trends have been obtained over the southwestern part of the country and over the eastern part. In general, the SPI trends follow the observed trends in the monthly precipitation totals, at country level. The results indicate that there is no spatial consistency in the occurrence of droughts at country level and the SPI at different time scales may vary in its usefulness in drought monitoring, due to the fact that in the case of shorter time scales the SPI values have the tendency to fluctuate frequently above and below the zero line, while for longer time scales there are well-defined dry and wet cycles.

Description: The relationships between the dominant modes of interannual variability of Diurnal Temperature Range (DTR) over Europe and large-scale atmospheric circulation and sea surface temperature anomaly fields are investigated through statistical analysis of observed and reanalysis data. It is shown that the dominant DTR modes as well as their relationship with large-scale atmospheric circulation and sea surface temperature anomaly fields are specific for each season. During winter the first and second modes of interannual DTR variability are strongly related with the North Atlantic Oscillation and the Scandinavian pattern, while the third mode is related with the Atlantic Multidecadal Oscillation. Strong influence of the Atlantic Multidecadal Oscillation and the Arctic Oscillation on spring DTR modes of variability was also detected. During summer the DTR variability is influenced mostly by a blocking-like pattern over Europe, while the autumn DTR variability is associated with a wave-train like pattern, which develops over the Atlantic Ocean and extends up to Siberia. It is also found that the response of DTR to global sea surface temperature is much weaker in spring and summer comparing to winter and autumn. A correlation analysis reveals a strong relationship between DTR modes of variability and the Cloud Cover anomalies during all seasons. The influence of the potential evapotranspiration and precipitation anomalies on DTR modes of variability is strongest during summer, but it is significant also in spring and autumn. It is suggested that a large part of interannual to decadal DTR variability over Europe is induced by the large-scale climate anomaly patterns via modulation of cloud cover, precipitation and potential evapotranspiration anomaly fields.