CHANGES IN SUMMER TYPES IN RELATION TO DROUGHT OCCURRENCE IN THE ROMANIAN PLAIN REGION
MICU DANA, HAVRIŞ LOREDANA-ELENA, DRAGOTĂ CARMEN-SOFIA, MĂRCULEŢ CĂTĂLINA
ABSTRACT Changes in summer types in relation to drought occurrence in the Romanian Plain region. This work aims at analysing the exposure of an important agricultural region of Romania (the Romanian Plain region) to hot summers and droughts over the 1961-2009 period, in response to the combined action of air temperature and precipitation. This study is focused on the changes of summer types, herein defined as four modes (warm/dry, warm/wet, cold/dry, cold/wet), based on the exceedence probabilities of the joint extreme quantiles (the 25th and the 75th) of mean daily temperature and precipitation, for a number of six weather stations located in the Romanian Plain region. The trends in the evolution of the four summer modes have been investigated in relation to the changes in the frequency, magnitude and duration of precipitation deficit and drought, as revealed by the Standardized Precipitation Index (SPI) and the maximum number of consecutive dry days. The changing behaviour of summer modes is strongly associated to the region wide signal of significant summer warming (both daytime and night-time) and less to the slight drying trend. The results show that most areas of the Romanian Plain region are subject to a greater exposure to heat stress in summer and also, to a slight intensification of dryness, more spatially extended since the mid 1980s to early 1990s. These findings are supported mainly by a significant increase of the frequency of the warm/dry summers and a slight lengthening of summer dry spells and less, by the long-term trends of summer SPI (at both 3- and 6-month time-scales), which suggest only a slight increase of the frequency of the moderately dry SPI values, yet not statistically significant.
Keywords: summer types, dry spells, SPI, drought, dryness.