Heat and cold waves trends in the Carpathian Region from 1961 to 2010

The past two decades of the 20th century and the first of the 21st century have been characterized by global temperature rise and increased frequency of weather-induced extreme events such as floods, droughts, heavy rainfall, and heat waves. We investigated the heat and the cold waves in the Carpathian Region, an area whose rich biosphere is endangered by extreme events. We used the daily minimum (T N ) and maximum (T X ) temperature data collected in the framework of the CARPATCLIM project. Such high-resolution (0.1∘ × 0.1∘) gridded data range from January 1961 to December 2010. In this study, a heat wave occurs when temperature is above the 90th percentile for at least five consecutive days and a cold wave occurs when temperature is below the 10th percentile for at least five consecutive days. The percentiles have been computed over the baseline period 1971 – 2000. We distinguish between night-time and daytime events and we discuss heat (and cold) waves considering at least five consecutive night and days with temperature above (below) the selected percentile. For each heat or cold wave event, we assigned duration, severity, and intensity. For these parameters and for frequency, we performed linear trend analysis for the period 1961 – 2010. The trends have been computed on an annual and seasonal basis and tested for statistical significance. Different spatial patterns of heat and cold waves characterize the Carpathian Region: heat wave events show general increase in all the parameters considered, while cold wave events show a decrease in all the variables West to the Carpathians and an increase North – East to the Carpathians. We also compiled a list of the most relevant heat waves that hit the Carpathian Region from 1961 to 2010: out of seven events, four occurred from 2000 to 2010. Instead, the 1960s and the 1980s have been the decades most hit by severe cold waves.JRC.H.7-Climate Risk Managemen

Climate change in the Carpathian Region

To investigate the climate of the Carpathian Region (17°-27°E; 44°-50°N), the European Commission launched in 2010 and financed the CARPATCLIM project. The CARPATCLIM consortium was made by nine country members (Austria, Croatia, Czech Republic, Hungary, Poland, Romania, Serbia, Slovakia, and Ukraine) under the scientific and technical coordination of the European Commission’s Joint Research Centre (JRC). The CARPATCLIM members collected, quality-checked, homogenized, harmonized, and interpolated daily data for sixteen meteorological variables and more than thirty derived indicators related to the period 1961-2010. The principal outcome of the project is the Climate Atlas of the Carpathian Region, hosted on a dedicated website (www.carpatclim-eu.org) and made of high-resolution daily grids (0.1°x0.1°) of all variables and indicators. In order to describe the climate evolution of the Carpathian Region, we analyzed the spatial and temporal variability of ten variables: minimum, mean, and maximum temperature, daily temperature range, precipitation, cloud cover, relative sunshine duration, relative humidity, surface air pressure, and wind speed. For each variable, we performed a linear trend analysis on an annual and seasonal basis. Temperature was found to increase in every season, in particular in the last three decades, confirming the trends occurring in Europe; wind speed decreased in every season; cloud cover and relative humidity decreased in spring, summer, and winter, and increased in autumn, whilst relative sunshine duration behaved in the opposite way; precipitation and surface air pressure showed no significant trend, though they increased slightly on an annual basis. In the Carpathian region positive/negative sunshine duration anomalies are highly correlated to the corresponding temperature anomalies during the global dimming (1960s-1970s) and brightening (1990s-2000s) periods.JRC.H.7-Climate Risk Managemen

An overview of drought events in the Carpathian Region in 1961-2010

The Carpathians and their rich biosphere are considered to be highly vulnerable to climate change. Drought is one of the major climate-related damaging natural phenomena and in Europe it has been occurring with increasing frequency, intensity, and duration in the last decades. Due to climate change, land cover changes, and intensive land use, the Carpathian Region is one of the areas at highest drought risk in Europe. In order to analyze the drought events over the last 50 yr in the area, we used a 1961–2010 daily gridded temperature and precipitation dataset. From this, monthly 0.1 × 0.1 grids of four drought indicators (Standardized Precipitation-Evapotranspiration Index (SPEI), Standardized Precipitation Index (SPI), Reconnaissance Drought Indicator (RDI), and Palfai Aridity/Drought Index (PADI)) have been calculated. SPI, SPEI, and RDI have been computed at different time scales (3, 6, and 12 months), whilst PADI has been computed on an annual basis. The dataset used in this paper has been constructed in the framework of the CARPATCLIM project, run by a consortium of institutions from 9 countries (Austria, Croatia, Czech Republic, Hungary, Poland, Romania, Serbia, Slovakia, and Ukraine) with scientific support by the Joint Research Centre (JRC) of the European Commission. Temperature and precipitation station data have been collected, quality-checked, completed, homogenized, and interpolated on the 0.1 × 0.1 grid, and drought indicators have been consequently calculated on the grid itself. Monthly and annual series of the cited indicators are presented, together with high-resolution maps and statistical analysis of their correlation. A list of drought events between 1961 and 2010, based on the agreement of the indicators, is presented. We also discuss three case studies: drought in 1990, 2000, and 2003. The drought indicators have been compared both on spatial and temporal scales: it resulted that SPI, SPEI, and RDI are highly comparable, especially over a 12-month accumulation period. SPEI, which includes PET (Potential Evapo-Transpiration) as RDI does, proved to perform best if drought is caused by heat waves, whilst SPI performed best if drought is mainly driven by a rainfall deficit, because SPEI and RDI can be extreme in dry periods. According to PADI, the Carpathian Region has a sufficient natural water supply on average, with some spots that fall into the “mild dry” class, and this is also confirmed by the FAO-UNEP aridity index and the K¨oppen-Geiger climate classification.JRC.H.7-Climate Risk Managemen

Homogeneity adjustments of in situ atmospheric climate data: A review

Long‐term in situ observations are widely used in a variety of climate analyses. Unfortunately, most decade‐ to century‐scale time series of atmospheric data have been adversely impacted by inhomogeneities caused by, for example, changes in instrumentation, station moves, changes in the local environment such as urbanization, or the introduction of different observing practices like a new formula for calculating mean daily temperature or different observation times. If these inhomogeneities are not accounted for properly, the results of climate analyses using these data can be erroneous. Over the last decade, many climatologists have put a great deal of effort into developing techniques to identify inhomogeneities and adjust climatic time series to compensate for the biases produced by the inhomogeneities. It is important for users of homogeneity‐adjusted data to understand how the data were adjusted and what impacts these adjustments are likely to make on their analyses. And it is important for developers of homogeneity‐adjusted data sets to compare readily the different techniques most commonly used today. Therefore, this paper reviews the methods and techniques developed for homogeneity adjustments and describes many different approaches and philosophies involved in adjusting in situ climate data. © 1998 Royal Meteorological Societ

Climate of the Carpathian Region in the period 1961–2010: climatologies and trends of 10 variables

The Carpathians are the largest mountain range in Europe and they represent a geographic barrier between Central Europe, Eastern Europe, and the Balkans. In order to investigate the climate of the area, the CARPATCLIM project members compiled the Climate Atlas of the Carpathian Region, which consists of high-resolution daily grids (0.1˚ x 0.1˚) of sixteen meteorological variables and many derived indicators related to 1961-2010. We computed the gridded climatologies for 1961-2010 for eight variables (air pressure, cloudiness, precipitation, relative humidity, minimum and maximum temperature, sunshine duration, and wind speed) and we discuss their spatial patterns. For each variable, we calculated the gridded linear trends related to 1961-2010 both on annual and seasonal basis. In general, temperature was found to increase in every season in 1986-2010, confirming the trends occurring in Europe in the last decades. On the other way, wind speed decreased in every season. Cloudiness and relative humidity decreased in spring, summer, and winter, and increased in autumn, whilst sunshine duration, as expected, behaved in the opposite way. Precipitation slightly increased and air pressure showed no significant trend, except of a few grid points. Then, we dealt with the correlation between the variables: excluding the high elevation points, the most correlated are sunshine duration and temperature. In particular, positive and negative sunshine duration anomalies are found to be respectively correlated with positive and negative temperature anomalies during the global dimming (60’s and 70’s) and brightening (90’s and 2000’s) periods.JRC.H.7-Climate Risk Managemen