Multi-model Approach for Projecting Extremes Related to the Lack and Excess of Precipitation in Central/Eastern Europe

Frequent hot weather in summer and overall increasingly warm regional climatic conditions are direct consequences of global warming. Global and regional warming induced effects on precipitation are not as clear as on temperature because the higher spatial and temporal variabilities might hide any robust changing signal. Nevertheless, precipitation is one of the most important meteorological variables since it considerably affects natural ecosystems and cultivated vegetation as well, as most of human activities. Extreme precipitation events – both excessive, intense rainfalls and severe droughts – may result in several environmental, agricultural, economical and natural disasters. The lack of precipitation for extended period and coincidental intense heat wave often lead severe drought events. In order to avoid or at least reduce the effects of these precipitation-related hazards, national and local communities need to develop regional adaptation strategies, and then, act according to them. For this purpose, results of global climate model (GCM) simulations must be downscaled to regional and local scales, hence better serving end-users' needs. Downscaling of coarse resolution GCM simulation outputs is especially important in case of precipitation because of the large temporal and spatial variabilities, and consequently, since appropriate precipitation impact assessment studies require fine resolution information. From the agricultural point of view, especially potential dry conditions induce long-term planning, for which estimation of precipitation is evidently the key element.

In this paper estimated trends of precipitation- and drought-related climate indices and the return period of the daily precipitation amount are analysed. The multi-model approach consists of 11 regional climate model (RCM) simulations from the ENSEMBLES project with 25 km horizontal resolution. Three different GCMs provided the necessary initial and boundary conditions using the emission scenario A1B. Validation analyses for the Central/Eastern European region showed that simulated precipitation values usually significantly underestimate the observations in summer and overestimate in the rest of the year. Therefore, we applied bias correction in order to eliminate these systematic errors. We used a quantile matching technique for each RCM simulation: the monthly empirical distribution functions of each grid point were fitted to the observed distributions (reference: E-OBS and CARPATCLIM databases), then, the calculated multiplicative bias correcting factors are applied to the raw outputs of RCM experiments. After the correction, we analyzed several precipitation-related climate indices (e.g., average number of dry days; maximum number of consecutive dry days; average number of precipitation days exceeding 1 mm, 5 mm, 10 mm, and 20 mm; maximum number of consecutive precipitation days exceeding 5 mm, 10 mm, and 20 mm; mean length of dry and wet spells; highest 1-day and 5-day precipitation totals; simple daily intensity index; 90th, 95th, and 99th percentiles of daily precipitation amounts) for nine sub-regions (SE-CZ, E-AT, SK, SW-UK, SI, HU, RO, CR, N-SR), as well, as the 10 and 20 year return periods of the daily precipitation amount for the 1951-2100 time period on seasonal and annual scales.

According to our results climate change results in more intense and more frequent precipitation extremes in Central/Eastern Europe. The return period of the daily precipitation amount is estimated to increase in summer (by a factor of 1.2-2) by the late 21st century relative to the 1961–1990 reference period. The projected changes are considerably smaller for the other three seasons compared to future summer changes. In case of consecutive dry days ~50% increase is estimated in summer, therefore substantially drier climatic conditions are projected for the future. In winter and in autumn more heavy precipitation days and more intense precipitation are very likely to occur in the 21st century. Overall, in the future we should expect both floods and droughts, as in winter and in autumn more frequent and more intense precipitation are projected, while summer is tend to be drier, especially in the southern parts of the selected domain.