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Published in: Natural environment of Poland and its protection in Łódź University Geographical Research, edited by E. Kobojek and T.Marszał The results presented in the work show the selected features of local climate modification caused by urbanisation in Łódź, Central Poland. The city structure is similar to many other mid-European towns, but the influences of urbanisation on local climate are not affected here by other factors. Thus, the outcomes of presented investigations can be generalised for many cities of the region. The findings about the urban heat island are similar to those of other cities and they confirm the general rules about the UHI phenomenon, its spatial distribution and temporal variations (see Arnfield 2003 for a comprehensive review). Similarly, the influence of the city on incoming shortwave radiation in Łódź simply quantify well established relations. More unique are the studies on the albedo and the influence of surface geometry on the absorption of radiation. The influence of the town on humidity is more disputable. On the average, our data confirm the findings on the urban-rural contrasts of these elements, but they also show that unlike the UHI evolution, the diurnal course of humidity differences can take different form even in favourable weather conditions. The measurements of turbulent fluxes of sensible and latent heat, carbon dioxide and methane are unique in Poland and one of the few in Europe; thus they just provide new data and extend our understanding of poorly known processes. At the present stage, it is hard to evaluate if these result are case-specific or more general. The comparison with other cities is problematic because of a small number of similar works – there are several concerning urban energy balance, very few on carbon dioxide flux, and almost none about the flux of methane.

Ponencia presentada en: VI Congreso Internacional de la Asociación Española de Climatología celebrado en Tarragona del 8 al 11 de octubre de 2008. [ES]Series de indices de temperatura y precipitación extremas en el periodo 1951-2006 se calcularon a partir de datos de precipitación diaria y temperatura máxima y mínima en 21 estaciones en Polonia. dado que la distribución de indices de extremos es en general bastante distinta de la normal, en particular para indices que expresan ocurrencias diarias, los estimadores de tendencias mas usuales no son robustos en este caso. Se utilizaron el test tau de Kendall y el estimador de tendencias de Sen y sus resultados fueron comparados con los obtenidos con métodos mas tradicionales. [EN]Daily precipitation totals and daily minimum and maximum temperatures from 21 Polish stations were used to calculate records of indices of temperature and precipitation extremes in the period 1951-2006. Because the distributions of extreme indices are generally far from normal, especially for indices defined as day counts, the popular trend estimators like linear trend calculated by the least mean squares method are not robust. The Kendall tau test and Sen's trend estimators were used and their results were compared with those obtained by more traditional methods. The work was supported by the Polish Ministry of Education and Science under the Grant PBZ-KBN-086/PO4/2003.

Artykuł powstał w wyniku prac badawczych prowadzonych w ramach Projektu Zamawianego MNiI (K091/P04/2004/11). The aim of this work is to analyze the waves of warmth and coldness in central part of Poland basing on a daily maximum and minimum temperature in Łódź between 1931 and 2006. Warm and cold periods were distinguished following daily maximum temperature course (warm and cold days) and daily minimum temperature course (warm and cold nights). A particular day was involved in warm (cold) period, if its daily temperature was higher (lower) than average +1.28 (-l.28) of standard deviation within this calendar day. The value of l.28 was chosen because it counterparts percentile of 90% (10%) if we assume that temperature distribution is normal. The trends of seasonal and annual changeability of the number of cold and warm days and nights as well as maximum length of warm and cold waves were estimated by Sen's method. The most frequently observed were the short waves, such as one- or two days long (Fig. 3 and 9). The average of day numbers, within at least three day-long waves and an their average lasting time of the longest waves had distinct annual cycle with its maximum in summer and minimum in winter. However, the absolute maxima of the waves lengths fell on winter half-year. The longest waves were 18 and 17 days. For comparison, the lengths of the warm and cold nights periods were significantly shorter and were about II and 14 days. The longest cold waves were slightly longer than equivalent waves of warmth. The following years: 1962, 1989, 1992, 1994, 2000, 2002 and 2006 are the years of particularly long warm periods or years of a great number of warm days, and are grouped in last 20 years of analyzed series with the exception of 1962, which represents series center. On the other hand, the years, during which cold waves were exceptionally long or those, which were characterized by a great number of cold days and nights (1954, 1956, 1963, 1979, 1996) were gathered during first 30s of the analyzed period. In spite of this, only some of studied series have statistically significant trend. Lasting time of the longest wave of warmth increased significantly in winter (0.28 of the day per ID years), while the number of waves of warmth grew in summer (0.33 of the day per ID years) and during the whole year (1.79 of the day per ID years). If it is about warm nights, the lasting time of the longest wave increased significantly in winter (0.17 of the day per 10 years) and in autumn (0.20 of the day per 10 years), while the number of the days increased significantly in summer (0.36 of the day per 10 years) and within the whole year (1.61 of the day per 10 years). The length of the longest wave of cold days significantly decreased in winter (0.18 of the day per ID years) and the number of cold days in a year decreased in 0.87 of the day per 10 years. In case of cold nights the lasting time of the longest wave shortened in winter (0.17 of the day per 20 years) and during the whole year (0.2 of the day per 10 years), while the number of cold nights in the year decreased in 1.43 days per 10 years and 0.43 of the day per ID years in spring. The influence of the atmospheric circulation either in macroscale or mesoscale on frequency and intensity of extreme thermal events in Poland is visible only in winter, however it explains no more than 25% of their changeability. Better results are obtained by composite method, which allows to single out such synoptic situations, which favor maintaining strong positive and negative thermal anomalies. Thermal conditions of central Poland primarily depend on baric centers, which centers locate in country's proximity (Fig. 14-17). The correlations between number of days during periods of warm days and nights, and maximum length of waves and northern hemisphere's temperature are positive and statistically significant for all seasons except summer (fable 6). Nonetheless, no more than 25% of the changes might be the direct results of big-scale temperature changes, the rest is influenced by regional or even local factors. The correlations between number of days during periods of cold days and nights and maximum length of waves and northern hemisphere's temperature are negative and statistically insignificant.

W pracy wykorzystano miesięczne sumy opadu ze stacji Łódź-Lublinek z okresu 1931-1995. Przedstawiono podstawowe charakterystyki statystycme miesięcznych, sezonowych i rocznych sum opadu: średnią, odchylenie standardowe, wartości ekstremalne, asymetrię, współczynnik zmienności oraz rozkłady częstości miesięcmych sum opadu. Analizowano związki między wartościami miesięcznych sum opadu a indeksem NAO i częstościami wybranych klas cyrkulacji. Monthly precipitation totals from Lódź-Lublinek meteorological station from the period 1931-1995 have been used. Basic statistical features of monthly, seasonal and annual totals such as mean, standard deviation, extreme values, assymetry and coefficient of variability were presented together with frequency distributions of monthly totals. Relations of monthly totals to NAO index and frequencies of selected circulation types were analysed.

W opracowaniu analizowano szereg dobowych sum opadu z Łodzi z okresu 1931-1995. Przedstawiono roczny bieg częstości występowania dni bez opadu i z opadem w poszczególnych przedziałach wartości. Stwierdzono, że pojawienie się opadu zależy w większym stopniu od charakteru cyrkulacji niż od kierunku napływu mas. Badano długoletnią zmienność częstości dni bez opadu, dni z sumą opadu powyżej 10 mm i największej dobowej sumy opadu w roku. Pokazano, że najwyższe dobowe sumy opadu pojawiają się w dniach o cyrkulacji Eo Record of daily precipitation totals from Łódź from the period 1931-1995 has been analysed. The annual courses of frequencies of days without precipitation and with precipitation in particular ranges were presented. It was shown that occurrence of precipitation is stronger related to the character of circulation than to direction of air mass advection. Long-term variability of frequencies of days without precipitation, days with totals exceeding 10 mm/day and long-term variability of the highest daily total during the year were analysed. It was shown that the highest daily totals occur in day with circulation of type Eo.

The regional climate model RegCM3 is used to investigate potential future changes of temperature indices in Poland for the period 2011–2030. The model is forced by ECHAM5/MPI-OM GCM data from World Data Centre (WDCC) database for the 1971–1990 reference period and 2011–2030 projection period under SRES B1, A1B and A2 emission scenarios. Model output statistics methods are used to transform simulated minimum and maximum temperature data into realistic data. Selected indices of temperature extremes and their differences between the scenario simulations and the reference were calculated, for all scenarios, for the entire period and for each season. Results show a mean yearly increase in the number of summer and hot days and a decrease in the number of frost and ice days. Highest decline in the number of frost and ice days in autumn and an increase in spring is noticed. An highest increase in the number of summer and hot days is seen in summer. Future projections of these indices are relevant for studies on climate change impact in agriculture, tourism, health, transportation, road and building infrastructure. This work was carried out as part of the project KLIMAT "Impact of climate change on the society, the environment and the economy (changes, effects and ways of limiting them, conclusions for science and engineering practice and economic planning)". No POIG.01.03.01- 14-011/08 in frames of the Operational Programme Innovative Economy, co-financed by the European Regional Development Fund. Authors thank anonymous reviewers for valuable comments.