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1

The SARIMA model-based monthly rainfall forecasting for the Turksvygbult Station at the Magoebaskloof Dam in South Africa

Tadesse Kassahun Birhanu, Dinka Megersa Olumana

Journal of Water and Land Development

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2022

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no. 53

100--107

EN

Rainfall forecast information is important for the planning and management of water resources and agricultural activities. Turksvygbult rainfall near the Magoebaskloof Dam (South Africa) has never been modelled and forecasted. Hence, the objective of this study was to forecast its monthly rainfall using the SARIMA model. GReTL and automatic XLSTAT software were used for forecasting. The trend of the long-term rainfall time series (TS) was tested by Mann-Kendall and its stationarity was proved by various unit root tests. The TS data from Oct 1976 to Sept 2015 were used for model training and the remaining data (Oct 2015 to Sept 2018) for validation. Then, all TS (Oct 1976 to Sept 2018) were used for out of sample forecasting. Several SARIMA models were identified using correlograms that were derived from seasonally differentiated TS. Model parameters were derived by the maximum likelihood method. Residual correlogram and Ljung–Box Q tests were used to check the forecast accuracy. Based on minimum Akaike information criteria (AI) value of 5642.69, SARIMA (2, 0, 3) (3, 1, 3)12 model was developed using GReTL as the best of all models. SARIMA (1, 0, 1) (3, 1, 3)12, with minimum AI value of 5647.79, was the second-best model among GReTl models. This second model was also the first best automatically selected model by XLSTAT. In conclusion, these two best models can be used by managers for rainfall forecasting and management of water resources and agriculture, and thereby it can contribute to economic growth in the study area. Hence, the developed SARIMA forecasting procedure can be used for forecasting of rainfall and other time series in different areas.

2

Rainfall and rainy days trend and ENSO phenomena in Himalayan Kingdom of Bhutan

Sharma Vasker, Adhikari Kirtan

Acta Geophysica

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2022

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Vol. 70, no 4

1855--1869

EN

The study explores the seasonal rainfall and rainy days trend in the Himalayan Kingdom of Bhutan. Mann-Kendall and Sen’s slope test was applied to detect the trend and magnitude of the trend for both the rainfall and rainy days. The trends are also analyzed with respect to the elevation of the climatic stations. Further, an attempt has been made to recognize the El-Ni ño-Southern Oscillation (ENSO)-rainfall interaction using station-based rainfall with the ENSO cycle considering the period of 33 years. Cross-correlation of ENSO and rainfall with respect to elevation has also been presented. The trend analysis showed that in the localized regions, both the rainfall and rainy days trend was significantly declining, however, the trend in most of the stations is hardly conspicuous which may be attributed to the influence of the orographic phenomena. From the ENSO-rainfall assessment, it was observed that rainfall in the southern foothills correlates negatively with the ENSO phenomena indicating intense rainfall after 1–2 months of the cooling phase of the Pacifc Ocean. However, such an ENSO effect is not observed in the majority of the meteorological stations which may be attributed to the location of the station in the mountainous region where the topography affects the rainfall variation.

3

Assessment of evidence based climate variability in Bhagirathi sub basin of India: a geostatistical analysis

Rehman Sufa, Sajjad Haroon, Masroor Md, Rahaman Md Hibjur, Roshani, Ahmed Raihan, Sahana Mehebub

Acta Geophysica

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2022

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Vol. 70, no 1

445--463

EN

Climate variability analysis is essential for predicting the behavior of various extreme weather events and making communities resilient. Notwithstanding the profound concerns, climate variability assessment faces numerous challenges due to inadequate and sometimes unavailability of data at spatiotemporal scales. This study makes an attempt to analyse climate variability in the Bhagirathi Sub-basin of India. Six meteorological variables were analysed from fourteen weather stations located in the Sub-basin during 1968–2017. Modified Mann–Kendall test was employed to ascertain the trends in meteorological variables. One-way ANOVA was used to assess the relationship between and within the variables. A total of 432 households were selected for reaffirming climate variability and impact on landscape. Significant trends were detected in highest maximum, mean maximum (Mmax) and mean minimum (Mmin) temperatures, relative humidity (Rh), rainfall and vapour pressure (Vp) at annual and seasonal scales. Stations located in eastern and deltaic Sub-basins registered varying trends in these meteorological variables due to anthropogenic activities-induced land use changes. ANOVA revealed a robust relation among rainfall, Vp, Mmin and Mmax. Perceptions of the sampled households revealed that climate variability has considerably affected food intensity, vegetation, soil, water resources and agricultural pattern. We find modified Mann– Kendall method effective in analysing climate variability in the Sub-basin. Thus, this method can be utilized for effective analysis of climate variability at spatial scales in geographical regions.

4

Trend and nonstationary relation of extreme rainfall: Central Anatolia, Turkey

Oruc Sertac

Acta Geophysica

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2021

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Vol. 69, no. 1

243--255

EN

The frequency of extreme rainfall occurrence is expected to increase in the future and neglecting these changes will result in the underestimation of extreme events. Nonstationary extreme value modelling is one of the ways to incorporate changing conditions into analyses. Although the defnition of nonstationary is still debated, the existence of nonstationarity is determined by the presence of signifcant monotonic upward or downward trends and/or shifts in the mean or variance. On the other hand, trend tests may not be a sign of nonstationarity and a lack of signifcant trend cannot be accepted as time series being stationary. Thus, this study investigated the relation between trend and nonstationarity for 5, 10, 15, and 30 min and 1, 3, 6, and 24 h annual maximum rainfall series at 13 stations in Central Anatolia, Turkey. Trend tests such as Mann– Kendall (MK), Cox–Stuart (CS), and Pettitt’s (P) tests were applied and nonstationary generalized extreme value models were generated. MK test and CS test results showed that 33% and 27% of 104 time series indicate a signifcant trend (with p<0.01–p<0.05–p<0.1 signifcance level), respectively. Moreover, 43% of time series have outperformed nonstationary (NST) models that used time as covariate. Among fve diferent time-variant nonstationary models, the model with a location parameter as a linear function of time and the model with a location and scale parameter as a linear function of time performed better. Considering the rainfall series with a signifcant trend, increasing trend power may increase how well fitted nonstationary models are. However, it is not necessary to have a signifcant trend to obtain outperforming nonstationary models. This study supported that it is not necessarily time series to have a trend to perform better nonstationary models and acceptance of nonstationarity solely depending on the presence of trend may be misleading.

5

Evaluation of different gridded precipitation products in trend analysis of precipitation features over Iran

Shobeiri Shahin, Sharafati Ahmad, Neshat Aminreza

Acta Geophysica

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2021

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Vol. 69, no. 3

959--974

EN

In recent years, gridded precipitation products have been widely used in hydrology studies and other felds of water sciences. This study evaluated the potential of several gridded precipitation products, including GPCC, TRMM, CRU, ERA-Interim, and ERA5, in trend analysis of precipitation depth and the number of rainy days in various regions of Iran. Moreover, the observational precipitation data of the daily time series were collected from 68 Iranian synoptic stations. The Mann–Kendall test was conducted to determine gridded and observed precipitation trends in the period of 1997 to 2017. The probability of detection (POD) and false alarm ratio (FAR) indices were utilized to compare gridded and observed precipitation trends. Results showed that the best consistency (POD: 52% ~ 80%, FAR: 60% ~ 88%) was observed between the observed trends of the number of rainy days and those obtained by TRMM product over different regions of Iran. Moreover, ERA-Interim ofered a better performance (POD: 50% ~ 100%, FAR: 58% ~ 72%) in the trend analysis of precipitation depth in Iran. The consistency between observational and gridded precipitation trends has never been analyzed in Iran at this level; therefore, this is considered a unique analysis. Besides, the generated maps of precipitation products’ performance provide a comprehensive view of better water resources management over different regions of Iran.

6

Water level trends in the ponds of Siemianice Experimental Forest Farm

Stasik Rafał, Kęsicka Barbara, Korytowski Mariusz

Journal of Water and Land Development

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2020

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no. 47

169--175

EN

The results of a long-term water level monitoring in three forest ponds are presented in the paper. The ponds are located in the Wielisławice and Laski forest districts in South Wielkopolska, Poland. Two of the analysed ponds are natural ones supplied by precipitation and the third now is disused artificial fishpond of throughflow water management. Systematic water level measurements, as well as measurement of basic meteorological conditions – precipitation and air temperature – were carried out in the 2000–2016 hydrological period. The basic statistics as well as the trends in long-time changes in water levels, were determined using the nonparametric Mann–Kendall test were calculated. The results obtained were statistically inconclusive, but they indicated downward trends in water levels in the natural ponds and upward trends in water levels in the artificial pond. Although a statistically significant downward trend was observed in only one natural pond, it may suggest some negative changes occurring in the catchment of ponds in general.

7

Analysis of distribution of precipitation duration and amounts in Legnica in the period of 1966–2015

Jakubczyk Teresa

Journal of Water and Land Development

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2019

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no. 41

69--76

EN

The paper presents the results of analysis of duration of precipitation sequences and the amounts of precipitation in individual sequences in Legnica. The study was aimed at an analysis of potential trends and regularities in atmospheric precipitations over the period of 1966–2015. On their basis a prediction attempt was made for trends in subsequent years. The analysis was made by fitting data to suitable distributions – the Weibull distribution for diurnal sums in sequences and the Pascal distribution for sequence durations, and then by analysing the variation of the particular indices such the mean value, variance and quartiles. The analysis was performed for five six-week periods in a year, from spring to late autumn, analysed in consecutive five-year periods. The trends of the analysed indices, observed over the fifty-year period, are not statistically significant, which indicates stability of precipitation conditions over the last half-century.

PL

W pracy przedstawiono wyniki analiz rozkładów długości trwania sekwencji opadowych oraz wielkości opadów w poszczególnych sekwencjach w Legnicy. Badania miały na celu przeprowadzenie analizy ewentualnych tendencji i regularności w opadach atmosferycznych w okresie 1966–2015. Na ich podstawie podjęto próbę predykcji dla tendencji w kolejnych latach. Analizę wykonano przez dopasowanie do danych odpowiednich rozkładów – rozkładu Weibulla do sum dobowych w sekwencjach oraz rozkładu Pascala do długości sekwencji, a następnie przez zbadanie zmienności poszczególnych wskaźników, takich jak średnia, wariancja i kwartyle. Analiza została przeprowadzona w odniesieniu do pięciu sześciotygodniowych okresów w ciągu roku od wczesnej wiosny do późnej jesieni, rozpatrywanych w kolejnych pięcioleciach. Tendencje badanych wskaźników zaobserwowane na przestrzeni pięćdziesięciolecia nie są istotne statystycznie, co świadczy o stabilności zjawiska opadów w ostatnim pięćdziesięcioleciu.

8

Assessment of the impact of climate change on the freshwater availability of Kaduna River basin, Nigeria

Okafor G. C., Ogbu K. N.

Journal of Water and Land Development

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2018

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no. 38

105--114

EN

Changes in runoff trends have caused severe water shortages and ecological problems in agriculture and human well-being in Nigeria. Understanding the long-term (inter-annual to decadal) variations of water availability in river basins is paramount for water resources management and climate change adaptation. Climate change in Northern Nigeria could lead to change of the hydrological cycle and water availability. Moreover, the linkage between climatic changes and streamflow fluctuations is poorly documented in this area. Therefore, this study examined temporal trends in rainfall, temperature and runoff records of Kaduna River basin. Using appropriate statistical tools and participatory survey, trends in streamflow and their linkages with the climate indices were explored to determine their amplifying impacts on water availability and impacts on livelihoods downstream the basin. Analysis indicate variable rainfall trend with significant wet and dry periods. Unlike rainfall, temperature showed annual and seasonal scale statistically increasing trend. Runoff exhibit increasing tendency but only statistically significant on annual scale as investigated with Mann–Kendall trend test. Sen’s estimator values stood in agreement with Mann–Kendall test for all variables. Kendall tau and partial correlation results revealed the influence of climatic variables on runoff. Based on the survey, some of the hydrological implications and current water stress conditions of these fluctuations for the downstream inhabitants were itemized. With increasing risk of climate change and demand for water, we therefore recommend developing adaptive measures in seasonal regime of water availability and future work on modelling of the diverse hydrological characteristics of the entire basin.

PL

Zmiany w prawidłowościach odpływu spowodowały poważne ograniczenia w dostępności wody, problemy ekologiczne w rolnictwie oraz zmiany warunków życia ludzi w Nigerii. Zrozumienie długoterminowej zmienności (w poszczególnych latach i dziesięcioleciach) dostępności wody w basenie rzeki jest ogromnie ważne w zarządzaniu zasobami wodnymi i adaptacji do zmian klimatycznych. Zmiany klimatu w północnej Nigerii mogą doprowadzić do zmian cyklu hydrologicznego i dostępności wody. Ponadto, związki między zmianami klimatu a zmiennym odpływem wody są dla tego obszaru słabo udokumentowane. Z tego powodu w przedstawionych badaniach analizowano czasowe zmiany opadu, temperatury i odpływu wody z basenu rzeki Kaduna. Stosując odpowiednie narzędzia statystyczne i badania ankietowe, badano trendy przepływu wody i ich związki ze wskaźnikami klimatycznymi, aby udokumentować ich rosnący wpływ na dostępność wody i warunki życia mieszkańców w dolnym biegu rzeki. Analiza wykazała zmienność opadów z wyraźnymi okresami suchymi i wilgotnymi. W przeciwieństwie do opadów temperatura cechowała się statystycznie istotnym trendem rosnącym w skali pór roku i lat. Odpływ wykazywał istotną statystycznie rosnącą tendencję tylko w skali roku, co wykazano testem trendu Manna–Kendalla. Wartości estymatora Sena były zgodne z wartościami uzyskanymi z zastosowaniem testu Manna–Kendalla dla wszystkich zmiennych. Wartości tau Kendalla i korelacje cząstkowe wykazały wpływ zmian klimatu na odpływ wody. Na podstawie badań ankietowych wykazano pewne skutki hydrologiczne i aktualne warunki stresu wodnego dla mieszkańców zamieszkujących tereny w dolnym biegu rzeki. Wobec rosnącego ryzyka zmian klimatycznych i zapotrzebowania na wodę zaleca się rozwijanie środków przystosowawczych do sezonowego reżimu dostępności wody i przyszłe prace poświęcone modelowaniu zmiennych cech hydrologicznych całego basenu.

9

Analysis of trend rainfall: Case of North-Eastern Algeria

Mrad D., Djebbar Y., Hammar Y.

Journal of Water and Land Development

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2018

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no. 36

105--115

EN

The climatic change is a reality largely recognized today in the scientific community. Nevertheless, its impact on precipitation, especially on annual, monthly and seasonally rainfall in arid and semi-arid regions is not yet certain. Indeed, very few studies have dealt with this matter in Algeria. In this context to examine spatial distribution of annual and seasonal rainfall an attempt has been made using the inverse distance weighting (IDW) method. Trends and magnitude estimate of change in rainfall series were detected by Mann–Kendall tests and Sen's test slope, has been applied to the data registered of 35 stations in the watershed Constantinois Seybouse Mellegue (CSM) North-Eastern Algeria over a period of 43 years (1969–2012). Results from spatial plot of annual rainfall showed that the rainfall increases with altitude, but is higher for the stations exposed to moist winds. It also increases from east to west and conversely decreases as one moves away from the coast to the south. From statistical method showed that there are increase trends at 95% confidence at annual scale in some rainfall stations with high altitude and coastal stations during winter season.

PL

Zmiana klimatu jest faktem powszechnie uznawanym obecnie przez społeczność naukową. Mimo to jej wpływ na opady, szczególnie na roczny, miesięczny i sezonowy opad na obszarach klimatu suchego i półsuchego, nie jest jeszcze dobrze rozpoznany. Do tej pory tylko kilka badań w Algierii dotyczyło tej kwestii. W związku z tym podjęto próbę zbadania przestrzennego rozmieszczenia rocznych i sezonowych opadów za pomocą metody odwrotnej odległości (IDW – ang. inverse distance weighting). Trendy i wielkość oszacowanych zmian w seriach opadów analizowano testem Manna–Kendalla, a test nachylenia Sena użyto do danych zgromadzonych w 35 posterunkach opadowych w zlewni Constantinois Seybouse Mellegue (CSM) w północno- -wschodniej Algierii w ciągu 43 lat (1969–2012). Wyniki analiz przestrzennego rozkładu rocznych opadów wykazały, że opad rośnie wraz z wysokością nad poziomem morza i jest większy w stanowiskach eksponowanych na wilgotne wiatry. Opad rośnie ze wschodu na zachód, a maleje od wybrzeża w kierunku południowym. Metody statystyczne ujawniły rosnący (przedział ufności 95%) trend opadów w niektórych posterunkach na dużych wysokościach i w posterunkach przybrzeżnych w okresie zimy.

10

Dynamika występowania niżówek w rzekach górskich i wyżynnych na przykładzie Wisłoki i górnego Wieprza. Cz. 2. Zmienność wieloletnia

Baran-Gurgul K., Raczyński K.

Woda-Środowisko-Obszary Wiejskie

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2017

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T. 17, z. 1

5--17

PL

Celem niniejszej pracy jest ocena częstości występowania niżówek w rzekach położonych w otoczeniu środowiska przyrodniczego o różnym charakterze – w rzece górskiej, tj. Wisłoce i jej dopływach, i w rzece wyżynnej, tj. górnym Wieprzu wraz z dopływami. Analizę dynamiki pojawiania się przepływów niżówkowych wykonano na podstawie zmienności podstawowych charakterystyk niżówek (tj. czasu trwania i objętości niżówki) w wieloleciu 1983–2013. W rozpatrywanym okresie zaobserwowano więcej niżówek w rzekach górskich niż wyżynnych, lecz były one krótsze. W rzekach wyżynnych stwierdzono więcej lat „bezniżówkowych”. Badanie stacjonarności rocznych szeregów charakterystyk niżówek wykonano z użyciem testu Shapiro–Wilka, Ljunga–Boxa i Manna–Kendalla z poprawką na autokorelację. Około połowy analizowanych szeregów nie spełniało warunku normalności. Do badania trendu wykorzystano test Manna–Kendalla. Test ten wykazał trend malejący badanych ciągów w prawie wszystkich przekrojach w rzekach wyżynnych i tylko w jednym – w rzekach górskich. W około połowie ciągów stwierdzono istotną, potwierdzoną testem Ljunga–Boxa, autokorelację rzędu pierwszego – zarówno w szeregach czasów trwania, jak i objętości niżówek. Stwierdzono, że w badanych ciągach występują dwa typy funkcji autokorelacji. Pierwszy typ funkcji, występujący głównie w rzekach wyżynnych, cechuje się dłuższą pamięcią, okresy podobne trwają około 10–11 lat. W pozostałych przypadkach ACF wskazują na pamięć krótszą i odnoszą się do rzek o większej dynamice przepływów.

EN

The main goal of this study is to assess the long-term dynamics of low flows occurrence in catchments located in different environment conditions: mountain river: Wisłoka and its tributaries and upland river: Upper Wieprz with tributaries. Analysis of low flows occurrence was based on variability of basic low flow characteristics (duration time and volume of low flow episode) in period 1983–2013. In studied period, more low flows occurred in mountain rivers, however the time of duration was shorter than in upland area. On uplands, more years without low flow episodes were observed. For stationary of annual series analysis Shapiro–Wilk, Ljung–Box and Mann–Kendall tests with autocorrelation correction were used. About half of studied series does not complete the terms of normal distribution. For this reason, trend studies were performed by using nonparametric tests. Mann–Kendal test showed descending trends in almost all gauging sections located in upland region and only in one located in mountain rivers. In half of series there was a significant, confirmed by Ljung–Box test, first rank autocorrelation – in both duration time and volume series. It was found that in tested series, there were two types of autocorrelation function. First type of function, that occurred mainly in upland area, was characterized by long-term memory, where similar periods last for about 10–11 years. In other cases, ACF indicated a short memory of episodes and occurred in catchments with higher flow dynamics.

11

Trend analysis of climatic variables in an arid and semi-arid region of the Ajmer District, Rajasthan, India

Pingale S. M., Khare D., Jat M. K., Adamowski J.

Journal of Water and Land Development

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2016

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no. 28

3--18

EN

In the present study, trends and variations in climatic variables (i.e. rainfall, wet day frequency, surface temperature, diurnal temperature, cloud cover, and reference and potential evapotranspiration) were analyzed on seasonal (monsoon and non-monsoon) and annual time scales for the Ajmer District of Rajasthan, India. This was done using non-parametric statistical techniques, i.e. the Mann–Kendall (MK) and Modified Mann–Kendall (MMK) tests, over a period of 100 years. The MK test with prewhitening (MK–PW) of climatic series was also applied to climatic variables and the results were compared to those obtained through the MK and MMK tests in order to assess the performance of trend detection methods. The Pettitt–Mann–Whitney (PMW) test was applied to detect the temporal shift in climatic series. The trend analysis revealed that annual and seasonal rainfall did not show any statistically significant trend at a 10% significant level. A noticeable trend increase was found in wet day frequency, surface temperature and reference evapotranspiration (ET) during the non-monsoon season from the three non-parametric statistical tests at a 10% significance level. A statistically significant decrease in maximum temperature was found during the non-monsoon season by the MK–PW test alone. This analysis of several climatic variables at the district scale is helpful for the planning and management of water resources and the development of adaptation strategies in adverse climatic conditions.

PL

W pracy analizowano trendy i zmienność czynników klimatycznych (opad, częstotliwość dni wilgotnych, temperaturę powierzchni ziemi, temperaturę dobową, zachmurzenie oraz ewapotranspirację wskaźnikową i potencjalną) w skali sezonowej i rocznej w dystrykcie Ajmer, w Radżasthanie (Indie). Analizę przeprowadzono za pomocą nieparametrycznych technik statystycznych Manna–Kendalla (MK) i zmodyfikowanej techniki MK (MMK) dla 100-letniego okresu. Test MK z eliminacją korelacji serii klimatycznych (prewhitening – MK–PW) zastosowano także do zmiennych klimatycznych, a wyniki porównano z uzyskanymi z użyciem testów MK i MMK, co pozwoliło na ocenę wiarygodności wykrywania trendu zmian w czasie. W celu wykrycia czasowych przesunięć serii klimatycznych zastosowano test Pettitta–Manna–Whitneya (PMW). Na podstawie analizy trendu stwierdzono, że opady roczne i sezonowe nie wykazywały statystycznie istotnego trendu na poziomie istotności 10%. Wykorzystując trzy testy nieparametryczne, stwierdzono rosnący trend w przypadku częstości występowania wilgotnych dni, temperatury powierzchni i ewapotranspiracji wskaźnikowej w okresie pozamonsunowym na poziomie istotności 10%. Statystycznie istotny spadek maksymalnej temperatury w tym okresie stwierdzono jedynie, gdy stosowano test MK–PW. Przedstawiona analiza kilku zmiennych klimatycznych w skali dystryktu może być pomocna w planowaniu i zarządzaniu zasobami wodnymi i w rozwoju strategii adaptacji do niekorzystnych warunków klimatycznych.

12

Changes in the Large-Scale Atmospheric Circulation over Romania Between 1961 and 2010 on Seasonal Basis

Barbu N., Burada C., Stefan S., Georgescu F

Acta Geophysica

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2016

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Vol. 64, no. 2

510--520

EN

The aim of this paper is to investigate the trends and shifts of the circulation types over Romania for 50-year period (1961-2010) on seasonal basis. In order to achieve this, two objective catalogues, namely GWT and WLK, from COST733 Action were employed. Daily circulation types were grouped according to the cyclonicity and anticyclonicity and were used to calculate the seasonal occurrence frequency of cyclonic and anticyclonic types. The trend of seasonal time series was investigated by using Mann–Kendall test and the shifts points were determined by using Pettitt test. The results reveal that the occurrence frequency of anticyclonic types increases in summer and winter seasons and the occurrence frequency of cyclonic ones decreases for the summer season (for alpha = 0.05).