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https://doi.org/10.5194/esd-2017-24
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
20 Mar 2017
Review status
This discussion paper is under review for the journal Earth System Dynamics (ESD).
Trends and regime shifts in climatic conditions and river runoff in Estonia during 1951–2015
Jaak Jaagus1, Mait Sepp1, Toomas Tamm2, Arvo Järvet1, and Kiira Mõisja1 1Department of Geography, University of Tartu, Tartu, 51014, Estonia
2Department of Water Mana gement, Estonian University of Life Sciences, Tartu, 51014, Estonia
Abstract. Time series of monthly, seasonal and annual mean air temperature, precipitation, snow cover duration and specific runoff of rivers in Estonia are analysed for detecting trends and regime shifts during 1951–2015. Trend analysis is performed using the Mann-Kendall test and regime shifts are detected with the Rodionov test (Sequential T-test Analysis of Regime Shifts). The results from Estonia are related to trends and regime shifts in time series of indices of large-scale atmospheric circulation. Annual mean air temperature has significantly increased at 12 observed stations by 0.3–0.4 K per decade. The warming trend was detected in all seasons but with the higher magnitude in spring and winter. Snow cover duration has decreased in Estonia by 3–4 days per decade. Changes in precipitation are not clear and uniform due to their very high spatial and temporal variability. The most significant increase in precipitation was observed during the cold half-year, from November to March. Time series of specific runoff measured at 21 stations has had significant seasonal changes during the study period. Winter values have increased by 0.4–0.9 l/s per km2 per decade while stronger changes are typical for western Estonia and weaker changes for eastern Estonia. At the same time, specific runoff in April and May has notably decreased indicating the shift of the runoff maximum to earlier time, i.e. from April to March. All meteorological and hydrological variables are highly correlated in winter, determined by the large-scale atmospheric circulation. Correlation coefficients between the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) indices reflecting the intensity of westerlies, and the studied variables were 0.5–0.8. The main result of the analysis of regime shifts was the detection of coherent shifts for air temperature, snow cover duration and specific runoff in the late 1980s, mostly since the winter 1988/1989, which are, in turn, synchronous with the shifts in winter circulation. For example, runoff abruptly increased in January, February and March but decreased in April. Regime shifts in the annual specific runoff correspond to the alternation of wet and dry periods. A dry period started since 1964 or 1963, a wet period since 1978 and the next dry period since the beginning of the 21st century.

Citation: Jaagus, J., Sepp, M., Tamm, T., Järvet, A., and Mõisja, K.: Trends and regime shifts in climatic conditions and river runoff in Estonia during 1951–2015, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2017-24, in review, 2017.
Jaak Jaagus et al.
Jaak Jaagus et al.
Jaak Jaagus et al.

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Short summary
Trends and regime shifts in climatic and hydrological parameters are analysed in Estonia during 1951–2015. The most important finding was the regime shift in the majority of parameters since the winter 1988/1989. The intensity of westerly circulation described by the NAO and AO indices increased, winter mean air temperature and precipitation also increased, and snow cover duration decreased. Consequently, specific runoff of rivers increased in January, February and March but decreased in April.
Trends and regime shifts in climatic and hydrological parameters are analysed in Estonia during...
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