Alterations of abiotic factors (e.g., river water temperature and discharge) will definitely affect the fundamental processes of aquatic ecosystems. The purpose of this study was to examine the ...impact of climate change on the structure of fish assemblages in fast-flowing rivers belonging to the catchment of the major Eastern European river, the Nemunas. Five catchments of semi-natural rivers were selected for the study. Projections of abiotic factors were developed for the near (2016–2035) and far future (2081–2100) periods, according to four RCP scenarios and three climate models using the HBV hydrological modelling tool. Fish metric projections were developed based on a multiple regression using spatial data. No significant changes in projections of abiotic and biotic variables are generally expected in the near future. In the far future period, the abiotic factors are projected to change significantly, i.e., river water temperature is going to increase by 4.0–5.1 °C, and river discharge is projected to decrease by 16.7–40.6%, according to RCP8.5. By the end of century, the relative abundance of stenothermal fish is projected to decline from 24 to 51% in the reference period to 0–20% under RCP8.5. Eurythermal fish should benefit from climate change, and their abundance is likely to increase from 16 to 38% in the reference period to 38–65% under RCP8.5. Future alterations of river water temperature will have significantly more influence on the abundance of the analysed fish assemblages than river discharge.
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•Future climate changes are likely to affect fish assemblages in rivers.•Projections were made using hydrological modelling and statistical methods.•River discharge is projected to decrease, while temperature is likely to increase.•Changes of abiotic factors will cause changes in abundance of investigated fishes.•Changes of river temperature will have most significant impact on fish abundance.
Changes in the reference evapotranspiration (ET₀) and precipitation (P) patterns in the Nemunas River basin (Baltic Sea catchment) are evident today and will be even more significant in the future. ...Nemunas basin aridity dynamics (1901–2010) and projections (2081–2100) were evaluated using the UNEP aridity index (AI). Historical analysis (CRU TS3.24.01) and future projections (EURO-CORDEX) of monthly air temperature and precipitation were used for the AI estimation. Projections of the meteorological parameters according to 4 Representative Concentration Pathway scenarios (RCP2.6, 4.5, 6.0 and 8.5) were used in the analysis. In the Nemunas River basin, evapotranspiration exceeded precipitation from April to August, and in a large part of the basin the climatic conditions during this part of the year could be described as dry subhumid (AI < 0.65). Since the 1980s, increased aridity has been observed between April and August due to a strong positive trend of ET₀ and a strong negative trend of P. Future projections (2081–2100) show that despite large uncertainties in the climate projections, it is more likely that the Nemunas basin climate will become more humid in April and May and drier between June and August. The increase in climate aridity during these months is more likely in the southern and central parts of the basin.
Abstract
The aim of this research is to analyse and project the effects of changing climate on Lithuanian river runoff and water temperature. Climate change is expected to affect the extremes of the ...major river indices that impact fundamental ecological processes in river ecosystems. The available runoff and temperature data of rivers from three different hydrological regions of Lithuania were used. HBV software was applied for modelling of hydrological processes in the selected river catchments. The expected future changes of runoff and water temperature were projected according to a new set of scenarios (called representative concentration pathways) presented in the Intergovernmental Panel on Climate Change Fifth Assessment Report. The projected extreme values of runoff (flood and low flow discharges) and water temperatures in the beginning and the end of the 21st century were compared to the ones from the past period. The results showed a decrease of spring flood discharges and summer low flows and an increase of river water temperature at the end of the 21st century. The results are going to be used for an integrated assessment of the impact of climate change on aquatic animal diversity and productivity.
Heavy precipitation events in Lithuania for the period 1961-2008 were analysed. The spatial distribution and dynamics of precipitation extremes were investigated. Positive tendencies and in some ...cases statistically significant trends were determined for the whole of Lithuania. Atmospheric circulation processes were derived using Hess & Brezowski's classification of macrocirculation forms. More than one third of heavy precipitation events (37%) were observed when the atmospheric circulation was zonal. The location of the central part of a cyclone (WZ weather condition subtype) over Lithuania is the most common synoptic situation (27%) during heavy precipitation events. Climatic projections according to outputs of the CCLM model are also presented in this research. The analysis shows that the recurrence of heavy precipitation events in the 21st century will increase significantly (by up to 22%) in Lithuania.
Factor analysis (FA) is applied to identify climate-forming factors and quantitatively evaluate their importance in the eastern part of the Baltic Sea region. Monthly data from 7 meteorological ...stations are used: average maximum and average minimum of air temperature (T₁ andT₂), atmospheric pressure (P), wind speed at a height of 10 m (v), monthly precipitation (Q), duration of sunshine (S) and partial pressure of water vapour (e). FA reveals that the variables form 2 main groups (meteorological complexes): a hygrothermal complex—T₁,T₂ ande—and a baric-radiational complex—P,QandS. Both meteorological complexes exist almost independently of each other (in cold seasons in particular), i.e. it is possible to distinguish the 2 most important types of climate-forming processes in the eastern part of the Baltic Sea region. One of them is advection related to the input of various air masses whose features are best reflected by air temperature and humidity. The other process mostly takes place within 1 pressure system (cyclone or anticyclone): air mass transformation, vertical mixing, formation of clouds and related precipitation and input of solar radiation.
The impact of the North Atlantic Oscillation (NAO) on long-term air temperature fluctuations in Lithuania was studied for the period 1865 to 2000. Mean monthly values of 2 NAO indices (NAO-1, NAO-2) ...and air temperatures at 9 Lithuanian meteorological stations were used as references. Synoptic situations, as well as the mean sea level pressure (SLP) and 500 hPa geopotential height field of a total of 265 months, were analysed. NAO conditions were classified as positive, negative or neutral. Air temperature fluctuations in Lithuania during the cold period of the year (November to March) are positively correlated with fluctuations of the NAO indices. During periods of extreme NAO indices (|I| > ±1.5σ), a negative NAO phase is usually correlated (75 to 88% of the cases) to negative temperature anomalies, whereas a positive NAO phase is correlated to positive temperature anomalies. In the other cases, reverse impact of positive and negative NAO patterns, the relation between NAO phases and regional temperature anomalies is opposite or not detectable. Also, this study includes the analysis of atypical periods of NAO-like circulation: when positive NAO phase was related to negative temperature anomalies and negative NAO phase to positive temperature anomalies in Lithuania.
This paper is concerned with atmospheric circulation as the central factor influencing snow melting conditions and consequently the spring runoff characteristics of the Nemunas River. The analysis ...includes snow water equivalent (SWE) accumulated before the start of snowmelt runoff and its relationship with maximal water discharge and flood volume. The results show that the relationship has a dipolar character. The cohesion between SWE and the maximal runoff was divided into two different groups: A and B. The increasing maximal values of SWE correspond to the rapidly increasing maximal water discharge during the runoff seasons in group A and slowly increasing discharge in group B. Intensive snow melting following significant warm advection in the lower troposphere or, conversely, dominant radiative snow melting despite the high values of snow water equivalent, cause the high magnitude spring floods of the Nemunas River. The importance of atmospheric circulation increases during the beginning of the spring runoff in particular.
The objective of this paper is to assess the accuracy of air temperature and precipitation monthly and seasonal forecasts generated for the territory of Lithuania using the NOAA’s Climate Forecast ...System, version 2 (CFSv2) and to determine the atmospheric circulation conditions present at the time of initialization of the respective forecasts. The air temperature and precipitation data are obtained from three-month mean and monthly mean spatial anomalies during the period between 2012 and 2019. The accuracy of forecasts was performed in accordance with three criteria: range, state and the absolute error of the respective predicted anomaly. The study has shown that forecasts initialized 0–20 days in advance of the target month or season tend to be the most skilful. The accuracy of CFSv2 forecasts may be significantly impacted by the initial atmospheric circulation conditions present during the generation thereof. The study determined which phases of Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) and which circulation types according to the Hess-Brezowsky classification are favourable/unfavourable for the monthly and seasonal forecasting of air temperature and precipitation.
In this paper, climatic analysis of non-precipitation periods (NPP) in Lithuania was performed, assessing their recurrence and trends from 1991 to 2020 using two criteria – when precipitation was ...<0.1 mm per day all year round and when precipitation was <1 mm per day during the warm period – and analysing typical atmospheric circulation in the middle troposphere and sea level during the longest NPP (≥20 days). From 1990 to 2020, NPP were most frequent in the Middle Lithuania lowland (according to both criteria), in Southern and South-western Lithuania (daily precipitation <0.1 mm) and in part of Eastern Lithuania (daily precipitation <1 mm), and least frequent in part of the Samogitian highland and in part of the Baltic Highlands (according to both criteria). NPP recurred most often in the spring months, as this is associated with a higher number of days with anticyclonic circulation and powerful anticyclones recorded. Based on the growth trend of NPP of various durations in Lithuania from 1990 to 2020, in the last decade NPP have become more frequent, but only a few stations have shown reliable trends. Analysis of the atmospheric circulation during the longest NPP (≥20 days) showed that NPP were mostly determined by the Azores anticyclone ridge or anticyclone over Northern, Central or Eastern Europe regardless of the time of year. The atmospheric circulation conditions for the formation of long NPP varied more in the cold period than in the warm period, but NPP often lasted ≥20 days only at one or a few stations.
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