Orthotidal signal in the electrical conductivity of an inland river.

An orthotidal signal is a tidal component found in a streamwater parameter when there is no oceanic tidal input, i.e. when the streamwater monitoring point is located far inland and at high elevation. This study analyses various parameters of Cib River in Carpathian Mountains, Romania. This river receives water from a rich karst aquifer when crossing Cib Gorge. Streamwater level, temperature and electrical conductivity were measured in 270 days grouped in three time intervals of consecutive days. The measurements were done every 15 minutes in order to capture any significant periodic variation. The streamwater measurements were paired with air measurements and measurements done in a thermal spring. Solar semidiurnal oscillations were found in the streamwater electrical conductivity. In case study time series, selected based on their good signal to noise ratio, there are average semidiurnal oscillations of approximately 4 µS/cm, while the maximum amplitude rise up to 20 µS/cm. The semidiurnal peaks in water are generally in phase with the two atmospheric tide maxima, which are the cause of the studied phenomenon. The higher mineralisations of the thermal waters that rise from beneath the karst aquifer are the most probable cause of finding significant orthotides only in the electrical conductivity time series of the studied river.

Diurnal, semidiurnal, and fortnightly tidal components in orthotidal proglacial rivers.

The orthotidal rivers are a new concept referring to inland rivers influenced by gravitational tides through the groundwater tides. "Orthotidal signals" is intended to describe tidal signals found in inland streamwaters (with no oceanic input); these tidal signals were locally generated and then exported into streamwaters. Here, we show that orthotidal signals can be found in proglacial rivers due to the gravitational tides affecting the glaciers and their surrounding areas. The gravitational tides act on glacier through earth and atmospheric tides, while the subglacial water is affected in a manner similar to the groundwater tides. We used the wavelet analysis in order to find tidally affected streamwaters. T_TIDE analyses were performed for discovering the tidal constituents. Tidal components with 0.95 confidence level are as follows: O1, PI1, P1, S1, K1, PSI1, M2, T2, S2, K2, and MSf. The amplitude of the diurnal tidal constituents is strongly influenced by the daily thermal cycle. The average amplitude of the semidiurnal tidal constituents is less altered and ranges from 0.0007 to 0.0969 m. The lunisolar synodic fortnightly oscillation, found in the time series of the studied river gauges, is a useful signal for detecting orthotidal rivers when using noisier data. The knowledge of the orthotidal oscillations is useful for modeling fine resolution changes in rivers.

Climatic water deficit and surplus between the Carpathian Mountains and the Dniester River (1961-2012).

The study addresses the climatic water deficit (WD) and surplus (WE) in the area located between the heights of the Eastern Carpathians (Romania) and the Dniester River (Moldova). The objective of this study is to discover the trend of WD/WE (past and future) and its variation in space. WD and WE were calculated as the difference between the amounts of precipitation (P) and the reference evapotranspiration (ET0). The P-ET0 trend, analyzed through Mann-Kendall and t tests, was negative for 83 and 80% of the analyzed stations and the Sen's slope had values between - 0.05 mm year-1 (t test) and - 6.73 mm year-1 (Mann-Kendall test). Seasonally, the slope values of P-ET0 trends were negative during winter, spring, and summer and positive in autumn. The P-ET0 index is positive (WE) only in the Carpathian and Eastern Subcarpathian areas, whereas for the rest of the investigated territory, we found negative values (WD). WD is more pronounced as we depart from the Carpathians towards the east, but also on a north to south direction, reaching the maximum in the southeastern part of the territory. In what concerns seasonal distribution, WE is identified everywhere only in winter, whereas, in spring, summer, and autumn, WD characterizes most of the territory, with the exception of the Carpathian and Subcarpathian areas. The increasing WD will have a growing negative influence on the agriculture of the studied area. For the year 2030, we anticipate a reduction in the climate water availability with 46 mm m-2 (reference period: 1961-2012).

Wavelet analysis of some rivers in SE Europe and selected climate indices.

The influence of some climatic oscillations and sunspot number on river flows in Romania, Ukraine, and Moldova is verified by using standard wavelet analyses. The selected climate oscillations are Arctic Oscillation (AO), Antarctic Oscillation (AAO), East Atlantic Oscillation (EAO), East Atlantic/West Russia Oscillation (EAWRO), NINO3.4, North Atlantic Oscillation (NAO), Pacific/North America Oscillation (PNAO), Pacific Decadal Oscillation (PDO), Polar/Eurasia Oscillation (PEO), Scandinavian Oscillation (ScandO), Southern Oscillation (SO), and West Pacific Oscillation (WPO). Forty-five hydrological stations from an area of 45,000 km(2) were used in order to discover the spatial evolution of the periodicities found in rivers. The wavelet analysis is novel for the rivers in the study area. There is an important difference between the periodicities found in mountain and plateau areas and those found in the plain area. There is a general downstream increase in the confidence level of the identified periods, even if the atmospheric precipitation has more relevant periodicities in the mountain area. The periodicities can be grouped into two compact groups: 1-16.5 and 27.8-55.6 years. The correlation matrix of the global wavelet spectrum (GWS) values indicates that NAO, EAWRO, PDO, and the sunspot number are the main factors that generate the periodicities in rivers. It is the first time when the influence of PDO on local rivers is proven. All river periodicities smaller than 16 years have a confidence level of 0.95 or above, as proven by the GWS analysis of the daily discharge data, and are caused by multiple external factors.

Wavelet analysis of lunar semidiurnal tidal influence on selected inland rivers across the globe.

The lunar semidiurnal influence is already known for tidal rivers. The moon also influences inland rivers at a monthly scale through precipitation. We show that, for some non-tidal rivers, with special geological conditions, the lunar semidiurnal tidal oscillation can be detected. The moon has semidiurnal tidal influence on groundwater, which will then export it to streamflow. Long time series with high frequency measurements were analysed by using standard wavelet analysis techniques. The lunar semidiurnal signal explains the daily double-peaked river level evolution of inland gauges. It is stronger where springs with high discharge occur, especially in the area of Edwards-Trinity and Great Artesian Basin aquifers and in areas with dolomite/limestone strata. The average maximum semidiurnal peaks range between 0.002 and 0.1 m. This secondary effect of the earth tides has important implications in predicting high resolution hydrographs, in the water cycle of wetlands and in water management.