Global trends in the environmental situation in the Dnipro Basin

3.3.1 Global trends in the environmental situation in the Dnipro Basin

Changes in air temperature

The reliable assessment of changes in air temperature can be made for those meteorological station locations where long-term time series of observation data are available. It is also desirable to make sure that the sites of these stations have remained unchanged during the whole period of their operation, and are located in relatively small towns where local impacts (from heating mains, etc.) are relatively low.

There are several meteorological stations meeting these requirements in the Dnipro Basin such as the Poltava meteorological station where observations have been carried out since 1886. Comparable time series of observation data are also available for the Gorki meteorological station located in the north of Belarus. Long-term variations of mean annual air temperatures at these stations are shown in Figure 3.10.

The data suggests that the net increase of mean annual air temperature over the period 1880 to 2000 was about 1.0°C, generally higher than the global increase of air temperature. Rates of increase have been especially high during the past 25-30 years. It should be noted that an increase of mean annual air temperature may affect the river flow in many ways. Moreover, seasonal variations can have an even stronger effect on the water resource. In particular, higher temperatures at cold periods of the year and frequent thaws are expected to result in lower discharges and decreased peak flows during the spring high flow period. This likely effect can be confirmed by actual observation data.

Figure 3.11 Long-term variations in maximum thickness of snow cover
at the Pokoshitchi meteostation (130 km north-east from Chernigiv)

Changes in atmospheric precipitation

Available data indicates that there is a strong relationship between changes in air temperature and changes in atmospheric precipitation, with the latter featuring a downward tendency in some areas of the Basin, and an upward tendency in other areas (Table 3.11). A similar picture emerges from an analysis of observation data obtained from a larger number of meteorological stations over the period 1946 to 2000. A significant body of research evidence is also available in various national and international reports.

The Dnipro River features a specific flow pattern with a markedly high flow in spring, when the river discharges more than half its annual flow. Therefore it is important to monitor variations in thickness of snow cover and water content.

Table 3.11 Changes in mean annual precipitation in Ukraine and Belarus over 1891-2000*

* Т- period (years)

These aspects have been studied at several meteorological stations located in the Polessie zone (where snow cover plays a major role in river flow formation). Despite significant variability of available data, there appears to be a downward tendency in snow cover thickness (Figure 3.11).

Variations in mean annual flow of the Dnipro River

Given that the Dnipro River flow is greatly affected by various human activities, mainly concentrated in the Lower Dnipro Basin, assessment of global climatic changes and their impact on water resource needs to be based on data collected in the relatively undisturbed upper river stretches. The most suitable for this purpose are hydrometric stations located in Rechitsa (catchment area 58,200 km²) and Kyiv (328,000 km²). Although flow measurements are not currently conducted at the Kyiv hydrometric station, flow estimates may be derived by summing up the actually measured flow values available for the Kyiv hydropower dam (239,000 km²) and the Letki hydrometric station (88,500 km²) located near the Desna River mouth.

The above mentioned climatic changes (increased air temperature during cold periods of the year, and reduced thickness of snow cover) have resulted in reduced discharges and peak flows during the spring high flow period, with a corresponding increase of discharges during winter and summer low flow periods (Figure 3.12).

Figure 3.12 Seasonal distribution of the Desna River flow (near Chernigov):
the left column reflects the whole observation period;
the right column, the period between 1970-1999

Apart from the Dnipro River flow, global processes also affect river water quality. This is caused by changes in the composition of precipitation falling within the catchment area as a result of anthropogenic impacts. For instance, the mineralisation level in water associated with various forms of precipitation is now higher than several decades ago.

Global transboundary transport of pollutants

Ukraine has common borders with many European countries, therefore transboundary transport of pollution is considered to have an effect on the state of catchment areas and surface waters within the Dnipro Basin. Westerly air-mass transport prevails in Ukraine, therefore pollution emitted to the atmosphere in Western and Central European countries is transported to the western and northern Oblasts of Ukraine, including the upper part of the Dnipro Basin. The major contributors of nitrogen dioxide (NO₂) load transported to Ukraine are Poland (450 tonnes), Germany (305 tonnes), and Slovakia (196 tonnes). Sulphur compounds are mainly brought with air masses from Poland (153 tonnes) and Romania (115 tonnes).

Next: Review of the 2000-2001 field survey results. Assessment of impact of transboundary pollution transport on the environmental situation in the Basin (local and global effects)

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