The human influence on hydrological cycle has created many surface problems in the Riga city. Rainfall amount increases year after year as a result of global warming and bad water exchange. Solid covering of squares and greened areas is one of the most significant results of urban development causing larger rainwater runoff from the territories and calling for the necessity to drain rain water rapidly in a short time. This phenomenon is observed in the last years due to the fast construction development and simultaneous expansion and improvement of streets and court yards. The main problem matter is the still existing old sewage co-system which encounters difficulties to work with full capacity during long term rainfall. Thus justifiable steps have to be taken in order to discover new engineering solutions to prevent overflow of streets in Riga during rains. To enquire into the matter, rain intensity in Riga, influence of rainwater on streets, overflowing of collectors, and operation of pumping stations are studied in this paper. Rain intensity measurements during 1980-2006 in Riga have been aggregated. As acquired data shows, maximum rain intensity was observed on July 30 of 2005 when the rainfall was 49.4 mm during a 3-hour time, which caused overflowing of some streets, collectors, and pumping stations. Data on local and main pumping stations at the right bank of the river Daugava during various rainfalls suggest that pumping stations start to overflow during enduring rainfalls, 1-3 hours long and with average intensity of 0.1-0.4 mm minE-1 (Ziemelnieks, Tilgalis, 2008). Data gathered indicate, that it is necessary to separate sewage systems for everyday necessities from those for rainwater.

Due to the recently increasing frequency of extreme changes in river runoff regime, scientific literature deals with the characteristics of runoff formation. Works are carried out in analyzing climate changes and a lot of attention falls on land–use structures. Following thorough analysis of the lithological structure of river basins in separate costal zones, this article aims at evaluating river runoff formation characteristics. The basin lithological factor was calculated based on Quaternary map of Lithuania M 1:200000 and Lithuanian river map M 1:50000 using ArcGis software. In order to carry out more thorough analysis of the influence of lithology in given territories, sections of 0–20 m, 50–200 m, 200–500 m, 500–800 m, 800–1000 m and is greater than 1000 m were established, calculating the distance in meters from the riverbank. Eight river basins of typical lithological structure (sandy, loamy, argillaceous) were selected and examined. The period of the years 1960–2007 was analyzed as this period saw the greatest amount of precipitation (up to 33% probability), and relation between the runoff and precipitation was established as well as that with the lithological structure, established following the derivation of a hydromodule.

Global warming undoubtedly influences the flow of rivers. It is essential to observe the climate changes, trace, analyse and forecast how they could influence the environment and, especially, how it can influence the flow of rivers. In this article two maximum flows of basins of two different rivers are analyzed: the river Venta (above Papile) and the river Krazante (above Pluskiai) during the period 1968–2008. Climatic parameters, such as the precipitation and the average air temperature, observed in the weather stations of Siauliai and Laukuva, influence the changes in flows the most. The correlation between the precipitation and maximum change of the flow was estimated though it was not strong: the ratio of correlation in the river Venta was 0.66, in the river Krazante the same ratio was 0.72. Significant negative trends of the both analyzed rivers during the spring period and significant negative trends of the river Venta during the period of winter have been established by the use of statistical analysis of the results obtained from a non-parametric Mann-Kendall test and linear regression test. This specific analysis is performed by using TREND programme. The collected data which were obtained to show that the most watery decade of the rivers Venta and Krazante were during the period 1978–1987, which formed 36% flow in the river of Venta and 35% in the river of Krazante for the whole period of forty years.

Prolonged summer drought periods are forecasted for the Baltic Sea region during the 21st century, thus increasing the risk of drought stress of saplings used in forest regeneration. Nevertheless, the vitality of young stands might be increased by the selection of suitable planting material. The aim of this study was to estimate the effect of changes in distribution of summer precipitation on height increment, biomass distribution and root morphology of Scots pine and silver birch planting material commonly used in the forest regeneration in Latvia. Containerized pine and bare rooted birch saplings, planted in three different soil types, were subjected to altered distribution of summer precipitation, provided by the use of automated shelter. Sheltered saplings were weekly irrigated with the sum of precipitation of a corresponding period, while afield planted saplings had an unchanged precipitation regime and served as control. Height increment was measured once per week and estimation of morphology of saplings was done after the end of every vegetation season. Significant (p is less than 0.05) differences in height increment, and shoot and root biomass were observed among the same planting material in different irrigation regimes and soil types. In the control plots of peat soil, pine had a significantly (p is less than 0.05) larger height increment while birch-significantly (p is less than 0.05) smaller compared to experiment. Forecasted longer drought periods might reduce the growth of Scots pine in fertile forest types but silver birch growth might be affected in fertile mineral soils in future.

Maize yield and quality are affected by many factors, including production practices, diseases, pests, and differences in the climate. Usually it is not possible to do much to change the effect of temperature, but it is important to grow better adapted or characterized with right maturity rating hybrids. The paper is aimed to determine the impact of accumulated growing degree days (GDD) on maize development, organic dry matter yield, ODM and chemical composition of maize hybrids. A field trial was carried out in the Research and Study farm ’’Vecauce’’ of the Latvia University of Agriculture (LLU) from 2008 till 2010. Ten (in 2008), eleven (in 2009) and fifteen (2010) maize hybrids with different maturity ratings according to FAO numbers (FAO 180-340) were harvested at three different times beginning on 5 September at fourteen-day intervals. GDD were calculated when maize reached a certain growth stage (full emergence, first tassels, full tassels, first ears, full ears, specific harvest date) to characterize conditions for maize growing in a specific year. Composition of fresh maize was analyzed for all hybrids using standard methods. Results were statistically processed using methods of correlation and regression analysis. Our results presented evidence that ODM yield in 2008 and 2009 on last harvest dates was lower than that on the first harvest date in 2010. Organic dry matter yield was higher in years when more GDD were accumulated. Results also showed that GDD negatively correlated with the total N, protein, fibre cellulose, hemi-cellulose, NDF, and ADF concentration.

Oil-flax has a wide range of utilization possibilities, inclusive of bioenergy production. In our research evaluated out two oil-flax varieties 'Scorpion' and 'Flanders' after the calorific value, oil, lignin, and ash content; and also the chemical composition in 2008 -2010. The results show that oil-flax shoves have a high calorific value and high lignin content but a low temperature for ash fusion. It was established that the growth year and some unexplored factors have influence on the ash content. The oil content in the seeds was 336-458 g kgE-1, depending on the chosen variety. The flax shoves can be used as a supplement for biofuel combustion, as they have a low fusion temperature, a high calorific value, but a comparatively low yield makes oil-flax unprofitable to grow for biofuel production.

The influence of forest distribution in the landscape on precipitation in middle latitudes is poorly researched. Moreover, results of such studies are controversial. Nevertheless, most researchers agree with findings, that influence of landscape roughness formed by forests on the amount of precipitation is significant. This study aimed to extend knowledge of the interface between forest distribution and the amount of precipitation during particular periods. Database of the amount of precipitation from 31 Lithuanian meteorological stations during the period of 2002-2010 was used in this study. Findings defined statistically significant correlations in the amount of precipitation increase due to shorter Euclidean distance to the nearest forest edge in the particular landscape (r = -0.421 – -0.359), p is less than 0.05), also shorter distance of the meteorological stations to the nearest forests (r = -0.380, p is less than 0.05) and higher density of the forests, treated as a perimeter per area ratio (PAR) (r = 0.359 – 0.551, p is less than 0.05).

This research deals with tendencies of growth of Norway spruce Picea abies (L.) Karst. during last 50 years (1960 – 2010) in eastern part of Latvia emphasizing trendal specificity of active periods during the first (t1: 1960-1985) and the second (t2: 1986-2010) time interval. There have been 150 superior stand trees bored in six mixed pine-spruce Pinus sylvestris L. – Picea abies (L.) H.Karst. stands. An active period of factor’s impact is the time span when some meteorological factor (decade average, minimal or maximal temperature and sum of decade precipitation) influences an increase of annual ring width significantly. Comparing average temperatures from two weather stations included in this research the difference between interval t1 and t2 is approximately 1 °C. Active periods of temperature impact on growth of Norway spruce in eastern part of Latvia during last decades have changed not only their location but also an impact direction from positive to negative. Minimal and maximal decade temperatures are those mostly determinating the radial growth of Norway spruce in the eastern part of Latvia. Interval t2 is quite rich in active periods both from minimal and maximal decade temperature. Research results prove hypothesis about trendal shift of meteorological factors’ impact active periods due to climate change. An increase in decade precipitation level in winter caused annual ring growth positively both in the interval t1 as well as in t2.

The American cranberry (Vaccinium macrocarpon Ait.) is a perspective and marketable crop both in Latvia and foreign markets, but berries are affected by rot in storage. The aim of the study was to detect the incidence level of cranberry fruit rot at the beginning of storage period in different places in Latvia. In 2007 - 2011, two hundred sound berries (out of 1000) were randomly collected by hand along a diagonal from five different cranberry plantations from locations all over Latvia. Berries were kept in plastic bags for a month and refrigerated at +7 °C. At the end of November, berries were sorted and rotten berries were separated from the sound ones. Over the period of 2007 - 2011, the incidence of storage rot reached 12 - 15% at the end of November, with an upwards trend observed every year, but the hot and rainy summer of 2010 significantly reduced the quality of fruit in storage, peaking on the average 33% of decayed berries. The incidence of fruit rot varied among the inspected cranberry plantations, but a tendency was observed that older plantations produced more rotting fruit and incidence of the disease was 12 - 50% after a month’s storage in the oldest plantation. The application of fungicides during the vegetation season did not affect development of post-harvest rot. Storage rot was a problem in the cranberry samples from all inspected plantations in Latvia, and in future the incidence of fruit rot is expected to increase.

Norway spruce (Picea abies (L.) H.Karst.) is amongst the most important tree species for forestry in Latvia. It has been suggested that due to the foreseen climate change the productivity of Norway spruce in Latvia may decrease. Continuous observations of radial increment allow to identify periods with different growth intensity and to study the effect of environmental conditions on radial increment during them. The aim of this study was to analyse stem radial variation of Norway spruce in mixed-species stand in response to meteorological conditions over one growing season. Stem radial variation of one Norway spruce tree was monitored by band dendrometer throughout the growing season of 2013. Cumulative radial increment was divided into contraction, recovery and increment phases by the stem cycle approach. Four periods with distinct apportionment of these phases were identified – winter/spring dormancy, spring/ summer growth, growth termination and autumn hydration fluctuations. Radial increment began in the second part of May and the most active increment was observed during period of spring/summer growth. This period lasted for 42 days with the mean amplitude of stem radial variations reaching 0.06 mm while the length of increment phase reached up to two days. Throughout the growing season increment was facilitated by an increase in the temperature. Meanwhile, the effect of precipitation was insignificant, presumably due to sufficient water availability and low interspecies competition for it, characteristic in mixed species stands due to differences in depth and distribution of root systems between the species.