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.

The aim of investigations was to compare different absorber material efficiency to examine collector tracking the Sun and stationary collector efficiency as well as the efficiency of insulated and non-insulated collectors. The 0.1x0.5x1.0 meter long experimental solar collectors were constructed for investigations and different types of absorber materials were made. The manifold length, the Sun radiation effect on the degree of air heating was analyzed. ASHARE used standard 93-2003 is determined for insulated and non-insulated solar collectors and absorber effectiveness. We determined the influence of the Sun radiation on the air heating degree for those types of absorbers. The experimental data were measured and recorded in the electronic equipment REG (electronic metering and recording equipment of temperature, radiation and lighting). The collector covered material was a polystyrol plate and different absorbers. We compared insulated and non-insulated collectors to prove that the insulated collector is more effective. The insulated collector was made of the collector surfaces faced with cellular plastic two cm plates. Our task was to calculate the air heating solar collector efficiency. The collector tracking the Sun is approximately 30% more efficient than the same type of stationary collectors in operation time for 6 hours. Insulation increases solar panel efficiency especially in windy weather. The insulated collector demonstrates almost two times higher efficiency than the non-insulated collectors (up to 93%) with absorbent material steel tinplate on top.

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 Duration of Load (DOL) effect is the combined influence of the mechanical loading history and climatic history on the strength of materials. DOL effect is one of the most important characteristics of wood and wood-based materials. The material degradation or damage induces strength reductions. Creep is one of the most important effects of DOL. Creep is a phenomenon that negatively affects functional compliance, behaviour and strength of timber structures in extended years of exploitation. The creep phenomenon is affected by surrounding temperature, relative humidity, timber moisture content and other factors. The study aimed to establish a correct factor system for accurate prediction of long-term deformations of timber structures that is corresponding to environmental conditions and timber properties in the region of Latvia. The experimental research was made in Jelgava, Latvia, and represents timber beam four-point long-term loading in bending with variable cross section height-span length ratio under uncontrolled climatic conditions. There were 12 timber beams with two different span lengths – 1.32 m and 1.50 m used. The timber beam cross section dimensions: height – 60 mm, width – 30 mm. The timber beams were not dried and the moisture content at the start of the experiment varied from 19% to 33%. The applied load values – 0.40 kN and 0.31 kN. Moisture content fluctuations and negative air temperature accelerated creep development and intensity. Prediction of final long-term deformations should rate not only the type of timber material and service class but the strength class, too.

An important factor in the development of forest ecosystem is the ability to regenerate. Natural intensity of self thinning of a forest depends on the tree species and environmental conditions. Due to abiotic and biotic factors in a continuous forest tract, there appears a clearing, which, depending on the size, forms new growth conditions. Over time, the resulting new space is occupied by herbaceous and woody vegetation. Most often regeneration of a new forest depends on the size of the plot. The study was conducted in 2013 during the growing season in a typical broadleaf forest stand. During the study woody vegetation and projection coverage of herbaceous vegetation was registered in large clearings. Light conditions in the plots and under tree canopies, as well as soil parameters were ascertained. Based on the collected data, the view of the structure of woody vegetation, projection coverage of herbaceous vegetation, light conditions, temperature, soil moisture content and pH changes were obtained. In order to clarify the influence of microclimatic conditions on natural forest regeneration, the data on light and soil characteristics were analyzed. The aim of the study - was to determine the changes of woody and herbaceous vegetation in spruce stand clearings and to assess the impact of microclimate. During the study it was found out that in large plots dominated species demanding higher amount of light, while herbaceous vegetation was attributed to the third, fourth groups of aggressiveness. Naturally regenerated seedlings condition was mostly influenced by light conditions and soil moisture content.

The homogeneous and light wood of birch is suitable for different types of treatment processes and is highly valued for products where visual aspect is important, however, birch assortments are highly susceptible to damages caused by fungi during the storage. Such fungal damages cause discoloration of birch roundwood intended for further woodworking. Sapwood discoloration development and its influencing factors for birch roundwood were analyzed in the summer - autumn period of the year 2016 (August, September and October). Control cut for assessment of sapwood discoloration development was made in four birch roundwood stacks in the districts of Auce and Daugavpils. In order to evaluate the influence of harvesting type, side surface damages, placement in pile, storage duration, diameter, distance from the end plane, daily average temperatures, precipitation amount and relative humidity on development of sapwood discoloration, 616 discs from birch log end planes were prepared. After conducting multiple factor linear regression, it was concluded that a significant development of discoloration and its changes for birch roundwood are promoted by harvesting type, placement in pile, distance from the end plane, daily average temperatures and relative humidity (R2 = 0.450). For birch logs that are prepared by harvester with the daily average air temperature + 6 °C, the first signs of discoloration appear after 17 – 18 days, but on all logs stacked in pile they appear after 68 – 69 days. Whereas, with the daily average temperature of + 18 °C, the first signs of discoloration can occur after only six days, but on all logs stacked in pile they appear after 23 days.

The aim of the paper is to present the spatial diversity of water resources in the Kuyavian-Pomeranian Voivodship during the drought in 2015. The region’s area is characterized by the lowest average annual precipitation in Poland, the lowest water resources and high water demand associated with intensive plant production. Hydrological research was carried out in September 2015 in 145 measurement points on various rivers. Despite the low precipitation recorded in August 2015 at the majority of meteorological stations, the volume of the specific discharge from the Kuyavian-Pomeranian region was characterized by high variability. The largest specific discharges were recorded for rivers located in the northern part of the region whose sources are located in the Pomeranian Lake District, i.e. Brda and Wda (over 2 dm3 sE−1 kmE−2) and the Masurian Lake District (Drwęca over 1 dm3 sE−1 km E−2). The smallest specific discharges (less than 0.5 dm3 sE−1 kmE−2) were recorded in the catchments located in the Kuyavian region (Tążyna, Zgłowiączka and Noteć) in the southern part of the Kuyavian-Pomeranian Voivodship and from the Osa River catchment. These areas are intensively used for agricultural purposes. The use of surface water resources as a potential source of irrigation water for crops can only be taken into account in connection with groundwater resources.

The objective of the work, carried out as part of research programme on current change of the regional climate, was to confirm the hypothesis about the increasing frequency and intensity of droughts in May and June in the region of Kujawsko-Pomorskie (central Poland) in the years 1981 – 2010. Furthermore, the aim was to confirm a significant relationship between indicators characterizing meteorological and agricultural droughts. Material for the research was the data from five meteorological measuring points located in the region. Atmospheric precipitation and air temperature in the period of high water needs of cereals and rapeseed (May–June) were used. Statistical methods widespread in climatological studies were applied, particularly the method of trends. The average multiannual totals (1981–2010) of rainfall in May–June allow ranking the region of Kujawsko-Pomorskie into the area of the lowest rainfall in Poland. The frequency of meteorological drought in May and June is 23.3–30.0% in the region. In the analysed period there were no significant changes in the frequency and intensity of these droughts with the passage of years. Rainfall shortages in cereal crops and rapeseed production range on average from -19 to -35 mm, and extend to maximum of -93 to -117 mm. The values of shortages did not show any significant changes in the years of the study. The significant dependence between the indicators of meteorological and agricultural droughts allows for determination of the rainfall shortages in crop production on the basis of the SPI values.

The research was done in 2006 with the aim to observe the earliness and sugar content of melons (Cucumis melo L.) in Tukums region of Latvia. Five lines of Latgale's melons ('8', '14', 'S4(3)', '5(2)', and '4(3)') and five varieties ('Noirdes Carmes', 'Ogen', 'Vedrantais', 'Cantaloup de Bellegarde', and 'Jaune Canaris') from South Europe were grown in high plastic tunnels: five plants from each line and variety. The most appropriate melon line for growing in Latvia conditions was selected according to earliness and sugar content. The study showed that Latgale's melons (Latvian origin) are most suitable for growing in high plastic tunnels under Latvia's conditions. Also some of South Europe melon varieties proved to be suitable for growing in Latvia conditions. All Latgale's melon lines were earlier than South Europe varieties. The highest sugar content was observed in Latgale's melon line '8' (113 g kg¡1) and in South Europe varieties 'Jaune Canaris' (110 g kgE-1) and 'Cantaloup de Bellegarde' (96 g kgE-1). The research demonstrated that in Latvia successful cultivation of melons is possible by using high plastic tunnels.

In order to get maximum economic effect, when setting a solar collector in a peasant yard, it is important to choose the correct place. The yield of obtained heat energy will be at its maximum, if the temperature of surrounding air and solar radiation are higher by the relative humidity of the air - lower. To define these parameters, a special device 'Meteorological Device' (MD-4) was developed. The device was supplied with a mechanism which tracks the sun all day round. So the direct solar radiation on the surface perpendicular to the sun beams was measured. The second measuring of the solar radiation was made in relation to the surface, which was perpendicular to the sun beams only at the middle of a day time. For the measuring of the air temperature and relative humidity, corresponding sensors were used. In every 15 minutes the data of these four meteorological parameters were automatically measured and the results were saved into a logger - the device for data accumulation. After a certain period of time the information was brought into the memory of a computer and analysed.