Browse

91 - 100 of 1,781 items :

  • Atmospheric Science and Climatology x
Clear All
Performance of simple temperature-based evaporation methods compared with a time series of pan evaporation measures from a standard 20 m2 tank

Abstract

Evaporation and evapotranspiration is crucial part of hydrological and water resource management studies e.g. water footprinting. Proper methods for estimating evaporation/potential evapotranspiration using limited climatic data are critical if the availability of climatic data is extremely limited. In a large scale studies are very often used generalized (modelled or gridded) input data. For a large scale water footprint studies is also important to find methods as simple as possible with quantifiable error. In our study, nine simple temperature-based empirical equations were compared with a long term time series of real evaporation data from a 20 m2 tank at Hlasivo station. In the first step, we used real temperature measured at Hlasivo station for validation of equations. In the second step, the gridded temperature data (interpolated datasets) derived from the meteorological stations were used. For both datasets, the differences between observed and predicted values were categorized into three groups of accuracy and the statistical indices of each equation were calculated. Very good results were achieved with the Hamon equation from 1961 and the Oudin equation for both datasets with index of agreement (d) higher than 0.9, cross-correlation coefficient (R 2) around 0.7 and root mean square error (RMSE) around 0.5 mm∙(24 h)−1 The Kharrufa equation, which was developed for semi-arid or arid areas, also provides results with sufficient accuracy. Comparison of the results with similar studies showed a lower accuracy of very simple equations against more complex equations, which have RMSE lower than 0.25 mm∙(24 h)−1. But for some kind of studies, quantifiable errors with sufficient accuracy can be more important than the absolute accuracy.

Open access
Polish DGPS System: 1995–2017 – Study of Positioning Accuracy

Abstract

This paper is the fourth in a series of publications presenting the process of installation, testing and long-term assessment of the navigational parameters of the Polish DGPS system. This series of publications intends to present – to the general public – the accomplishments of teams of Polish scientists who have been working for years to make the DGPS the main positioning system used in the Polish sea areas. A considerable part of the materials presented in this paper has never been published.

The article presents changes in the position accuracy of the Polish DGPS system over 20 years. Both dynamic tests performed on vessels as well as static measurements campaigns were analysed. The publication contains selected results achieved in its installation and testing in 1995–1997 supplemented with the results of studies conducted in the years: 2006, 2010, 2014, 2017. During this period the position accuracy increased from 2–8 m (1996) to approx. 1–2 m (2010) due to three reasons: turning – off the Selective Availability (2000), technical modernization of reference stations (2010) and continuous – over many years – reducing GPS signal-in-space pseudorange errors, which results in increased position accuracy in all GPS augmentation systems.

Open access
The possibility of using Lake Rawa Pening as a source of drinking water

Abstract

The water of Lake Rawa Pening is used as a source of drinking water. Indonesian Government Regulation Number 82 of 2001 on Management of Water Quality and Water Pollution Control stated that the water quality of Lake Rawa Pening should meet the quality standard of first grade and be categorized as no polluted water. The purpose of this research was to assess the water quality based on Indonesian regulation and to assess water quality based on international regulations. The quality of water was assessed using a survey method in 7 sites of the Lake Rawa Pening 3 times for 3 months. Parameters measured were all the water quality parameters required in accordance with Government Regulation No. 82 of 2001. The results indicated that there were 13 values that exceeded the water quality standard of first grade. These exceeded parameters were total suspended solids (TSS), biological oxygen demand (BOD), chemical oxygen demand (COD), orthophosphate (PO4), NO3, As, Se, Cd, Mn, Cu, Pb, H2S, faecal coliform, and total coliform. Water quality status of Lake Rawa Pening was categorized as heavily polluted. The water quality of Lake Rawa Pening should be improved by reducing the pollutants entering the lake by restriction of human activities causing lake pollution.

Open access
Pre-Filtered Backstepping Control for Underactuated Ship Path Following

Abstract

Robust path following control for underactuated surface ships is an important issue in marine control practice. This paper aims to improve the robustness of the close-loop system with model uncertainties and time-varying disturbances. A practical adaptive backstepping control scheme with a pre-filter is proposed to force a surface vessel to track the predefined path generated by the virtual ship. Based on the Lyapunov stability theorem, this algorithm can guarantee all error signals in the overall system to be uniformly ultimately bounded, and it can be implemented without exact knowledge of the nonlinear damping structure and environmental disturbances. The proposed pre-filter can smooth the commanded heading order and obtain a better performance of the waypoint-based navigation control system. Two simulation cases are drawn to illustrate the validity of the proposed control strategy.

Open access
The Prediction of Hull Gesture and Flow Around Ship Based on Taylor Expansion Boundary Element Method

Abstract

Based on the potential flow theory and traditional boundary element method (BEM), Taylor expansion boundary element method (TEBEM) is introduced in this paper for the prediction of the flow field around ship, as a result, hull gesture and pressure distribution on hull surface are obtained. By this method, dipole strength of every field point is expanded in Taylor expansion, so that approximately continuous hull and free surface boundary condition could be achieved. To close the new equation system, the boundary condition of tangent velocity in every control point is introduced. With the simultaneous solving of hull boundary condition and free surface condition, the disturbance velocity potential could be obtained. The present method is used to predict the flow field and hull gesture of Wigley parabolic hull, Series 60 and KVLCC2 models. To validate the numerical model for full form ship, the wave profile, the computed hull gesture and hull surface pressure of KVLCC2 model are compared with experimental results.

Open access
Preliminary reflectivity analysis of severe convective events in in the proximity of Goczałkowice-Zdrój, Poland

Abstract

At the beginning of 2018, the X-band radar in Goczałkowice-Zdrój (southern Poland) was launched. The scanning area corresponds with the scanning area of the POLRAD C-band radar system operated by the Polish Institute of Meteorology and Water Management. New opportunities were created for imaging phenomena by comparing some reflectivity features from C-Band radar and X-Band local weather radar. Moreover, some of the signatures located in the lower troposphere can be better documented by local X-Band radar. Firstly, reports from the ESWD (European Severe Weather Database) have been thoroughly analysed. All severe weather reports in the proximity of Goczałkowice-Zdrój (100-km radius) were gathered into one-storm events. Then the reflectivity from both radars was analysed to determine which reflectivity patterns occurred and when. X-band radars are known from the more intensive attenuation of the radar beam by the scatterers located closer to the radar, thus it is essential to compare capabilities of these two different radar systems. It was found that the average reflectivity for all convective incidents is higher when using POLRAD C-band radar data. In some events it was possible to find some spatial reflectivity signatures. We also discuss other reflectivity signatures previously described in the literature. Taking into account stronger Goczałkowice-Zdrój X-band radar attenuation, we suggest that some of these should be reviewed by reduction of the reflectivity thresholds.

Open access
Private for-profit rural water supply in Nigeria: Policy constraints and options for improved performance

Abstract

Water scarcity is a major and growing problem in Nigerian rural areas, leading to the emergence of private for-profit water services providers (PPWSPs). This paper characterizes the landscape of PPWSPs in Nigerian rural communities using information collected from field observations, in-depth interviews, questionnaire surveys, and from published water resources literature. The data collected were analysed through the use of descriptive statistical tools. The results revealed the characteristics, categories, contributions and concerns of water users regarding water supplies by PPWSPs. Responses show that PPWSPs are helping to engender development, guarantee end-users with access to sufficient and reliable supplies and reduce water shortages in the study communities. Sixty four percent of sampled households depend on PPWSPs for their water requirements. Many PPWSPs operate outside the purview of government regulations and have differentiated service modes and prizes to gain wider acceptability. Despite the progress made by PPWSPs, however, the strategy can neither guarantee universal access nor the supply of safe drinking water. Significant barriers to the operations of PPWSPs, how to close the policy-gaps that constrain services delivery by PPWSPs and improve performances through setting of standards and regulatory reforms are discussed.

Open access
Programs for Prevention and Management of Natural Disasters in the European Countries of The Larger Area of The Black Sea Basin

Abstract

The hazards that have cross-border consequences and represent a great problem for communities, become an obstacle to sustainable development and lead to disasters when combined with vulnerability and insufficient capacity to mitigate the risk. A short overview of research already implemented and in progress presents us a shift in systematic evaluation of the hazards and disasters at local and areal level. Hazard assessment of natural disasters (earthquakes, landslides and floods) on these scales can give results which can be directly used to take right decisions regarding preventive measures and plan effective actions of post-event management. The issue is widely recognized in the european union (eu) implicitly also in the black sea area, and a lot of efforts have already been made to mitigate the effects of disasters, obviously through the formation of numerous eu institution, established organizations and funded projects. The key elements for an effective mitigation of natural disasters are hazard identification and risk assessment, which must be based on scientifically grounded methodologies, reliable and accurate data. Successful resolution of the issues mentioned above will provide the ability to systematically assess natural disasters on regional and local scales, even in cross-border areas, by providing comparable hazard maps that will support the decision-making process in relation to mitigation measures required. The effective way of action against them is by providing applied research and technology transfer between partners in different countries by solving the problems such as lack of reliable information and lack of 'common ground' in the methodologies used to assess natural hazards and adopted procedures for mitigation.

Open access
Projections of Climate Suitability for Wine Production for the Cotnari Wine Region (Romania)

Abstract

Climate projections have revealed the perspective of changing the climate of the world's wine regions in the coming decades by diversifying heliothermal resources. Research in the Cotnari winegrowing region over the past decade has shown that the local climate has been affected by such developments especially after 1980. This research continues the series of studies on the climate of the Cotnari winegrowing region through projections of the climatic conditions for the 2020-2100 time period based on the RCP 4.5 scenario. Average annual temperature, warmest month temperature, precipitation during the growing season, length of the growing season and the Huglin, IAOe and AvGST bioclimatic indices for the 2020-2050, 2051-2080 and 2081-2100 time periods indicate the evolution of Cotnari area climate towards suitability for red wines and loss of suitability for the white wines. Climatic suitability classes for wine production, shift between 2020-2100 to the higher, cooler zone of the winegrowing region, narrowing down their surface and disappearing successively at the maximum altitude of 315 m asl. They are further replaced from the lower zone by classes specific to warmer climates. The suitability for white wines, specific to wine region, disappears at the maximum altitude of 315 m asl around 2060, being replaced by climate suitability for the red wine production. The average temperature of the growing season will exceed 19.5°C after 2080, becoming unsuitable for the production of red quality wines of Cabernet Sauvingnon variety. After 2050, in the lower zone of the winegrowing region the warm IH5 class, suitable for Mediterranean varieties such as Carignan and Grenache will install, as compared to temperate IH3 class which characterizes today the lower zone and allows the production of white wines of the local Feteasca albă, Grasa de Cotnari, Frâncușa and Tămâioasa românească varieties. The results suggest the need to develop strategies for adapting the viticulture of the Cotnari area to climate change.

Open access
Regional Climate Change and Surface Waters

Abstract

The actual period marred by the global warming requires expanding our knowledge on the regional particularities of climate changes manifestations as consequences of global climatic changes. It was stated that within the limits of Republic of Moldova’s territory the pace of warming is much more accelerated than the global one. These consequences, in their turn, had led to the increase in degree of evaporation of surface waters, which had conditioned the doubling of still water’s pollution in the region (Lake Beleu). We consider that the obtained results could contribute to the adequate management of water resources in the new climatic conditions.

Open access