Estimation of the regional evapotranspiration from remotely sensed crop surface temperatures. Grassland

Estimation of the regional evapotranspiration from remotely sensed crop surface temperature

Why do Gull-billed Terns Gelochelidon nilotica feed on fiddler crabs Uca tangeri in Guinea-Bissau?

Gull-billed Terns Gelochelidon nilotica wintering in Guinea Bissau mainly fed on fiddler crabs Uca tangeri and were occasionally seen feeding on fish and locusts. As fiddler crabs have a low energy content, terns need a large gross intake to meet daily energy demands. Fiddler crabs also have a low ratio of digestible flesh to exoskeleton, and therefore tern food intake may be limited by gut capacity. Activity budgets of Gullbilled Terns feeding on fiddler crabs showed that a considerable part of the time was spent resting. The duration of resting intervals increased with energy intake and was positively correlated with the metabolisable energy content of the crab eaten, suggesting that resting periods were required for a proper digestion. The poor quality of fiddler crabs was offset by high capture rates. So daily energy expenditure of the terns could easily be met by feeding on fiddler crabs. Even when resting pauses were included in foraging time, foraging for only 1.5 hours on fiddler crabs satisfied the terns&rsquo; daily energy demands. Instead, feeding on energy-rich fish would require about 2.5 hours to satisfy daily energy demands. Compared to the more specialised piscivorous Little Tern Sternula albifrons and Sandwich Tern Sterna sandvicensis, capture rate of fish was poor in Gull-billed Terns. From an energetic point of view, wintering Gull-billed Terns feeding on fiddler crabs seem to have an easy living in Guinea Bissau.<br /

Attenuation in Melting Layer of Precipitation

A model of the melting layer is employed on radar measurements to simulate the attenuation of radio waves at 12, 20 and 30GHz. The attenuation in the melting layer is simulated to be slightly larger than that of rain with the same path length and precipitation intensity. The result appears to depend on the maximum reflectivity in the melting layer

UN/ECE Workshop on Exploring European Sulfur Abatement Strategies

This paper, prepared as a background document for the UN/ECE "Workshop on Exploring European Sulfur Abatement Strategies" (24-26 June 1991, Laxenburg, Austria), provides an analysis of the major approaches presently being explored for further reducing SO2 emissions in Europe. By using an integrated assessment model, the analysis reflects the current stake of various model developments, taking into account the most recent information on energy strategies, emission projections, atmospheric long-range transport and sensitivities of ecosystems in Europe. The paper provides quantitative results from the the "Regional Acidification Information and Simulation" (RAINS) model by analyzing various scenarios. Some more general qualitative conclusions and lessons are drawn from the model results. Further, the paper also attempts to illustrate the current limitations for scenario analysis caused by the limited availability and reliability of present data and models. The paper explores the advantages and disadvantages of alternative approaches by analyzing and evaluating different aspects of the various abatement strategies, such as relative emission reductions (compared to the baseyear 1980); cost of abatement measures; the burden to national economies as implied by emission control expenditures (i.e. the fraction of GDP required for emission reductions); the consequences on acid deposition; and their environmental impacts in terms of critical loads achievement. It should be noted however, that it is not the intention of this paper to perform any value judgments on the various strategies. Such preferences have to be established by negotiators. Undoubtedly, other considerations, which are not incorporated into this formalized analysis, will also influence the decisionmaking on the topic

Do Red Knots (Calidris Canutus Islandica) routinely skip Iceland during southward migration?

Subspecies Calidris canutus islandica of the Red Knot breeds on the arctic tundra of northeastern Canada and northern Greenland and winters along the coasts of northwestern Europe. During northward migration, it stops over in either Iceland or northern Norway. It has been assumed that it does the same during southward migration. Using ratios of stable carbon isotopes (&delta; 13 C) in whole blood, blood cells, and plasma, we investigated evidence for a stopover in Iceland en route from the breeding grounds to the Dutch Wadden Sea. With the expected diet (shellfish) and stopover duration at Iceland (12-15 days, maximum 17 days) and the turnover rates of blood cells (15.1 days) and plasma (6.0 days), Red Knots that stopped in Iceland should arrive with a blood (cell) &delta; 13 C midway between a tundra (-24.7[per thousand]) and a marine value (-14.0[per thousand]) and a plasma &delta;13 C approaching the marine value (-15.3[per thousand]). However, many adults arriving at the Wadden Sea had &delta;13 C ratios in blood (cells) and plasma below these levels, and some arrived with clear tundra signals in blood cells, suggesting that they skipped Iceland during southward migration. Surprisingly, available data suggest this also to be true for juveniles during their first southward migration. The &delta; 13 C signature of second-year birds confirmed that they oversummered in the Wadden Sea. Our findings contradict the largely untested idea that juvenile shorebirds make more stopovers than adults as well as the idea that the migration between the Nearctic and Europe is necessarily a two-leg process. <br /

Water storage and evaporation as constituents of rainfall interception

Intercepted rainfall may be evaporated during or after the rain event. Intercepted rain is generally determined as the difference between rainfall measurements outside and inside the forest. Such measurements are often used to discriminate between water storage and evaporation during rain as well. Two well-accepted methods underestimate water storage by a factor two as compared to direct observations. The underestimation of storage is compensated by an overestimation of evaporation during rain by a factor of three. The direct observations of water storage and evaporation appear to agree with previous direct observations. Thus, it is concluded that these observations are representative Also, our results based on methods using only rainfall measurements inside and outside the forest appear to agree with previous results, This would result in the conclusion that the common methods systematically underestimate water storage and overestimate evaporation during rain. Indeed, the systematic errors can be explained by the neglect of drainage before saturation. Water storage is better simulated assuming an exponential saturation of a larger storage capacity. A smaller evaporation can be simulated using an appropriate resistance to vapour transport. The observations in dense coniferous forest showed water storage to be the dominant process in rainfall interception, but this conclusion should not be generalized to other forests and climates. Direct observations of water storage and evaporation are recommended to build a realistic set of parameters for rainfall interception studies of the main vegetation types. (C) 1998 Elsevier Science B.V. All rights reserved