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Some considerations on the behaviour of the Piche evaporimeter
Abstract
L'influence de la radiation, de la conduction de la chaleur, du vent et de l'humidité de l'air sur l'évaporation d'eau par un évaporomètre de Piche, est décrite quantitativement. Une théorie sur l'évaporation d'une surface mouillée soumise à la radiation, élaborée par Penman, a servi de base pour ces considérations.
On a obtenu expérimentalement pour les rondelles depaier vert, employées avec le Piche, un coefficient de réflection de 0.2 pour le rayonnement à courte longueur d'ondes.
Cette valeur représente une moyenne satisfaisante du coefficient de réflexion d'un tapis végétal vert, telle une prairie par exemple. L'influence de la conduction de la chaleur dans l'instrument de Piche, est faible. L'influence du vent est exprimée dans la description théorique par le coefficient de transmission de la chaleur de la surface évaporante. La relation entre ces deux grandeurs est déduite des données expérimentales sur la base de la théorie. Le résultat est représenté à la figure 2.
En s'appuyant sur quelques exemples, les auteurs ont montré que la théorie permet d'interpréter des phénomènes observés quantitativement (comparez les tableaux 1 et 2).
En comparant les données de l'évaporomètre de Piche avec l'évaporation d'un tapis végétal, et pour autant que cette évaporation est influencée par les conditions atmosphériques (le contrôle de l'évaporation par des causes physiologiques ou autres est écarté), il résulte de la théorie, que le Piche n'est pas assez sensible à l'action de la radiation, mais par contre réagit trop fortement sous l'influence du vent.
... Of the sunken pans, Colorado pans are perhaps the most widely known. Other smaller evaporimeters (or atmometers), such as the Piche evaporimeter (Piche 1872, de Vries andVenema 1953), are gaining renewed interest as cheaper, reliable replacements to pans for use in, for example, metering ET rc in irrigation scheduling. It was against observations from evaporation pans that Penman (1948) verified estimates of his new meteorological parameterpotential evaporation (E p ). Bridging the gap between such purely physical models and instrumented observations are synthetic estimates that attempt to emulate the performance of instrumentation, such as the PenPan formulation (Linacre 1994, Rotstayn et al. 2006) that adjusts the Penman (1948) equation for E p to better characterize the enhanced radiative and advective dynamics of US Class A evaporation pans. ...
... The evaporation follows the seasons; it is an important factor to take into account because it indicates the xericity degree of the study stations. The evaporation was monitored from July 1994 to September 1995 using the Piche evaporimeter (De Vries & Venema, 1954Lecarpentier, 1975Stigter & Uiso, 1981Papaioannou et al., 1996, Kidney, 1996Stanhill, 1962Stigter et al., 1984. Compared to other climatic areas of the island, the evaporation is much higher in the dry sub-humid southern zone. ...
In the light of our knowledge of the Antilles' plant ecosystems we were able to underline their influence on the main factors of the general climate. By using climate measuring stations, three of which were located within the shrubland, pre-forest and young forest formations, two metres above the ground, we have demonstrated a tangible relationship between the plant biomass structure of these formations and their internal environments. The plant potential in the Lesser Antilles is of the forest type, it seems that during the progressive floristic succession the intra-vegetation environments become increasingly out of phase with the macroclimate. This phenomenon results in an increasingly specialised replacement of the species range. In fact from the dynamic shrub floors to the climacic forests, the intra-vegetation environments first select the pioneer general and post-pioneer (transitory) species and then the specialised species called late species which are pre-climacic and climacic antagonist species. The trends that emerge from this study should be analysed in-depth in more systematic studies.
... Consequently, a comparison of pan evaporation data with other estimates of atmospheric evaporative demand (McMahon et al. 2013) is needed in order to use these data as a proxy measure for evaporative demand. Equally, an analysis of measurements of the less well-known Piché evaporimeter (De Vries & Venema 1954, WMO 2008 to assess decadal changes in evaporation, as an alternative to pan evaporation data, has not yet been performed to our knowledge. ...
Interest is growing in the trends of atmospheric evaporation demand, increasing the need for long-term time series. This work describes, for the first time, the development of a dataset on evaporation in Spain based on long-term series of Piché and pan measurement records. Piché measurements have been reported for >50 stations since the 1960s. Measurements of pan evaporation, which is a much more widely studied variable in the literature, are also available, but only since 1984 for 21 stations. Particular emphasis was placed on the homogenization of this dataset. Both the mean annual Piché and pan series over Spain showed evaporative increases during the common study period (1985−2011), by a rate of around +0.1 mm d−1 decade−1. Furthermore, using the annual Piché records since the 1960s, an evaporation decline was detected from the 1960s to the mid-1980s, which resulted in a non-significant trend over the entire 1961−2011 period. Our results indicate agreement between the decadal variability of reference evapotranspiration and the surface solar radiation previously reported and the evaporation from Piché and pan measurements, especially during summer. The suitability of Piché records compared to pan evaporation data to represent past trends is discussed.
... Besides very sophisticated methods for obtaining evaporation data, very simple ones are still in use, like evaporation pans and Piche evaporimeters. The Piche instrument dates from over 100 years and comprehensive studies of its operational behavior and potential over the years are presented in Prescott and Stirk (1951) and de Vries and Venema (1954). Independently, both Stanhill (1962) and Bouchet (1963 were the first to point out that its exposure within a meteorological screen responds primarily to wet bulb depression and to wind speed, the essential variables in the second term of Penman's equation (Penman, 1948Penman, , 1963), and their idea was worked out further by Brochet and Gerbier (1972). ...
Daily meteorological measurements taken in Athens during the period
1951-1984 are used to investigate the feasibility of calculating
Penman-Monteith's evapotranspiration estimates when wind measurements
are not available. Daily sheltered Piche data (from a large
meteorological screen) are shown to be satisfactorily related to the
second term in Penman-Monteith's equation on a daily basis. Furthermore,
daily conventional Penman-Monteith evapotranspiration estimates are
compared with the ones obtained from the adjusted Piche readings and the
results show that daily, monthly or yearly evapotranspiration estimates,
acquired over long periods, can be successfully estimated by using the
substantial backlogs of Piche evaporimeter data. The analysis suggests
monthly relationships to be justified for adjusting Piche data, although
even one annual relationship seems to be able to estimate
evapotranspiration in most of the months, or in a whole year period,
satisfactorily.
Measurements with Piche evaporimeters have been conducted within a thermometer screen over a grass surface at several heights. The results show a good correlation with model calculations but differ somewhat in absolute value. Comparisons with the Penman potential evaporation results show a considerable overestimation. With a simple factor, or with a lower measuring position, the results can be brought in a better agreement. The idea of G. Stanhill was verified and proved to be useful only for long periods.
Water loss measured by the Piche evaporimeter, E, was found to be highly correlated with the calculated aerodynamic term, Ea, in Penman's evaporation formula. The error introduced by using the more convenient Piche evaporimeter measurements was less than that caused by the use of a single daily observation of vapour pressure in the calculation of the aerodynamic term.
No significant difference was found between the relationship in the Judean hills and the arid Negev region of Israel which was
A test of a simplified form of Penman's formula, based on local Piche evaporimeter readings for the aerodynamic term and a regional value for the energy term, gave close agreement with the evaporation values calculated using the full formula.
Annual and seasonal characteristics of precipitation and evapotranspiration were analysed of an 80-year data record (1928–2008) at Wageningen (the Netherlands). The precipitation series shows a mean annual rainfall of 765 ± 130 mm with a relatively high interannual variability [coefficient of variation (CV) = 17.0%]. Both the annual and seasonal rainfall trends show a small but statistically insignificant increase. Potential evapotranspiration was estimated by Makkink's formula, using observations of incoming solar radiation and air temperature as inputs. This provides a mean evapotranspiration of (525 ± 50) mm annum−1 with a relatively low interannual variability (CV = 9.5%). The annual and seasonal trends appear to be statistically significant, except for the summer season. In addition, since 1992, actual evapotranspiration is measured by the eddy-covariance technique and these results were found to be highly correlated with the potential evapotranspiration (Eact ≈ 0.75Epot). A comparison is made with a class A evaporation pan operating between 1984 and 1989. Copyright © 2009 Royal Meteorological Society
To investigate the feasibility of estimating Penman's potential transpiration (Erp) without recourse to sophisticated instrumentation, the rates of evaporation from a Class-A pan and from a Piche atmometer exposed within a thermometer screen were analysed in detail using continuous micrometeorological measurements taken on the same site. Evaporimeter and other associated manual measurements were made not only on a routine daily basis but also on certain days from hour to hour. the latter measurements were of particular help in interpreting physically the behaviour of both evaporimeters.
It is shown:
The franework for the general application of conclusions (i) and (iii) in generating a synthetic series of values of Erp is introduced and discussed.
Micrometeorology is the study of atmospheric processes at the earth's surface. If the leaves of plants and the skins of animals are regarded as extensions of that surface, micrometeorological principles can help the biologist to investigate the influence of physical environment on living material. Two examples are considered in illustration. First, the surface temperature of plants and animals and the cooling produced by evaporation are discussed in terms of heat-balance equations. Second, it is shown that the uptake of carbon dioxide by a field crop can be measured by a micrometeorological technique.
The rates of evaporation from a Piche evaporimeter exposed within a meteorological screen are compared with the aerodynamic term in the Penman equation using meteorological measurements taken in Athens, over a sixty years period. Regression of monthly grouped data against the Penman aerodynamic term showed that the evaporation from the sheltered Piche in this urban area, is closely proportional to the (complete) second term in Penman's equation with a systematic monthly variation of the regression gradient.
A new type of instrument is used to estimate evaporation figures. A model of this instrument is presented which describes the physical behaviour. The model represents the measurement results well for a height of 0.30m. The model underestimates systematically (18%) the results for 1.50m. Comparisons have been made with Piche evaporimeters. Both instruments behave more or less alike.Comparisons have been made with the potential evaporation according to Penman. The capillary atmometer is able to estimate evaporation figures and is relatively cheap.
Although considerable progress has been made in understanding and measuring evaporation, it remains extremely difficult to determine or estimate evaporation rates under natural conditions. In this paper a critical review is presented of methods for determining or predicting evaporation in current use. Stress is laid on the physical background of these methods.From a physical viewpoint local instantaneous evaporation is well defined, but integration with respect to time and place, in order to arrive at evaporation rates for extended periods and areas — as required in hydrology — is generally impossible. Therefore, so called characteristic evaporation values are introduced and discussed.The importance of reliable direct measurements of natural evaporation is pointed out. Some experimental results obtained through application of the energy balance method combined with direct measurement of the turbulent flux of sensible heat are presented.
The study was of some aspects of the occurrence of springs in the Netherlands, in particular those of the Veluwe Fringe, but also in Twente and south Limburg. These aspects were compared with those in Germany, France, Belgium and Austria. Along the Veluwe Fringe water percolates through layers of gravel or coarse sand to the impermeable layers of clay or sand and mud be neath; the springs rise where the junction of these layers reaches the surface. Many springs have arisen through excavations higher in the. valleys. Most springs in south Limburg arise where permeable water-holding calcareous layers meet impermeable layers of sand or clay. The temperature and the oxygen content of the large springs of the Veluwe Fringe proved to be constant, those of the smaller ones a bit less so. Their water proved to be generally rich in nitrate, with least solutes near preglacial sands and richest in minerals near loess. In south Limburg it was shown to be very rich in lime.
Discussion of microclimate and physical and chemical status of the soil is followed by an extensive description of plant communities, ecology of the woods, the undergrowth on the forest flushes and of plants in the actual springs and their streams.
The Piche atmometer is still used throughout the world, a century after its invention. As with most evaporation instruments, the meaning and utility of Piche readings have been questioned. In the present study, a linearized energy budget for a leaf is used to predict the daily evaporation from a Piche atmograph. This approach showed a one-to-one relationship with observed evaporation, and accounted for 70–90% of the observed variance. Successful predictions were possible even when the meteorological data were taken at 12-h intervals, although the most accurate predictions were based on data taken at 1-h intervals. Sensitivity analysis predicts that Piche evaporation is strongly affected by air temperature, relative humidity, wind speed and long-wave radiation; albedo and short-wave radiation had lesser effects. The present study supports the idea that the Piche atmograph models the potential evapotranspiration of an individual leaf.
Hourly evaporation rates from a Piché evaporimeter installed inside a Stevenson screen were compared with rates measured from a Piché exposed to the atmosphere, but screened from direct short- and long-wave radiation (shaded) and with rates registered on a carborundum evaporimeter similarly exposed.Strict linear relationships exist between evaporation from the shaded Piché evaporimeter, the Piché in a screen and the shaded carborundum evaporimeter. The latter was 1.6 times more sensitive than the shaded Piché. The shaded Piché was 1.4 times more sensitive than the screened Piché.Regression equations for the aerodynamic term (AT) in the Penman-Monteith equation were developed. AT was expressed in terms of hourly evaporation measured by a Piché in a Stevenson screen (Epsc), an exposed, but shaded Piché (Eps), and a carborundum evaporimeter (Ecs). The following relationships were found: 1.(i) AT = 0.018 (Epsc) + 0.09 (mm h−1) r = 0.952.(ii) AT = 0.014 (Eps) + 0.05 (mm h−1) r = 0.963.(iii) AT = 0.008 (Ecs) + 0.06 (mm h−1) r = 0.95Estimates of maximum evapotranspiration rates, ETm, obtained by substituting these relationships for AT in the Penman-Monteith equation were then tested against lysimeter measurements of ETm. In 1985, values of the index of agreement varying between 0.94 and 0.95, and mean absolute difference varying from 0.10 to 0.09 mm h−1, for the three types of evaporimeters were obtained from these comparisons. In 1986, values of the corresponding test parameters were 0.92 and 0.09 mm h−1 when the carborundum evaporimeter was used. These values demonstrate the reliability of the proposed model. While the sensitivity of the evaporimeters varied greatly, no one proved more accurate than any other. The carborundum evaporimeter proved to be the most sensitive.
Concerning an interference in the environment due to landscape management
research was carried out on the vegetation of an inland dune area in the national park
De Hoge Veluwe (NL). Altogether 21 vegetation units were defined in Corynephorus
vegetation, other grasslands, heathland, and pinewoods. These units were
characterized by means of soil and climatological data acquisition and analysis.
Further, the cryptogames of bark, decaying wood, and pebbles were inventoried.
Vegetation units and biotope types were mapped. After evaluation of the vegetation the
value of different parts of the research area could be determined. Finally,
recommendations to modify the inter-ference in the environment in favour of species
protection were made based on the calculated loss in value of vegetation caused by
the human intervention.
It turned out that spontaneous pinewood and Corynephorus canescens vegetation
(Spergulo-Corynephoretum) which in this case were poor in vascular plant species
are the most valuable of all vegetation units because of their psammophilous soil lichen
flora. In total nine endangered or rare taxa were recorded. These disappear where
competitive grasses supersede Corynephorus or an organic layer totally covers the
sand. This happens mainly in an area where pineforest was cut down in the past.
Another diminution in value of vegetation can be observed near the edges of forests by
reason of massive invasion of the neophytic moss Campylopus introflexus. On
decaying trunks in the pine forests also several endangered species were found.
Based on the evaluation of the areas for some parts an exclusion from the target area
of the interference is recommended. In some cases supporting measures are
considered necessary. Stands of Stereocaulon condensatum, Cladonia strepsilis und
Cladonia squamosa var. squamosa are effected. Other endangered or rare species are
protected through these measures as well. Besides, areas with a valuable flora are
proposed for exclusion to guarantee the recolonization of the effected ground by
valuable species. Moreover, measures of protection of border areas are proposed as
well as the extension of the environmental interference in some parts to compensate
the above mentioned restrictions.
The Veluwe is a stretch of high ground in the central part of the Netherlands, north of the river Rhine and south of the IJssel Meer, i.e. the former Zuiderzee, and the polders reclaimed from the latter. Geologically the area consists of three formations: 1. ridges which owe their origin to the pressure of the land ise, and which consist of sands deposited as river sediments in preglacial times; 2. a fluvioglacial formation; on some of these plains small but steep hills are found; 3. aeolian sediments: loss and cover-sands (cf. VINK, 1949); they were deposited in the late-glacial period.
After describing the continental subtropical climate of central Iraq, Wartena assembled other meteorological observations necessary to estimate evaporation from a lake and irrigation project.
Usual formulae correlating total global radiation with duration of sunshine gave an overestimate with clear sky, an underestimate with cloud cover. A new relationship was derived which gave better results.
A critical discussion of the energy balance of an evaporation pan clearly showed that 'pan factors' could not be constants but depended on weather conditions and time of year. Kohler's theory yielded inaccurate results. Especially in and regions, to assume a constant ratio between 'potential' and actual evaporation may lead to considerable error but a 'class A' pan satisfactorily indicated irrigation requirements. The 'Piche' evaporimeter was not satisfactory.
To estimate evaporation from the projected storage lake, its surface temperatures were calculated by using elementary meteorological quantities. The method was in reasonable agreement with actual values on the existing Lake of Tiberias. The evaporation from fictitious lakes 10 and 50 metres deep was calculated to be different.
Qualitative influences of wind, humidity and temperature of the atmosphere on evaporation were discussed.
Yearly evaporation from the two lakes was estimated at 2500 mm.<p/
At several heights and times of day within a crop of Zea mays, internal leaf diffusion resistance (r(i)) and external boundary layer diffusion resistance (r(a)) were evaluated by measuring the temperature of a transpiring and a non-transpiring leaf (simulated by covering both sides of a normal leaf with strips of poly-ethylene tape), and by measuring the immediate air temperature, humidity and windspeed.Both r(a) and r(i) increased with depth into the crop. However, r(a) generally was less than 10% of r(i).Profiles of latent-heat flux density and source intensity of transpiration showed that transpiration corresponded roughly to foliage distribution (with an upward shift) and were not similar to the profile of radiation absorption.The data were compared with heat budget data. The 2 approaches yielded quite similar height distributions of transpiration per unit leaf area and total transpiration resistance.The total crop resistance to transpiration was computed as 0.027 min cm(-1). This compares to Monteith's values of 0.017 to 0.040 min cm(-1) for beans (Phaseolus vulgaris L.), and Linacre's values of 0.015 to 0.020 min cm(-1) for turf.
The diurnal variation of the measured transpiration from pots with alfalfa plants and the readings of several evaporimeters for a case reported by Briggs and Shantz are compared with the calculated values according to Penman's theory. The influence of radiation on transpiration and evaporation is clearly illustrated. The ratio between transpiration and calculated evaporation is almost constant and shows less variation than the transpiration/evaporimeter-reading ratios. The differences in magnitude between the transpiration and the evaporation values and the limitations of the theoretical treatment are discussed. It is pointed out that the evaporation from isolated plants or groups of plants which project above their surroundings will usually be greater than the evaporation from a closed homogeneous vegetation with the same height as these plants. (Abstract retrieved from CAB Abstracts by CABI’s permission)
Two theoretical approaches to evaporation from saturated surfaces are outlined, the first being on an aerodynamic basis in which evaporation is regarded as due to turbulent transport of vapour by a process of eddy diffusion, and the second being on an energy basis in which evaporation is regarded as one of the ways of degrading incoming radiation. Neither approach is new, but a combination is suggested that eliminates the parameter measured with most difficulty-surface temperature-and provides for the first time an opportunity to make theoretical estimates of evaporation rates from standard meteorological data, estimates that can be retrospective. Experimental work to test these theories shows that the aerodynamic approach is not adequate and an empirical expression, previously obtained in America, is a better description of evaporation from open water. The energy balance is found to be quite successful. Evaporation rates from wet bare soil and from turf with an adequate supply of water are obtained as fractions of that from open water, the fraction for turf showing a seasonal change attributed to the annual cycle of length of daylight. Finally, the experimental results are applied to data published elsewhere and it is shown that a satisfactory account can be given of open water evaporation at four widely spaced sites in America and Europe, the results for bare soil receive a reasonable check in India, and application of the results for turf shows good agreement with estimates of evaporation from catchment areas in the British Isles.
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