Application of the Priestley-Taylor evaporation model to assess the influence of soil moisture on the evaporation from a large weighing lysimeter and class a pan

The influence of soil moisture on evaporation from a 6-m grass-covered lysimeter and from Class A pans was assessed for one summer using the -parameter of the Priestley-Taylor evaporation model appropriate for the individual surfaces computed on a daily basis. Net radiation over the pan was estimated from above-grass measurements using a correlation established between the two, using measurements made in the previous two summers. Changes in heat storage of the water were considered in the derivation of for the pan. A unique relationship for the particular conditions of the site was determined between the for the lysimeter and soil moisture, approaching 1.29 at soil moisture near field capacity, but decreasing to as low as 0.5 for dry soil. The corresponding relationship for the pan showed more scatter, but this was improved by using 5-day running means of evaporation and stratifying the data in terms of wind speed to yield a family of curves. Values for at wet soil conditions varied from 1.07 for 100 km day^–1 wind run to 1.17 for 250 km day^–1 wind run. For each curve, values of increased by about 20%; as the soil dried. The relationships may be used to reduce observed Class A pan evaporation to equivalent values for wet-soil conditions and to estimate near-surface soil moisture and actual evapotranspiration for this particular site. Extension of the technique to other areas requires derivation of similar relationships appropriate for those other locations     

On the annual variation of evaporation from lakes in the middle latitudes

Summary It is concluded from heat balance considerations that in the middle latitudes, the form of the annual variation of evaporation from nonshallow lakes is a double wave. In addition to the accepted winter minimum of evaporation, a second (but not necessarily secondary) minimum of evaporation occurs in spring or in summer about the time when the rate of heating of the lake waters is at its greatest. Thus the annual variation of evaporation resembles that from the oceans in similar latitudes except for a phase difference whose magnitude is to an extent an inverse function of the lake depth. In support of the above statements, observational data and results of studies are cited from the U. S. A., Switzerland and Israel.

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Zusammenfassung Aus Wärmebilanzbetrachtungen wird geschlossen, daß in mittleren Breiten der Jahresgang der Verdunstung von nicht seichten Seen eine Doppelwelle aufweist. Zusätlich zum bekannten Winterminimum der Verdunstung tritt ein zweites (aber nicht notwendig sekundäres) Minimum der Verdunstung im Frühling oder im Sommer zur Zeit der raschesten Erwärmung des Seewassers auf. Damit ähnelt der Jahresgang der Verdunstung der Seen dem der Verdunstung von Ozeanen gleicher Breiten bis auf eine Phasenverschiebung, deren Größe zu einem gewissen Grad eine invese Funktion der Seetiefe ist. Zur Stütze dieser Ansicht werden Beobachtungsdaten und Untersuchungsergebnisse aus USA, aus der Schweiz und aus Israel angeführt.

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Résumé En considération du bilan de chaleur appliqué aux latitudes moyennes, on est arrivé à la conclusion que, dans les lacs qui ont une certaine profondeur, la variation annuelle d'évaporation est une onde double. En addition au minimum hibernal accepté d'évaporation, un second (mains pas necessairement secondaire) minimum d'évaporation se trouve en printemps ou en été environ au temps où la vitesse de réchauffement des eaux de lac atteint son maximum. Ainsi la variation annuelle d'évaporation ressemble à celle des océans de latitude similaire, à l'exception d'une différence de phase dont la magnitude est jusqu'à un point une fonction inverse de la profondeur du lac. Pour supporter la thèse ci-dessus, des données observées et les résultats d'études faites aux Etats-Unis, en Suisse et en Israël sont citées.

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Mit 1 Figure.     

Atmospheric factors governing winter thunderstorms in the coastal region of the eastern Mediterranean

The factors controlling lightning activity over central Israel and the adjacent Mediterranean Sea were studied. Potential predictors were correlated at 12-h intervals with total number of flashes. Since during the winter season lightning is generated in this region by Cyprus Lows, the data includes 283 observations on days in which this system prevailed for December to February, which covered four winters. The average lightning rate was 26.8 h^-1, with a high standard deviation of 55.2 h^-1. The total number of flashes at night exceeded the daytime number by 35%, in agreement with previous studies. The CAPE values were on the order of hundreds of J kg^-1. A statistical linear multi-regression model was developed for the number of lightning flashes based on 35 atmospheric variables. The correlation between the modeled and the observed number of lightning flashes was 0.67, and 0.81 for the logarithm of the number of lightning flashes (log-lightning). This suggests that the lightning intensity responds exponentially to its governing factors. A linear multi-regression stepwise model for the log-lightning selected seven predictors as significant and yielded a correlation of 0.74. This model was validated by three holdout and three leave-one-out validation experiments. The composition and hierarchy of the significant predictors reflect the dominance of the thermodynamic factors, in particular instability, in determining lightning activity. Though thunderstorms are local or meso-scale phenomena, the synoptic-scale atmospheric variables were found to be powerful predictors for their intensity.     

The influence of errors in precipitation measurements on the accuracy of the evaporation measurements performed by a class A evaporation pan

Summary Since uncorrected precipitation measurements are used for calculating the evaporation measured by a class A pan, precipitation measurement errors are introduced into the evaporation results. In defining the total error of the evaporation measurement it is necessary to consider the fact that the class A pan orifice and the rain gauge orifice are at different elevations. This paper presents a model to estimate the average value for the total error of evaporation. It is also shown that the evaporation measured by a class A pan is smaller than the actual evaporation by between 5 and 20%.     

Evaluating persistence and identifying trends and abrupt changes in monthly and annual rainfalls of a semi-arid region in Western India

In this study, 43-year (1965–2007) monthly and annual rainfall time series of ten rainfall stations in a semi-arid region of western India are analyzed by adopting three tests for testing normality and by applying autoregressive technique for exploring persistence. Gradual trends are identified by three tests, and their magnitudes are assessed by the Sen’s slope estimator. Also, abrupt changes are detected by using four tests and they are further confirmed by two tests. Box-whisker plots revealed that the rainfalls of June and September are right skewed for all the stations. The annual rainfalls of Bhinder, Dhariawad, and Gogunda stations are found considerably right skewed. The normality tests indicated that the rainfall of July does not deviate from the normal distribution at all the stations. However, the annual rainfall is found non-normal at five stations. The monthly rainfalls of June, July, and August have persistence respectively at three (Mavli, Salumber, and Sarada), two (Kherwara and Sarada), and one (Mavli) stations, whereas the annual rainfall has persistence at Girwa and Mavli stations. Significantly increasing trend is detected at Mavli in the rainfall of July and in the annual rainfall (p value?>?0.05), while the negative trend in August rainfall at Dhariawad is found significant (p value?>?0.10). This study revealed that the presence of serial correlation does not affect the performance of the Mann-Kendall test. Mean values of trend magnitudes for the rainfalls of June, July, August, and September are 0.3, 0.8, ?0.4, and 0.4 mm year^?1, respectively, and the overall mean value for the annual rainfall is 0.9 mm year^?1. It is found that the standard normal homogeneity test and the Pettitt test are biased towards the end of the series to locate a change point. Conversely, the Bayesian test has a tendency to look for a change point in the beginning of time series. Confirmed abrupt changes in the rainfall time series are found in the year 2003 (Bhinder) in June; years 1974 (Mavli) and 1989 (Dhariawad and Salumber) in July; years 1972 (Sarada), 1990 (Dhariawad), and 2003 (Mavli) in August; years 1977 (Dhariawad), 1991 (Sarada), and 2004 (Kotra) in September; and in the year 1972 (Mavli and Sarada stations) in the annual series. It is emphasized that the significantly increasing trend of rainfall may have linkages with climate change and/or variability. Finally, this study recommends use of multiple statistical tests for analyzing hydrologic time series in order to ensure reliable decisions.     

An annual cycle of vegetation in a GCM. Part I: implementation and impact on evaporation

The sensitivity of evaporation to a prescribed vegetation annual cycle is examined globally in the Met Office Hadley Centre Unified Model (HadAM3) which incorporates the Met Office Surface Exchange Scheme (MOSES2) as the land surface scheme. A vegetation annual cycle for each plant functional type in each grid box is derived based on satellite estimates of Leaf Area Index (LAI) obtained from the nine-year International Satellite Land Surface Climatology Project II dataset. The prescribed model vegetation seasonality consists of annual cycles of a number of structural vegetation characteristics including LAI as well as canopy height, surface roughness, canopy water capacity, and canopy heat capacity, which themselves are based on empirical relationships with LAI. An annual cycle of surface albedo, which in the model is a function of soil albedo, surface soil moisture, and LAI, is also modelled and agrees reasonably with observed estimates of the surface albedo annual cycle. Two 25-year numerical experiments are completed and compared: the first with vegetation characteristics held at annual mean values, the second with prescribed realistic seasonally varying vegetation. Initial analysis uncovered an unrealistically weak relationship between evaporation and vegetation state that is primarily due to the insensitivity of evapotranspiration to LAI. This weak relationship is strengthened by the adjustment of two MOSES2 parameters that together improve the models LAI-surface conductance relationship by comparison with observed and theoretical estimates. The extinction coefficient for photosynthetically active radiation, k _par , is adjusted downwards from 0.5 to 0.3, thereby enhancing the LAI-canopy conductance relationship. A canopy shading extinction coefficient, k _sh , that controls what fraction of the soil surface beneath a canopy is directly exposed to the overlying atmosphere is increased from 0.5 to 1.0, which effectively reduces soil evaporation under a dense canopy. When the experiments are repeated with the adjusted parameters, the relationship between evaporation and vegetation state is strengthened and is more spatially consistent. At nearly all locations, the annual cycle of evaporation is enhanced in the seasonally varying vegetation experiment. Evaporation is stronger during the peak of the growing season and, in the tropics, reduced transpiration during the dry season when LAI is small leads to significantly lower total evaporation.     

Spatial and temporal patterns of the mean annual precipitation at decadal time scale in southern Italy (Calabria region)

Mean annual precipitation variability at decadal time scale over a southern Italy area (Calabria) was investigated to quantify the spatial and temporal patterns. A multivariate approach has been applied to analyse spatial?Ctemporal (1921?C2000) data of annual precipitation. A nested isotropic linear model of coregionalization was fitted to the experimental variograms including three basic structures: a nugget effect, an exponential model and a spherical model. The correlation structure between the decades was analysed by applying principal component analysis at each spatial scale, and specific factors at each characteristic scale were cokriged and mapped. Two components were identified: the first is mainly linked to local factors, which could be identified by the orographic characteristics of the region, while the long range component could be related to large-scale factors, like for example the processes of the global atmospheric circulation. In addition, in order to obtain a better insight into the pattern of relatively dry or wet zones, a standardized relative difference was calculated. The results showed that the annual precipitation decreased during the period 1921?C2000 and the spatial distribution changed with an increase of dry areas.     

Spatial variability of Holocene changes in the annual precipitation pattern: a model-data synthesis for the Asian monsoon region

This study provides a detailed analysis of the mid-Holocene to present-day precipitation change in the Asian monsoon region. We compare for the first time results of high resolution climate model simulations with a standardised set of mid-Holocene moisture reconstructions. Changes in the simulated summer monsoon characteristics (onset, withdrawal, length and associated rainfall) and the mechanisms causing the Holocene precipitation changes are investigated. According to the model, most parts of the Indian subcontinent received more precipitation (up to 5 mm/day) at mid-Holocene than at present-day. This is related to a stronger Indian summer monsoon accompanied by an intensified vertically integrated moisture flux convergence. The East Asian monsoon region exhibits local inhomogeneities in the simulated annual precipitation signal. The sign of this signal depends on the balance of decreased pre-monsoon and increased monsoon precipitation at mid-Holocene compared to present-day. Hence, rainfall changes in the East Asian monsoon domain are not solely associated with modifications in the summer monsoon circulation but also depend on changes in the mid-latitudinal westerly wind system that dominates the circulation during the pre-monsoon season. The proxy-based climate reconstructions confirm the regional dissimilarities in the annual precipitation signal and agree well with the model results. Our results highlight the importance of including the pre-monsoon season in climate studies of the Asian monsoon system and point out the complex response of this system to the Holocene insolation forcing. The comparison with a coarse climate model simulation reveals that this complex response can only be resolved in high resolution simulations.     

Recent trends in annual snowline variations in the northern wet outer tropics: case studies from southern Cordillera Blanca,Peru

TL-moments approach has been used in an analysis to identify the best-fitting distributions to represent the annual series of maximum streamflow data over seven stations in Johor, Malaysia. The TL-moments with different trimming values are used to estimate the parameter of the selected distributions namely: Three-parameter lognormal (LN3) and Pearson Type III (P3) distribution. The main objective of this study is to derive the TL-moments (t ₁,0), t ₁?=?1,2,3,4 methods for LN3 and P3 distributions. The performance of TL-moments (t ₁,0), t ₁?=?1,2,3,4 was compared with L-moments through Monte Carlo simulation and streamflow data over a station in Johor, Malaysia. The absolute error is used to test the influence of TL-moments methods on estimated probability distribution functions. From the cases in this study, the results show that TL-moments with four trimmed smallest values from the conceptual sample (TL-moments [4, 0]) of LN3 distribution was the most appropriate in most of the stations of the annual maximum streamflow series in Johor, Malaysia.     

京津冀地区7—9月极端降水分型及趋势分析

本文采用K-means聚类分析的方法,将京津冀地区1979—2022年7—9月极端降水事件按照强度和位置分为四类,并在此基础上分析了此地区7—9月极端降水的环流特征、变化趋势及可能原因。通过分析不同高度层四类极端降水对应的大气环流可知,低层的西南气流、中层的副热带高压、高层的南亚高压、西风急流等天气系统以不同的配置组合共同对京津冀地区的极端降水产生影响。在长期趋势方面,1979—2022年7—9月京津冀地区的极端降水频率呈上升趋势,这是由于7月类型Ⅱ和Ⅲ极端降水的增加,以及9月类型Ⅳ极端降水的增长所致。通过对背景场的分析发现,低层水汽场及高层位势高度场有利于7月极端降水的增加,而9月类型Ⅳ极端降水的增加则源自于低层和高层背景动力场及位势高度场的增加。     

Climate change vulnerability to agrarian ecosystem of small Island: evidence from Sagar Island,India

Theoretical and Applied Climatology - The present study assessed climate change vulnerability in agricultural sector of low-lying Sagar Island of Bay of Bengal. Vulnerability indices were estimated...     

Variability and trends of sub-continental scale surface climate in the twentieth century. Part I: observations

An analysis is presented of observed temperature and precipitation variability and trends throughout the twentieth century over 22 land regions of sub-continental scale. Summer, winter and annual data are examined using a range of variability measures. Statistically significant warming trends are found over the majority of regions. The trends have a magnitude of up to 2 K per century and are maximum over cold climate regions. Only a few precipitation trends are statistically significant. Regional temperature and precipitation show pronounced variability at scales from interannual to multidecadal, with maximum over cold climate regions. The interannual variability shows significant variations and trends throughout the century, the latter being mostly negative for precipitation and both positive and negative for temperature. Temperature and precipitation anomalies show a chaotic-type behavior in which the regional conditions oscillate around the long term mean trend and occasionally fall into long-lasting (up to 10 years or more) anomaly regimes. A generally modest temporal correlation is found between anomalies of different regions and between temperature and precipitation anomalies for the same region. This correlation is mostly positive for temperature in cases of adjacent regions or regions in the same latitude belts. Several cases of negative inter-regional precipitation anomaly correlation are found. The ENSO significantly affects the anomaly variability patterns over a number of regions, primarily in tropical areas, while the NAO significantly affects the variability over northern mid- and high-latitude regions of Europe and Asia.     

The impact of climate change on cropland productivity: evidence from satellite based products at the river basin scale in Africa

We investigate the effect of climate change on crop productivity in Africa using satellite derived data on land use and net primary productivity (NPP) at a small river basin scale, distinguishing between the impact of local and upper-catchment weather. Regression results show that both of these are determining factors of local cropland productivity. These estimates are then combined with climate change predictions obtained from two general circulation models (GCMs) under two greenhouse gas emissions (GHG) assumptions to evaluate the impact of climate change by 2100. For some scenarios significant decreases are predicted over the northern and southern parts of Africa.     

Towards a better understanding of gendered power in small scale fisheries of the Western Indian Ocean

Scholarship on gender in fisheries is not new. However, while there are many studies on the context and politics of gender and fisheries, understanding how power influences gender equality remains understudied, especially in the Western Indian Ocean. Based on evidence gathered from an interdisciplinary set of literature, including sectoral policies, this article provides nuanced insight at rethinking - how gendered-power dynamics constrain and enable choices and opportunities for addressing gender inequality in small-scale fisheries. Compelling evidence shows that a gendered-power dynamic is crucial for renegotiating gender equality with social norms and politics, including challenging simplistic views on poverty, vulnerability, and subordination of women. The article presents a latent chance for greater reflexivity among development practitioners, researchers, and policymakers on the politics of and transformation towards gender equality in small-scale fisheries.     

Variability and trends of sub-continental scale surface climate in the twentieth century. Part II: AOGCM simulations

This work presents an analysis of simulated temperature and precipitation variability and trends throughout the twentieth century over 22 land regions of sub-continental scale in the HADCM3 and HADCM2 (two realizations) coupled models. Regional temperature biases in the HADCM3 and HADCM2 are mostly in the range of -5 K to +3 K for the seasonal averages and -3 K to +2 K for the annual average. Seasonal precipitation biases are mostly in the range of -50% to 75% of present day precipitation, with a tendency in both models to overpredict cold season precipitation. Except for cold season temperature in mid- and high-latitude Northern Hemisphere regions, the average climatology of the HADCM2 and HADCM3 is of comparable quality despite the lack of an ocean flux adjustment in the HADCM3. Both models show warming trends of magnitude in line with observations, although the observed inter-regional patterns of warming trend are not well reproduced. Measures of temperature and precipitation interannual to interdecadal variability in the models are in general agreement with observations except for Northern Hemisphere summer temperature variability, which is overestimated. The models somewhat underestimate the inter-decadal variations in interannual variability measures observed during the century and overestimate the range of anomalies. Both models tend to overpredict the occurrences of short persistences (1-3 years) and underpredict the occurrence and maximum length of long persistences (greater than three years), which is an indication of a deficiency in the simulation of long-lived anomaly regimes. Compared to observations, the models produce a higher magnitude of temporal anomaly correlation across regions and correlation between temperature and precipitation anomalies for a given region. This suggests that local processes that may be effective in decoupling the observed regional anomalies are not captured well. Overall, the variability measures in the HADCM2 and HADCM3 are of similar quality, indicating that the use of a flux correction in the HADCM2 does not strongly affect the regional variability characteristics of the model.     

The adjustment of the wind field to small scale topography in a numerical weather prediction model

Numerical experiments are performed to test one reasonably economical method of producing regional forecasts. Starting with initial conditions interpolated from a 20 hour coarse grid Northern Hemisphere forecast, a fine mesh model is integrated for a further period of 4 hours over a limited area. The fine mesh is located over the north‐eastern part of North America and its resolution is sufficient to re‐produce topographic features such as the St. Lawrence and Richelieu Valleys. The resulting forecast at hour 24 is then compared with the coarse mesh prediction for the same time. The comparison reveals how the horizontal and vertical components of the wind are affected by the small scale topography. In particular, the channelling effect of the main valleys is demonstrated.     

The spray contribution to net evaporation from the sea: A review of recent progress

The part that sea spray plays in the air-sea transfer of heat and moisture has been a controversial question for the last two decades. With general circulation models (GCMs) suggesting that perturbations in the Earth's surface heat budget of only a few W m^–2 can initiate major climatic variations, it is crucial that we identify and quantify all the terms in that heat budget. Thus, here we review recent work on how sea spray contributes to the sea surface heat and moisture budgets. In the presence of spray, the near-surface atmosphere is characterized by a droplet evaporation layer (DEL) with a height that scales with the significant-wave amplitude. The majority of spray transfer processes occur within this layer. As a result, the DEL is cooler and more moist than the atmospheric surface layer would be under identical conditions but without the spray. Also, because the spray in the DEL provides elevated sources and sinks for heat and moisture, the vertical heat fluxes are no longer constant with height. We use Eulerian and Lagrangian models and a simple analytical model to study the processes important in spray droplet dispersion and evaporation within this DEL. These models all point to the conclusion that, in high winds (above about 15 m/s), sea spray begins to contribute significantly to the air-sea fluxes of heat and moisture. For example, we estimate that, in a 20-m/s wind, with an air temperature of 20°C, a sea surface temperature of 22°C, and a relative humidity of 80%, the latent and sensible heat fluxes resulting from the spray alone will have magnitudes of order 150 and 15 W/m², respectively, in the DEL. Finally, we speculate on what fraction of these fluxes rise out of the DEL and, thus, become available to the entire marine boundary layer.     

Supporting evidence for a positive water vapor/infrared radiative feedback on large scale SST perturbations from a recent parameterization of surface long wave irradiance

Summary In this note a recent parameterization of surface infrared irradiance as a function of screen temperature and precipitable water is studied. The primary purpose is to investigate whether this parameterization supports previous studies of the surface infrared radiation that show a positive water vapor/infrared radiative feedback on large scale surface temperature perturbations. The parameterization studied here, which uses screen temperature and precipitable water as input, has been shown previously to resemble observations very well compared with other simple parameterizations of the irradiance. The results of the present study, where precipitable water has been parameterized as a function of screen temperature, provide supporting evidence for a positive value of the water vapor/infrared radiative feedback. The estimated magnitude of the feedback lies within the range of previous studies.Revised April 2, 2002; accepted March 11, 2003 Published online: August 7, 2003