Spatiotemporal distribution of reference evapotranspiration in the Republic of Moldova (original) (raw)
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Recent changes in reference evapotranspiration in Romania
Global and Planetary Change, 2013
In the last few decades, climate changes have become the most important topic in the field of climatology. Reference evapotranspiration (ET0) is often used to identify regions prone to drought or aridity. In this paper, we used monthly data recorded in 57weather stations in Romania over the period 1961–2007. The FAO Penman–Monteith method, based on air temperature, sunshine duration, relative humidity andwind speed,was employed in order to calculate ET0. Seasonal, annual, winter wheat and maize growing seasons data sets of ET0 were generated. The trends were detected using the Mann–Kendall test and Sen's slope, while an ArcGIS software was employed for mapping the results. The main findings of the study are: positive slopes were found in 71% of the data series considered and almost 30% of the total number of series were found significant at α = 0.05; the highest frequency of the increasing trends as well as their absolute maximum magnitude were detected during summer and maize growing season; in winter, significant increasing changes are specific mainly to the extra-Carpathians regions; in autumn decreasing ET0 is specific to more than 80% of the locations, but the significant decrease characterizes mainly the southern half of the country; during the growing seasons of maize and winter wheat, the increase of the ET0 is dominant for the entire country. The relative change decreases with the increase of the length of the period considered: the most intense changes were detected for climatic seasons, followed by crop growing seasons and annual values. Among the climatic seasons, the highest relative increase is specific to winter followed by summer, spring and autumn, while for the crop growing seasons the values detected are similar.
Polish Journal of Environmental Studies, 2014
The trends of the seasonal (April-September) and monthly reference evapotranspiration time series were analyzed using linear regression. In addition, the trends of air temperature and sunshine hours also were investigated to show possible causes of the increase in reference evapotranspiration. The spatial variability of reference evapotranspiration was lower than the temporal variability and is similar to the spatial distribution of precipitation in the area of Poland. The highest reference evapotranspiration was recorded in the region with the lowest rainfall. The statistically significant linear increasing trends of reference evapotranspiration were determined at each analyzed station in 1971-2010. The increase in the growing season sum of reference evapotranspiration, averaged over 18 stations, was 30 mm per 10 years. The significant increase in reference evapotranspiration can be explained by the statistically significant increasing trends of air temperature and sunshine hours.
Statistically significant FAO-56 Penman-Monteith (FAO-56 PM) and adjusted Hargreaves (AHARG) reference evapotranspiration (ET 0) trends at monthly, seasonal and annual time scales were analysed by using linear regression, Mann-Kendall and Spearman's Rho tests at the 1 and 5% significance levels. Meteorological data were used from 12 meteorological stations in Serbia, which has a humid climate, for the period 1980–2010. Web-based software for conducting the trend analyses was developed. All of the trends significant at the 1 and 5% significance levels were increasing. The FAO-56 PM ET 0 trends were almost similar to the AHARG trends. On the seasonal time scale, for the majority of stations significant increasing trends occurred in summer, while no significant positive or negative trends were detected by the trend tests in autumn for the AHARG series. Moreover, 70% of the stations were characterized by significant increasing trends for both annual ET 0 series.
Meteorology Hydrology and Water Management, 2016
evapotranspiration values (ET) are crucial for agriculture where estimates of water reserves available for crops are the basis for scheduling the time and intensity of irrigation, yield prognoses, etc. detailed evapotranspiration data are, therefore, of essential value. However, stations performing direct measurements of evapotranspiration are very scarcely distributed in poland, and for this reason the interpolation of data is necessarily biased. Hence, evapotranspiration values are calculated using indirect methods (usually empirical formulas). data from geostationary meteorological satellites are used operationally for the determination of evapotranspiration with good spatial and temporal resolution (e.g. Land-saF product). The study of the relation between evapotranspiration values determined with the use of satellite data and those calculated using the penman-Monteith formula was performed for the study area in poland. daily values and cumulated (i.e. decadal, monthly and yearly) values were analysed to determine the quality and possible added value of the satellite product. The relation between the reference ET and actual ET in two consecutive years was discussed, both for the whole test area and for individual stations, taking into account land use and possible water deficit in the root zone, represented by H-saF (eUMeTsaT satellite application facility supporting operational Hydrology and water Management) soil wetness index product. The differences are presented and discussed.
Theoretical and Applied Climatology
Strong global warming has been observed in the last three decades. Central Europe, including Poland, is not an exception. Moreover, climate projections for Poland foresee further warming as well as changes in the quantity as well as spatial and seasonal distribution of precipitation. This will result in changes in all elements of the water balance, including the areal evapotranspiration. For estimating the areal evapotranspiration, the heat balance method (HBM) is used in this paper for the growing season (March-October), whereas for the remaining months (November-February), evaporation is calculated according to the Ivanov equation. Values of areal evapotranspiration from selected land units are examined and compared for the average conditions in two time horizons, i.e. 1961-1990 (control period) and 2061-2090 (projection horizon) over the Wielkopolska Region in Poland, based on multi-model ensemble climate projections. Projections for the future, based on the MPI-M-REMO model, indicate that the regional average increases of the annual sum of areal evapotranspiration (connected mainly with an increase of air temperature) is equal to 45 mm, with the biggest changes during winter. In the growing season, the highest increases are expected to appear in July and June. As regards the spatial distribution, the highest increases are projected for the areas with presently highest evapotranspiration, e.g. the southwestern parts of the region.
2013
Evapotranspiration is one of the most important components of the hydrological cycle which is directly influenced by atmospheric conditions. This study investigated annual and seasonal trends in reference evapotranspiration (ET0) and its key influencing climatic variables during 1966-2005 at 10 stations in southern Iran (with centrality of Fars province). First, multivariate regression analysis was performed to identify the major meteorological variables affecting ET0. Second, annual and seasonal trends in climatic variables as well as ET0 were assessed using the Mann-Kendall test, Spearman's rho, the Pearson correlation and linear regression to evaluate their contribution to the temporal trend in ET0. Results suggested that the more effective variables for ET0 were wind speed (U2), relative humidity (RH) and sunshine hours (n). Also, the majority of trends in seasonal and annual ET0 were non-significant and after that decreasing and increasing trends had higher frequencies. In addition, distributions of relative frequencies of trend types at all considered time-scales were similar for both parametric and non-parametric techniques. Hence, the disagreement between parametric and non-parametric trend results did not depend on the degree of normality in the annual and seasonal ET0 distributions in the study area.
Changes in precipitation (P), evapotranspiration (ET) and, implicitly, in the climatic water balance (CWB), are imminent effects of climate warming. However, changes in the CWB, as a response to changes in P and ET, have not yet been analysed thoroughly enough in many parts of the world, including Romania. The present study explores the spatio-temporal changes of the CWB (difference between P and reference evapotranspiration, ET o) in Romania, based on a wide range of climatic data (P, as well as temperature, relative air humidity, sunshine duration and wind speed, necessary for computing ET o with the FAO-56 Penman-Monteith method) recorded at 70 weather stations across the country in the 1961–2013 period. As a secondary objective, the study attempts to identify the possible connections between the index's trends and large-scale atmospheric circulation, assessed based on the dynamics of certain European-scale relevant teleconnection indices. Thus, the Mann–Kendall test and Sen's slope methods were used to analyse CWB trends (but also P and ET o trends, in order to explain CWB pattern changes) annually, seasonally and in the maize and wheat growing seasons. Also, the Spearman correlation procedure and a composite analysis between interannual series of teleconnection indices and CWB were used to assess the influence of atmospheric circulation on the index's variability for all analysed time scales. The results generally showed CWB decreases (for the most part of up to −2 mm/yr, yet with a relatively low statistical significance) and highlighted an overall amplification of drier conditions on all time scales, except for autumn (CWB increases, generally of up to 1 mm/yr, but with low statistical significance). Moreover, net changes of even under −200 mm/53 yrs annually and −175 mm/53 yrs in summer and for the maize and wheat growing seasons were found in the CWB. Spatially, it was found that the country's southwestern and southeastern regions are the main epicentres of drier trends, while the northwest appears to have become wetter. Overall, the negative CWB trends are due to partial P decreases (statistically insignificant) and general ET o increases (highly statistically significant, even 100% in summer). It seems that the amplification of the climatic water deficit across the country is especially linked to the positive phases of the Arctic Oscillation and North Atlantic Oscillation, but also, in part, to those of several other teleconnection indices that affect Europe. Our results signal the necessity to adapt anthropic and ecological systems to future dryness trends countrywide, which will most likely intensify against the background of climate change expected to occur by the end of the century.
Determination of seasonal variation in reference evapotranspiration using regression analysis
Akademik Ziraat Dergisi
In the study, variability in reference evapotranspiration (ET0) from Southeastern Anatolian Project (GAP) area was investigated with linear regression method. For the purpose, seasonal ET0 time series were formed from monthly reference evapotranspiration (ET0). The ET0 data sets of three sites showed a statistically significance decreasing trend while there was upward trend in some seasons of two sites. But, variation in all seasonal ET0 time series of Kilis site was not detected.
Effects of variations in climatic parameters on evapotranspiration in the arid and semi-arid regions
Global and Planetary Change, 2011
The main objective of this study is to investigate the effects of climatic parameters variability on evapotranspiration in five climatologically different regions of Iran. The regions include Tehran, Esfahan, Shiraz, Tabriz and Mashhad. Fifty four-year monthly records of temperature, relative humidity, sunshine duration, wind speed, and precipitation depth from 1951 to 2005 comprise the database. Trend and persistence analyses of the data are performed using the Mann-Kendall test, the Cumulative Deviation test, Linear Regression, and the Autocorrelation Coefficient. A sensitivity analysis of meteorological variables in these five regions is carried out using Penman-Monteith formula. In all of the studied regions, sensitivity analysis reveals that, temperature and relative humidity are the most sensitive parameters in Penman-Monteith formula respectively. The results of this study indicate that the effective climatic variables on evapotranspiration are changing, though in each region the variables have significant long-term trends and persistence.
Reference evapotranspiration variability and trends in Spain, 1961–2011
Global and Planetary Change, 2014
In this study we analyzed the spatial distribution, temporal variability and trends in reference evapotranspiration (ET 0 ) in Spain from 1961 to 2011. Twelve methods were analyzed to quantify ET 0 from quality controlled and homogeneous series of various meteorological variables measured at 46 meteorological stations. Some of the models used are temperature based (e.g., Thornthwaite, Hargreaves, Linacre), whereas others are more complex and require more meteorological variables for calculation (e.g., Priestley-Taylor, Papadakis, FAO-Blaney-Criddle). The Penman-Monteith equation was used as a reference to quantify ET 0 , and for comparison among the other methods applied in the study. No major differences in the spatial distribution of the average ET 0 were evident among the various methods. At annual and seasonal scales some of the ET 0 methods requiring only temperature data for calculation provided better results than more complex methods requiring more variables. Among them the Hargreaves (HG) equation provided the best results, at both the annual and seasonal scales. The analysis of the temporal variability and trends in the magnitude of ET 0 indicated that all methods show a marked increase in ET 0 at the seasonal and annual time scales. Nevertheless, results obtained suggested substantial uncertainties among the methods assessed to determine ET 0 changes, due to differences in temporal variability of the resulting time series, but mainly for the differences in the magnitude of change of ET 0 and its spatial distribution. This suggests that ET 0 trends obtained by means of methods that only require temperature data for ET 0 calculations should be evaluated carefully under the current global warming scenario.