scholarly journals Estimation of evapotranspiration by the Food and Agricultural Organization of the United Nations (FAO) Penman–Monteith temperature (PMT) and Hargreaves–Samani (HS) models under temporal and spatial criteria – a case study in Duero basin (Spain)

2020 ◽  
Vol 20 (3) ◽  
pp. 859-875 ◽  
Author(s):  
Rubén Moratiel ◽  
Raquel Bravo ◽  
Antonio Saa ◽  
Ana M. Tarquis ◽  
Javier Almorox
Keyword(s):  
Wind Speed ◽  
Relative Humidity ◽  
United Nations ◽  
Irrigated Agriculture ◽  
Arid Zones ◽  
Empirical Coefficient ◽  
Minimum Relative Humidity ◽  
Duero Basin ◽  
The United Nations ◽  
Agricultural Organization

Abstract. The evapotranspiration-based scheduling method is the most common method for irrigation programming in agriculture. There is no doubt that the estimation of the reference evapotranspiration (ETo) is a key factor in irrigated agriculture. However, the high cost and maintenance of agrometeorological stations and high number of sensors required to estimate it make it non-plausible, especially in rural areas. For this reason, the estimation of ETo using air temperature, in places where wind speed, solar radiation and air humidity data are not readily available, is particularly attractive. A daily data record of 49 stations distributed over Duero basin (Spain), for the period 2000–2018, was used for estimation of ETo based on seven models against Penman–Monteith (PM) FAO 56 (FAO – Food and Agricultural Organization of the United Nations) from a temporal (annual or seasonal) and spatial perspective. Two Hargreaves–Samani (HS) models, with and without calibration, and five Penman–Monteith temperature (PMT) models were used in this study. The results show that the models' performance changes considerably, depending on whether the scale is annual or seasonal. The performance of the seven models was acceptable from an annual perspective (R2>0.91, NSE > 0.88, MAE < 0.52 and RMSE < 0.69 mm d−1; NSE – Nash–Sutcliffe model efficiency; MAE – mean absolute error; RMSE – root-mean-square error). For winter, no model showed good performance. In the rest of the seasons, the models with the best performance were the following three models: PMTCUH (Penman–Monteith temperature with calibration of Hargreaves empirical coefficient – kRS, average monthly value of wind speed, and average monthly value of maximum and minimum relative humidity), HSC (Hargreaves–Samani with calibration of kRS) and PMTOUH (Penman–Monteith temperature without calibration of kRS, average monthly value of wind speed and average monthly value of maximum and minimum relative humidity). The HSC model presents a calibration of the Hargreaves empirical coefficient (kRS). In the PMTCUH model, kRS was calibrated and average monthly values were used for wind speed and maximum and minimum relative humidity. Finally, the PMTOUH model is like the PMTCUH model except that kRS was not calibrated. These results are very useful for adopting appropriate measures for efficient water management, especially in the intensive agriculture in semi-arid zones, under the limitation of agrometeorological data.

The Impact of Desertification as Revealed by Mapping

1978 ◽  
Vol 5 (1) ◽  
pp. 45-56 ◽  
Author(s):  
John A. Mabbutt
Keyword(s):  
Land Use ◽  
United Nations ◽  
Aridity Index ◽  
Mean Annual Precipitation ◽  
Arid Zones ◽  
Continental Scale ◽  
The United Nations ◽  
The Impact ◽  
Very High ◽  
Semi Arid

Maps prepared for the United Nations Conference on Desertification are critically reviewed and parts of selected maps are illustrated.The World Map of Desertification, called for by the United Nations General Assembly, delineates areas at risk of desertification as determined by bioclimatic stress, the inherent vulnerability of the land, and pressure of land-use. Areas of very high desertification hazard are shown to be those arid and semiarid regions with very heavy pressure of land-use. The threat of desertification is shown to be highest beyond the margins of the full deserts, but the risk extends wherever drought marks the seasonal or periodic extension of aridity. The term ‘drylands’ is used to define areas in which this risk occurs.Alternative maps at global scale include the Climate Aridity Index map based on the Budyko Ratio, which is the ratio between annual net radiation and mean annual precipitation. This allows a more sensitive depiction of aridity gradients and reveals that larger areas are under drought-stress than were previously recognized.The map of Experimental World Scheme of Aridity and Drought Probability uses soil features as an integrative record of past and present environmental conditions, including ‘land aridity’, but is constrained by the concept of soil zonality, without sufficient consideration of topographic and inherited factors which determine soil properties.The map of the Status of Desertification in the Hot Arid Regions shows the existing degree of desertification as judged by the difference between former (in the pristine state) and existing productivity. This is revealed as increasing outwards from the desert cores into the semi-arid lands, but the map does not extend into the sub-humid zone. However, it usefully depicts desertification as an expression of human impact on the land. Only very restricted areas are shown as having undergone very serious or irreversible desertification.Global maps are too generalized to depict actual desertification in quantitative terms, but the continental scale of the unpublished Desertification Hazards Map of Africa North of the Equator allows this to be done, in addition to depiction of the degree of vulnerability to desertification. Areas shown as already degraded occur mainly in the arid zone, whereas those of very high vulnerability lie mainly in the semi-arid zones.The U.N. Conference on Desertification recommended the compilation of an atlas of desertification to depict the state of the world's drylands and to serve as a cartographic basis for planning combative programmes. Regional maps of this kind, as exemplified in the synoptic maps accompanying the Case Studies of Desertification presented to the Conference, range in scale from 1:1,000,000 to 1:100,000—depending on the type of desertification portrayed—with the smaller scales for pastoral lands and more detailed scales for irrigation projects.

World Environmental Trends Between 1972 and 1982

1982 ◽  
Vol 9 (1) ◽  
pp. 11-29 ◽  
Author(s):  
Martin W. Holdgate ◽  
Mohamed Kassas ◽  
Gilbert F. White
Keyword(s):  
Developing Countries ◽  
United Nations ◽  
Stratospheric Ozone ◽  
Developed Countries ◽  
United Nations Environment Programme ◽  
Limiting Factors ◽  
Irrigated Agriculture ◽  
Environmental Damage ◽  
The World ◽  
The United Nations

The United Nations General Assembly has instructed the Governing Council of the United Nations Environment Programme to keep the world environmental situation under review. In 1982, 10 years after the UN Conference on the Human Environment at Stockholm, the first comprehensive report on the state of the global environment is being published. The present paper, by the Editors of that Report, summarizes its main findings. It first reviews changes in the sectors of The Biosphere (while recognizing that the interlinkages between them have been stressed increasingly during the past decade), before turning to the human components of the total Man—environment system.In the atmosphere, rising carbon dioxide concentrations, acidification of rain and snow in or by industrial regions, and stratospheric ozone depletion, remain the chief concerns, although the last has not yet been demonstrated instrumentally. In the oceans, pollution (including oil) has not been shown to have more than a local impact on ecosystems, and overall fishery yields have continued to rise slowly and erratically despite some overexploitation. The world's freshwater resources are better known than in 1970, and pollution control and the prevention of problems in irrigated agriculture have advanced; but the targets of the Drinking Water and Sanitation Decade appear less attainable as time passes. Mineral production rose without a concomitant increase in environmental damage. Changes in terrestrial life—especially loss of tropical forests—were the subject of widely varying estimates. Food production rose, but fell short of needs in many areas, while desertification, waterlogging, salinization, pest-resistance, post-harvest crop-losses, and the side-effects of agricultural chemicals, remained serious problems.The dominance of the human element in the Manenvironment system was increasingly recognized during the decade. Human population growth slowed somewhat, except in Africa, although the world total passed 4,400 millions in 1980. The cities of the developing world expanded rapidly, outstripping public services and threatening new problems. In the Third World, infectious and parasitic diseases remained major killers, whereas hypertension, coronary heart disease, and cancers—some due to self-inflicted influence—dominated the statistics in developed nations: environmental factors remained important in both. The 1970s showed that industrial growth could occur without environmental damage or unacceptable cost. The energy crisis of 1974 had a serious impact on developing countries with strategies based on cheap oil, and firewood shortages led to severe environmental problems there also: in contrast, many developed countries were able to adjust their energy plans with only moderate difficulty.Transport and international tourism grew dramatically during the decade, consuming energy and land, and inspiring countermeasures to curb pollution, increase safety, and avoid social and environmental disturbances in areas that were frequented by many visitors. Environmental education schemes expanded—especially in developed countries, where the coverage of environmental issues in popular media grew dramatically between 1960 and 1970, falling back subsequently. The environmental impact of past wars and increasing military preparations caused concern, and the arms race continued to absorb resources that developing countries could ill afford.Reviewing the decade, four dominant trends can be recognized. First, scientific and popular interest in environmental protection have come together to form a new kind of conservation movement. Second, there has been a data explosion in the environmental field, but much of the information is of limited value in assessing trends or as a foundation for decisions and actions. Third, new understanding of the structure and functioning of environmental systems offers a prospect of more reliable planning. Fourth and finally, it has become apparent that the lack of social organization, education, training, and political will, are commonly the limiting factors in environmental improvement, rather than a shortage of scientific knowledge.

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