The oasis effect in an extremely hot and arid climate: The case of southern Israel

Potchter, Oded; Goldman, Daphne; Kadish, D.; Iluz, David

doi:10.1016/j.jaridenv.2008.03.004

Cited by 87 publications

(69 citation statements)

References 15 publications

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“…Pochter et al (2008) and Chow et al (2011) have also pointed out that excessive nocturnal cooling depended on evapotranspiration. Further, Pochter et al (2008) found that irrigated vegetation cooled faster than unirrigated, i.e. in spite of higher soil wetness and higher thermal admittance and thus better conditions for compensating upward soil heat flux during the evening the irrigated area cooled faster.…”

Section: Phase 1 -Site-dependent Coolingmentioning

confidence: 99%

“…At night, the cooling effect is supposed to be a result of increased outgoing radiation due to higher sky view factor (SVF) compared to built-up areas, although this is counteracted by the higher soil-water content (higher thermal admittance) in vegetated areas compared to built-up areas (Spronken-Smith and Oke, 1998). On the contrary, Pochter et al (2008) found that irrigated garden trees and grass were colder at night than unirrigated. They also observed that the irrigated area was cooler than the surrounding open desert while the unirrigated was warmer.…”

Section: Introductionmentioning

confidence: 99%

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Evening evapotranspirative cooling in relation to vegetation and urban geometry in the city of Ouagadougou, Burkina Faso

Holmer

Thorsson

Lindén

2012

Intl Journal of Climatology

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Intra-urban cooling in the city of Ouagadougou, capital of Burkina Faso in the Sahel zone of West Africa, was studied during the dry seasons in 2003, 2004 and 2007. The aim was to see how vegetation, built structure and position within the built-up area influenced the nocturnal cooling. Cooling was divided into two phases. In Phase 1 (16 : 00-20 : 00 hours LST = CET), cooling was very different between the sites while in Phase 2 (20 : 00-06 : 00 hours LST), cooling rates differed insignificantly and the whole area cooled almost at the same rate. Thus the temperature differences between the sites developed during these few hours in Phase 1 were preserved during the rest of the night. In Phase 1, Evening Evapotranspirative Cooling was intensive at vegetated sites that cooled almost twice as fast as sparsely vegetated. This was indicated by a humidity rate (increase of specific humidity per hour) that was high at a vegetated site, but considerably lower at a sparsely vegetated. In Phase 2 the humidity rate was slightly negative with little difference between the sites. After a division in vegetated and sparsely vegetated sites built structure (sky view factor) were shown to influence cooling, but no influence of the position within the built-up area was traced. Thus, the site-specific properties dominated cooling, giving large intra-urban temperature differences. The study also showed the importance of considering a large enough source area to account for micro-scale advection.

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Section: Phase 1 -Site-dependent Coolingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evening evapotranspirative cooling in relation to vegetation and urban geometry in the city of Ouagadougou, Burkina Faso

Holmer

Thorsson

Lindén

2012

Intl Journal of Climatology

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“…Therefore, the overall yield is reduced because of the non-satisfactory yield of the upwind series. The climatic definition of the 'oasis effect' or 'cold island effect' refers to the phenomenon of a cooling effect caused by vegetation (Givoni, 1991;Potchter et al, 2008). According to Oke (1987) this cooling effect is due to the fact that the energy required for evaporation (Q E ) is more than that supplied by radiation (Q*).…”

Section: Introductionmentioning

confidence: 99%

“…Kai et al (1997) also explained the cooling effect by the difference of the energy balance between oasis and the surrounding area. The oasis effect phenomenon is observed in different climates and urban or rural conditions (Oke, 1987;Potchter et al, 2008; SpronkenSmith et al, 2000). Therefore, the use of the term 'oasis effect' has a wider definition than the classical term (Potchter et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

“…The oasis effect phenomenon is observed in different climates and urban or rural conditions (Oke, 1987;Potchter et al, 2008; SpronkenSmith et al, 2000). Therefore, the use of the term 'oasis effect' has a wider definition than the classical term (Potchter et al, 2008).According to Oke (1987) any cool moist surface dominated by larger scale warmer, drier surroundings has the characteristics of an oasis effect situation: a lake in an area with a dry summer climate; an urban park; an isolated tree in a street or on open bare ground etc. A common characteristic of all these cases is that evaporation rates are higher than those from extensive areas of the same composition.…”

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confidence: 99%

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Evapotranspiration and simulation of soil water movement in small area vegetation

Paraskevas¹,

Georgiou²,

Ilias³

et al. 2013

International Agrophysics

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A b s t r a c t. In Greece, crops are frequently cultivated in small isolated areas in close proximity to roads and bare soils and therefore evapotranspiration is affected by local advection. Under these circumstances, oasis effect conditions are present and evapotranspiration is higher than what is expected. In this paper, the evapotranspiration and soil water dynamics of a cotton crop cultivated in small areas under the oasis effect is studied. To this end, two isolated free-drainage lysimeters cultivated with cotton in the year 2007 were used. Soil moisture of the soil profile of both the lysimeters was monitored with two capacitance water content probes. The soil water balance method was used to estimate crop evapotranspiration and corresponding crop coefficients in one of the two lysimeters. These coefficients were 75% larger than the FAO-56 crop coefficients at the mid-season stage. The FAO-56 and the derived crop coefficients were used for the simulation of the water dynamics in the second lysimeter by the SWBACROS model. The derived crop coefficients for these conditions produced much better results than the FAO-56 crop coefficients. The results were improved when crop coefficient value equal to 2.5 was used for the mid-season stage.K e y w o r d s: modelling soil water flow, evapotranspiration, oasis-effect, crop coefficients INTRODUCTIONCrop evapotranspiration (ET c ) can be calculated under standard or non-standard conditions and various management practices. Standard conditions refer to crops grown in large fields under non-limiting agronomic and soil conditions. Non-standard conditions and various management practices refer to management and environmental conditions that deviate from standard conditions such as salt toxicity, pests, diseases, surface mulches, small areas vegetation etc. (Allen et al., 1998).Frequently, fields in Greece are very small (<1 000 m 2 )representing typical non-standard conditions. Under these circumstances, the crops are growing under conditions of the oasis effect resulting in very high evapotranspiration values. Increased evapotranspiration is also observed at the upwind series of crops resulting in lower yields since these series obtain the same amount of water as the interior series. Therefore, the overall yield is reduced because of the non-satisfactory yield of the upwind series. The climatic definition of the 'oasis effect' or 'cold island effect' refers to the phenomenon of a cooling effect caused by vegetation (Givoni, 1991;Potchter et al., 2008). According to Oke (1987) this cooling effect is due to the fact that the energy required for evaporation (Q E ) is more than that supplied by radiation (Q*). It has been observed that the ratio Q E /Q* can be as large as 2.5 over an irrigated field of cotton (Lemon et al., 1957). Kai et al. (1997) also explained the cooling effect by the difference of the energy balance between oasis and the surrounding area. The oasis effect phenomenon is observed in different climates and urban or rural conditions (Oke, 1987;Potchter e...

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Evapotranspiration of urban landscapes in Los Angeles, California at the municipal scale

Litvak

Manago

Hogue

et al. 2017

Water Resources Research

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Evapotranspiration (ET), an essential process in biosphere‐atmosphere interactions, is highly uncertain in cities that maintain cultivated and irrigated landscapes. We estimated ET of irrigated landscapes in Los Angeles by combining empirical models of turfgrass ET and tree transpiration derived from in situ measurements with previously developed remotely sensed estimates of vegetation cover and ground‐based vegetation surveys. We modeled irrigated landscapes as a two‐component system comprised of trees and turfgrass to assess annual and spatial patterns of ET. Annual ET from vegetated landscapes (ETveg) was 1110 ± 53 mm/yr and ET from the whole city (vegetated and nonvegetated areas, ETland) was three times smaller, reflecting the fractional vegetation cover. With the exception of May and June, monthly ETland was significantly higher than predicted by the North American Land Data Assimilation System. ETveg was close to potential ET, indicating abundant irrigation inputs. Monthly averaged ETveg varied from 1.5 ± 0.1 mm/d (December) to 4.3 ± 0.2 mm/d (June). Turfgrass was responsible for ∼70% of ETveg. For trees, angiosperm species (71% of all trees) contributed over 90% to total tree transpiration, while coniferous and palm species made very small contributions. ETland was linearly correlated with median household income across the city, confirming the importance of social factors in determining spatial distribution of urban vegetation. These estimates have important implications for constraining the municipal water budget of Los Angeles and improving regional‐scale hydrologic models, as well as for developing water‐saving practices. The methodology used in this study is also transferable to other semiarid regions for quantification of urban landscape ET.

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The oasis effect in an extremely hot and arid climate: The case of southern Israel

Cited by 87 publications

References 15 publications

Evening evapotranspirative cooling in relation to vegetation and urban geometry in the city of Ouagadougou, Burkina Faso

Evening evapotranspirative cooling in relation to vegetation and urban geometry in the city of Ouagadougou, Burkina Faso

Evapotranspiration and simulation of soil water movement in small area vegetation

Evapotranspiration of urban landscapes in Los Angeles, California at the municipal scale

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