scholarly journals Reservoir evaporation in a Mediterranean climate: Comparing direct methods in Alqueva Reservoir, Portugal

2020 ◽  
Author(s):  
Carlos Miranda Rodrigues ◽  
Madalena Moreira ◽  
Rita Cabral Guimarães
Keyword(s):  
Eddy Covariance ◽  
Mediterranean Climate ◽  
Direct Methods ◽  
Irrigated Agriculture ◽  
Pan Evaporation ◽  
Water Losses ◽  
Southern Portugal ◽  
Alqueva Reservoir ◽  
June July ◽  
Water Scarce

Abstract. Alqueva Reservoir is one of the largest artificial lakes in Europe and is a strategic water storage for public supply, irrigation, and energy generation. The reservoir is integrated within the Multipurpose Alqueva Project (MAP), which includes almost 70 reservoirs in a water-scarce region of Portugal. The MAP contributes to sustainability in southern Portugal and has an important impact for the entire country. Evaporation is the key component of water losses from the reservoirs included in the MAP. To date, evaporation from Alqueva Reservoir has been estimated by indirect methods or pan evaporation measurements. Eddy covariance measurements were performed at Alqueva Reservoir from July to September in 2014 as this time of the year provides the most representative evaporation volume losses in a Mediterranean climate. This period is also the most important for irrigated agriculture, and is therefore the most problematic part of the year in terms of managing the reservoir. The direct pan evaporation approach was first tested and compared to eddy covariance evaporation measurements. A relationship was then established based on a pan coefficient (Kpan) multivariable function by using the identified governing factors: air temperature, relative humidity, wind speed, and incoming solar radiation. The mean Kpan for the period from June to September 2014 was 0.59, and the modelled mean daily reservoir evaporation in June, July, August, and September was 3.9 mm d−1, 4.2 mm d−1, 4.5 mm d−1, and 2.7 mm d−1, respectively. The total estimated reservoir evaporation for this 4-month period was 455.8 mm. The correlation between the estimated evaporation and the measured EC evaporation had an R2 value of 0.7. The developed Kpan function was validated for the same period in 2017, and yielded an R2 value of 0.68. This study provides an applicable method for calculating evaporation based on pan measurements in Alqueva Reservoir, which can support regional water management. Moreover, the methodology presented here could be applied to other reservoirs, and the developed equation for Alqueva Reservoir could act as a first evaluation for the management of other Mediterranean reservoirs.

scholarly journals Reservoir evaporation in a Mediterranean climate: comparing direct methods in Alqueva Reservoir, Portugal

2020 ◽  
Vol 24 (12) ◽  
pp. 5973-5984
Author(s):  
Carlos Miranda Rodrigues ◽  
Madalena Moreira ◽  
Rita Cabral Guimarães ◽  
Miguel Potes
Keyword(s):  
Eddy Covariance ◽  
Mediterranean Climate ◽  
Direct Methods ◽  
Irrigated Agriculture ◽  
Pan Evaporation ◽  
June July August ◽  
Alqueva Reservoir ◽  
Pan Coefficient ◽  
June July ◽  
Water Scarce

Abstract. Alqueva Reservoir is one of the largest artificial lakes in Europe and is a strategic water storage for public supply, irrigation, and energy generation. The reservoir is integrated within the Multipurpose Alqueva Project (MAP), which includes almost 70 reservoirs in a water-scarce region of Portugal. The MAP contributes to sustainability in southern Portugal and has an important impact on the entire country. Evaporation is the key component of water loss from the reservoirs included in the MAP. Evaporation from Alqueva Reservoir has been estimated by indirect methods or pan evaporation measurements; however, specific experimental parameters such as the pan coefficient were never evaluated. Eddy covariance measurements were performed at Alqueva Reservoir from June to September in 2014 as this time of the year provides the most representative evaporation volume losses in a Mediterranean climate. This period is also the most important period for irrigated agriculture and is, therefore, the most problematic period of the year in terms of managing the reservoir. The direct pan evaporation approach was first tested, and the results were compared to the eddy covariance evaporation measurements. The total eddy covariance (EC) evaporation measured from June to September 2014 was 450.1 mm. The mean daily EC evaporation in June, July, August, and September was 3.7, 4.0, 4.5, and 2.5 mm d−1, respectively. A pan coefficient, Kpan, multivariable function was established on a daily scale using the identified governing factors: air temperature, relative humidity, wind speed, and incoming solar radiation. The correlation between the modelled evaporation and the measured EC evaporation had an R2 value of 0.7. The estimated Kpan values were 0.59, 0.57, 0.57, and 0.64 in June, July, August, and September, respectively. Consequently, the daily mean reservoir evaporation (ERes) was 3.9, 4.2, 4.5, and 2.7 mm d−1 for this 4-month period and the total modelled ERes was 455.8 mm. The developed Kpan function was validated for the same period in 2017 and yielded an R2 value of 0.68. This study proposes an applicable method for calculating evaporation based on pan measurements in Alqueva Reservoir, and it can be used to support regional water management. Moreover, the methodology presented here could be applied to other reservoirs, and the developed equation could act as a first evaluation for the management of other Mediterranean reservoirs.

scholarly journals The Impacts of Climate Change on Irrigated Agriculture in Southern Portugal

2016 ◽  
Vol 66 (1) ◽  
pp. 3-18 ◽  
Author(s):  
João Rolim ◽  
José Luís Teixeira ◽  
João Catalão ◽  
Shakib Shahidian
Keyword(s):  
Climate Change ◽  
Irrigated Agriculture ◽  
Southern Portugal ◽  
Impacts Of Climate Change

scholarly journals Opportunities for saving and reallocating agricultural water to alleviate water scarcity

Water Policy ◽  
2017 ◽  
Vol 19 (5) ◽  
pp. 886-907 ◽  
Author(s):  
Brian D. Richter ◽  
James D. Brown ◽  
Rachel DiBenedetto ◽  
Adrianna Gorsky ◽  
Emily Keenan ◽  
...  
Keyword(s):  
Water Use ◽  
Water Scarcity ◽  
Water Saving ◽  
Internet Survey ◽  
Irrigated Agriculture ◽  
Irrigation Systems ◽  
Water Savings ◽  
Consumptive Water Use ◽  
Water Scarce ◽  
Consumptive Water

As water scarcity worsens globally, there is growing interest in finding ways to reduce water consumption, and for reallocating water savings to other uses including environmental restoration. Because irrigated agriculture is responsible for more than 90% of all consumptive water use in water-scarce regions, much attention is being focused on opportunities to save water on irrigated farms. At the same time, many recent journal articles have expressed concern that claims of water-saving potential in irrigation systems lack technical credibility, or are at least exaggerated, due to failures to properly account for key elements of water budgets such as return flows. Critics have also asserted that opportunities for reallocating irrigation savings to other uses are limited because any freed-up water is taken up by other farmers. A comprehensive literature and internet survey was undertaken to identify well-documented studies of water-saving strategies in irrigated agriculture, as well as a review of case studies in which water savings have been successfully transferred to other uses. Our findings suggest that there is in fact considerable potential to reduce consumptive water use in irrigation systems when proper consideration is given to water budget accounting, and those savings can be beneficially reallocated to other purposes.

scholarly journals Biophysical Effects of Evapotranspiration on Steppe Areas: A Case Study in Naâma Region (Algeria)

2021 ◽  
Author(s):  
Abdelkrim Benaradj ◽  
Hafidha Boucherit ◽  
Abdelkader Bouderbala ◽  
Okkacha Hasnaoui
Keyword(s):  
Mediterranean Climate ◽  
Potential Evapotranspiration ◽  
Thick Layer ◽  
Soil Surface ◽  
Cold Season ◽  
Perennial Grasses ◽  
Herbaceous Plants ◽  
Humid Climate ◽  
Water Losses ◽  
Steppe Vegetation

The Algerian steppe is of great interest in terms of vegetation, mainly in the Naâma region. This steppe vegetation is generally composed of annual and perennial grasses and other herbaceous plants, as well as, bushes and small trees. It is characterized by an arid Mediterranean climate where the average annual precipitation (100 to 250 mm) is insufficient to ensure the maintenance of the vegetation, in which the potential evaporation always exceeds the precipitations. This aridity has strong hydrological effect and edaphic implications from which it is inseparable. Water losses are great than gains due to the evaporation and transpiration from plants (evapotranspiration). The wind moves soils for one location to another, and causes a strong evapotranspiration of the plants, which is explained by a strong chronic water deficit of climatic origin of these compared to the potential evapotranspiration, opposed to a humid climate. Evapotranspiration is certainly closely linked to climate factors (solar radiation, temperature, wind, etc.), but it also depends on the natural environment of the studied region. Potential evapotranspiration (PET) data estimated from Thornthwaite’s method for the three stations (Mécheria, Naâma and Ainsefra). The average annual value of potential evapotranspiration is of the order of 807 mm in Mécheria, of 795 mm in Naâma de and in Ainsefra of 847 mm. It is more than 3 times greater than the value of the rainfall received. This propels it globally in the aridity of the region and from which the water balance of plants is in deficit. The potential evapotranspiration of vegetation in arid areas is very important due to high temperature and sunshine. During the cold season, precipitation covers the needs of the potential evapotranspiration and allows the formation of the useful reserve from which the emergence of vegetation. From the month of April there is an exhaustion of the useful reserve which results of progressive deficit of vegetation. Faced with this phenomenon of evatranspiration, the steppe vegetation of the region then invests in “survival” by reducing the phenomena of evapotranspiration, photosynthetic leaf surfaces, in times of drought. These ecophysiological relationships can largely explain the adaptation of steppe species (low woody and herbaceous plants) to the arid Mediterranean climate. Mechanisms and diverse modalities were allowing them to effectively resist for this phenomenon. The adaptation of the steppe vegetation by the presence of a root system with vertical or horizontal growth or both and seems to depend on the environmental conditions, and by the reduction of the surface of transpiration, and by the fall or the rolling up of the leaves, and by a seasonal reduction of transpiration surface of the plant to reduce water losses during the dry season (more than 6 months) of the year.. Some xerophytes produce “rain roots” below the soil surface, following light precipitation or during dew formation. Other persistent sclerophyllous species by which decreases transpiration by the hardness of the leaves often coated with a thick layer of wax or cutin.

scholarly journals Evapotranspiration over agroforestry sites in Germany

2020 ◽  
Vol 17 (20) ◽  
pp. 5183-5208
Author(s):  
Christian Markwitz ◽  
Alexander Knohl ◽  
Lukas Siebicke
Keyword(s):  
Land Use ◽  
Eddy Covariance ◽  
Small Scale ◽  
Agricultural Practice ◽  
Land Uses ◽  
Water Losses ◽  
Order Of Magnitude ◽  
Set Up ◽  
Mean Square Errors ◽  
Measurement Campaigns

Abstract. In the past few years, the interest in growing crops and trees for bioenergy production has increased. One agricultural practice is the mixed cultivation of fast-growing trees and annual crops or perennial grasslands on the same piece of land, which is referred to as one type of agroforestry (AF). The inclusion of tree strips into the agricultural landscape has been shown – on the one hand – to lead to reduced wind speeds and higher carbon sequestration above ground and in the soil. On the other hand, concerns have been raised about increased water losses to the atmosphere via evapotranspiration (ET). Therefore, we hypothesise that short rotation coppice agroforestry systems have higher water losses to the atmosphere via ET compared to monoculture (MC) agriculture without trees. In order to test the hypothesis, the main objective was to measure the actual evapotranspiration of five AF systems in Germany and compare those to five monoculture systems in the close vicinity of the AF systems. We measured actual ET at five AF sites in direct comparison to five monoculture sites in northern Germany in 2016 and 2017. We used an eddy covariance energy balance (ECEB) set-up and a low-cost eddy covariance (EC-LC) set-up to measure actual ET over each AF and each MC system. We conducted direct eddy covariance (EC) measurement campaigns with approximately 4 weeks' duration for method validation. Results from the short-term measurement campaigns showed a high agreement between ETEC-LC and ETEC, indicated by slopes of a linear regression analysis between 0.86 and 1.3 (R2 between 0.7 and 0.94) across sites. Root mean square errors of LEEC-LC vs. LEEC (where LE is the latent heat flux) were half as small as LEECEB vs. LEEC, indicating a superior agreement of the EC-LC set-up with the EC set-up compared to the ECEB set-up. With respect to the annual sums of ET over AF and MC, we observed small differences between the two land uses. We interpret this as being an effect of compensating the small-scale differences in ET next to and in between the tree strips for ET measurements on the system scale. Most likely, the differences in ET rates next to and in between the tree strips are of the same order of magnitude, but of the opposite sign, and compensate each other throughout the year. Differences between annual sums of ET from the two methods were of the same order of magnitude as differences between the two land uses. Compared to the effect of land use and different methods on ET, we found larger mean evapotranspiration indices (∑ET/∑P) across sites for a drier than normal year (2016) compared to a wet year (2017). This indicates that we were able to detect differences in ET due to different ambient conditions with the applied methods, rather than the potentially small effect of AF on ET. We conclude that agroforestry has not resulted in an increased water loss to the atmosphere, indicating that agroforestry in Germany can be a land-use alternative to monoculture agriculture without trees.

scholarly journals Spatio-Temporal Trends of Monthly and Annual Precipitation in Aguascalientes, Mexico

Atmosphere ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 437
Author(s):  
Osías Ruiz-Alvarez ◽  
Vijay P. Singh ◽  
Juan Enciso-Medina ◽  
Ronald Ernesto Ontiveros-Capurata ◽  
Arturo Corrales-Suastegui
Keyword(s):  
Time Series ◽  
Annual Precipitation ◽  
Irrigated Agriculture ◽  
Monthly Precipitation ◽  
Precipitation Trend ◽  
Precipitation Time Series ◽  
June July August ◽  
Precipitation Decrease ◽  
Weather Stations ◽  
June July

The objective of this research was to analyze the temporal patterns of monthly and annual precipitation at 36 weather stations of Aguascalientes, Mexico. The precipitation trend was determined by the Mann–Kendall method and the rate of change with the Theil–Sen estimator. In total, 468 time series were analyzed, 432 out of them were monthly, and 36 were annual. Out of the total monthly precipitation time series, 42 series showed a statistically significant trend (p ≤ 0.05), from which 8/34 showed a statistically significant negative/positive trend. The statistically significant negative trends of monthly precipitation occurred in January, April, October, and December. These trends denoted more significant irrigation water use, higher water extractions from the aquifers in autumn–winter, more significant drought occurrence, low forest productivity, higher wildfire risk, and greater frost risk. The statistically significant positive trends occurred in May, June, July, August, and September; to a certain extent, these would contribute to the hydrology, agriculture, and ecosystem but also could provoke problems due to water excess. In some months, the annual precipitation variability and El Niño-Southern Oscillation (ENSO) were statistically correlated, so it could be established that in Aguascalientes, this phenomenon is one of the causes of the yearly precipitation variation. Out of the total annual precipitation time series, only nine series were statistically significant positive; eight out of them originated by the augments of monthly precipitation. Thirteen weather stations showed statistically significant trends in the total precipitation of the growing season (May, June, July, August, and September); these stations are located in regions of irrigated agriculture. The precipitation decrease in dry months can be mitigated using shorter cycle varieties with lower water consumption, irrigation methods with high efficiency, and repairing irrigation infrastructure. The precipitation increase in humid months can be used to store water and use it during the dry season, and its adverse effects can be palliated with the use of varieties resistant to root diseases and lodging. The results of this work will be beneficial in the management of agriculture, hydrology, and water resources of Aguascalientes and in neighboring arid regions affected by climate change.

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