Sensible Heat Flux Values Research Articles

Sensible, latent heat and store energy fluxes in the suburban São Paulo Megacity: seasonal and interannual variations and empirical modeling

Half-hourly values of turbulent sensible (H) and latent (LE) heat fluxes, net radiation (𝑄∗) at the surface, and heat store in the canopy (𝛥𝑄𝑆) are used to characterize seasonal and interannual changes during three not-consecutive years (2009–12) in a suburban area (LCZ 6) of the megacity of São Paulo. Turbulent fluxes are estimated applying eddy covariance method to turbulence measurements performed with sampling rate of 10 Hz, between 25 and 26 m above the surface, and enforcing quality control procedures. The diurnal evolution of monthly average hourly values of 𝐻, 𝐿𝐸, 𝑄∗ and 𝛥𝑄𝑆 observed in 2012 indicate a seasonal variation with a daytime maximum with 𝐻 varying from a maximum of 180 ± 12 W m-2 in October to a minimum of 80.1 ± 9 W m2 in June, 𝐿𝐸 varying from a maximum of 152.0 ± 7.6 W m-2 in February to a minimum of 66.4 ± 7.6 W m-2 in September, -𝑄∗ varying from a maximum of 554 ± 14 W m-2 in February to a minimum of 369±13 W m-2 in July, and -𝛥𝑄𝑆 varying from a maximum of 249± 47 W m-2 in April to a minimum of 181 ± 58 W m-2 in July. Monthly average daily values of H, LE and 𝑄∗ corroborate seasonal pattern displayed by monthly average hourly values, with maximum of 5 ± 0.5 MJ m-2 day-1 for H and 5.3 ± 0.6 MJ m-2 day-1 for LE in November (summer), and minimum of 1.3 ± 0.2 MJ m-2 day-1 for H in June and 1.9 ± 0.2 MJ m-2 day-1 for LE in August. −𝑄∗ shows a maximum of 11.6 ± 1.1 MJ m2 day-1 in March and a minimum of 4.5±0.9 MJ m-2 day-1 in June. Similar patterns was observed during 2009 and 2010. An empirical model based on Modified Priestly-Taylor Method coupled to Objective Hysteresis Method was validated with observations carried out during May and June (2009–2010, 2012) and applied successfully to estimate monthly average hourly values of 𝐻, LE and 𝛥𝑄𝑆 during February–April and August–Novemb 2012.

Effects of Artificial Green Land on Land–Atmosphere Interactions in the Taklamakan Desert

Land–atmosphere interactions are influenced by the earth’s complex underlying subsurface, which in turn indirectly affects atmospheric motion and climate change. Human activities are increasingly exerting an influence on desert ecosystems, and artificial green land with clear functional orientation has been established in many desert areas. Consequently, the previously dominant, shifting, sand-covered, underlying surface in these desert regions is gradually transforming. This transformation has significant implications for the characteristics of land–atmosphere interactions, causing them to deviate from their original state. At present, existing studies still have not presented a systematic understanding of this change and have ignored the impact of human activities on land–atmosphere interactions in artificial green land. To address these research gaps, this study specifically targets artificial green land in the Tazhong region of Taklamakan Desert. We carried out observation experiments on land–atmosphere interactions in three different functional units from outside to inside: natural shifting sands, the shelter forest, and the living area. We also analyzed the differences and attribution of land–atmosphere interactions characteristics of different functional units. Compared with the natural shifting sands, the daily average maximum values of wind speed in the shelter forest decreased by 78%, and the daily average maximum air temperature and soil (0 cm) temperature decreased by 2.6 °C and 7 °C, respectively. Additionally, the soil moisture level was significantly increased throughout the green land due to the shelter forest. The surface albedo experienced a decrease, with an annual average of 0.21. Furthermore, the aerodynamic roughness and bulk transport coefficient increased by two orders of magnitude. The daily average maximum values of sensible heat flux and soil heat flux (G05) decreased by 18.7% and 75%, respectively, and the daily average maximum value of latent heat flux increased by 70.3%. This effectively improved the microclimate environment of the green land. The living area was greatly reduced by the shelter forest coverage and influenced by the buildings. Consequently, the environmental improvement was not as large as it was inside the shelter forest. However, it still provided a good shelter for production and living in the desert area. Throughout the year, a total of 4.60 × 105 t water was consumed through evapotranspiration in the artificial green land. The findings of this study have the potential to enhance our comprehension of land–atmosphere interactions in desert regions, thereby offering valuable insights for the establishment and effective management of artificial desert green lands.

Construction of a spatially gridded heat flux map based on airborne flux Measurements using remote sensing and machine learning methods

Acquiring the relative truth values of land surface sensible (H) and latent (LE) heat fluxes at the regional scale is important for monitoring and simulating evapotranspiration at a global scale using satellite data or process-based models. However, it is difficult to directly obtain these values with fine spatial representation at regional scales using conventional ground-based measurement methods. Therefore, airborne measurements of turbulent flux are highly advantageous. By leveraging airborne measurements of H and LE fluxes collected in the Netherlands in August 2008, in this study we evaluated five machine learning methods for the construction of a regional gridded heat flux map, including artificial neural networks, boosted regression trees, random forest regression, deep neural networks, and support vector regression. The models were trained and tested using a dataset compiled from observations of H and LE, the digital elevation model, MODIS land surface temperature, enhanced vegetation index, and albedo data for each flux footprint. The best performing model was used to construct a regional gridded heat flux map over a case region located in the center of the Netherlands. The results shown that the support vector regression performed better than other models, with R2=0.91,RMSE=9.6W/m2 for H, and R2=0.89,RMSE=26.32W/m2 for LE. The constructed heat flux maps achieved a relative prediction error of ≤32.8% (R2>0.71) for H and ≤43.5% (R2>0.53) for LE compared to aircraft measurements. The constructed heat flux maps were then aggregated for each land cover type, providing individual estimates of source strength (52< H< 66 W/m2 and 108< LE< 218 W/m2) and spatial variability (52< σH< 66 W/m2 and 108< σLE< 218 W/m2) with an ensemble precision of < 6% (1σ). Finally, the limitations and future prospects of the current study were summarized and discussed.

Boundary-dependent urban impacts on timing, pattern, and magnitude of heavy rainfall in Istanbul

An emphasis on whether the modeled response of rainfall to urban signature is consistent across different boundary forcings is lacking. Here, using the Weather Research and Forecasting (WRF) model, we compare urban impacts in the boundary-dependent simulations of a record-breaking rainfall event in Istanbul, designing urban and nourban land cover scenarios. The data used for the boundaries are ECMWF Reanalysis v5 (ERA5) and NCEP Final Analysis (FNL), and we perform simulations with variable boundary and parameterization configurations and use their ensemble mean in our analysis. Our results highlight that some aspects of the urban impact on rainfall produced by different boundary conditions resemble each other. First, hourly rainfall intensifies over and upwind part of the urban domain independent of the employed boundary forcing. Especially within the urban borders, the boost in rainfall amounts during the investigation period totals 6% and 21% for the simulations forced with ERA5 and FNL, respectively. In addition, our simulations exhibit urban signals not only in the rainfall amounts but also in their timing and concentration. This signal in timing is evident by the urban rainfall system that moves slightly ahead of its nourban counterpart at each analyzed hour. We, in particular, observe a spatially less concentrated rainfall pattern as the system positions over the urban area and point out a potential urbanization-topography interaction. We further support these findings with cross-section and integrated water vapor transport analyses. By contrast, the main dissimilarities between the simulations forced with different boundary data include rainfall changes downwind of the city center. This behavior is commensurate with the increase in the temperature and sensible-heat flux values that are not similar in strength in the simulations forced with ERA5 and FNL. These findings suggest that different boundary data can promote similar urban impacts only to some extent, underlining the importance of considering their regional performance before using them in modeling studies.

Statistical Analysis of Intra- and Interannual Variability of Extreme Values of Sensible and Latent Heat Fluxes in the North Atlantic in 1979–2021

Statistical Analysis of Intra- and Interannual Variability of Extreme Values of Sensible and Latent Heat Fluxes in the North Atlantic in 1979–2021

Environmental factors driving evapotranspiration over a grassland in a transitional climate zone in China

AbstractThe surface evapotranspiration (ET) process is the key link in the interaction between land and atmosphere. However, the influence of different environmental factors on ET over transitional climate zones and the physical pattern of the interaction between multiple factors remain unclear. Therefore, based on the continuous observation data during the vegetation growing season of a typical grassland in the Semi‐Arid Climate and Environment Observation of Lanzhou University (SACOL) station from 2007 to 2012, the influence pattern of multiple environmental factors on ET over China's transitional climate zone was analysed. Each environmental factor exhibited significant seasonal and interannual variations. The mean value of ET was 1.67 mm day−1. Although the maximum values of sensible heat flux and vapour pressure deficit occurred in April and June, respectively, the maximum values of other environmental factors appeared from July to August. Net radiation, soil moisture, and normalized difference vegetation index (NDVI) were the main controlling factors of ET over the grassland, with correlation coefficients of 0.54, 0.52, and 0.46, respectively. The analysis of multiple environmental factors showed that when soil moisture, wind speed, net radiation, and NDVI reached 0.2 m3 m−3, 2 m s−1, 100 W m−2, and 0.2, respectively, ET varied in contrast with vapour pressure, vapour pressure deficit, and air temperature under the influences of weather processes, land–atmosphere coupling, and drought stress. These findings deepen our understanding of the role of ET in the land–atmosphere coupling process over the transitional climate zone in China.

WRF v.3.9 sensitivity to land surface model and horizontal resolution changes over North America

Abstract. Understanding the differences between regional simulations of land–atmosphere interactions and near-surface conditions is crucial for a more reliable representation of past and future climate. Here, we explore the effect of changes in the model's horizontal resolution on the simulated energy balance at the surface and near-surface conditions using the Weather Research and Forecasting (WRF) model. To this aim, an ensemble of 12 simulations using three different horizontal resolutions (25, 50 and 100 km) and four different land surface model (LSM) configurations over North America from 1980 to 2013 is developed. Our results show that finer resolutions lead to higher surface net shortwave radiation and maximum temperatures at mid and high latitudes. At low latitudes over coastal areas, an increase in resolution leads to lower values of sensible heat flux and higher values of latent heat flux, as well as lower values of surface temperatures and higher values of precipitation, and soil moisture in summer. The use of finer resolutions leads then to an increase in summer values of latent heat flux and convective and non-convective precipitation and soil moisture at low latitudes. The effect of the LSM choice is larger than the effect of horizontal resolution on the near-surface temperature conditions. By contrast, the effect of the LSM choice on the simulation of precipitation is weaker than the effect of horizontal resolution, showing larger differences among LSM simulations in summer and over regions with high latent heat flux. Comparison between observations and the simulation of daily maximum and minimum temperatures and accumulated precipitation indicates that the CLM4 LSM yields the lowest biases in maximum and minimum mean temperatures but the highest biases in extreme temperatures. Increasing horizontal resolution leads to larger biases in accumulated precipitation over all regions particularly in summer. The reasons behind this are related to the partition between convective and non-convective precipitation, specially noticeable over western USA.

Mapping of biophysical and biochemical properties of coastal tidal wetland habitats with Landsat 8

Coastal tidal wetlands are significant and vulnerable aquatic ecosystems. Quantitative remote sensing of biophysical and biochemical properties in coastal tidal wetland habitats through the inversion of physical models has vital practical significance for monitoring ecosystem function, environmental restoration, the global carbon, and nitrogen cycles. The objectives of this research were to map leaf area index (LAI), chlorophyll content, as well as the sensible heat flux, latent heat flux, and productivity in Chongming Dongtan coastal tidal wetland habitats of China and to provide a mapping protocol of biophysical and biochemical properties in Chongming Dongtan wetland for environmental protection and restoration as well as assessment and monitoring. In order to obtain significant information for biodiversity protection and management, a method based on the Soil Canopy Observation of Photosynthesis and Energy fluxes model and lookup table approach has been developed. The results derived from our study contain the reflectance values of Scirpus mariqueter and Phragmites australis spectra are lower than those commonly found for vegetated areas. This may be caused by the dark soil background and low LAI. Moreover, as for the values of latent heat flux (between 120 and 190 W m − 2) and productivity (between 3 and 14 μmol m − 2 s − 1), mudflats are lower than vegetation. However, the values of sensible heat flux (between 140 and 170 W m − 2) of mudflats are higher than that of vegetation.

Comparative Analysis of Water-Energy Cycle Processes Based on High-Resolution Assimilation Dataset of the Water-Energy Cycle in China Data Over Different Underlying Surfaces in Qinghai-Tibet Plateau

We used a High-Resolution Assimilation Dataset of the water-energy cycle in China (HRADC) to study the land-atmosphere interactions and meteorological characteristics in inhomogeneous underlying surface of the Qinghai-Tibet Plateau (QTP). Three different underlying surfaces (i.e., grassland, open shrubland, and barren or sparsely vegetated) of the QTP are selected and the meteorological elements on each underlying surface grid are averaged. We compared and analyzed the Green Vegetation Fraction (GVF), precipitation, soil moisture and soil temperature, and energy fluxes for three different land-use types in QTP. The results showed that the vegetation coverage of HRADC showed a gradual decrease trend from southeast to northwest throughout the Qinghai-Tibet Plateau. The GVF of the grassland in the southeast can reach more than 60% in summer, and only about 20% in sparse vegetation areas. HRADC can well reproduce the seasonal change trend of soil temperature and soil moisture in different underlying surfaces. The annual variation trend of soil temperature shows that the time of the deep soil temperature reaching the peak value lags behind the shallow layer. The annual averaged soil moisture over grassland is higher than that of open shrubland and barren land, which is consistent with the plateau precipitation distribution. The peak value of sensible heat flux over grassland is only 80 W·m-2 in April, and the latent heat flux can reach 90 W·m-2, and the net radiation of the barren land can reach 210 W·m-2 in July. This study is important to discover the water-energy cycle characteristics of QTP.

Estimation of Surface Heat Fluxes Over the Central Tibetan Plateau using the Maximum Entropy Production Model

AbstractSurface heat fluxes over the central Tibetan Plateau have been estimated using the maximum entropy production (MEP) model with the surface energy balance and the observation data from the Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX‐III). The MEP surface heat fluxes are highly correlated with those of the TIPEX‐III observations. The agreement between the MEP and TIPEX‐III heat fluxes is higher when the observed surface energy balance closure is better. The errors of the MEP heat fluxes are smaller compared to those of the fluxes derived from the bulk transfer method, the Land Data Assimilation Systems, and the Simple Biosphere Model version 2 reported in the previous studies. The values of MEP sensible and latent heat fluxes tend to be less than those of the previous bulk heat fluxes. Thus, the MEP model can reasonably estimate surface heat fluxes over the central Tibetan Plateau.

The energy mechanism controlling the continuous development of a super-thick atmospheric convective boundary layer during continuous summer sunny periods in an arid area

In the arid regions of the world, due to the specific climatic and environmental background, a super-thick convective boundary layer (SCBL) often develops on sunny days in summer, whereas such phenomena rarely occur in other areas. This special boundary layer structure has an important synoptic and climatic significance, but there have been few studies of its development mechanism in arid areas, which greatly restricts the parametric improvement of the SCBL and our understanding of the interaction between weather and climate processes. This study was conducted in Dunhuang, which is located in the hinterland of northwest China. Based on data obtained from land-air interaction experiments and long-term operational sounding observations in this region, the energy mechanism controlling the development of the CBL and the developmental process of the SCBL were systematically analyzed. In arid northwest China, it is possible that the thickness of the CBL can extend to over 3 km for most of the year, except winter. Even in the early summer, when there is little rain and strong solar radiation, the thickness of the CBL may reach an extreme state of 5.4 km. The thickness of the CBL at this time is higher than that observed in midsummer, when there is slightly more precipitation in this area. This is basically consistent with the extreme thickness of the CBL recently discovered in the Sahara Desert in Africa. In the general mechanism that controls the development of the CBL, there is a close relationship between the development of the CBL and the sensible heat flux of the surface. However, the correlation between the thickness of the CBL and the surface sensible heat flux at the same time is not strong, whereas the correlation between the thickness of the CBL and the cumulative surface sensible heat flux is very strong. This indicates that the development of the CBL is the result of the continuous accumulation of the sensible heat flux on the surface, which is consistent with the energy mechanism controlling the CBL. Although the development of the CBL is closely related to the cumulative heating effect of the daytime surface sensible heat flux, the CBL would still continue to increase even if the integral value of the daytime surface sensible heat flux remained unchanged or even weakened during the continuous clear sky period. The energy provided through sensible heat does not fully explain the energy required to develop the CBL. This is mainly because the deep near-neutral residual layer (RL) background plays an important role in the development of the SCBL. The entrainment energy from the deep RL to the CBL is the key energy supply for the continuous development of the CBL. The sum of the entrainment energy and surface sensible heat energy coincides with the energy absorbed by the development of the SCBL. The reason for the occurrence of an SCBL in arid areas is not only the strong sensible heating in summer but also the persistent clear skies in such areas. In each continuous clear sky period, the positive feedback mechanism between the CBL and the RL will become operational. Under this mechanism, the daily maximum thickness of the CBL and the thickness of the RL will increase continuously. The thickness of the SCBL is generally over 3 km, although depths of over 5 km can develop through a cyclic growth mechanism during periods of strong surface heating. Otherwise, the thickness of the CBL can only reach 2–3 km in summer, and it is unlikely that an SCBL will develop. Strong sensible heating is the key trigger of the positive feedback cycle growth mechanism between the CBL and the RL, which explains why the SCBL phenomenon can only occur in dry areas, with intense surface heating in summer.

Effects of variable fetch and footprint on surface renewal measurements of sensible and latent heat fluxes in cotton

Understanding crop evapotranspiration (ET) is important for efficient irrigation management. The eddy covariance (EC) technique is useful in measuring whole canopy latent heat flux from field crops. However, it requires expensive equipment and complex data analysis; hence, is relevant for research only. With the aim of developing a low-cost and simple method, we investigated here the surface-renewal (SR) method. This method estimates sensible heat flux from high frequency temperature measurements by using a fine wire thermocouple (TC). Next, latent heat flux is derived from the energy balance closure. Since fine wire thermocouple measurements of air temperature can be performed near the canopy top, it was hypothesized (Castellvi, 2012) that fetch requirements can be relaxed relatively to those for EC, and a relatively small fetch is sufficient for reliable flux measurements by SR. In the present study, the SR technique was examined in a cotton field in southern Israel. Seven fine wire thermocouples were installed at various distances from field edges and at different heights above the ground, providing variable fetch from 50 to 200 m, depending on field geometry and wind direction. An EC system was installed within the field at a position that provided sufficient fetch (400 m) for reliable reference values of sensible and latent heat fluxes. Excellent energy balance closure of 0.96 (R2 = 0.95) was obtained from a non-continuous period of 31 days of measurements. SR data from fine-wire thermocouples at all heights were classified by either available fetch or by 90% flux footprint. Only cases in which footprint was smaller than the available fetch were included in the analysis. Two footprint models were examined, KJ (Kljun et al., 2015) and HS (Hsieh et al., 2000). Results of fetch classification showed that the SR weighting factor varied between 0.67 and 1.34 and was independent of fetch. Footprint classification provided weighting factors between 0.46 and 1.18 for the KJ model and between 0.8 and 1.26 for the HS model. LE derived from SR sensible heat flux and energy balance closure, was regressed against LE reference values measured by the eddy covariance. Results showed deviations of up to 15% and 30% between SR and EC, for the KJ and HS model data, respectively. We conclude that in the cotton field under study the SR technique was reliable in estimating sensible and latent heat fluxes and the weighting factor was essentially independent of the geometrical fetch and the flux footprint of the sensors.

The marine atmospheric boundary layer under strong wind conditions: Organized turbulence structure and flux estimates by airborne measurements

AbstractDuring winter, cold air outbreaks take place in the northwestern Mediterranean sea. They are characterized by local strong winds (Mistral and Tramontane) which transport cold and dry continental air across a warmer sea. In such conditions, high values of surface sensible and latent heat flux are observed, which favor deep oceanic convection. The HyMeX/ASICS‐MED field campaign was devoted to the study of these processes. Airborne measurements, gathered in the Gulf of Lion during the winter of 2013, allowed for the exploration of the mean and turbulent structure of the marine atmospheric boundary layer (MABL). A spectral analysis based on an analytical model was conducted on 181 straight and level runs. Profiles of characteristic length scales and sharpness parameter of the vertical wind spectrum revealed larger eddies along the mean wind direction associated with an organization of the turbulence field into longitudinal rolls. These were highlighted by boundary layer cloud bands on high‐resolution satellite images. A one‐dimensional description of the vertical exchanges is then a tricky issue. Since the knowledge of the flux profile throughout the entire MABL is essential for the estimation of air‐sea exchanges, a correction of eddy covariance turbulent fluxes was developed taking into account the systematic and random errors due to sampling and data processing. This allowed the improvement of surface fluxes estimates, computed from the extrapolation of the stacked levels. A comparison between those surface fluxes and bulk fluxes computed at a moored buoy revealed considerable differences, mainly regarding the latent heat flux under strong wind conditions.

The Urban Tree as a Tool to Mitigate the Urban Heat Island in Mexico City: A Simple Phenomenological Model

The urban heat island (UHI) is mainly a nocturnal phenomenon, but it also appears during the day in Mexico City. The UHI may affect human thermal comfort, which can influence human productivity and morbidity in the spring/summer period. A simple phenomenological model based on the energy balance was developed to generate theoretical support of UHI mitigation in Mexico City focused on the latent heat flux change by increasing tree coverage to reduce sensible heat flux and air temperature. Half-hourly data of the urban energy balance components were generated in a typical residential/commercial neighborhood of Mexico City and then parameterized using easily measured variables (air temperature, humidity, pressure, and visibility). Canopy conductance was estimated every hour in four tree species, and transpiration was estimated using sap flow technique and parameterized by the envelope function method. Averaged values of net radiation, energy storage, and sensible and latent heat flux were around 449, 224, 153, and 72 W m, respectively. Daily tree transpiration ranged from 3.64 to 4.35 Ld. To reduce air temperature by 1°C in the studied area, 63 large would be required per hectare, whereas to reduce the air temperature by 2°C only 24 large trees would be required. This study suggests increasing tree canopy cover in the city cannot mitigate UHI adequately but requires choosing the most appropriate tree species to solve this problem. It is imperative to include these types of studies in tree selection and urban development planning to adequately mitigate UHI.

Use of MODIS Images to Quantify the Radiation and Energy Balances in the Brazilian Pantanal

MODIS images during the year 2012 were used for modelling of the radiation and energy balance components with the application of the SAFER algorithm (Simple Algorithm for Evapotranspiration Retrieving) in the Brazilian Pantanal area. Pixels from the main sub-regions of Barão de Melgaço (BR), Paiaguás (PA) and Nhecolândia (NH) were extracted in order to process microclimatic comparisons. In general, the net radiation (Rn) relied much more on the global solar radiation (RG) levels than on water conditions and ecosystem types, in accordance with the low Rn standard deviation values. The fraction of the available energy used as latent heat flux (λE) were, on average, 65, 50 and 49% for the BR, PA and NH sub-regions, respectively. Horizontal heat advection, identified by the negative values of sensible heat flux (H), made several pixels with λE values higher than those for Rn in the middle of the year. Taking the evaporative fraction (Ef) as a surface moisture indicator, the Tree-Lined Savanna (TLS) was considered the moister ecosystem class, with 58% of the available energy being used as λE, while the driest one was the modified ecosystem Anthropogenic Changes (AC), presenting a λE/Rn fraction of 0.46. According to the spatial and temporal consistencies, and after comparisons with other previous point and large-scale studies, the SAFER algorithm proved to have sensibility to quantify and compare the large-scale radiation and energy balance components in the different ecosystems of the Brazilian Pantanal. The algorithm is useful for monitoring the energy exchange dynamics among the different terrestrial and aquatic ecosystem types throughout the seasons of the year.

Impacts of soil moisture content on simulated mesoscale circulations during the summer over eastern Spain

The Regional Atmospheric Modeling System (RAMS) version 6.0 has been used to investigate the impact and influence of initial soil moisture distributions on mesoscale circulations. To do this, two different events have been selected from the 2011 summer season: one at the beginning of the season (June) and the other one at the end of the season (August). For each of these mesoscale frameworks a total of five distinct simulations were performed varying the initial soil moisture content: a control run and four additional sensitivity tests. The control run, corresponding to a low soil moisture content, is the one used within the real-time weather forecasting system implemented in the Valencia Region. In the corresponding sensitivity simulations this low value has been progressively increased in different steps until the original soil moisture content doubled. It has been found that high soil moisture is associated with colder near-surface temperature, a moister relative humidity and a slightly lower near-surface wind speed, whereas a drier soil resulted in a dryer relative humidity, warmer temperature and a slight low-level wind. In general, the highest soil moisture contents are required to reproduce the near-surface daily cycles of temperature and relative humidity through higher values of latent heat flux and lower values of sensible heat flux. In this regard, moistening the soil improves the previous results obtained using the RAMS configuration used within the operational forecasting system. However, the wind speed is not quite sensitive to changes in the soil moisture content over flatter terrain. Finally, although a warming and dryer mixing layer is obtained with the lowest soil moisture content, the mixing layer height remains practically unchanged when using the distinct configurations over flat terrain. These differences are enhanced over more complex terrain.

Flooding Regime Impacts on Radiation, Evapotranspiration, and Latent Energy Fluxes over Groundwater-Dependent Riparian Cottonwood and Saltcedar Forests

Radiation and energy balances are key drivers of ecosystem water and carbon cycling. This study reports on ten years of eddy covariance measurements over groundwater-dependent ecosystems (GDEs) in New Mexico, USA, to compare the role of drought and flooding on radiation, water, and energy budgets of forests differing in species composition (native cottonwoodversusnonnative saltcedar) and flooding regime. After net radiation (700–800 W m−2), latent heat flux was the largest energy flux, with annual values of evapotranspiration exceeding annual precipitation by 250–600%. Evaporative cooling dominated the energy fluxes of both forest types, although cottonwood generated much lower daily values of sensible heat flux (&lt;−5 MJ m−2 d−1). Drought caused a reduction in evaporative cooling, especially in the saltcedar sites where evapotranspiration was also reduced, but without a substantial decline in depth-to-groundwater. Our findings have broad implications on water security and the management of native and nonnative vegetation within semiarid southwestern North America. Specifically, consideration of the energy budgets of GDEs as they respond to fluctuations in climatic conditions can inform the management options for reducing evapotranspiration and maintaining in-stream flow, which is legally mandated as part of interstate and international water resources agreements.

Evapotranspiration and crop coefficients of rice (Oryza sativa L.) under sprinkler irrigation in a semiarid climate determined by the surface renewal method

The evapotranspiration (ETc) of sprinkler-irrigated rice was determined for the semiarid conditions of NE Spain during 2001, 2002 and 2003. The surface renewal method, after calibration against the eddy covariance method, was used to obtain values of sensible heat flux (H) from high-frequency temperature readings. Latent heat flux values were obtained by solving the energy balance equation. Finally, lysimeter measurements were used to validate the evapotranspiration values obtained with the surface renewal method. Seasonal rice evapotranspiration was about 750–800 mm. Average daily ETc for mid-season (from 90 to 130 days after sowing) was 5.1, 4.5 and 6.1 mm day−1 for 2001, 2002 and 2003, respectively. The experimental weekly crop coefficients fluctuated in the range of 0.83–1.20 for 2001, 0.81–1.03 for 2002 and 0.84–1.15 for 2003. The total growing season was about 150–160 days. In average, the crop coefficients for the initial (Kcini), mid-season (Kcmid) and late-season stages (Kcend) were 0.92, 1.06 and 1.03, respectively, the length of these stages being about 55, 45 and 25 days, respectively.

Evapotranspiration of grapevine trained to a gable trellis system under netting and black plastic mulching

The evapotranspiration (ET c) of a table grape vineyard (Vitis vinifera, cv. Red Globe) trained to a gable trellis under netting and black plastic mulching was determined under semiarid conditions in the central Ebro River Valley during 2007 and 2008. The netting was made of high-density polyethylene (pores of 12 mm2) and was placed just above the ground canopy about 2.2 m above soil surface. Black plastic mulching was used to minimize soil evaporation. The surface renewal method was used to obtain values of sensible heat flux (H) from high-frequency temperature readings. Later, latent heat flux (LE) values were obtained by solving the energy balance equation. For the May–October period, seasonal ET c was about 843 mm in 2007 and 787 mm in 2008. The experimental weekly crop coefficients (K cexp) fluctuated between 0.64 and 1.2. These values represent crop coefficients adjusted to take into account the reduction in ET c caused by the netting and the black plastic mulching. Average K cexp values during mid- and end-season stages were 0.79 and 0.98, respectively. End-season K cexp was higher due to combination of factors related to the precipitation and low ET o conditions that are typical in this region during fall. Estimated crop coefficients using the Allen et al. (1998) approach adjusting for the effects of the netting and black plastic mulching (K cFAO) showed a good agreement with the experimental K cexp values.

Soil Surface Energy and Water Budgets during a Monsoon Season in Korea

Abstract In this study, attention has been focused on the climatology of some variables linked to the turbulent exchanges of heat and water vapor in the surface layer during a summer monsoon in Korea. In particular, the turbulent fluxes of sensible and latent heat, the hydrologic budget, and the soil temperatures and moistures have been analyzed. At large scale, because the measurements of those data are not only fragmentary and exiguously available but also infeasible for the execution of climatologic analyses, the outputs of a land surface scheme have been used as surrogate of observations to analyze surface layer processes [this idea is based on the methodology Climatology of Parameters at the Surface (CLIPS)] in the Korean monsoonal climate. Analyses have been made for the summer of 2005. As a land surface scheme, the land surface process model (LSPM) developed at the University of Torino, Italy, has been employed, along with the data collected from 635 Korean meteorological stations. The LSPM predictions showed good agreement with selected observations of soil temperature. Major results show that, during the rainfall season, soil moisture in the first tenths of centimeters frequently exceeds the field capacity, whereas most of the rainfall is “lost” as surface runoff. Evapotranspiration is the dominant component of the energy budget, sometimes even exceeding net radiation, especially during the short periods between the precipitation events; in these periods, daily mean soil temperatures are about 28°C or even more. The Gyeonggi-do region, the metropolitan area surrounding Seoul, shows some particularities when compared with the neighboring regions: solar radiation and precipitations are lower, causing high values of sensible heat flux and soil temperatures, and lower values of latent heat flux and soil moistures.