Mean Value Of Evapotranspiration Research Articles

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.

How Will Climate Change Affect the Water Availability in the Heihe River Basin, Northwest China?

Abstract This paper presents a detailed analysis of how future climate change may affect water availability in a typical arid endorheic river basin, the Heihe River basin (HRB), in northwest China. The analysis is based on the improved Soil Water Assessment Tool (SWAT), which is calibrated and validated with historical streamflow data from the upper HRB and is used to predict future hydrological responses. Six general circulation models (GCMs), under two emission scenarios (RCP4.5 and RCP8.5), are downscaled to construct future climate change scenarios. The results suggest that the climate of the upper HRB will likely become warmer and wetter in the near future (2021–50), with the largest increase in precipitation occurring in the summer. Correspondingly, the basinwide evapotranspiration, snowmelt, and runoff are projected to increase over the same period. The mean temperature in the near future is projected to rise, relative to the recent 30 years (1981–2010), by 1.2°–1.7°C under scenario RCP4.5 and by 1.4°–2.1°C under scenario RCP8.5. The mean precipitation is projected to increase by 10.0%–16.6% under scenario RCP4.5, and by 10.5%–22.0% under scenario RCP8.5. The mean values of evapotranspiration, snowmelt, and runoff are expected to increase by 14.2%, 4.3%, and 11.4%, respectively, under scenario RCP4.5 and to increase by 18.7%, 5.8%, and 12.8%, respectively, under scenario RCP8.5. Though the model simulations forecast an increase in streamflows in the headwater region of the HRB, future water availability varies significantly over space and time. The findings of this study will help to frame more effective water management strategies for the HRB under changing climatic conditions.

Fluxos de água no consórcio milho-pastagem na microbacia hidrográfica do Rio Mundaú, Pernambuco

In the context of world climate changes, the quantification of evapotranspiration (ET) of crops and grasslands is extremely important to anticipate how these changes will affect the hydrological cycle. Many researches were made to measurement of ET ongrasslands; however, there are few researches that measured ET and another soil water balance components in maize-pasture intercropping. The objective of this study was to assess the soil water balance components (soil water storage variations, drainage, capillary rise and evapotranspiration) of the maize-pasture intercropping under rainfed in the catchment Rio Mundau, Pernambuco State.The study was carried out in an experimental area located at the “Riacho do Papagaio” farm(8o 52’ 30’’ S, 36o 22’ 00’’ Wand 705 m), county of Sao Joao, from 01/01/2013 to 31/12/2013. TDR probes to measure the soil water content were installed at depths of 0.10, 0.20, 0.30 and 0.40 m. Rainfall was monitored with rain gauge installed on a tower at the center of the area. For the determination of drainage and capillary rise, infiltration tests were performed in field to obtain the saturated hydraulic conductivity. The soil water retention curve was determined in laboratory. The ETo was obtained by the Penman-Monteith method. It was observed that substantial soil water storage and ET values occurred in the high rainfall periods. The ET throughout the experimental period was the main water outlet of system with a total value of 406.8 mm and average of 1.1 mm d-1.The mean values of ET for periods with bare soil, maize-pasture intercropping and pasture alone were 0.8, 1.5 and 1.1 mm d-1, respectively. The maize-pasture intercropping must have suffered water stress, in almost all experimental period, due the values of the ratio ET/ETo being lower than the 1. The best period for the development of the forages (grasslands and maize) in the region is from april to august

Surface Energy Fluxes and Evapotranspiration of a Mango Orchard Grown in a Semiarid Environment

Data from field experiments conducted in the semiarid climatic conditions of northeast Brazil were used to investigate the energy flux relations and evapotranspiration (ET) of a mango (Mangifera indica L.) orchard. The Bowen ratio–energy balance method was applied during the 1998–1999 fruiting cycles to estimate the energy balance components of the mango orchard, while the FAO Penman–Monteith approach was used for determining the reference evapotranspiration (ETo). Results indicated that latent heat flux density (λE) could be obtained, with reasonable precision, as a function of measured net radiation flux density (Rn). The percentage of Rn used as λE was higher for the fruit growth and fruit maturation phenological stages, and lower for the flowering and fruit fall stages. For both field campaigns, λE was found to be the major component of energy balance, comprising >70% of the available energy. Soil heat flux was always the smaller component, comprising <8%. Daily mean value of ET was higher during the 1998 fruiting cycle than that observed in 1999. Inversely, the ET increased approximately 6% from the 1998 to 1999 fruiting cycle. These results may be used for planning and management of irrigation for mangos grown in similar environmental conditions.

アラスカ北極域ツンドラにおける熱収支解析

Using the micrometeorological data (Harazono et al., 1995) obtained at the Arctic Tundra at Barrow, Alaska in the summer of 1993, preliminary analysis was made and the daily and seasonal variations of evapotranspiration, radiation, ground heat flux, and surface temperature were estimated.On fine days, the value of sensible and latent heat fluxes increased to maximums of approximately 200 to 300Wm-2 during the midday, then decreased to about zero (sensible heat flux) and -30 to -80Wm-2 (latent heat flux) around the time of the sun's northing. It is found that the surface evaporation efficiency β, having a mean value of 0.3, decreases with increasing wind speed. Using a model calculation, it is obtained that the mean value of evapotranspiration at the IBP site for 71 days, from 16 July to 25 August, is 0.89mmd-1 which is 40% of the potential evaporation (defined by Kondo and Xu, 1997a).

Estimation of Standard Deviation of Potential Evapotranspiration

Some weather simulation procedures require mean values of potential evapotranspiration (ETP) and the standard deviations in ETP. For purposes of irrigation planning and design it may be desirable to know the probable deviations from mean values of ETP. Various crop production or crop yield models have been developed that require input of daily measurements of climate. A weather simulation procedure utilizing a monthly climatic data base can be substituted for the daily climatic data to produce very comparable results. The weather simulation procedure recommended requires the standard deviation of ETP. A series of monthly mean values of maximum and minimum temperatures provides the required data for estimating mean ETP and the standard deviation. If only long‐term mean maximum and minimum temperatures and the mean temperatures for a series of years are available, the standard deviation of mean temperature provides a means for making an estimate of the standard deviation in ETP. The relationship is influenc...