Saturation Vapour Pressure Deficit Research Articles

Innovative approach for predicting daily reference evapotranspiration using improved shallow and deep learning models in a coastal region: A comparative study

Accurate and reliable estimation of Reference Evapotranspiration (ETo) is crucial for water resources management, hydrological processes, and agricultural production. The FAO-56 Penman-Monteith (FAO-56PM) approach is recommended as the standard model for ETo estimation; nevertheless, the absence of comprehensive meteorological variables at many global locations frequently restricts its implementation. This study compares shallow learning (SL) and deep learning (DL) models for estimating daily ETo against the FAO-56PM approach based on various statistic metrics and graphic tool over a coastal Red Sea region, Sudan. A novel approach of the SL model, the Catboost Regressor (CBR) and three DL models: 1D-Convolutional Neural Networks (1D-CNN), Long Short-Term Memory (LSTM), and Gated Recurrent Unit (GRU) were adopted and coupled with a semi-supervised pseudo-labeling (PL) technique. Six scenarios were developed regarding different input combinations of meteorological variables such as air temperature (Tmin, Tmax, and Tmean), wind speed (U2), relative humidity (RH), sunshine hours duration (SSH), net radiation (Rn), and saturation vapor pressure deficit (es-ea). The results showed that the PL technique reduced the systematic error of SL and DL models during training for all the scenarios. The input combination of Tmin, Tmax, Tmean, and RH reflected higher performance than other combinations for all employed models. The CBR-PL model demonstrated good generalization abilities to predict daily ETo and was the overall superior model in the testing phase according to prediction accuracy, stability analysis, and less computation cost compared to DL models. Thus, the relatively simple CBR-PL model is highly recommended as a promising tool for predicting daily ETo in coastal regions worldwide which have limited climate data.

Response of Vegetation to Drought in the Source Region of the Yangtze and Yellow Rivers Based on Causal Analysis

The vegetation and ecosystem in the source region of the Yangtze River and the Yellow River (SRYY) are fragile. Affected by climate change, extreme droughts are frequent and permafrost degradation is serious in this area. It is very important to quantify the drought–vegetation interaction in this area under the influence of climate–permafrost coupling. In this study, based on the saturated vapor pressure deficit (VPD) and soil moisture (SM) that characterize atmospheric and soil drought, as well as the Normalized Differential Vegetation Index (NDVI) and solar-induced fluorescence (SIF) that characterize vegetation greenness and function, the evolution of regional vegetation productivity and drought were systematically identified. On this basis, the technical advantages of the causal discovery algorithm Peter–Clark Momentary Conditional Independence (PCMCI) were applied to distinguish the response of vegetation to VPD and SM. Furthermore, this study delves into the response mechanisms of NDVI and SIF to atmospheric and soil drought, considering different vegetation types and permafrost degradation areas. The findings indicated that low SM and high VPD were the limiting factors for vegetation growth. The positive and negative causal effects of VPD on NDVI accounted for 47.88% and 52.12% of the total area, respectively. Shrubs were the most sensitive to SM, and the response speed of grassland to SM was faster than that of forest land. The impact of SM on vegetation in the SRYY was stronger than that of VPD, and the effect in the frozen soil degradation area was more obvious. The average causal effects of NDVI and SIF on SM in the frozen soil degradation area were 0.21 and 0.41, respectively, which were twice as high as those in the whole area, and SM dominated NDVI (SIF) changes in 62.87% (76.60%) of the frozen soil degradation area. The research results can provide important scientific basis and theoretical support for the scientific assessment and adaptation of permafrost, vegetation, and climate change in the source area and provide reference for ecological protection in permafrost regions.

Combined Effects of Meteorological Factors, Terrain, and Greenhouse Gases on Vegetation Phenology in Arid Areas of Central Asia from 1982 to 2021

Spatiotemporal variations in Central Asian vegetation phenology provide insights into arid ecosystem behavior and its response to environmental cues. Nevertheless, comprehensive research on the integrated impact of meteorological factors (temperature, precipitation, soil moisture, saturation vapor pressure deficit), topography (slope, aspect, elevation), and greenhouse gases (carbon dioxide, methane, nitrous oxide) on the phenology of Central Asian vegetation remains insufficient. Utilizing methods such as partial correlation and structural equation modeling, this study delves into the direct and indirect influences of climate, topography, and greenhouse gases on the phenology of vegetation. The results reveal that the start of the season decreased by 0.239 days annually, the length of the season increased by 0.044 days annually, and the end of the season decreased by 0.125 days annually from 1982 to 2021 in the arid regions of Central Asia. Compared with topography and greenhouse gases, meteorological factors are the dominant environmental factors affecting interannual phenological changes. Temperature and vapor pressure deficits (VPD) have become the principal meteorological elements influencing interannual dynamic changes in vegetation phenology. Elevation and slope primarily regulate phenological variation by influencing the VPD and soil moisture, whereas aspect mainly affects the spatiotemporal patterns of vegetation phenology by influencing precipitation and temperature. The findings of this study contribute to a deeper understanding of how various environmental factors collectively influence the phenology of vegetation, thereby fostering a more profound exploration of the intricate response relationships of terrestrial ecosystems to environmental changes.

Substantial Reduction in Vegetation Photosynthesis Capacity during Compound Droughts in the Three-River Headwaters Region, China

Solar-induced chlorophyll fluorescence (SIF) is a reliable proxy for vegetative photosynthesis and is commonly used to characterize responses to drought. However, there is limited research regarding the use of multiple high-resolution SIF datasets to analyze reactions to atmospheric drought and soil drought, especially within mountain grassland ecosystems. In this study, we used three types of high-spatial-resolution SIF datasets (0.05°), coupled with meteorological and soil moisture datasets, to investigate the characteristics of atmospheric, soil, and compound drought types. We centered this investigation on the years spanning 2001–2020 in the Three-River Headwaters Region (TRHR). Our findings indicate that the TRHR experienced a combination of atmospheric drying and soil wetting due to increases in the standardized saturation vapor pressure deficit index (SVPDI) and standardized soil moisture index (SSMI). In the growing season, atmospheric drought was mainly distributed in the southern and eastern parts of the TRHR (reaching 1.7 months/year), while soil drought mainly occurred in the eastern parts of the TRHR (reaching 2 months/year). Compound drought tended to occur in the southern and eastern parts of the TRHR and trended upward during 2001–2020. All three SIF datasets consistently revealed robust photosynthetic activity in the southern and eastern parts of the TRHR, with SIF values generally exceeding 0.2 mW· m−2·nm−1·sr−1. Overall, the rise in SIF between 2001 and 2020 corresponds to enhanced greening of TRHR vegetation. Vegetation photosynthesis was found to be limited in July, attributable to a high vapor pressure deficit and low soil moisture. In the response of CSIF data to a drought event, compound drought (SVPDI ≥ 1 and SSMI ≤ −1) caused a decline of up to 14.52% in SIF across the source region of the Yellow River (eastern TRHR), while individual atmospheric drought and soil drought events caused decreases of only 5.06% and 8.88%, respectively. The additional effect of SIF produced by compound drought outweighed that of atmospheric drought as opposed to soil drought, suggesting that soil moisture predominantly governs vegetation growth in the TRHR. The reduction in vegetation photosynthesis capacity commonly occurring in July, characterized by a simultaneously high vapor pressure deficit and low soil moisture, was more pronounced in Yellow River’s source region as well. Compound drought conditions more significantly reduce SIF compared to singular drought events. Soil drought evidently played a greater role in vegetation growth stress than atmospheric drought in the TRHR via the additional effects of compound drought.

Observed decreasing trend in pan evaporation in a tropical rainforest region during 1959–2021

Abstract Pan evaporation (Epan) is a critical measure of the atmospheric evaporation demand. Analyzing meteorological data from the Tropical Rainforest Comprehensive Meteorological Observation Field in the Xishuangbanna Tropical Botanical Garden (XTBG Meteorological Observing Station) based on physical models is helpful to improve our understanding of the state of the hydrological cycle in the Xishuangbanna tropical rainforest region. In this study, we investigated the long-term trend in Epan using the observation data from 1959 to 2021. Moreover, correlation analyses of Epan were performed, such as trend test, assessment of periodic properties and abrupt change analysis. Then, D20 Epan data and related meteorological data from 1979 to 2008 were used to drive Penman‒Monteith and PenPan models for simulating Epan. The partial derivative attribution method was used to analyze the dominant factors affecting Epan. The results showed that Epan exhibits obvious periodic changes, the 19a is the first primary period. In addition, there was a clear ‘evaporation paradox’ phenomenon in Xishuangbanna. Epan showed a decreasing trend during both 1959–2008 and 2009–2018, and the decreasing trend reached a significant level with a rate of −3.404 mm·a−2 during 1959–2008. Through comparative analysis, the PenPan model was considered more suitable for simulating Epan in Xishuangbanna. In order to identify the main meteorological factors influencing Epan, complete data from the D20 pan monitoring period, namely, 1979–2008, were selected for attribution calculations. The variations in the net radiation and saturated vapor pressure deficit are the main triggers that explain the ‘evaporation paradox’ phenomenon in Xishuangbanna.

Characteristics of spring maize sap flow and its environmental influencing factors in typical mollisol area.

Clarifying the variations of sap flow rate of spring maize in the typical mollisol area and its main control factors is of great significance to explore water consumption from transpiration and regulate field water management. In this study, we installed the wrapped sap flow sensors and TDR probes to continuously monitor the sap flow rate of spring maize during filling-maturity stage and soil water and heat conditions of topsoil. In combination with meteorological data collecting from a nearby automatic weather station, we analyzed the correlation between the sap flow rate of spring maize and environmental factors at different time scales. The results showed that the sap flow rate of spring maize in typical mollisol area had an obvious fluctuation of high diurnal and low nighttime. The instantaneous sap flow rate peaked at daytime, with a value of 139.9 g·h-1, but being weak at nighttime. The starting time, closing time, and peak values of spring maize sap flow were significantly inhibited in cloudy and rainy days, compared with that in sunny days. On hourly scale, the sap flow rate was significantly correlated to solar radiation, saturated vapor pressure deficit (VPD), relative humidity, air temperature, and wind speed. On daily scale, only solar radiation, VPD, and relative humidity were significantly correlated with sap flow rate, with the absolute values of correlation coefficient being all above 0.7. Due to high soil water content during the observation period, the sap flow rate was not significantly correlated with soil water content and soil temperature of 0-20 cm layer, with the absolute values of correlation coefficient being less than 0.1. Under the condition without water stress, solar radiation, VPD, and relative humidity were the top three influencing factors of sap flow rate in this region, on both hourly scale and daily scale.

不同时间尺度下华北落叶松人工林冠层蒸腾与环境因子的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 不同时间尺度下华北落叶松人工林冠层蒸腾与环境因子的关系 DOI: 10.5846/stxb202107151903 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 内蒙古自治区关键技术攻关计划项目(2021GG0033);内蒙古自治区林业和草原局科研能力提升项目;内蒙古自治区自然科学基金项目(2021MS03101) Relationship between canopy transpiration of larch plantation and environmental factors at different time scales Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在半干旱区连续2年监测华北落叶松(Larix principis-rupprechtii)的树干液流、气象因子和土壤体积含水量,分析不同时间尺度下人工林冠层蒸腾与环境因子的关系。结果表明:不同时间尺度下,华北落叶松人工林冠层蒸腾的季节变化均呈单峰曲线,即先增大后减小的趋势;2016年、2017年日蒸腾量分别为1.58 mm/d和1.71 mm/d,生长季蒸腾总量分别为241.30 mm和260.97 mm。在日尺度下,气温、太阳辐射强度和饱和水汽压差是影响华北落叶松人工林冠层蒸腾主要环境因子;月尺度下,气温、风速、降水和土壤水分是冠层蒸腾的主要影响因子;冠层蒸腾与降水、大气相对湿度的相关关系由日尺度下的负相关到月尺度的正相关,相关性增强。总体来看,随时间尺度由小到大,气温、风速、大气相对湿度、降水、土壤水分对冠层蒸腾的影响作用增大,而太阳辐射强度、饱和水汽压差的作用减弱;在未来增温增雨趋势下,研究区生长季将延长,华北落叶松人工林冠层蒸腾量可能会加大。 Abstract:Canopy transpiration is a major part of forestland water balance and a fundamental datum in understanding the planted forest ecophysiology in dry regions. Quantitatively analyzing variation of canopy transpiration induced by the environmental factors is beneficial for a better estimation forestland water balance and prediction the plantation ecophysiology. But the response mechanism of canopy transpiration to environmental factors may be different in different time scales, so it needs to be further understood. This study was conducted in a 42-year-old Larix principis-Rupprechtii plantation (a density of 1933 trees/hm2) at the middle position of a north facing slope in the Inner Mongolian Daqingshan National Nature Reserve, a semi-arid region of China. Firstly, the sap flow velocity in ten healthy and dominant Larix principis-Rupprechtii trees, soil volumetric water content and meteorological factors including air temperature, precipitation, solar radiation intensity, air relative humidity and wind speed, were observed during two growing seasons (May 1 to September 30) in 2016 and 2017 which precipitation was 435.00 mm and 348.80 mm, respectively. Then, sap flow velocity values which was measured by the thermal diffusion method, were upscaled to the forest canopy level. Finally, the relationship between canopy transpiration and the environmental factors at different time scales was analyzed. The results showed that the seasonal changes of canopy transpiration showed a single peak curve under the different time scales, that was, the trend of increase first and then decrease. In 2016 and 2017, the average value of daily canopy-level transpiration was 1.58 mm/d and 1.71 mm/d, respectively, and the total transpiration in the growing season was 241.30 mm and 260.97 mm, respectively. On the daily scale, air temperature, solar radiation intensity and saturated vapor pressure deficit markedly affected canopy transpiration. At the monthly scale, air temperature, wind speed, precipitation and soil volumetric water content were the main influencing factors of canopy transpiration. The correlation between transpiration and precipitation and air relative humidity increased from negative correlation on the daily scale to positive correlation on the monthly scale. In general, with time scale from small to large, the effects of air temperature, wind speed, air relative humidity, precipitation and soil water content on canopy transpiration increase, while the effects of solar radiation intensity and saturated vapor pressure deficit decrease. With the trend of increasing temperature and rainfall in the future, the growing season of Larix principis-Rupprechtii in the study area will be prolonged, and the canopy transpiration may increase. 参考文献 相似文献 引证文献

气候和密度对刺槐径向生长和干旱脆弱性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 气候和密度对刺槐径向生长和干旱脆弱性的影响 DOI: 10.5846/stxb202112133525 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划项目(2020YFA0608101) Effects of climate and density on the radial growth and drought vulnerability of Robinia pseudoacacia Author: Affiliation: Fund Project: National Key Research and Development Program of China (Project No. 2020YFA0608101) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为评估气候和竞争对刺槐径向生长、抗性和弹性的影响,使用年轮气候学方法建立河南省民权和济源不同密度刺槐的生长年表,确定不同密度刺槐径向生长与气象因子的关联,利用胸高断面积增量变化获得干旱事件前后不同密度刺槐的干旱脆弱性,旨在确定气候和密度对刺槐径向生长和干旱脆弱性影响。结果表明:在生长前期,不同密度刺槐的径向生长无显著差异,随着树木的生长,高密度刺槐的年轮宽度和胸高断面积增量(BAI)开始显著低于低密度(P<0.05)。Pearson相关分析结果显示,生长季的标准化植被蒸散指数、降水、相对湿度、温度和饱和水汽压亏缺是影响刺槐生长的重要因素。路径分析结果显示降水和温度是年尺度上影响刺槐生长关键因素。受干旱事件的影响,刺槐的年轮宽度和BAI均下降,低密度刺槐恢复力、弹性、相对弹性均显著高于高密度(P<0.05),在第1次干旱事件发生后,不同密度刺槐均恢复生长,但无法恢复到干旱前的生长水平。在多次干旱事件后,高密度刺槐相对弹性趋于或小于0,表明受多次干旱影响,其生长不能恢复到干旱前水平。随着时间的推移,济源刺槐在经历3次干旱后仍保留一定的弹性,但民权高密度刺槐在第2次干旱事件后相对弹性出现丧失,在未来干旱中其死亡风险增加。研究结果为研究气候对暖温带刺槐生长的影响提供了重要见解,并为密度影响下的刺槐恢复力和弹性研究提供了新视角。 Abstract:The aim of this study was to evaluate the effects of climate and competition on the radial growth and drought vulnerability of Robinia pseudoacacia (locust). Dendroclimatology was used to characterize the recovery, resilience, and chronology of locust in two sites varying in tree density (Minquan and Jiyuan, Henan Province). The correlations between the radial growth of locust and meteorological factors were determined, and the drought vulnerability of locust during drought periods was estimated by measuring the breast area increase (BAI). There was no significant difference in the radial growth of locust at sites varying in locust density in the early growth stage. The ring width and BAI of locust became increasingly lower at the high-density site than at the low-density site with growth (P<0.05). Pearson correlation analysis revealed that the standardized precipitation evapotranspiration index, precipitation, relative humidity, temperature, and the saturated vapor pressure deficit were important factors affecting the growth of locust during the growing season. Path analysis revealed that precipitation and temperature were the key factors affecting the annual growth of locust. The ring width and BAI of locust decreased under drought, and the recovery, resilience, and relative resilience of locust were significantly higher at the low-density site than at the high-density site (P<0.05). The growth of locust at both sites recovered after the first drought event, but growth did not return to its pre-drought level. After several drought events, the relative resilience of locust at the high-density site was equal to or less than 0, indicating that its growth did not return to the pre-drought level because of the multiple drought events. Locust at the low-density site still exhibited high resilience after three droughts; however, the relative resilience of locust at the high-density site decreased substantially, and the risk of death under future droughts increased after the second drought event. Overall, our findings provide the important insights into the effect of climate and density on the growth of locust in warm temperate areas as well as a new perspective on the study of locust recovery and resilience. 参考文献 相似文献 引证文献

Quantifying canopy conductance in a pine forest during drought from combined sap flow and canopy surface temperature measurements

• Measurement of canopy temperature using near infrared camera enhances the accuracy of canopy conductance determination. • Isothermal assumption leads to substantial bias in the stomatal conductance determination. • The Penman-Monteith equation applied to the canopy layer and combined with a radiative transfer model provides reliable estimates of canopy conductance. • Canopy temperature of a pinus pinaster stand is strongly coupled with the atmosphere. • The use of an infrared camera improve stomatal conductance estimation. • Isothermal assumption leads to bias in the canopy stomatal conductance determination. • At our site, Penman-Monteith inversion with eddy covariance inputs is not reliable. • The divergence between studied methods is higher when the water stress is low. Precise determination of canopy conductance ( g s ) is needed to quantify the water loss and CO 2 exchange from forest canopies and their response to changing environmental conditions. In this study, we combined measurements of the leaf-to-air vapour pressure difference ( D L ) derived from canopy surface temperature, and tree transpiration to calculate canopy g s in a pine forest at the ICOS site FR-Bil. The period covered was characterized by two consecutive droughts. The inversion of the generalised water transport equation (GT), along with its isothermal simplification (GT’), were used to calculate canopy g s and compared with g s determined from the inversion of the Penman-Monteith equation (PMT). A thermal infrared camera continuously monitored the canopy temperature and allowed to assess the time course of D L with half-hourly resolution. On average a 0.3 °C temperature difference was found between the canopy and surrounding air, with values ranging from − 2 °C to +5 °C depending on the time of day, soil moisture and humidity. The three methods used to calculate g s , GT, GT’ and PMT were in agreement under wet soil and low atmospheric demand, but differences up to 40% were found under water stress conditions when the canopy to air temperature differences led to substantial discrepancies between D L and air saturation vapour pressure deficit at 8.2 m in the crown ( D 8 ). Under such conditions the GT’ method overestimated g s whereas the PMT method was closer from values estimated with the GT method. The contrasted behaviour of the atmospheric exchanges between the tree canopy and the overall ecosystem limits the use of the above canopy flux measurements alone to quantify the response of surface conductance to environmental drivers. Our results also advocate the use of in situ surface temperature measurements to better understand the response of plant canopies to environmental conditions.

Bloodmeal regulation in mosquitoes curtails dehydration-induced mortality, altering vectorial capacity

Mosquitoes readily lose water when exposed to any humidity less than that of near saturated air unless mitigated, leading to shifts in behavior, survival, distribution, and reproduction. In this study, we conducted a series of physiological experiments on two prominent species in the Culicinae subfamily: Culex pipiens, a vector of West Nile virus, and Aedes aegypti, a vector of yellow fever and Zika to examine the effects of dehydration. We exposed C. pipiens and A. aegypti to non-dehydrating conditions (saturated air), dehydrating conditions (air at a 0.89 kPa saturation vapor pressure deficit), several recovery conditions, as well as to bloodfeeding opportunities. We show that dehydrated mosquitoes increase bloodfeeding propensity, improve retention, and decrease excretion of a post-dehydration bloodmeal. In addition, mosquitoes that take a bloodmeal prior to dehydration exposure show increased survival over non-bloodfed counterparts. Dehydration-induced alterations in survival, reproduction, and bloodfeeding propensity of C. pipiens and A. aegypti resulted in marked changes to vectorial capacity. Ultimately, these results become increasingly important as drought intensifies in association with climate change and mosquitoes become more likely to experience arid periods.

Asymmetric response of short- and long-duration dry spells to warming during the warm-rain season over Eastern monsoon China

Changes in dry spell duration have been analyzed over China and worldwide. However, the asymmetric response (i.e. skewed distribution) of short- and long-duration dry spells to warming temperature and possible mechanisms remain unknown. Here, we investigate this response based on daily weather observations during the warm-rain season (May-September) over 1961–2019 from 1540 quality-controlled stations across Eastern Monsoon China (EMC). Our results show a 1℃ warming in surface air temperature (SAT) and a considerable elongation of dry spells. Specifically, the regional average, maximum, and total dry spell duration over EMC increased by +7.06%, +6.17%, and +5.16%, respectively over 1961–2019. The areas in EMC with long dry spells and high SAT are also the areas that have experienced faster increases in the duration of dry spells per degree of warming. We find increases in the frequency of long-duration dry spells, but significant decreases in the frequency of short-duration dry spells. The increasing frequency of long-duration dry-spells can be explained by the slight increase in land evaporation (+1.6%/℃) over EMC and the decrease in integrated moisture vapor transport (-3.8%/℃) with warming, such that atmospheric moisture sources cannot meet the warming-induced demand, resulting in significant decreases in relative humidity (−2.4%/℃) and precipitation (−7.0%/℃). In contrast, the decreasing frequency of short-duration dry spells during hotter warm-rain seasons occurs when the saturation vapor pressure deficit is enhanced, leading to prolonged periods where the atmosphere is replenished to necessary saturation levels for local precipitation. Relative to cold warm-rain seasons, hot warm-rain seasons with higher SAT witness cold-dry air advection in the upper level, lower convective available potential energy, and stronger vapor divergence over EMC, which tends to suppress precipitation occurrence. With future warming, the increasing frequency and duration of dry spells in the warm-rain season is likely to be conducive to the occurrence of severe droughts and heatwaves in EMC, with negative impacts on socio-economic development in China.

Seasonal variation and controlling factors of evapotranspiration over dry semi-humid cropland in Guanzhong Plain, China

The Guanzhong Plain is a critical food production area in the Yellow River Basin that frequently suffers from water shortages. In this study, long-term (June 2013 to June 2018) water and energy fluxes were observed, and path analysis was conducted over an irrigated winter wheat (Triticum aestivum L.) / summer maize (Zea mays L.) rotation field to identify the controlling factors of evapotranspiration (ET). Total ET for each crop year ranged from 627 to 775 mm, with an average growing season ET of 398 mm for wheat and 310 mm for maize. There is significant seasonal variation in both ET and surface conductance (Gs). Daily ET varied from 0.0 to 6.0 mm d–1 for wheat and 0.0 to 6.7 mm d–1 for maize. The peak daily values of Gs were 29.5 mm s–1 for wheat and 19.5 mm s–1 for maize. The direct and indirect effects of environmental and biological factors—net radiation (Rn), surface conductance (Gs), saturation vapor pressure deficit (VPD), leaf area index (LAI), air temperature (Tair), and volumetric soil water content (VWC)—on ET were calculated using the path analysis method. Rn was determined to be the primary controlling factor of ET for both the summer maize and winter wheat growing seasons. Also, Gs was found to be another controlling factor that has more controlling power in the summer maize growing season than in the winter wheat season. VPD had a significant positive and direct effect on ET for both of the crop seasons, while it had a significant negative and indirect effect on ET through Gs in the summer maize season. VWC and Tair only directly affected the wheat ET. In addition, VWC had two significant paths that can indirectly affect ET through LAI and Gs. The revealed seasonal patterns and controlling factors of evapotranspiration in this agroecosystem provide a theoretical basis for optimizing water resources management of the Yellow River.

Variation of stem radius of Larix principis-rupprechtii and its influencing factors in the semi-humid Liupan Mountains, China

We measured stem radius of Larix principis-rupprechtii at the semi-humid Liupan Mountains using the automatic band dendrometer over the growing season in 2016. We examined the diurnal and seasonal variations of stem radius, determined the main stem growth period, and analyzed the response of stem radius to environmental factors during the main stem growth period. The aim was to accurately understand the effects of short-term environmental variation on tree growth. The results showed that stem radius had a clear diurnal variation, with the phases of daytime shrin-kage, nighttime recovery, and increment. The seasonal variation of stem radius could be divided into three distinct stages, including stem relatively stable, stem continuous increasing, and stem swell-shrinking fluctuation. Under the meteorological, soil moisture and topographic conditions of 2016, main stem growth period of L. principis-rupprechtii started from 14th May and ended on the 31th July, with the maximum radius growth rate occurred on 8th June. The environmental factors influencing the daily radius shrinkage at different phases (shrinkage phase, daily, cycle) were gene-rally the same, including temperature (including the air and soil temperature), solar radiation intensity, saturation vapor pressure deficit and soil water content. Temperature had the highest contribution (50.3%-71.0%). However, the influencing factors of daily radius increment varied at different phases. Precipitation (with a contribution of 86.9%) and maximum air temperature (13.1%) were the influencing factors at the radius increment phase. Precipitation (50.3%), saturation vapor pressure deficit (29.9%), relative humidity (12.7%) and solar radiation intensity (7.1%) were the factors at stem cycle. Precipitation and solar radiation intensity were the factors at diurnal scale. Radius increment was more sensitive to environmental variation at the time of stem cycle than that at diurnal scale.

Assessment of bio-inspired metaheuristic optimisation algorithms for estimating soil temperature

Root zone temperature is one of the most important soil characteristics, controlling many of the physical, chemical and biological processes in the soil. Temperature varies by soil depth, and exerts a profound impact on plant germination and growth. In this study, the accuracy of two artificial intelligence models including support vector regression (SVR) and elman neural network (ENN) and their hybrids with firefly algorithm (SVR-FA and ENN-FA) and krill herd algorithm (SVR-KHA and ENN-KHA) was assessed in estimating soil temperature (Ts) at 5, 10, 20, 30, 50 and 100 cm depths at Maragheh meteorological station in north-western Iran. The results of the models were evaluated under 5 scenarios with various inputs including the main meteorological parameters measured at the station (air temperature, sunshine hours, relative humidity, wind speed and saturation vapour pressure deficit). Daily Ts data recorded from January 1, 2006 to December 30, 2012 and from January 1, 2013 to December 30, 2015 were used for model training and testing, respectively. The results showed that error rates have decreased from 5 to 10 cm soil depth (root mean square error (RMSE) reduced by 2.97, 4.68 and 3.19% for the best scenarios of SVR, SVR-FA and SVR-KHA models, respectively), whereas error rates have been increasing from 10 to 100 cm soil depths (RMSE increased by 62.4, 80.9 and 73.6% for the best scenarios of SVR, SVR-FA and SVR-KHA models, respectively). For the best scenarios of ENN, ENN-FA and ENN-KHA models, RMSE values decreased by 2.1, 1.6 and 3.1% from 5 to 10 cm depth and increased by 61.1, 84.1 and 81.1% from 10 to 100 cm depth, so that all six models reached their best performance at 10 cm soil depth. Examination of the results in terms of under-estimation or over-estimation of Ts indicated that the lowest and highest differences in performance between under- and over-estimation sets were 0.01 °C (SVR-FA at 5 cm depth) and 1.64 °C (SVR at 100 cm depth) for SVR-based models and 0 °C (ENN at 10 cm depth) and 0.56 °C (ENN at 100 cm depth) for ELM-based models, respectively. According to the results from the best scenarios of SVR, SVR-FA and SVR-KHA models in the under-estimation set at 100 cm depth, all the three models have exhibited a poorer performance over the temperature range 15–25 °C (RMSE increased by 56.7, 47 and 61.3% for SVR, SVR-FA and SVR-KHA, respectively) compared to temperature values outside that range. Exactly the same trend was also observed for ELM-based models, where the mentioned increases in RMSE were about 37.7, 59.4 and 55.5% for ELM, ELM-FA and ELM-KHA, respectively. According to the results, bio-inspired metaheuristic optimisation algorithms based on SVR and ENN which use appropriate meteorological parameters as inputs can have a relatively satisfactory performance in estimating Ts under climatic conditions similar to our study area, especially in lower depths, and can be used as an alternative to direct measurement of this important parameter.

Climate-induced historical drift of reference evapotranspiration in Mymensingh region of Bangladesh

Reference crop evapotranspiration (ETo) is essential for planning and management of irrigation to ensure optimum utilization of a region’s available water resources. ETo being an indicator of atmospheric evaporative demand provides a measure of the integrated effect of climatic parameters like solar radiation, wind, temperature and humidity. Variation of these climatic parameters over long period of time alters ETo. The modified ETo is crucial for periodic adjustment of irrigation planning and management. This study evaluated variation of ETo and contribution of the climatic parameters to ETo-variation in Mymensingh region of Bangladesh by analyzing climatic data of 28 years (1990–2017). ETo was determined by FAO Penman-Monteith method and trends of ETo and its governing climatic parameters were evaluated by MAKESENS trend model. The ETo-governing climatic parameters revealed contrasting trends, which also varied in different months of the year. Net radiation and wind speed showed decreasing trend, while temperature and saturation vapor pressure deficit showed increasing trend. In spite of contrasting contributions of the climatic parameters, their combined effect reduced ETo with a resulting decreasing trend of the monthly average daily ETo over the months of the year except July. These results enhance our understanding of the effects of climate change on ETo and can help correct-planning of water resources for irrigated agriculture.&#x0D; J. Bangladesh Agril. Univ. 17(2): 258–264, June 2019

Estimation of wind drift and evaporation losses in sprinkler irrigation of urban green spaces

The wind drift and evaporation losses (WDEL) are high in arid, semi-arid and windward areas, and reduce the efficiency of the sprinkler irrigation system; therefore, this study was carried out in order to achieve a practical criterion and provide a relationship for accurate estimation of the wind drift and evaporation losses in different atmospheric conditions. The experiments were done at the Meteorological Station of the Faculty of Agriculture of Ferdowsi University of Mashhad using a line-source sprinkler irrigation system based on the single sprinkler installation method. To achieve the objectives of this plan, factorial experiment was performed on PGP sprinkler with regard to the two factors, the pressure of the sprinkler function (with three levels 1.6, 2.5 and 3.4 bar) and the diameter of the nozzle (with three levels of 4, 5 and 6 mm) with three replications (morning, noon and night). Assessing the result of the data variance analysis showed that the effects of pressure, aperture diameter, and time on the wind drift and evaporation losses are not significant. Investigating the main effects of these factors showed that the effect of aperture diameter on irrigation losses is significant at the level of the 1%. In order to further investigate, the comparison of mean losses data in three aperture diameter was done using Duncan′s test. The results indicated that aperture 4 with the losses of 44% had a significant difference with other diameters. This result suggests an increase in losses for smaller diameters due to the small droplets and the increase in wind drift. Also, the comparison of the mean losses data in three times showed that irrigation at noon with the losses of 44% had a significant difference compared to other times due to a significant increase in temperature and radiation of the sun and saturation vapor pressure deficit, and there is no significant difference between morning and evening irrigation. Also, analysis of variance showed that the effect of water pressure change between 1.6 and 4.3 bar does not have a significant effect on the WDEL in this sprinkler. In general, the results showed that increasing wind speed increases the losses of evaporation and wind. Also, this study suggested that changing the irrigation time in areas with hot and dry days, from day to night in summer, leads to a significant reduction of the wind drift and evaporation losses.

Reference evapotranspiration changes in Slovenia, Europe

Evapotranspiration is an important element of the water cycle and possible trends in the evapotranspiration can, among others, influence on the water management and agricultural production. Since actual evapotranspiration values are rare and difficult to estimate, reference evapotranspiration was examined in order to document changes in the climatic conditions that affect evapotranspiration. The daily reference evapotranspiration data calculated using the Penman-Monteith method from 18 meteorological stations located in three different climate types in Slovenia was examined in this study. 55 years of data from 1961 until 2016 was analysed. The Mann-Kendall test was applied in order to detect trends in different samples that were defined based on the daily reference evapotranspiration data. Relationship between the evapotranspiration and influencing factors was also investigated using the generalized boosted regression trees model. The calculated trends for different samples are mostly increasing and statistically significant while no consistent trend could be detected for all 18 stations. The maximum increase in the daily reference evapotranspiration for the observed period was 0.5 mm and the maximum decrease −0.4 mm. Moreover, upward trend was detected for two mountain stations and downward for one sub-Mediterranean station. No uniform trend could be found for the stations located in the temperate continental climate. Furthermore, generalized boosted regression trees model indicated that solar radiation has the largest impact on the reference evapotranspiration values, generally followed by air temperature, saturation vapour pressure deficit and wind speed.

Canopy transpiration of Larix principis-rupprechtii plantation and its impact factors in diffe-rent slope locations at the south side of Liupan Mountains, China.

Based on a continuous field observation in the Larix principis-rupprechtii plantation plots, located at the upper (P1), middle-upper (P2), middle (P3), middle-lower (P4), and lower (P5) positions, in a southeast-facing slope of the Xiangshuihe watershed of Liupan Mountains, China, the stem sap flow was observed with the thermal diffusivity probe method. The soil water potential and meteorological factors were monitored from May to October, 2014. We found significant differences among slope positions in the daily forest transpiration (Tr, mm·d-1), with an order of P2 (0.975)＞P4 (0.876)＞P3 (0.726)＞P1 (0.653)＞P5 (0.628). Tr was significantly positively correlated with the daily maximum temperature (Tmax), daily mean solar radiation (SR), daily mean saturated vapor pressure deficit (VPD), potential evapotranspiration (PET), and daily mean soil water potential (Ψ), but negatively correlated with the daily mean air relative humidity (RH), daily precipitation (P), and daily minimum temperature (Tmin). According to the upper boundary line ana-lysis, significant differences were found in the degree of Tr responding to each single environmental factor among slope positions. The degree of its responses gradually decreased for average daily air temperature (T), RH, VPD, PET and Ψ, whereas increased for the SR and daily average volumetric soil water content (VSM) from the upper position to the lower. Results from regression and partial correlation analysis showed that variation of Tr was mainly controlled by VPD, PET and RH in different slope positions. Tr was also strongly affected by Ψ and T in the upper-slope positions and by SR, Tmin and VSM at the lower-slope positions. Generally, the Tr difference among slope positions was a consequence of joint contributions of soil water and meteorological factors. It is necessary to consider the changes of soil water and meteorological factors in different positions along the slope when examining slope-scale or watershed-scale forest transpiration with sap flow estimated from xylem sap flux density measurements of a particular plot.

Coupling a firefly algorithm with support vector regression to predict evaporation in northern Iran

ABSTRACTEvaporation accounts for varying shares of water balance under different climatic conditions, and its correct prediction poses a significant challenge before water resources management in watersheds. Given the complex and nonlinear behavior of the evaporation component, and according to the fact that this parameter is not measured at many meteorological stations, at least during some timeframes, and that the meteorological stations measuring this component are not properly distributed in many developing countries, including Iran, the main objective of this work was to predict the evaporation component at two meteorological stations (Rasht and Lahijan) located in Gilan province in northern Iran over the 2006–2016 time period. To that end, those meteorological parameters recorded at the two stations which had the highest impact on evaporation prediction were identified using Pearson correlation coefficient. Selected parameters were then used, under separate scenarios, as inputs to support vector regression (SVR) and SVR model coupled with firefly algorithm (SVR-FA) in order to simulate evaporation values on a daily scale. Evaporation amounts showed the highest correlation with net solar radiation and saturation vapor pressure deficit at Lahijan and Rasht stations, respectively. Root mean square error values of evaporation prediction at testing phase of SVR and SVR-FA ranged from 1.05 to 1.43 and 1.02 to 1.31 mm, respectively, at Lahijan station and from 1.02 to 1.28 and 0.88 to 1.17 mm, respectively, at Rasht station for various scenarios. For underpredicted evaporation data set, the magnitude of RMSE reduction from SVR1 to SVR7 was 27% at Lahijan and 18% at Rasht station; whereas RMSE decrement from SVR-FA1 to SVR-FA7 was 18 and 26 percent at Lahijan and Rasht stations, respectively. This means that for the underpredicted data set, the role of increasing the number of SVR and SVR-FA input parameters in decreasing evaporation prediction error has been more conspicuous at Lahijan and Rasht stations, respectively. Analysis of SVR and SVR-FA performance at various 2-mm intervals of measured evaporation showed that prediction error has generally been increasing with increment of evaporation values, with the highest errors observed at the 8-10 mm interval for both Lahijan and Rasht stations (error rates of 3.42 and 2.42 mm/day at Lahijan and 6.13 and 5.84 mm/day at Rasht station, with SVR1 and SVR-FA1 models, respectively).

The effect of different meteorological parameters on the temporal variations of reference evapotranspiration

Temporal changes of meteorological variables can affect reference evapotranspiration (ET0). The goal of the present research is to analyze the changes of ET0 and identify the impact of effective meteorological parameters to the changes of ET0. For this purpose, daily meteorological data recorded in 30 synoptic stations of Iran during 1960–2014 were used. The annual and seasonal values of ET0 were calculated by the recorded data. To calculate ET0, FAO56 Penman–Monteith method (standard method) was used. The annual and seasonal trends of ET0 and its eight effective parameters were analyzed. Then the contributions of effective parameters changes on ET0 were determined. To analyze ET0 trend at annual and seasonal scales, two common methods, Spearman’s Rho and Mann–Kendall tests, were used. The R 2 = 0.99 showed that the results of the mentioned methods were similar and on the basis of T-statistic <0.057, their difference was not significant (95% confidence level). Therefore, only one method’s results (Spearman’s Rho) were reported. On the basis of Spearman’s Rho results, the annual and seasonal values of ET0 had negative trend in most of arid and semi-arid stations while the trend of this parameter was positive in humid and very humid stations. At annual and seasonal scales, decreasing in wind speed (W), temperature (T), sunshine hours (n), minimum temperature (TN), dew point temperature (TD), maximum temperature (TX), saturation vapor pressure deficit (SVPD) and solar radiation (RS) was observed in 58, 54, 39, 43, 56, 65, 65 and 37% studied stations, respectively. In many scales, the results showed that TX and W were the most effective meteorological variables on ET0 changes and then SVPD was located in second step in arid and semi-arid stations. In humid and very humid stations, W was the first effective parameter at all scales, except autumn.