极端干旱区葡萄园蒸散量的日间变化研究

利用波文比能量平衡法对新疆吐哈盆地葡萄园葡萄蒸散量进行了测定.结果表明,在晴朗无云的条件下,葡萄蒸散速率日变化呈单峰型.蒸散从8:00时以后出现,迅速增加,到13:00-14:00时达到峰值,随后蒸散速率迅速下降.净辐射对植物蒸散起决定作用,蒸散速率的变化趋势与净辐射变化基本一致,其日变化具有相同的峰型.在干旱区,热量垂直传输的昼夜变幅较大,净辐射的大部分能量用于土壤蒸发和植物蒸腾,因而日间蒸散速率的变化趋势与净辐射变化基本一致.葡萄蒸散量随风速的增加而增加,当风速超过4m/s时,由于风速的变化引起水汽压差的变化紊乱而导致蒸散速率变化过程比较复杂.相关分析表明,环境因子对蒸散速率影响的贡献依次为:净辐射>风速>空气温湿度.     

半湿润地区葡萄园水热通量特征及其对环境因子的响应

研究稀疏植被下垫面水热通量特征对于提高农业水管理和高效利用农业气候资源极为重要,利用2018年葡萄园波文比系统数据和气象资料,分析了半湿润地区葡萄园下垫面水热通量在不同生育阶段和典型天气条件下的分配特征及潜热通量对相关气象因素的响应,并运用BP神经网络对葡萄园潜热通量进行预测,根据预测模型,分析比较潜热通量对环境因子变化的敏感性。结果表明,水热通量的日变化呈单峰二次曲线,从7∶00左右开始增长,12∶30左右达到峰值后开始减小,夜间基本不变。感热通量在全部生育期都占了地表能量的绝大部分,潜热通量较小,所占比例随生育期时间逐渐增大,在果实膨大期达到最大后开始减小。在雨天,水热通量各分量都比晴天小,潜热通量略大于感热通量。而阴天潜热通量的变化幅度明显比其他天气条件下都大。BP神经网络根据气象因子模拟出的潜热通量与波文比法的计算值相关性较高,同时,潜热通量对净辐射和土壤热通量的变化最为敏感,而对风速变化的敏感性较低。     

西北干旱地区葡萄园作物耗水规律研究

通过大田试验,分析土壤蒸发、作物蒸腾和总耗水的变化。结果表明,葡萄园土壤蒸发、作物蒸腾和总耗水平均日变化均呈"钟型"曲线;全生育期葡萄园耗水420 mm,其中土壤蒸发量193 mm,占46%,作物蒸腾量227mm,占54%;日均总耗水、土壤蒸发和作物蒸腾分别为2.32、1.08、1.24mm/d。微型蒸渗仪结合茎流计测定的耗水与涡度相关仪测定的在小时和日尺度上均比较接近,差异不足10%;灌溉和降雨使土壤蒸发加剧,作物蒸腾对灌溉的响应滞后于土壤蒸发,而对降雨无明显响应。     

基于大型蒸渗仪的1年2作滴灌小麦-玉米耗水特征

利用大型称质量式蒸渗仪,分析了滴灌条件下小麦-复玉米蒸散耗水过程。结果表明,中等灌水条件下,滴灌小麦-玉米蒸散耗水总量为777.93mm,其中小麦耗水占45.8%,玉米耗水占54.2%,小麦拔节期和抽穗期耗水量为188.03mm,占1年2作耗水总量的24.2%,玉米拔节期和抽雄期耗水量为235.42mm,占1年2作耗水总量的30.26%;1年2作滴灌小麦-玉米全生育期平均耗水强度为4.25mm/d,其中小麦、复播玉米平均耗水强度分别为3.93、4.57mm/d。不同天气状况下玉米蒸散耗水强度的差异大于小麦,玉米蒸散日变化具有明显"午休"现象。滴灌小麦-玉米受各气象因子的影响不同,春小麦和夏玉米蒸散强度与各气象因子的相关性分别表现为净辐射相对湿度30cm土壤水分总辐射光合辐射日平均气温风速和相对湿度光合辐射净辐射30cm土壤水分总辐射风速日平均气温。     

南方节水灌溉稻田能量通量特征及其规律分析

利用涡度相关系统在江苏省昆山市试验研究基地2013年水稻生育期所测的净辐射量、土壤热通量、潜热通量和显热通量等观测资料,分析了能量各通量在典型晴天、阴天的日变化规律和稻季能量通量的日变化、月变化及分配特征,讨论了能量各组分占净辐射量的比例和不同时间尺度上稻田的能量闭合情况。结果表明:能量平衡各分量在亚热带南部季风区节水灌溉稻田典型晴天以及水稻生育期间月均日变化均呈明显的倒"U"型单峰趋势,典型阴天能量平衡各分量日均值和峰值均小于晴天,但也呈单峰型变化趋势。稻季潜热通量占净辐射量的86.2%,土壤热通量占净辐射量的1.3%,不同时间尺度上净辐射量均主要以潜热形式加湿大气,感热通量占净辐射量的0.8%,与潜热通量差异显著,且占净辐射量的比例呈此消彼长的关系。在能量通量的测量过程中,与净辐射量相比,感热、潜热通量滞后于净辐射量约0.5 h,土壤热通量滞后1.5~2.5 h。热传输速度不同步,从而影响了能量的短期闭合率。但与其他生态系统相比,该节水灌溉稻田生态系统能量闭合度较高,说明该试验区涡度数据可靠,通量特征及规律具有较好的代表性,有利于通量研究的进一步开展。     

基于涡度系统的干旱区枣林能量平衡分析

【目的】揭示干旱区枣林的能量循环与能量变化规律。【方法】利用涡度相关法得到干旱区枣林连续2 a的通量数据,分析了能量变化规律、分配方式以及热存储项能量的日平均变化规律。【结果】(1)干旱区枣林生态系统的净辐射Rn、潜热通量LE、显热通量H、土壤热通量G在各月份的日均值变化均呈以净辐射变化规律为基础的单峰变化。(2)干旱区枣林2018年和2019年的整年度30 min尺度能量闭合率为73.45%、73.11%,计入热储存项后,能量闭合率分别提高了3.72%、2.75%,达到了77.17%、75.86%。(3)干旱区枣林的土壤热储存项日均值在生育期和休眠期变化规律相似;潜热热储存项和显热热储存项在生育期和休眠期变化规律不同;光合热储存项和冠层热储存项在休眠期均为0,但在生育期有典型的日变化。【结论】热存储项对干旱区枣林生态系统的能量平衡闭合程度贡献不大,干旱区枣林的能量分配方案受水分条件、植被类型和气候特征的影响。     

基于Priestley-Taylor模型的低丘红壤区水热通量变化及影响因素

Priestley-Taylor参考作物蒸散模型系数的本地化是提高区域蒸散模拟精度的关键。以江西省低丘红壤区农田为研究对象,基于大孔径闪烁仪的观测数据,利用通径分析方法对农田不同时间尺度水热通量特征进行了定量研究。同时,采用Priestley-Taylor模型模拟了红壤区作物蒸散,与实测蒸散进行了比较,并对该模型的系数进行了修正,评价了P-T_(1.26)及P-T_(1.07)模型在本地模拟蒸散的适用性。结果表明,逐日尺度下农田水热通量变化曲线呈单峰形且受天气条件影响明显,逐月尺度下净辐射通量、潜热通量及土壤热通量呈减小的变化趋势;净辐射通量、空气温度及水汽压亏缺是影响潜热通量的主导因子,均对潜热交换有促进作用;P-T_(1.26)模拟的蒸散比实测偏高13.77%,P-T_(1.07)模拟的蒸散比实测偏低3.39%,参数修正后的P-T_(1.07)模型模拟精度明显提高,α=1.07可以作为研究区Priestley-Taylor模型的本地化适宜参数。     

低丘红壤区旱田水热通量特征及其气象影响因素

为研究低丘红壤区近地层农田水热通量特征,更好地利用农业气候资源、理解农业水文生态系统过程,利用2013年和2014年田间波文比系统数据和气象资料,分析了红壤区近地层的水热通量分配特征及相关气象因素的影响。结果表明:1能量平衡各个分量的日变化呈单峰趋势且受到天气条件影响很大,其中潜热通量所占份额最大,感热和土壤热通量均较小。2能量平衡各分量的分配具有季节性变化,7月份净辐射和潜热通量较大,土壤热通量在5月、7月为正值,10月、12月为负,表明研究区土壤在秋冬季节向外输出热量;在花生的生长季,花生地的波文比小于橘园,表明花生地的潜热交换多于橘园。3对旱地潜热和感热影响较大的气象因素有净辐射、相对湿度,其次有气温,而风速和水汽压对潜热、感热交换的影响并不显著。雨季降水量与农田潜热、感热总体呈负相关,旱季降水量影响相对较小。     

冬小麦生育中期农田水分与二氧化碳通量研究

以大兴实验站冬小麦为研究对象,采用涡度相关技术监测农田显热、潜热和二氧化碳通量,依据实测数据分析了冬小麦碳、热通量的变化特征,并研究各分量在抽穗期的关系和农田群体水分利用效率的变化规律。结果表明,①CO2通量的日变化成单谷型下凹曲线,极值出现在12:00左右,潜热和显热通量则呈单峰型上凸变化;②抽穗期,CO2通量与净辐射和潜热通量都呈现出极显著相关关系,而与显热通量在晴天成极显著相关关系;③作物农田水分利用效率在08:00—11:30较高,范围在0.02~0.04 g(CO2)/g(H2O)。     

秦岭华北落叶松人工林耗水规律与环境因子关系研究

以不同林龄(幼龄、中龄、老龄)华北落叶松为研究对象,依托国家级森林生态系统定位观测站,连续5年采用热扩散式茎流计法(树木蒸腾)和称重法(土壤蒸发)对华北落叶松土壤蒸发与植被蒸散耗水及其环境因子进行定量监测,定量分析蒸腾、蒸发等各蒸散的强度与环境因子的关系。结果表明:2012-2017年不同林龄土壤蒸发量和蒸腾耗水量均呈"几"字形变化规律,在7-8月达到最大,4-6月呈急剧增加趋势,9月以后有所降低;当土壤含水量18%,地被植物并不抑制土壤水分的蒸发;当土壤含水量18%,地被植物抑制了土壤水分的蒸发;土壤蒸发量与土壤温度和土壤含水量均呈显著的正相关。相关性分析表明林木蒸腾强度与土壤含水量、太阳辐射强度、土壤温度呈正相关,即华北落叶松林木蒸腾强度随各环境因子变量值的增加而增加;然而,林木蒸腾强度与自身属性(冠幅、胸径、株高)呈负相关关系,即随着林木的生长,其蒸腾作用受到了一定的抑制。综合分析表明:影响华北落叶松耗水最直接的因素是土壤水分含量,当土壤含水量较小时,华北落叶松首先满足自身对于土壤水分的需求。     

Estimation of actual evapotranspiration in winegrape vineyards located on hillside terrain using surface renewal analysis

Sensible and latent heat flux densities were estimated in a level vineyard, a northeast aspect vineyard and a southwest aspect vineyard in the Napa Valley of California using the eddy covariance and surface renewal methods. Surface renewal is theoretically not limited to level or extensively homogeneous terrain because it examines a more localized process of scalar exchange as compared with eddy covariance. Surface renewal estimates must be calibrated against eddy covariance data to account for unequal heating of the air parcels under a fixed measurement height. We calibrated surface renewal data against eddy covariance data in a level vineyard, and the calibration factor (α) was applied to the surface renewal measurements on the hillside vineyards. Latent heat flux density was estimated from the residual of the energy balance. In the level vineyard, the average daily actual evapotranspiration (ET _a ) for the period of June through September was 2.4?mm per day. In the northeast aspect vineyard, the average daily ET _a was 2.2?mm per day, while in the southwest aspect vineyard it was 2.7?mm per day. The net radiation values for the level vineyard, the northeast aspect vineyard, and the southwest aspect vineyard were compared against the Ecosystem Water Program with good agreement.     

基于SEBAL模型和Landsat-8遥感数据的农田蒸散发估算

【目的】及时准确地获取农田蒸散发量,为科学管理农田灌溉、精准估算作物产量和预报土壤水分动态、合理开发水资源等提供有效依据。【方法】以广利灌区为研究对象,基于SEBAL模型利用Landsat-8数据对研究区域农田蒸散发进行估算,通过地表参数计算净辐射通量、土壤热通量和感热通量,利用余项法求得潜热通量及瞬时蒸散发。假定24 h内蒸散比不变,由瞬时蒸散发扩展到日蒸散发量,最终求得研究区的日平均蒸散发量,将模型计算结果与彭曼公式进行了对比,同时结合灌区提供数据对计算结果进行了验证。【结果】彭曼公式计算2014年5月6日和2015年9月14日蒸散量与实测结果相差分别为5.2%和9.4%,SEBAL模型估算得到2014年5月6日和2015年9月14日的日蒸散量与灌区提供日蒸散量相差4.5%、6.0%,且冬小麦及夏玉米蒸散发在空间上存在一定的差异性,主要集中在灌区中部区域及西南区域。【结论】SEBAL模型计算结果具有较高的精度,而且方法相对快捷高效。     

基于SEBAL模型的小麦水分生产率研究

基于能量平衡原理,运用SEBAL模型和Landsat8影像反演估算了山西省晋中市的小麦水分生产率。首先根据Landsat8卫星影像,反演了晋中地区净辐射通量、土壤热通量和感热通量,使用能量平衡方程计算了水分蒸散;然后基于晋中小麦的产量统计数据,对晋中小麦的产量进行插值并栅格化;最后利用水分生产率公式计算了研究区小麦水分生产率。结果表明,研究区内的太谷、榆社、介休3站点反演的日蒸散量分别为2.93、3.82、3.17 mm/d,范围为0.41~7.22 mm/d,与根据Penman-Monteith公式计算的结果 (2.57、3.48、3.43 mm/d)大致相等,误差范围在10%左右;研究区小麦水分生产率均值为0.94 kg/m3,最高达到2.50 kg/m3,处于合理范围内,可以对晋中地区提高水分利用效率提供有效参考。     

芦苇群落日蒸发蒸腾量变化规律及

了解芦苇湿地蒸发蒸腾量变化规律和影响因子并准确估算蒸发蒸腾量，对湿地水资源评估有十分重要的意义。根据2005年盘锦芦苇湿地监测站的小气候梯度系统和涡动相关系统的监测数据，结合芦苇生理生态特性的观测，分析芦苇群落的蒸发蒸腾量日变化规律及其主导影响因子，采用波文比—能量平衡法、梯度法对芦苇群落的日蒸发蒸腾过程进行模拟，并与涡动相关系统的实测数据进行比较。结果表明，芦苇群落蒸发蒸腾量日变化过程表现为早晚低、中午高的单峰曲线；从相关分析结果看，气象因素和芦苇生理生态特性对芦苇蒸发蒸腾的影响显著，其中辐射强度、相对湿度、温度、叶片光合速率和叶片气孔导度是芦苇群落蒸发蒸腾的主导影响因子；从计算蒸发蒸腾量的两种方法与涡动数据的比较结果看，梯度法更适合芦苇群落蒸发蒸腾量的模拟，可为芦苇湿地蒸发蒸腾的计算提供依据。     

Calibration and validation of a remote sensing algorithm to estimate energy balance components and daily actual evapotranspiration over a drip-irrigated Merlot vineyard

A study was carried out to calibrate and validate a remote sensing algorithm (RSA) for estimating instantaneous surface energy balance components and daily actual evapotranspiration (ETa) over a drip-irrigated Merlot vineyard located in the Maule Region of Chile (35° 25′ LS; 71° 32′ LW; 125?m.a.s.l.). ETa was estimated as a function of instantaneous evaporative fraction and average daily net radiation (Rn_day) using meteorological variables in combination with reflectance data measured by a hand-held multi-spectral radiometer. The sub-models used to estimate the instantaneous net radiation (Rn_ins), soil heat flux (G _ins), and Rn_day were calibrated and validated using measurements of the surface energy balance components, incoming longwave radiation $(L \downarrow_{\text{ins}})$ , outgoing longwave radiation $(L \uparrow_{\text{ins}})$ , and surface albedo (α). The validations of instantaneous sensible heat flux (H _ins), latent heat flux (LE_ins), and ETa were carried out using turbulent energy fluxes obtained from an eddy correlation (EC) system. For reducing the moderate EC imbalance (about 11?%), turbulent energy fluxes were recalculated using the Bowen ratio method. The validation analysis indicated that the calibrated sub-models of the RSA were able to estimate Rn_ins, G _ins, H _ins, and LE_ins with a root-mean-square error (RMSE), mean absolute error (MAE), and index of agreement (IA) ranging between 16–54, 13–44?W?m^?2, and 0.72–94, respectively. Also, the RSA was able to estimate ETa with RMSE?=?0.38?mm?day^?1, MAE?=?0.32?mm?day^?1 and IA?=?0.96. These results demonstrate the potential use of reflectance and meteorological data to estimate ETa of a drip-irrigated Merlot vineyard.     

Accuracy of canopy temperature energy balance for determining daily evapotranspiration

The application of a single-layer canopy temperature energy balance (CTEB) model for determining integrated daily ET rates was tested, with possible applications towards determining irrigation requirements (“how much to irrigate”) as a complement to crop water stress index (CWSI) measurements (“when to irrigate”), an irrigation scheduling tool which uses much of the same data. Evapotranspiration (ET) rates estimated using the CTEB model were compared to Bowen ratio energy balance (BREB) measurements made over substantial portions of the growing seasons of corn and potato crops. Canopy temperature, net radiation and soil heat flux data were collected and analyzed at 20-minute intervals, and ET for each interval was summed to obtain daily and multi-day estimations. Only full canopy conditions were examined. Two methods for atmospheric stability correction were applied to the aerodynamic resistance required by the CTEB model; an iterative procedure proposed by Campbell, and a second procedure proposed by Monteith which uses an adjustment coefficient. To reduce instrumentation requirements for combined CTEB/CWSI data collection, estimates of ET were also determined using net radiation and soil heat flux values estimated from solar radiation measurements. Results showed that uncorrected CTEB ET estimates agreed reasonably well with BREB measurements over corn and potato canopies (RMSE = 0.5 to 0.7 mm day⁻ for observed average ET ranging from 4.8 to 5.5 mm day⁻, with a trend toward seasonal overprediction with corn. Stability corrections usually lowered the daily RMSE 0.1 to 0.2 mm day⁻, with seasonal ET more in agreement with BREB ET. The Monteith-based adjustment gave slightly better results. CTEB ET model with estimated net radiation and soil heat flux terms produced similar average and total ET, but somewhat larger daily errors (RMSE=0.5 to 0.9 mm day⁻). Seasonal total ET by the uncorrected CTEB model generally overestimated within 10% (ranging from 1% to 10%) of the observed BREB total ET, an acceptable error for most irrigation practices. Stability corrections generally caused seasonal ET to be underestimated within 1% to 9%.     

Evaluating the Crop Water Stress Index and its correlation with latent heat and CO2 fluxes over winter wheat and maize in the North China plain

Plant water status is a key factor impacting crop growth and agricultural water management. Crop water stress may alter canopy temperature, the energy balance, transpiration, photosynthesis, canopy water use efficiency, and crop yield. The objective of this study was to calculate the Crop Water Stress Index (CWSI) from canopy temperature and energy balance measurements and evaluate the utility of CWSI to quantify water stress by comparing CWSI to latent heat and carbon dioxide (CO₂) flux measurements over canopies of winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.). The experiment was conducted at the Yucheng Integrated Agricultural Experimental Station of the Chinese Academy of Sciences from 2003 to 2005. Latent heat and CO₂ fluxes (by eddy covariance), canopy and air temperature, relative humidity, net radiation, wind speed, and soil heat flux were averaged at half-hour intervals. Leaf area index and crop height were measured every 7 days. CWSI was calculated from measured canopy-air temperature differences using the Jackson method. Under high net radiation conditions (greater than 500 W m⁻²), calculated values of minimum canopy-air temperature differences were similar to previously published empirically determined non-water-stressed baselines. Valid measures of CWSI were only obtained when canopy closure minimized the influence of viewed soil on infrared canopy temperature measurements (leaf area index was greater than 2.5 m² m⁻²). Wheat and maize latent heat flux and canopy CO₂ flux generally decreased linearly with increases in CWSI when net radiation levels were greater than 300 W m⁻². The responses of latent heat flux and CO₂ flux to CWSI did not demonstrate a consistent relationship in wheat that would recommend it as a reliable water stress quantification tool. The responses of latent heat flux and CO₂ flux to CWSI were more consistent in maize, suggesting that CWSI could be useful in identifying and quantifying water stress conditions when net radiation was greater than 300 W m⁻². The results suggest that CWSI calculated by the Jackson method under varying solar radiation and wind speed conditions may be used for irrigation scheduling and agricultural water management of maize in irrigated agricultural regions, such as the North China Plain.     

冬小麦田间蒸发蒸腾与棵间蒸发规律研究

利用2010-2011年的大型称量式蒸渗仪和小型棵问蒸发器的实测资料,研究了冬小麦田间蒸散和棵闽蒸发变化规律。结果表明,冬小麦总蒸发蒸腾量为360．974mm,抽穗-灌浆期蒸发蒸腾量达到最大为84．706mm,日均蒸发蒸腾量在全生育期内呈双峰变化,2个峰值处于播种-分蘖、抽穗-灌浆期;冬小麦的棵间蒸发量达到了115．8...     

Evapotranspiration of flood-irrigated pecans

Pecan orchards require more irrigation water to maximize yield than any other crop grown in the Southwest US. This paper reports daily evapotranspiration (Et) measurements for 2001 and 2002 in a 5.1 ha, mature pecan orchard on the Rio Grande floodplain, 7 km south of Las Cruces, NM, USA. The 21-year-old stand had an average tree height of 12.8 m, diameter at breast height of 30 cm, and tree spacing of 9.7 m × 9.7 m. Additional pecan orchards surrounded the study orchard. When the tensiometer reached a suction of 65 kPa at the 45 cm depth, the orchard was flood-irrigated. Sparling meters were installed on the pumps and read before and after each irrigation. The total irrigation amount was 1940 mm in 2001 and 1870 mm in 2002. A walk-up tower was placed in the orchard’s center to support flux sensors at 16 m height. The instrument package included a net radiation (Rn), discs for soil heat flux (G), and two sets of one-propeller eddy covariance (OPEC) sensors. OPEC systems measure sensible heat flux (H) with a sensitive, vertically oriented propeller anemometer and a fine-wire thermocouple. Latent heat flux (LE) was obtained as a residual in the surface energy balance LE = Rn − G − H. The maximum daily evapotranspiration was 8 mm/day, and the yearly cumulative evapotranspiration averaged for 2 years was 1420 mm, resulting in a yearly average irrigation application efficiency of 79%. The crop coefficient (daily measured Et/reference Penman Et) ranged from 0.2 to 1.1. Increased evaporation due to irrigation was detected only for the April 9 irrigation in 2001. The seasonal water use was 4% lower in 2001 and 12% lower in 2002 than previously reported values.