Evaluation of Actual Evapotranspiration and Crop Coefficient in Carrot by Remote Sensing Methodology Using Drainage and River Water to Overcome Reduced Water Availability

Searching for alternative methods for traditional irrigation is World trend at days due to a reduction in water and increased of drought due to climate changes therefore farmers need use modern methods of scheduling water and minimizing water losses while also increasing yield. To meet the future increasing demands water and food there is a need to utilize alternative methods to reduce evaporation, transpiration and deep percolation of water. Any countries use recycled water (drain and sewage) and desalination water from the sea or drains to irrigate crops plus computing actual crop evapotranspiration (ETc) so as to calculate the amount of water to apply to a crop. The paper aims to assess the actual evaporation and evaporation coefficient of carrots, by planting carrots in a field and the crop was exposed to several sources of water (DW and RW) and comparing ETc, Kc and production among plots of three sites (A, B and C). The study used two types of irrigation water (drain water (DW) and river water (RW)). The results were to monthly rate and accumulated actual evapotranspiration to C (irrigation by RW only) more than A (67% RW and 33% DW) and B (17% RW and 83% DW) via 7% and 58%, respectively. The yield to C more than A and B by 17% and 75%, respectively. In conclusion the use of DW can cause a reduction in crop consumptive of carrot crops also causes a reduction in yield, crop length, root length, root size, canopy of crop, number of leaves and biomass of the plant therefore, the drainage water needs to treated before irrigating crops And making use of it to irrigate the fields and fill the shortfall in the amount of water from the river. The drain water helped on filling the water shortage due to climate changes and giving production of carrot crop but less than river water.

Estimation of the Actual Evapotranspiration by the SEBAL Method in the Irrigated Rice Perimeter of Zatta (Yamoussoukro—Côte d’Ivoire)

In this study, the SEBAL (Surface Energy Balance Algorithm for Land) model was used to map the spatio-temporal distribution of actual evapotranspiration in the Yamoussoukro department (Côte d’Ivoire). Like other regions of the country, the Yamoussoukro district is confronted with the phenomenon of evapotranspiration (ET). This is a very important component that comes into play in the water balance but also in the calculation of the water needs of agricultural crops. Consequently, its estimation is of paramount importance in research related to the rational management of water resources, particularly agricultural water. The objective of this study was to analyze the spatio-temporal distribution of actual evapotranspiration (AET) as a function of land cover and land use. The methodology used is based on the SEBAL model which uses remote sensing (Landsat 8_OLI/TIRS) and climatic data to estimate actual evapotranspiration and analyze the spatio-temporal distribution of AET. The results reveal that the AET varied from 0 to 5.44 mm/day over the period from December 2019 to February 2020 with an average value of 4.92 mm/day. The highest average values occurred for water bodies (4.90 mm/day) and flooded vegetation (4.88 mm/day) while the lowest values occurred in residential areas (2.04 mm/day). Furthermore, the results show that the difference between the SEBAL model and the FAO-Penman-Monteith method is minimal with an average RMSE of 0.36 mm/day for all the satellite images. This study demonstrates the considerable potential of remote sensing for the characterization and estimation of spatial evapotranspiration in the Zatta irrigated rice-growing area.

A Study on the Assessment and Integration of Multi-Source Evapotranspiration Products over the Tibetan Plateau

Evapotranspiration(ET)is a crucial variable in the terrestrial water,carbon,and energy cycles.At present,a large number of multi source ET products exist.Due to sparse observations,however,great challenges exist in the evaluation and integration of ET products in remote and complex areas such as the Tibetan Plateau(TP).In this paper,the applicability of the multiple collocation(MC)method over the TP is evaluated for the first time,and the uncertainty of multisource ET products(based on reanalysis,remote sensing,and land surface models)is further analyzed,which provides a theoretical basis for ET data fusion.The results show that 1)ET uncertainties quantified via the MC method are lower in RS-based ET products(5.95 vs.7.06 mm month^(-1))than in LSM ET products(10.22 vs.17.97 mm month^(-1))and reanalysis ET estimates(7.27 vs.12.26 mm month-1).2)A multisource evapotranspiration(MET)dataset is generated at a monthly temporal scale with a spatial resolution of 0.25°across the TP during 2005-15.MET has better performance than any individual product.3)Based on the fusion product,the total ET amount over the TP and its patterns of spatiotemporal variability are clearly identified.The annual total ET over the entire TP is approximately 380.60 mm.Additionally,an increasing trend of 1.59±0.85 mm yr^(-1)over the TP is shown during 2005-15.This study provides a basis for future studies on water and energy cycles and water resource management over the TP and surrounding regions.

Unveiling evapotranspiration patterns and energy balance in a subalpine forest of the Qinghai-Tibet Plateau:observations and analysis from an eddy covariance system

Evapotranspiration is an important parameter used to characterize the water cycle of ecosystems.To under-stand the properties of the evapotranspiration and energy balance of a subalpine forest in the southeastern Qinghai-Tibet Plateau,an open-path eddy covariance system was set up to monitor the forest from November 2020 to October 2021 in a core area of the Three Parallel Rivers in the Qing-hai-Tibet Plateau.The results show that the evapotranspira-tion peaked daily,the maximum occurring between 11:00 and 15:00.Environmental factors had significant effects on evapotranspiration,among them,net radiation the greatest(R^(2)=0.487),and relative humidity the least(R^(2)=0.001).The energy flux varied considerably in different seasons and sensible heat flux accounted for the main part of turbulent energy.The energy balance ratio in the dormant season was less than that in the growing season,and there is an energy imbalance at the site on an annual time scale.

Actual evapotranspiration of subalpine meadows in the Qilian Mountains, Northwest China

As a main component in water balance,evapotranspiration(ET)is of great importance for water saving,especially in arid and semi-arid areas.In this study,the FAO(Food and Agriculture Organization)Penman-Monteith model was used to estimate the magnitude and temporal dynamics of reference evapotranspiration(ET0)in 2014 in subalpine meadows of the Qilian Mountains,Northwest China.Meanwhile,actual ET(ETc)was also investigated by the eddy covariance(EC)system.Results indicated that ETc estimated by the EC System was 583 mm,lower than ET0(923 mm)estimated by the FAO Penman-Monteith model in 2014.Moreover,ET0 began to increase in March and reached the peak value in August and then declined in September,however,ETc began to increase from April and reached the peak value in July,and then declined in August.Total ETc and ET0 values during the growing season(from May to September)were 441 and 666 mm,respectively,which accounted for 75.73%of annual cumulative ETc and 72.34%of annual cumulative ET0,respectively.A crop coefficient(kc)was also estimated for calculating the ETc,and average value of kc during the growing season was 0.81(ranging from 0.45 to 1.16).Air temperature(Ta),wind speed(u),net radiation(Rn)and soil temperature(Ts)at the depth of 5 cm and aboveground biomass were critical factors for affecting kc,furthermore,a daily empirical kc equation including these main driving factors was developed.Our result demonstrated that the ETc value estimated by the data of kc and ET0 was validated and consistent with the growing season data in 2015 and 2016.

Actual Evapotranspiration Estimation Using Remote Sensing: Comparison of SEBAL and SSEB Approaches

The main objective of this paper was to evaluate the daily actual evapotranspiration (ET) accuracy obtained by remote sensing algorithms when compared with Bowen ratio measurements performed in the cotton fields. The experiment was conducted in a cotton experimental field of EMBRAPA located in Ceará State, Brazil. Seven TM Landsat-5 images acquired in 2005 and 2008 were used to perform SEBAL and SSEB algorithms. The comparison between the estimated values by remoting sensing algorithms and the measured values in situ showed an acceptable accuracy. Besides, SSEB algorithm showed to be an important tool for ET analysis in the semi-arid regions, due to the fact that it does not need the meteorological data to solve the energy balance, but only the average temperature of the “hot” and “cold” pixels. Additionally, SSEB presents simpler processing than SEBAL algorithm that needs to solve an iterative process to obtain the sensible heat flux values.

Estimating daily actual evapotranspiration of a rice–wheat rotation system in typical farmland in the Huai River Basin using a two-step model and two one-step models

The objective of this study is to evaluate the performance of three models for estimating daily evapotranspiration(ET) by employing flux observation data from three years(2007, 2008 and 2009) during the growing seasons of winter wheat and rice crops cultivated in a farmland ecosystem(Shouxian County) located in the Huai River Basin(HRB), China. The first model is a two-step model(PM-Kc);the other two are one-step models(e.g., Rana-Katerji(R-K) and advection-aridity(AA)). The results showed that the energy closure degrees of eddy covariance(EC) data during winter wheat and rice-growing seasons were reasonable in the HRB, with values ranging from 0.84 to 0.91 and R2 of approximately 0.80. Daily ET of winter wheat showed a slow decreasing trend followed by a rapid increase, while that of rice presented a decreasing trend after an increase. After calibrating the crop coefficient(Kc), the PM–Kc model performed better than the model using the Kc recommended by the Food and Agricultural Organization(FAO). The calibrated key parameters of the R-K model and AA model showed better universality. After calibration, the simulation performance of the PM-Kc model was satisfactory. Both the R-K model and AA model underestimated the daily ET of winter wheat and rice. Compared with that of the R-K model, the simulation result of the AA model was better, especially in the simulation of daily ET of rice. Overall, this research highlighted the consistency of the PM-Kc model to estimate the water demand for rice and wheat crops in the HRB and in similar climatic regions in the world.

SPATIO-TEMPORAL VARIATION OF ACTUAL EVAPOTRANSPIRATION AND ITS RELATION WITH CLIMATE PARAMETERS IN THE PEARL RIVER BASIN,CHINA

Spatio-temporal variation of actual evapotranspiration(ETa) in the Pearl River basin from 1961 to 2010 are analyzed based on daily data from 60 national observed stations. ETa is calculated by the Advection-Aridity model(AA model) in the current study, and Mann-Kendall test(MK) and Inverse Distance Weighted interpolation method(IDW)were applied to detect the trends and spatial variation pattern. The relations of ETa with climate parameters and radiation/dynamic terms are analyzed by Person correlation method. Our findings are shown as follows: 1) Mean annual ETa in the Pearl River basin is about 665.6 mm/a. It has significantly decreased in 1961-2010 at a rate of-24.3mm/10 a. Seasonally, negative trends of summer and autumn ETa are higher than that of spring and winter. 2) The value of ETa is higher in the southeast coastal area than in the northwest region of the Pearl River basin, while the latter has shown the strongest negative trend. 3) Negative trends of ETa in the Pearl River basin are most probably due to decreasing radiation term and increasing dynamic term. The decrease of the radiation term is related with declining diurnal temperature range and sunshine duration, and rising atmospheric pressure as well. The contribution of dynamic term comes from increasing average temperature, maximum and minimum temperatures in the basin. Meanwhile, the decreasing average wind speed weakens dynamic term and finally, to a certain extent, it slows down the negative trend of the ETa.

Field Assessment of Soil Water Storage and Actual Evapotranspiration of Rainfed Maize (<i>Zea mays</i>L.) Genotypes in a Coastal Savannah Environment

A field experiment was carried out in a coastal savannah agro-ecological zone of Ghana to assess the dynamics of stored soil water and actual evapotranspiration (AET) of three maize genotypes (Obatanpa, Mamaba, and Golden Crystal) grown under rainfed conditions. Access tubes were installed to a depth of 120 cm for soil water content monitoring using a neutron probe meter. The soil water balance model of plant root zone was used to estimate AET at different crop growth stages. On average, the rate of AET for Obatanpa, Mamaba, and Golden Crystal maize genotypes were estimated as 4.32, 4.46, and 3.72 mm·day–1, respectively, for the major cropping season as against corresponding values of 3.88, 4.00 and 3.72 mm day–1 for the minor cropping season. Mamaba had higher values of AET from 42 DAE (days after emergence) to 84 DAE during the minor cropping season while it had low AET values during the major cropping season. The positive balance in stored soil water in the root zone of Obatanpa was the highest from 42 DAE to 84 DAE followed by Mamaba and Golden Crystal during the major cropping season. Mamaba, on the other hand, had the highest AET from 70 DAE to 84 DAE. Obatanpa used 55.6% of stored soil water for AET, which was the highest among the maize genotypes during the major cropping season. Golden Crystal and Mamaba followed with 53.3% and 51.5%. For the minor cropping season, 48.5% of stored soil water was used by Mamaba for AET, followed by Obatanpa, (46.4%) and Golden Crystal (43.2%). A strong positive significant (p ≤ 0.05) linear correlation existed between AET and precipitation with the coefficient of determination (R2) being 69.2 for Obatanpa, 88.5 for Mamaba and 82.8 for Golden Crystal for the major cropping season. Higher R2 values (98.0, for Obatanpa, 94.1 for Mamaba and 98.9 for Golden Crystal) were, however, obtained for the minor cropping season. Additionally, a strong linear relationship was found between AET and precipitation, suggesting the need to formulate strategies for enhancing effective use of precipitation in sustained rainfed maize production.

Stochastic Modelling of Actual Black Gram Evapotranspiration

The study was undertaken to develop and evaluate evapotranspiration model for black gram (Vigna Mungo L.) crop under climatic conditions of Udaipur, India. Pan evaporation data for the duration of twenty three years (1978-2001) and measured black gram evapotranspiration data by electronic lysimeter for duration of kharif season of 2001 were used for analysis. Black gram is an important crop of Udaipur region. No sys-tematic study on modelling of black gram evapotranspiration was conducted in past under above said cli-matic conditions. Therefore, stochastic model was developed for the estimation of daily black gram evapotranspiration using 24 years data. Validation of the developed models was done by the comparison of the estimated values with the measured values. The developed stochastic model for black gram evapotran-spiration was found to predict the daily black gram evapotranspiration very accurately.

SimET: An open-source tool for estimating crop evapotranspiration and soil water balance for plants with multiple growth cycles

Accurate estimation of crop evapotranspiration(ETc) and soil water balance, which is vital for optimizing water management strategy in crop production, can be performed by simulation. But existing software has many deficiencies, including complex operation, limited scalability, lack of batch processing, and a single ETc model. Here we present simET, an open-source software package written in the R programming language. Many concepts involved in crop ETc simulation are condensed into functions in the package. It includes three widely used crop ETc models built on these functions: the single-crop coefficient,double-crop coefficient, and Shuttleworth–Wallace models, along with tools for preparing model data and comparing estimates. SimET supports ETc simulation in crops with repeated growth cycles such as alfalfa, a perennial forage crop that is cut multiple times annually.

Estimating Evapotranspiration Using Chloride Mass Balance in a New Mexico Paired Basin Study 2009-2019

A paired basin study in the upper Santa Fe River watershed following forest thinning and prescribed burns successfully measured water budget components in a treated and an untreated (control) basin. The paired basin study was established to investigate questions that have arisen regarding changes in water yield from forest treatments. Precipitation, stream flow, soil moisture, and chloride concentrations in precipitation and stream flow were measured to quantify the water budget components. The results from eleven years of data collection and analysis have a high degree of confidence with respect to measuring the water budget components based on the mass balance of water and chloride. The differences in the geologic structure and topography between the two paired basins appeared to impact the water budgets more than the forest treatments, except during periods when winter precipitation and snowmelt represented a significant component of inflow. Although this paired basin study was not able to portray a simple relationship between forest thinning and water yield, the chloride concentration methodology used to estimate evapotranspiration (ET) was successful. These detailed observations of chloride deposition and transport characteristics may be relevant for other researchers working in forested basins with substantial ET. ET rates were estimated by examining the cycle of chloride entering and exiting each basin over six integration periods. ET was estimated to be about 90% to 94% of precipitation in the treated basin and 77% to 86% in the control basin. The higher ET in the treated basin both before and after forest treatments may be due to the much greater area of west-facing hillslopes in the treated basin, which receive warm afternoon sun, and the greater area of rock cover in the control basin. Variation in the chloride concentration of collected precipitation samples from different sites indicates that horizontal precipitation of chloride in the tree canopy is an important consideration when using the chloride mass balance approach to calculate water budget components.

Responses of vegetation yield to precipitation and reference evapotranspiration in a desert steppe in Inner Mongolia,China

Drought,which restricts the sustainable development of agriculture,ecological health,and social economy,is affected by a variety of factors.It is widely accepted that a single variable cannot fully reflect the characteristics of drought events.Studying precipitation,reference evapotranspiration(ET_(0)),and vegetation yield can derive information to help conserve water resources in grassland ecosystems in arid and semi-arid regions.In this study,the interactions of precipitation,ET_(0),and vegetation yield in Darhan Muminggan Joint Banner(DMJB),a desert steppe in Inner Mongolia Autonomous Region,China were explored using two-dimensional(2D)and three-dimensional(3D)joint distribution models.Three types of Copula functions were applied to quantitatively analyze the joint distribution probability of different combinations of precipitation,ET_(0),and vegetation yield.For the precipitation–ET_(0)dry–wet type,the 2D joint distribution probability with precipitation≤245.69 mm/a or ET_(0)≥959.20 mm/a in DMJB was approximately 0.60,while the joint distribution probability with precipitation≤245.69 mm/a and ET_(0)≥959.20 mm/a was approximately 0.20.Correspondingly,the joint return period that at least one of the two events(precipitation was dry or ET_(0)was wet)occurred was 2 a,and the co-occurrence return period that both events(precipitation was dry and ET_(0)was wet)occurred was 5 a.Under this condition,the interval between dry and wet events would be short,the water supply and demand were unbalanced,and the water demand of vegetation would not be met.In addition,when precipitation remained stable and ET_(0)increased,the 3D joint distribution probability that vegetation yield would decrease due to water shortage in the precipitation–ET_(0)dry–wet years could reach up to 0.60–0.70.In future work,irrigation activities and water allocation criteria need to be implemented to increase vegetation yield and the safety of water resources in the desert steppe of Inner Mongolia.

荒漠草原不同植物群落蒸散组分特征及其环境因子影响分析

蒸散发是生态水文过程的关键环节,掌握蒸散组分的变化特征及其影响因子,对干旱半干旱地区的可持续发展至关重要。以荒漠草原多年生植物针茅群落和一年生植物猪毛蒿群落为研究对象,利用小型蒸渗仪开展了连续3年监测,分析了蒸散组分的日、月和年变化规律,探讨了影响蒸散组分的主要环境因子。结果表明:晴天时,多年生和一年生植物群落蒸散组分呈先增加后减小的抛物线型,夜间蒸散活动较弱,累积蒸散量较低,不足全天总累积蒸散量的20%;阴天时各蒸散组分无明显峰值,且日累积量均较小,一年生和多年生植物群落的蒸散量、蒸发量和蒸腾量无显著差异;10.64 mm/d及以上降雨对蒸散和蒸发的日变化具有明显影响,随着降雨量的增多,蒸散量和蒸发量也呈增大趋势,但蒸腾量则相对较小。从月动态来看,7—9月占全年蒸散量和蒸发量的一半左右,冬春季蒸散量和蒸发量维持在全年最低水平。年蒸散量与年降雨量接近,而蒸腾量占蒸散量的比例低于10%。总体来看,多年生植物群落蒸散量较一年生植物群落多。采用Mantel检验方法分析不同时间尺度影响蒸散组分的主要气候因素,在小时尺度上太阳辐射与蒸发量和蒸腾量显著性水平较高(P<0.01),但相关性较低(r<0.2);在日尺度上,蒸散量、蒸发量和蒸腾量与降雨量的显著性(P<0.01)和相关性(r≥0.4)均最高;而月尺度上,降雨量和降雨速率与蒸散量、蒸发量的相关性较高(0.2≤r<0.4),但显著性较低(P≥0.05)。因此,蒸散组分受环境因子的影响在不同时间尺度上具有较大差异,说明蒸散组分受多种因子共同影响。

基于遥感和通量观测的实际蒸散发时空变化特征——以黄河流域水源涵养区为例

蒸散发是地表水热平衡的关键要素,分析蒸散发的时空分布特征及其影响因素,对于深入理解区域水文循环与生态系统过程至关重要。基于通量观测站数据,评估GLEAM、MTE、GLDAS和AVHRR共4种蒸散发产品在黄河流域水源涵养区的适用性,利用水量平衡方法验证其在流域尺度上的精度,并探讨实际蒸散发的影响因素。结果表明:在站点尺度上,GLEAM蒸散发产品精度最高;在流域尺度上,校正后的GLEAM蒸散发产品与实际蒸散发的相对误差在渭河南山支流区最小,其次是兰州以上地区;1982—2015年黄河流域水源涵养区实际蒸散发整体呈增加趋势,空间分布上自西到东逐渐增加;不同植被类型年均蒸散发差异较大,阔叶林的蒸散发最大(575.2 mm),其次是农田(504.3 mm),高山草甸的蒸散发最小(358.2 mm);实际蒸散发变化主要受到太阳辐射与气温的影响。

基于实际蒸散量修订标准化降水蒸散干旱指数研究

为改进SPEI在农业干旱监测中的效果,从水分平衡的角度提出了一种修订的标准化降水蒸散指数(MSPEI).该指数通过计算降水与实际蒸散量的差值,并基于最长连续干旱时间对差值进行自适应修正,采用目视检查概率拟合曲线与Kolmogorov-Smirnov检验2种方法选择适宜分布函数,最后进行标准化转换生成干旱指数.干旱指数有效性检验表明:MSPEI能够准确反映不同季节间干湿状态的差异,在湿润比例低于20%的春季,MSPEI均低于-0.5;在反映干旱趋势时,MSPEI与SPEI具有高度一致性;MSPEI与植被指数具有稳定且较高的相关性,在0.57~0.78之间;在典型干旱过程监测中,MSPEI对旱灾发生、发展和解除过程的描述更符合实际.MSPEI适应于不同气候背景,无需选择时间尺度,即可较准确地反映农业干旱演化过程.

气候变化背景下山西省气象干旱时空演变特征

干旱频发对生态资源、农业发展造成了严重影响,为揭示山西省干旱时空演变特征,基于1971—2020年山西省24个气象站点的逐月气象资料,利用改进的Mann-Kendall方法检验各气象因子的年变化趋势,采用FAO56 Penman-Monteith公式计算参考作物腾发量(ET0),分析单个气象因子变化情况下ET0的变化特征和对气象因子的敏感性,比较各时间尺度(月、季、年尺度)不同干旱指数(降水距平百分率(Pa)、标准化降水指数(SPI)和标准化降水蒸散指数(SPEI))对山西省干旱灾害监测能力。结果表明:ET0与相对湿度呈负相关,气象因子对ET0的敏感性由大到小依次为相对湿度、日最高气温、2 m处风速、日最低气温、日平均气温,ET0呈波动下降趋势。SPEI能够在多时间尺度上有效反映山西省干旱状况,是该地区干旱监测的有效工具。在月、季、年尺度下,比较3个干旱指数,Pa检测效果较差,SPI和SPEI在某些地理区域存在较大差异,整体而言,SPEI在多数地区检测干旱的性能更好;SPEI-1尺度下,各干旱等级发生频率由大到小依次为轻旱(14.8%)、中旱(10.6%)、重旱(5.6%)、特旱(1.9%),3月干旱发生率最高(34%),12月发生率最低(31.8%),吕梁市、晋中市、大同市干旱情况较为严重;SPEI-3尺度下,季节发生干旱频率由大到小依次为秋季(33.5%)、夏季(32.5%)、春季(31.9%)、冬季(31.4%),大同市、长治市特旱发生频率最高,旱情最为严重,忻州市轻旱频率、朔州市中旱频率、吕梁市重旱频率最高;SPEI-12尺度下,轻、中、重、特旱频率分别为14.8%、10.5%、5.4%、2.3%,SPEI-12相较SPEI-1和SPEI-3识别重旱、特旱的站点更多,并基于游程理论得出,山西省南部干旱频次更多,东部干旱历时更长、干旱严重程度更大,干旱峰值主要出现在山西省南北部,由于年均降水呈波动性下降,年均气温整体上升,山西省的气候趋于暖干化,南北部旱情将有所加重,中部地区旱情有所减缓,全域性干旱仍有很大发生可能。

陆浑灌区实际蒸散发影响因素分析

实际蒸散发是水文循环的关键环节,分析灌区实际蒸散发及其影响因素对灌区水资源的高效利用和农业高质量发展具有重要意义。然而,目前蒸散发的影响因素研究在确定主要因素时往往采用解释力较差的传统统计学方法,在相关性分析时忽略了蒸散发与其影响因素在空间上的相关性。因此利用改进的随机森林模型确定实际蒸散发的主要影响因素,并通过岭回归模型和地理加权回归模型探究实际蒸散发与其影响因素的时空相关关系。结果表明:(1)在灌溉期,地表净辐射、平均气温、叶面积指数和实际水汽压是实际蒸散发的主要影响因素;在非灌溉期,地表净辐射、平均气温、风速和日照时间是实际蒸散发的主要影响因素。实际蒸散发在一定程度上代表了灌区的作物耗水量。因此,灌区作物耗水在灌溉期和非灌溉期的影响作用有一定的差异。(2)在时间上,风速与实际蒸散发为负相关关系且呈显著负相关(P<0.05),其余影响因素与实际蒸散发均为正相关关系且呈显著正相关(P<0.05);在空间上,除风速与实际蒸散发在大部分区域呈负相关关系,其余影响因素都与实际蒸散发在大部分区域呈正相关关系。因此,除风速外,其余影响因素对灌区作物耗水在大部分区域都为正向促进作用。

北京市主城区高分辨率的城市水碳通量模拟研究

城市化通过影响地表蒸散发(ET)过程改变了区域水热平衡等水文和生态过程,进而改变了陆地生态系统的结构与功能。为科学评估城市水碳过程,基于哨兵二号卫星数据的植被信息,估算了2016—2021年逐月北京市主城区10 m×10 m空间分辨率的植被指数,进一步结合PT-JPLim四源蒸散发模型、InVEST模型以及解析型生态系统水分利用效率(WUE)模型,模拟了2016—2021年北京市主城区10 m×10 m空间分辨率的蒸散发、蒸散发分量(植被蒸腾E t、土壤蒸发E b、截留蒸发E i和不透水面蒸发E u)、总初级生产力(GPP)、碳储量以及WUE的月值,并分析了其相关关系。植被指数较大值集中在西部山区,其次为北京市的公园区域,归一化植被指数NDVI最大值为0.65。主城区多年平均蒸散发量为497 mm,ET随着叶面积植被指数LAI和增强植被指数EVI的增加而增加。2016—2021年期间,NDVI、LAI和EVI分别以每年0.0048、0.016 m^(2)·m-2和0.0047的速度增加。区域平均E t为141.51 mm,E i为50.77 mm,E b为272 mm,不透水面上的E u ET为18.2%。碳储量较高的区域主要分布在西部山区,该区域海拔相对较高,植被覆盖率较高,总碳储量密度高值超过5 t hm^(2)。研究区GPP的平均值为2.7 g·m^(-2)·d^(-1),多年平均WUE为0.63 g·mm^(-1)。WUE和E t ET呈显著负相关(R=-0.44,p<0.001),WUE随GPP的增加呈现显著的上升趋势。精细化的城市水碳模拟能够为海绵城市的建设和评估提供理论基础,对“双碳”目标的实现具有重要意义。

基于蒸散发干旱指数的子牙河流域干旱时空变化特征分析

为探究子牙河流域干旱时空分布特征,基于2001—2021年逐月降水和遥感蒸散栅格数据,采用标准化降水蒸散指数(SPEI)和标准化蒸散发亏缺指数(SEDI)表征流域干旱情况,运用Sen斜率估计和Mann-Kendall检验法分析了流域2001—2021年季尺度干旱时空分布及变化趋势,统计了干旱面积、干旱次数、干旱历时和干旱烈度等特征变量。结果表明:SPEI对子牙河流域旱情发生时间、程度和范围识别的准确率更高,2001—2021年流域SPEI呈上升趋势,表现出湿润化态势,冬季SPEI呈下降趋势,表现为干旱化态势,忻州、阳泉市等地存在显著干旱化的区域;流域各季节干旱面积占比呈现波动变化,部分年份出现大范围季节性干旱,夏旱和秋旱干旱面积占比最高,超过90%;忻州和阳泉市部分区域、石家庄市西部区域和衡水市北部区域呈现干旱次数少、历时长、烈度大的特点,邯郸和邢台市部分区域、衡水市南部区域、石家庄市东部区域表现为干旱次数多、历时短、烈度小的特征。