Contrasting characteristics of the surface energy balance between the urban and rural areas of Beijing   总被引：1，自引：0，他引：1  

Linlin Wang  Zhiqiu Gao  Shiguang Miao  Xiaofeng Guo  Ting Sun  Maofeng Liu  Dan Li 《大气科学进展》2015,32(4):505-514

A direct comparison of urban and rural surface energy balances, as well as a variety of other variables including incoming shortwave/longwave radiation and aerosol optical depth, is conducted for the Beijing metropolitan area. The results indicate that, overall, the urban area receives a smaller amount of incoming shortwave radiation but a larger amount of incoming longwave radiation. However, comparisons in the aerosol optical depth and cloud fraction at the two locations suggest that neither aerosol optical depth nor cloud fraction alone can explain the difference in the incoming shortwave radiation. The urban–rural differences in the incoming longwave radiation are unlikely to be caused by the presence of more abundant greenhouse gases over the urban area, as suggested by some previous studies, given that water vapor is the most dominant greenhouse gas and precipitable water is found to be less in urban areas. The higher incoming longwave radiation observed over the urban area is mostly likely due to the higher temperatures of the ambient air. The urban area is also found to always produce higher sensible heat fluxes and lower latent heat fluxes in the growing season. Furthermore, the urban area is associated with a larger amount of available energy(the sum of sensible and latent heat fluxes) than the rural area, except in May and October when evapotranspiration in the rural area significantly exceeds that in the urban area. This study provides observational evidence of urban–rural contrasts in relevant energy-balance components that plausibly arise from urban–rural differences in atmospheric and land-surface conditions.  相似文献   

Comprehensive study on the influence of evapotranspiration and albedo on surface temperature related to changes in the leaf area index     

Jiawen Zhu  Xiaodong Zeng 《大气科学进展》2015,32(7):935-942

Many studies have investigated the influence of evapotranspiration and albedo and emphasize their separate effects but ignore their interactive influences by changing vegetation status in large amplitudes. This paper focuses on the comprehensive influence of evapotranspiration and albedo on surface temperature by changing the leaf area index(LAI) between 30–90 N.Two LAI datasets with seasonally different amplitudes of vegetation change between 30–90N were used in the simulations.Seasonal differences between the results of the simulations are compared, and the major findings are as follows.(1) The interactive effects of evapotranspiration and albedo on surface temperature were different over different regions during three seasons [March–April–May(MAM), June–July–August(JJA), and September–October–November(SON)], i.e., they were always the same over the southeastern United States during these three seasons but were opposite over most regions between30–90 N during JJA.(2) Either evapotranspiration or albedo tended to be dominant over different areas and during different seasons. For example, evapotranspiration dominated almost all regions between 30–90N during JJA, whereas albedo played a dominant role over northwestern Eurasia during MAM and over central Eurasia during SON.(3) The response of evapotranspiration and albedo to an increase in LAI with different ranges showed different paces and signals. With relatively small amplitudes of increased LAI, the rate of the relative increase in evapotranspiration was quick, and positive changes happened in albedo. But both relative changes in evapotranspiration and albedo tended to be gentle, and the ratio of negative changes of albedo increased with relatively large increased amplitudes of LAI.  相似文献   

基于SPEI的河南省冬小麦生育期干旱时空特征分析     

闫研  李忠贤 《南京气象学院学报》2015,7(2):159-167

利用河南省24个地面气象站1961-2009年逐日降水和气温资料计算SPEI(标准化降水蒸散指数),并按照SPEI的标准界值将干旱强度划分为轻度干旱、中度干旱和极端干旱.根据河南省冬小麦的生长特点将小麦生育期划分为生育前期、分蘖期和返青-抽穗-成熟期.采用Meteoinfo软件、Morlet小波分析方法、线性回归研究不同生育期干旱变化趋势、覆盖范围、发生频率、周期及空间分布,结果表明,冬小麦各个生育阶段均出现过不同程度的干旱,只是不同地区、不同年份发生的频率和强度不同,但各阶段均存在着轻度干旱发生的概率最大,而极端干旱发生的概率最小的特点.驻马店地区在各阶段发生干旱的概率都较大.对河南省冬小麦全生育期的SPEI分析表明,全生育期干旱出现概率的极值中心有显著的10 a左右的周期变化特征,近年来干旱指数呈逐渐增大的趋势.  相似文献   

耦合MOD16和SMAP的微波土壤湿度降尺度研究     

孙灏  周柏池  李欢  阮琳 《遥感学报》2021,25(3):776-790

局域尺度上的水文或农业应用亟需较高空间分辨率的土壤湿度(SM)数据,微波土壤湿度空间降尺度是实现这一需求的重要途径。其中"光学/热红外与微波数据融合"的降尺度方法展现出了较大的应用潜力,然而这类方法依赖于遥感地表温度LST (Land Surface Temperature)或由LST分解得到的SM指数,受限于LST"云污染"、LST与SM解耦效应和LST分解不确定性等问题。为规避上述问题,本文通过构建3种地表蒸散效率LEE(Land surface Evapotranspiration Efficiency)与SM的降尺度函数关系(指数、余弦、余弦平方),利用MODIS地表蒸散数据(MOD16A2)计算得到的LEE (空间分辨率500 m)实现了SMAP土壤湿度产品(空间分辨率36 km)的空间降尺度。研究从动态范围、能量守恒、SM地面稀疏验证站、SM地面核心验证站等角度对降尺度算法进行评价分析。结果表明,本算法有效增加了原SM产品的空间细节特征、保持了原SM产品的动态范围并且降尺度前后能量守恒;与地面验证数据的对比分析表明,降尺度结果有效保持了原SM与地面实测数据的良好一致性;敏感性分析表明,余弦平方函数对MOD16A2产品误差的敏感性相对最小。  相似文献   

Water uptake and nutrient concentrations under a floodplain oak savanna during a non‐flood period,lower Cedar River,Iowa     

Keith E. Schilling  Peter Jacobson 《水文研究》2009,23(21):3006-3016

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Spatiotemporal variations of reference evapotranspiration in recent five decades in the arid land of Northwestern China          下载免费PDF全文

Chaolei Zheng  Quan Wang 《水文研究》2014,28(25):6124-6134

Spatial and temporal variations of reference evapotranspiration (ET₀) are useful for regional agricultural and water resources management as well as required in most distributed hydrological modelling. In the current study, the Penman–Monteith estimated ET₀ in the arid land of Northwestern China has been explicitly explored using the Mann–Kendall test. Most stations in the study region exhibited significant decreasing trend of ET₀ (P < 0.05) with only few occasions showing significant increasing trend (P < 0.05), despite the increase of temperature in the entire region. Analysis results revealed that the overall decreasing wind speed contributed most to the decreasing trend of ET₀, whereas the contributions of relative humidity and sunshine duration were limited. Temperature played the second important role on determining ET₀ trend, but its effect was opposite to that of wind speed and was largely offset by the decreasing wind speed. Furthermore, sensitivity analysis suggested the impact of temperature to ET₀ was much larger than formerly reported if its effect on saturated vapour deficit was taken into account. The results obtained in the current study will help for better understanding of the effects of climate changes to water resource management in the arid land of northwest China. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Modelling evapotranspiration in an alpine grassland ecosystem on Qinghai‐Tibetan plateau          下载免费PDF全文

Gaofeng Zhu  Yonghong Su  Xin Li  Kun Zhang  Changbin Li  Na Ning 《水文研究》2014,28(3):610-619

Thus far, measurements and estimations of actual evapotranspiration (ET) from high‐altitude grassland ecosystems in remote areas like the Qinghai‐Tibetan plateau are still insufficient. To address these issues, a comparison between the results of the eddy covariance (EC) measurements and the estimates, considering the Katerji and Perrier (KP), the Todorovic (TD) and the Priestley–Taylor (PT) models, was carried out over an alpine grassland (38^o03'1.7'' N, 100^o 27’ 26'' E; 3032 m a.s.l.) during the growing seasons in 2008 and 2009. The results indicated that the KP model after a particularly simple calibration gave the most effective ET values in different time scales, the PT model slightly underestimate ET at night and the TD model significantly overestimated ET at noon. In addition, the canopy resistance calculated by the TD model was completely different from that calculated using the inverted EC‐measured data and the KP model, which may be due to some unrealistic assumptions made by the TD model. The KP parameters were a = 0.17 and b = 1.50 for the alpine grassland and appeared to be interannually stable. However, the PT parameter showed some interannual variations (α = 0.83 and 0.74 for 2008 and 2009, respectively). Therefore, the KP model was preferred to estimate the actual ET at both hourly and daily time scales. The PT model, being the simplest approach and field condition dependent, was recommended when available weather data were rare. On the contrary, the TD model always overestimated the actual ET and should be avoided in case of the alpine grassland ecosystems. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Long‐term variability in the water budget and its controls in an oak‐dominated temperate forest          下载免费PDF全文

Jing Xie  Ge Sun  Hou‐Sen Chu  Junguo Liu  Steven G. McNulty  Asko Noormets  Ranjeet John  Zutao Ouyang  Tianshan Zha  Haitao Li  Wenbin Guan  Jiquan Chen 《水文研究》2014,28(25):6054-6066

Water availability is one of the key environmental factors that control ecosystem functions in temperate forests. Changing climate is likely to alter the ecohydrology and other ecosystem processes, which affect forest structures and functions. We constructed a multi‐year water budget (2004–2010) and quantified environmental controls on an evapotranspiration (ET) in a 70‐year‐old mixed‐oak woodland forest in northwest Ohio, USA. ET was measured using the eddy‐covariance technique along with precipitation (P), soil volumetric water content (VWC), and shallow groundwater table fluctuation. Three biophysical models were constructed and validated to calculate potential ET (PET) for developing predictive monthly ET models. We found that the annual variability in ET was relatively stable and ranged from 578 mm in 2009 to 670 mm in 2010. In contrast, ET/P was more variable and ranged from 0.60 in 2006 to 0.96 in 2010. Mean annual ET/PET_FAO was 0.64, whereas the mean annual PET_FAO/P was 1.15. Annual ET/PET_FAO was relatively stable and ranged from 0.60 in 2005 to 0.72 in 2004. Soil water storage and shallow groundwater recharge during the non‐growing season were essential in supplying ET during the growing season when ET exceeded P. Spring leaf area index (LAI), summer photosynthetically active radiation, and autumn and winter air temperatures (T_a) were the most significant controls of monthly ET. Moreover, LAI regulated ET during the whole growing season and higher temperatures increased ET even during dry periods. Our empirical modelling showed that the interaction of LAI and PET explained >90% of the variability in measured ET. Altogether, we found that increases in T_a and shifts in P distribution are likely to impact forest hydrology by altering shallow groundwater fluctuations, soil water storage, and ET and, consequently, alter the ecosystem functions of temperate forests. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Reference evapotranspiration trends and their sensitivity to climatic change on the Tibetan Plateau (1970–2009)     

Hong Xie  Xuan Zhu 《水文研究》2013,27(25):3685-3693

Evapotranspiration is an important component of the water and energy balance. It is dependent on climate. Precipitation, solar radiation, temperature, humidity, and wind all contribute to the rate of evapotranspiration. In this study, the temporal trends of reference evapotranspiration (ET_ref) and four main ET_ref drivers, namely, mean air temperature (T_a), wind speed (u₂), net radiation (R_n) and actual vapour pressure (e_a) from 1970 to 2009, were calculated based on 75 meteorological stations on the Tibetan Plateau. The results showed that the ET_ref on the Tibetan Plateau decreased on average by 0.6909 mm a^‐1a^‐1 from 1970 to 2009. T_a and e_a showed an increasing trend, whereas u₂ and R_n exhibited a decreasing trend. To explore the underlying causes of the ET_ref variation, an attribution analysis was performed to quantify the contribution of T_a, u₂, R_n and e_a, which showed that the changes in u₂, R_n and e_a produced the negative effect, whereas T_a produced the positive effect on ET_ref rates. The changes in u₂ were found to produce the largest decrease (?0.7 mm) in ET_ref, followed by e_a (?0.4 mm) and R_n (?0.1 mm). Although the significant increase in T_a had a large positive effect (0.51 mm) on ET_ref rates, changes in the other three variables each reduced ET_ref rates, resulting in an overall negative trend in ET_ref. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Evapotranspiration of a drip‐irrigated,film‐mulched cotton field in northern Xinjiang,China     

Shiqiao Zhou  Jin Wang  Jingxian Liu  Jinghui Yang  Yan Xu  Jihui Li 《水文研究》2012,26(8):1169-1178

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