【作者】 孙福宝；

【导师】 杨大文；

【作者基本信息】 清华大学 ， 水利工程， 2007， 博士

【摘要】 蒸散发是流域水循环和能量循环的关键环节,在一定的气候和下垫面条件下有其一定的规律。目前,在全球气候变化的研究中发现了蒸发悖反现象。由此,围绕气候变化引起的实际蒸散发变化及水文循环响应的研究,得出了不同的结论,其中以Penman蒸发正比假设和Bouchet蒸发互补假设之间的争论最为典型。为更好地理解上述差异,本文引入基于Budyko水热耦合平衡假设的傅抱璞公式,试图统一认识流域实际蒸散发与潜在蒸散发之间的关系,从水热耦合关系来探讨估算流域年实际蒸散发的新方法,并基于Budyko假设定量分析气候变化的水文响应演变趋势及区域特征。首先,论文分析了我国近50年气候水热状况的变化及区域特征。结果发现:蒸发悖反现象出现在1990年之前,之后逐渐消失;降水和潜在蒸发的长期趋势之间有较大差异和显著的区域特征,且降水和潜在蒸发在多年平均尺度上呈相反分布,在年尺度上呈负相关关系,而在月尺度上呈正相关关系。基于对我国非湿润区108个研究流域的水量平衡分析以及基于傅抱璞公式的理论分析,提出了年尺度上流域蒸散发的解释:湿润地区实际蒸发主要受潜在蒸发控制,因此两者呈正比关系;而非湿润地区的实际蒸散发主要受降水控制,这时降水与潜在蒸发间的负相关关系导致实际蒸发与潜在蒸发间呈互补关系。从而通过Budyko假设将蒸发正比假设和蒸发互补假设在年尺度上统一起来。针对108个研究流域的分析发现傅抱璞公式的参数与流域下垫面条件密切相关并具有显著的区域特征。通过逐步回归分析提出了估算该参数的半经验公式。验证结果表明:利用傅抱璞公式和该半经验公式一起能较准确地估算流域多年平均及逐年的实际蒸散发量。结合田间水热通量观测数据,分析了不同时间尺度上实际蒸散发与潜在蒸散发之间的关系并进行了理论解释。结果表明:在非湿润地区多年平均和年尺度上二者呈互补关系,而在日和小时尺度上呈正相关关系。基于傅抱璞公式分析了气候变化的水文响应并结合非湿润区水量平衡分析发现,非湿润区潜在蒸发对实际蒸发的控制作用在一些研究中已被夸大。通过傅抱璞公式的计算结果,揭示了我国潜在蒸发和实际蒸发之间相关关系的全貌。更多还原

【Abstract】 Evapotranspiration links with both water and energy cycles in a watershed, plays a key role in the climate-soil-vegetation interactions under a certain climate and landscape condition. Currently, increase in air temperature and decrease in pan evaporation was found to be common worldwide during the past half century, which is termed as pan evaporation paradox. This results in controversy in view of the changes to the hydrological cycle expected by using the Penman and Bouchet hypotheses. In order to reconcile this controversy, this study introduced Fu’s analytical solutions to Budyko’s coupled water and energy balance hypothesis.Building on the previous investigations, this study is aimed to understanding the relationships between the actual and potential evapotranspiration, to develop a coupled water-energy balances method for watershed evapotranspiration, and to predict the hydrologic response to climate change and its regional feature.First of all, the change of climate condition over China from 1956 to 2005 has been examined. It has been shown that the pan evaporation paradox phenomenon occured from 1956 to 1990, whereas disappears since 1990 gradually. In the longterm trends, precipitation and potential evapotranspiration show large difference with significant regional feathers. For the whole China, they show inverse distribution at the long-term timescale, are negatively correlated at annual timescale, and positively related at the month timescale.Secondly, in terms of water balance analysis in 108 catchments of nonhumid regions in China and the theoritial analysis based on Fu’s equation, this study has explained the evapotranspiration at the catchment scale as: in humid regions, change in actual evapotranspiration is controlled mainly by change in potential evapotranspiration rather than precipitation, and this is identical to the Penman hypothesis; in non-humid regions, change of actual evapotranspiration is dominated mainly by change in precipitation rather than potential evapotranspiration, and the Bouchet complementary relationship between actual evapotranspiration and potential evapotranspiration comes about because actual and potential evapotranspiration are correlated via precipitation. Thus the consistency of the two opposite hypothesis has been unified into the Budyko’s hypothesis.Further, it has been found that besides the annual climate conditions, the regional pattern of annual water-energy balance is also closely correlated with the relative infiltration capacity, relative soil water storage, and the average slope. This enables one to estimate the parameterω|- from catchment characteristics without calibration from the long time series of water balances. By stepwise regression analysis, a semi-empirical formula for the parameterω|- in terms of the dimensionless landscape parameters is proposed. Applications of Fu’s equation together with the parameterω|- estimated by this empirical formula have shown that Fu’s equation can predict both long-term mean and annual value of actual evapotranspiration accurately. This implies that the Fu’s equation can be used for predicting the annual water balance in ungauged basins.Together with the experimental flux data observed at an irrigated agricultural field, the relationships in evapotranspiration are examined at different timescales, namely long-term, annual, daily and hourly timescale. It has been found that they show complementary at both the long-term annual and annual timescales, whereas at both daily and hourly timescales they show propotional relationships. This apparently paradoxal phenomenon has been explained by using the Budyko coupled water-energy balances hypothesis.Finally, in terms of the theoretical analysis for the hydrological response to the climate change based on Fu’s equation and the water balance analysis in nonhumid regions, it is found that the impact of potential evapotranspiration on actual evapotranspiration at the annual timescale has been magnified in previous researches. This study estimate the annual actual evapotranspiration throughout China on the basis of Fu’s equation together with the semi-empirical formula ofω|- . It is also found that the relationship in evapotranspiration is positive in humid regions and then gradually turns to negative in non-humid regions at the annual timescale.更多还原