Leszek Sobkowiak

Evapotranspiration estimation methods in hydrological models

Actual evapotranspiration is a key process of hydrological cycle and a sole term that links land surface water balance and land surface energy balance. Evapotranspiration plays a key role in simulating hydrological effect of climate change, and a review of evapotranspiration estimation methods in hydrological models is of vital importance. This paper firstly summarizes the evapotranspiration estimation methods applied in hydrological models and then classifies them into the integrated converting methods and the classification gathering methods by their mechanism. Integrated converting methods are usually used in hydrological models and two differences exist among them: one is in the potential evaporation estimation methods, while the other in the function for defining relationship between potential evaporation and actual evapotranspiration. Due to the higher information requirements of the Penman-Monteith method and the existing data uncertainty, simplified empirical methods for calculating potential and actual evapotranspiration are widely used in hydrological models. Different evapotranspiration calculation methods are used depending on the complexity of the hydrological model, and importance and difficulty in the selection of the most suitable evapotranspiration methods is discussed. Finally, this paper points out the prospective development trends of the evapotranspiration estimating methods in hydrological modeling.

Spatial Pattern Characterization and Multivariate Hydrological Frequency Analysis of Extreme Precipitation in the Pearl River Basin, China

Consecutive extreme rainfall events, especially those having unfavourable spatio-temporal patterns, always trigger large floods. This paper aims to examine, through the multivariate hydrological frequency analysis, the probability of the synchronous occurrence of rainfall extremes in the Pearl River basin. The copula method together with the stationarity and independence tests, which are crucial to the valid use of statistical methods in regional frequency analyses, were applied in the study. The obtained results indicate that: (1) major precipitation events of the annual maximum 1-, 3-, 5- and 7-day rainfall recorded at 42 stations are the flat looking series and variables are independent, (2) the marginal distribution of all extreme rainfall variables in four homogeneous hydrologic regions fits the log-normal probability distribution and most of their joint distribution fits the Gumbel-Hougaard distribution, (3) on that basis the contour maps of the joint distribution of annual maximum 1-, 3-, 5- and 7-day rainfall between different regions are drawn and the probability of the synchronous occurrence of the extreme rainfalls in different regions are estimated. These findings have great practical value for the regional water resources and flood risk management and are important in exploration of the spatial patterns of rainfall extremes in the Pearl River basin in order to reveal the underlying linkages between precipitation and floods from a broader geographical perspective.

Changes in Lake Ice Cover on the Morskie Oko Lake in Poland （1971-2007）

Abstract On the basis of data from the period 1971–2007, and by applying trend analysis, a study on formation, disappearance and duration of lake ice cover on the Morskie Oko Lake in the Tatra Mountains in southern Poland was carried out. The results show decreasing trends in the maximum thickness of winter lake ice cover and in duration of lake ice phenomena, while air temperature recorded at the same period at the foot of the Tatra Mountains shows increasing trend. There are strong relationships between the course of lake ice phenomena and air temperature. Citation Choinski, A., L. Kolendowicz, J. Pociask-Karteczka, et al., 2010: Changes in lake ice cover on the Morskie Oko Lake in Poland (1971–2007). Adv. Clim. Change Res., 1 , doi: 10.3724/SP.J.1248.2010.00071.

Impact of urban landscape and environmental externalities on spatial differentiation of housing prices in Yangzhou City

In this study, housing prices data for residential quarters from the period 2001–2012 were used and Global Differentiation Index (GDI) was established to measure the overall differentiation trend in housing prices in Yangzhou City, eastern China. Then the influence of the natural landscape and environment on prices of global housing market and housing submarkets was evaluated by the hedonic price model. The results are shown as follows. (1) There have been increasing gaps among housing prices since 2001. In this period, the differentiation trend has shown an upward fluctuation, which has been coupled with the annual growth rate of housing prices. (2) The spatial distribution of residential quarters of homogenous prices has changed from clustered in 2001 into dispersed in 2012. (3) Natural landscape and environmental externalities clearly influence spatial differentiation of housing prices. (4) In different housing submarkets, the influence of natural landscape and environmental externalities are varied. Natural landscape characteristics have significant impact on housing prices of ordinary commercial houses and indemnificatory houses, while the impact of environmental characteristics have obvious influence on housing prices of cottages and villas.

Comparative Mountain Hydrology: A Case Study of Wisłok River in Poland and Chaohe River in China

Hydrological processes in river basins of similar size and morphology may differ significantly due to different climatic conditions. This paper presents a comparative analysis of hydrological characteristics of two river basins located in different climatic zones: the Wisłok River Basin in the south-eastern Poland and the Chaohe River Basin in the northern China. The criteria of their choice were similarities in the basin area, main river length and topography. The results show that climate plays a key role in shaping fluvial conditions within the two basins. It is concluded that: 1) precipitation in the Wisłok River Basin is more evenly distributed in the yearly cycle, while in the Chaohe River Basin it is highly concentrated in the few summer months; 2) spring snowmelt significantly contributes to runoff in the Wisłok River Basin, while its role in the Chaohe River Basin is negligible; 3) in the Wisłok River Basin, besides the peak flow in spring, there is also a period of high water in summer resulting from precipitation, while in the Chaohe River Basin there is only one high water period in summer; 4) the Wisłok River Basin shows relatively higher stability in terms of the magnitude of intra- and inter-seasonal discharges; 5) during the multi-year observation period, a decrease in both precipitation and runoff was recorded in the two river basins.

The Climatic Characterization of Reference Evapotranspiration of Beijing Meteorological Station

Analysis of the climatic characterization of reference evapotranspiration (ETp) is significant for understanding the impact of climate change on water cycle. Based on the Penman-Monteith method, this paper estimates ETp at Beijing meteorological station and analyzes its annual and intra-annual variation. Furthermore, the causes of variation of ETp are analyzed and quantified using the detrending method and the combination method that consider both the sensitivity coefficient and the fluctuation of the climatic variables. The obtained results show that ETp increased significantly during 1951-2009. At the same time, air temperature had a significant increasing trend; relative humidity and solar radiation showed a significant decreasing trend at 5% significance level, while wind speed had no significant trend. The contributions of air temperature, relative humidity, solar radiation and wind speed to the ETp intra-annual variation is 60%, -82%, 51% and 71%, respectively. However, the sensitivity analysis shows that wind speed is the least sensitive factor, but it has larger fluctuation than the other variables. So the contribution to the annual or intra-annual variation is not only determined by the sensitivity of those climatic variables, but also by their annual trends or intra-annual fluctuations.