Rainfall erosivity is an important climatic factor for predicting soil loss. Through the application of high-resolution pluviograph data at 5 stations in Huangshan City, Anhui Prov- ince, China, we analyzed the perfor...Rainfall erosivity is an important climatic factor for predicting soil loss. Through the application of high-resolution pluviograph data at 5 stations in Huangshan City, Anhui Prov- ince, China, we analyzed the performance of a modified Richardson model that incorporated the seasonal variations in parameters α andβ. The results showed that （1） moderate to high seasonality was presented in the distribution of erosive rainfall, and the seasonality of rainfall erosivity was even stronger; （2） seasonal variations were demonstrated in both parameters α and β of the Richardson model; and （3） incorporating and coordinating the seasonality of parameters αandβgreatly improved the predictions at the monthly scale. This newly modi- fied model is therefore highly recommended when monthly rainfall erosivity is required, such as, in planning soil and water conservation practices and calculating the cover-management factor in the Universal Soil Loss Equation （USLE） and Revised Universal Soil Loss Equation （RUSLE）.展开更多
In this paper, the equilibrium entrainment into a shear-free, linearly stratified atmosphere is discussed under the framework of bulk models, namely, the zero-order jump model （ZOM） and the first-order jump model （...In this paper, the equilibrium entrainment into a shear-free, linearly stratified atmosphere is discussed under the framework of bulk models, namely, the zero-order jump model （ZOM） and the first-order jump model （FOM）. The parameterizations for the dimensionless entrainment rate versus the convective Richard- son number in the two models are compared. Based on the assumption that the parameterized entrainment rates in ZOM and FOM should be the same, the inherent relationships among the entrainment parameters in the bulk models are revealed. These relationships are supported by tank experiments and large-eddy sim- ulations. The validity of these inherent relationships indicates that, for a convective boundary layer growing into a linearly stratified free atmosphere, the only dominant factors of the growth rate are the turbulent buoyancy in the mixed layer and the stratification in the free atmosphere. In the point of the similarity view, the former is characterized by turbulent temperature and mixing length scales （mixed layer depth）, and the latter is characterized by the lapse rate of potential temperature in the free atmosphere. Thus, the commonly-used Richardson number scheme for the parameterization of the entrainment rate is just as an equivalent description. The variability of the total entrainment flux ratio in FOM, which is connected with the entrainment zone thickness, can implicitly describe the effect of the stratification in the free atmosphere, but the entrainment zone thickness is not an independent parameter. These results demonstrate the validity of the hypothesis that there exists a similarity limit in which the mixed layer depth is the only lengthscale.展开更多
This study presents an extended version of a single site daily weather generator after Richardson. The model is driven by daily precipitation series derived by a first-order two-state Markov chain and considers the an...This study presents an extended version of a single site daily weather generator after Richardson. The model is driven by daily precipitation series derived by a first-order two-state Markov chain and considers the annual cycle of each meteorological variable. The evaluation of its performance was done by deploying its synthetic time series into the physical based hydrological model BROOK90. The weather generator was applied and tested for data from the Anchor Station at the Tharandt Forest, Germany. Additionally its results were compared to the output of another weather generator with spell-length approach for the precipitation series (LARS-WG). The comparison was distinguished into a meteoro-logical and a hydrological part in terms of extremes, monthly and annual sums and averages. Extreme events could be preserved adequately by both models. Nevertheless a general underestimation of rare events was observed. Natural correlations between vapour pressure and minimum temperature could be conserved as well as annual cycles of the hydro-logical and meteorological regime. But the simulated spectrums of extremes, especially, of precipitation and temperature, are more limited than the observed spectrums. While LARS-WG already finds application in practice, the results show that the data derived from the presented weather generator is as useful and reliable as those from the established model for the simulation of the water balance.展开更多
基金Fund for Creative Research Groups of National Natural Science Foundation of China, No.41321001 the National Natural Science Foundation of China, No.51379008 the Open Research Fund of the State Key Lab of Simulation and Regulation of Water Cycle in River Basin, No.2014QN04.
文摘Rainfall erosivity is an important climatic factor for predicting soil loss. Through the application of high-resolution pluviograph data at 5 stations in Huangshan City, Anhui Prov- ince, China, we analyzed the performance of a modified Richardson model that incorporated the seasonal variations in parameters α andβ. The results showed that （1） moderate to high seasonality was presented in the distribution of erosive rainfall, and the seasonality of rainfall erosivity was even stronger; （2） seasonal variations were demonstrated in both parameters α and β of the Richardson model; and （3） incorporating and coordinating the seasonality of parameters αandβgreatly improved the predictions at the monthly scale. This newly modi- fied model is therefore highly recommended when monthly rainfall erosivity is required, such as, in planning soil and water conservation practices and calculating the cover-management factor in the Universal Soil Loss Equation （USLE） and Revised Universal Soil Loss Equation （RUSLE）.
基金supported by the National Natural Science Foundation of China underGrant No. 40475009
文摘In this paper, the equilibrium entrainment into a shear-free, linearly stratified atmosphere is discussed under the framework of bulk models, namely, the zero-order jump model （ZOM） and the first-order jump model （FOM）. The parameterizations for the dimensionless entrainment rate versus the convective Richard- son number in the two models are compared. Based on the assumption that the parameterized entrainment rates in ZOM and FOM should be the same, the inherent relationships among the entrainment parameters in the bulk models are revealed. These relationships are supported by tank experiments and large-eddy sim- ulations. The validity of these inherent relationships indicates that, for a convective boundary layer growing into a linearly stratified free atmosphere, the only dominant factors of the growth rate are the turbulent buoyancy in the mixed layer and the stratification in the free atmosphere. In the point of the similarity view, the former is characterized by turbulent temperature and mixing length scales （mixed layer depth）, and the latter is characterized by the lapse rate of potential temperature in the free atmosphere. Thus, the commonly-used Richardson number scheme for the parameterization of the entrainment rate is just as an equivalent description. The variability of the total entrainment flux ratio in FOM, which is connected with the entrainment zone thickness, can implicitly describe the effect of the stratification in the free atmosphere, but the entrainment zone thickness is not an independent parameter. These results demonstrate the validity of the hypothesis that there exists a similarity limit in which the mixed layer depth is the only lengthscale.
基金supported by the German Academic Exchange Service(DAAD).
文摘This study presents an extended version of a single site daily weather generator after Richardson. The model is driven by daily precipitation series derived by a first-order two-state Markov chain and considers the annual cycle of each meteorological variable. The evaluation of its performance was done by deploying its synthetic time series into the physical based hydrological model BROOK90. The weather generator was applied and tested for data from the Anchor Station at the Tharandt Forest, Germany. Additionally its results were compared to the output of another weather generator with spell-length approach for the precipitation series (LARS-WG). The comparison was distinguished into a meteoro-logical and a hydrological part in terms of extremes, monthly and annual sums and averages. Extreme events could be preserved adequately by both models. Nevertheless a general underestimation of rare events was observed. Natural correlations between vapour pressure and minimum temperature could be conserved as well as annual cycles of the hydro-logical and meteorological regime. But the simulated spectrums of extremes, especially, of precipitation and temperature, are more limited than the observed spectrums. While LARS-WG already finds application in practice, the results show that the data derived from the presented weather generator is as useful and reliable as those from the established model for the simulation of the water balance.
