PIV measurement of buffer and logarithmic layers with detached eddies which mimics the neutral atmospheric surface layer

Accurate comprehension of turbulence characteristics in the atmospheric surface layer (ASL) under near neutral conditions, which is a lower part of the atmospheric boundary layer and a very high-Re number flow, is critically required in view of the increasing and broadening use of numerical weather prediction models. The models need to estimate turbulence fluxes of momentum, heat and moisture in the ASL as boundary conditions. On the other hand, observations (Högström 1990, Drobinski et al. 2007) have revealed that the fluxes under near-neutral conditions are often inconsistent with Monin-Obukhof theory, which has been widely used in models. The observations were conducted over flat surfaces with homogeneous roughness, and thus the violation from the theory might not be due to the underlying surface conditions. Thus, aiming to investigate an origin of the violation from the theory, we have carried out a wind tunnel experiment on the logarithmic layer along a smooth flat wall with a larger-scale disturbance, which mimics the near-neutral atmospheric surface layer (Hattori et al. 2010). In the present study, we especially examine a PIV measurement with a long-distance microscope lens to discuss the interaction of turbulences structures between buffer and logarithmic layers, which must give a clue on Reynolds number effects

Characteristics of temporal and spatial evolution of rainfall under the influence of urbanization---A case study of the Beijing-Tianjin-Hebei region

Based on the rainfall data from 197 rain gauge stations for the period 1960 to 2019, linear regression, moving average, and SURFER spatial analysis were used to analyze the temporal and spatial characteristics of rainfall in the Beijing-Tianjin-Hebei region, and compare the difference in rainfall between the mountainous areas and plains, during the flood season. The results show that (1) the overall duration of rainfall in each region of Beijing-Tianjin-Hebei exhibit a downward trend, and the overall spatial performance gradually decreases from east to west. (2) The mountainous areas in the Beijing-Tianjin-Hebei region are prone to light and moderate rainfall events; the plains are more prone to rainfall events at levels above moderate rain, especially rainstorms and heavy rain events; the probability of light and moderate rainfall events in the suburbs is close to that of the urban areas, but the probability of rainfall events at levels above heavy rain is less than that of the urban areas; the probability of rainfall events of all levels in the outer suburbs is higher. (3) Increase in rainfall in urban areas compared to the southern suburbs is greater than when compared with the northern suburbs which are at different stages of urbanization, but the effect of urbanization on rainfall is also reflected in the comparison between the urban areas and the northern suburbs. (4) With increasing urbanization, the built environment in the mountainous areas and plains of the Beijing-Tianjin-Hebei region has continued to grow, and the original underlying surface conditions have changed. Because the urbanization process is faster in the urban areas than in the suburbs, the changes to the underlying surface conditions lead to greater increase in rainfall in urban areas during the flood season compared to the suburbs; the urban areas are also more prone to rainfall events at levels above heav

Effects of Rainfall and Underlying Surface on Flood Recession—The Upper Huaihe River Basin Case

The effects of rainfall and underlying surface conditions on flood recession processes are a critical issue for flood risk reduction and water use in a region. In this article, we examined and clarified the issue in the upper Huaihe River Basin where flood disasters frequently occur. Data on 58 rainstorms and flooding events at eight watersheds during 2006–2015 were collected. An exponential equation (with a key flood recession coefficient) was used to fit the flood recession processes, and their correlations with six potential causal factors—decrease rate of rainfall intensity, distance from the storm center to the outlet of the basin, basin area, basin shape coefficient, basin average slope, and basin relief amplitude—were analyzed by the Spearman correlation test and the Kendall tau test. Our results show that 95% of the total flood recession events could be well fitted with the coefficient of determination (R2) values higher than 0.75. When the decrease rate of rainfall intensity (Vi) is smaller than 0.2 mm/h2, rainfall conditions more significantly control the flood recession process; when Vi is greater than 0.2 mm/h2, underlying surface conditions dominate. The result of backward elimination shows that when Vi takes the values of 0.2–0.5 mm/h2 and is greater than 0.5 mm/h2, the flood recession process is primarily influenced by the basin’s average slope and basin area, respectively. The other three factors, however, indicate weak effects in the study area.

System response curve correction method of runoff error for real-time flood forecast

Multiple factors including rainfall and underlying surface conditions make river basin real-time flood forecasting very challenging. It is often necessary to use real-time correction techniques to modify the forecasting results so that they reach satisfactory accuracy. There are many such techniques in use today; however, they tend to have weak physical conceptual basis, relatively short forecast periods, unsatisfactory correction effects, and other problems. The mechanism that affects real-time flood forecasting error is very complicated. The strongest influencing factors corresponding to this mechanism affect the runoff yield of the forecast model. This paper proposes a feedback correction algorithm that traces back to the source of information, namely, modifies the watershed runoff. The runoff yield error is investigated using the principle of least squares estimation. A unit hydrograph is introduced into the real-time flood forecast correction; a feedback correction model that traces back to the source of information. The model is established and verified by comparison with an ideal model. The correction effects of the runoff yield errors are also compared in different ranges. The proposed method shows stronger correction effect and enhanced prediction accuracy than the traditional method. It is also simple in structure and has a clear physical concept without requiring added parameters or forecast period truncation. It is readily applicable in actual river basin flood forecasting scenarios.

The research status of flash flood warning in China

The article discusses from the disaster mechanism of flash flood to the current situation of early warning system. The formation of flash flood is closely related to rainfall intensity, underlying surface conditions and antecedent soil moisture content, and analysis of the physical process of flash flood disasters is crucial for the study of flash flood warning. Flash flood disaster warning indexes are mainly divided into two types: rainfall warning index and water level warning index. Data-driven statistical induction method and hydro-hydraulic methods based on physical mechanisms are used to determine rainfall warning index; The water level warning index can be directly determined by the upstream and downstream corresponding water level method or by the disaster water level. And summed up the current situation and development trend of China's flash flood warning research.

Study on Non-Point Source Pollution in the Agricultural Watershed

This paper gives a review on the study of related factors of non-point source pollution (NPS) in water cycle. Hydrological process features, underlying surface conditions, human activities are sorted to introduce the recent research on NPS progress. Several major factors are divided in each item with developing process. The NPS models in world are introduced as well. Additionally, control approaches for NPS and their effects are summarized. Furthermore, the potential trends of NPS study are discussed.

Comprehensive Diagnosis of Kuyehe Flood Series Change-Point

The comprehensive diagnosis method can avoid the unreasonable of single analysis method and inconsistency of various analysis methods. This paper used the method to diagnosis the change-point of Kuyehe flood series. The result is consistent with the hydrological investigated results, which can provide the basis of quantifying the impact of changes of underlying surface conditions on the watershed runoff.