Heping Hu

The Influence of Precipitation Variability and Partial Irrigation within Grid Cells on a Hydrological Simulation

Abstract The effects of natural and anthropogenic heterogeneity on a hydrological simulation are evaluated using a distributed biosphere hydrological model (DBHM) system. The DBHM embeds a biosphere model into a distributed hydrological scheme, representing both topography and vegetation in a mesoscale hydrological simulation, and the model system includes an irrigation scheme. The authors investigated the effects of two kinds of variability, precipitation variability and the variability of irrigation redistributing runoff, representing natural and anthropogenic heterogeneity, respectively, on hydrological processes. Runoff was underestimated if rainfall was placed spatially uniformly over large grid cells. Accounting for precipitation heterogeneity improved the runoff simulation. However, the negative runoff contribution, namely, the situation that mean annual precipitation is less than evapotranspiration, cannot be simulated by only considering the natural heterogeneity. This constructive model shortcom...

Hydrological Cycles Change in the Yellow River Basin during the Last Half of the Twentieth Century

Abstract A distributed biosphere hydrological (DBH) model system was used to explore the internal relations among the climate system, human society, and the hydrological system in the Yellow River basin, and to interpret possible mechanisms for observed changes in Yellow River streamflow from 1960 to 2000. Several scenarios were evaluated to elucidate the hydrological response to climate system, land cover, and irrigation. The results show that climate change is the dominant cause of annual streamflow changes in the upper and middle reaches, but human activities dominate annual streamflow changes in the lower reaches of the Yellow River basin. The annual river discharge at the mouth is affected by climate change and by human activities in nearly equal proportion. The linear component of climate change contributes to the observed annual streamflow decrease, but changes in the climate temporal pattern have a larger impact on annual river discharge than does the linear component of climate change. Low flow i...

Positive or negative correlation between actual and potential evaporation? Evaluating using a nonlinear complementary relationship model

Understanding whether a positive or negative correlation between actual (E) and potential (Ep) evaporation is of great importance in detecting changes of E from Ep. In this study, such correlation was evaluated via the linear regression slope (k) between E and Ep derived from a nonlinear complementary relationship model. k varies with the relative degree of variability in the radiation term (Erad) and aerodynamic term (Eaero) of Ep, and is further affected by water availability. The sign of k is always positive under conditions with high Erad variability but at the same time with low Eaero variability (commonly true on an hourly basis). Under conditions with high Eaero variability but at the same time with low Erad variability, the sign of k tends to change from negative to positive with more readily water availability. On a daily or annual basis, the sign of k would be related with water availability. Under water-limited conditions, the Eaero variability is more significant than the Erad variability, and negative k is expected. Under energy-limited conditions, the Erad variability is compared to or even much obvious than the Eaero variability, and positive k is expected. This implies a negative correlation between E and Ep under water-limited conditions but a positive correlation under energy-limited conditions on the daily or annual basis. The above analysis is confirmed in a grassland site in Northeast China at daily and half-hourly time scales. The correlation between annual E and Ep over China was evaluated using data of 690 meteorological stations from 1956 to 2005. The k values change from negative in arid regions to positive in humid regions. According to k and the decreasing trends in annual Ep, it is deduced that E increased for most stations in arid regions but decreased for most stations in humid regions.

The role of run-on for overland flow and the characteristics of runoff generation in the Loess Plateau, China

Abstract The Loess Plateau in China is overlain by deep and loose soil. As in other semi-arid regions, convective precipitation produces storms, typically of short duration, relatively high intensity and limited areal extent. Infiltration excess (Hortonian mechanism) of precipitation is conventionally assumed to be more prominent than saturation excess (Dunne mechanism) for storm runoff generation. This assumption is true at a point during the storm. However, the runoff generation mechanism is altered when the runoff is conditioned by a lateral redistribution movement of water, i.e. run-on, as the spatial scale increases. In the Loess Plateau, the effects of run-on may be significant, because of the deep and loose surface soil layer. In this study, the role of run-on for overland flow in the Upper Wei River basin, located in the Loess Plateau, is evaluated by means of a simple numerical model at the hillslope scale. The results show that almost all the Hortonian overland flow infiltrates into the soil along the flat hillslope and dry gully before it reaches the river channel. Most of the runoff is generated from the saturated soil near the river channel and from the subsurface. The run-on process takes much longer than the infiltration, facilitating rainfall–runoff modelling at a daily time step. A hydrological model is employed to investigate the characteristics of runoff generation in the Upper Wei River basin. The analysis shows that the subsurface flow contribution to total streamflow is more than 53% from October to March, while the overland flow contribution exceeds 72% from April to September. Editor D. Koutsoyiannis; Associate editor Dawen Yang Citation Liu, D.F., Tian, F.Q., Hu, H.C., and Hu, H.P., 2012. The role of run-on for overland flow and the characteristics of runoff generation in the Loess Plateau, China. Hydrological Sciences Journal, 57 (6), 1107–1117.

Nonsmooth Dynamic Behaviors Inherited from an Ecohydrological Model: Mutation, Bifurcation, and Chaos

The existence of nontrivial dynamic behaviors in a hydrological system is intensively discussed in the literature. However, most of the work has been done from the nonlinear data analysis perspective, with only a few exceptions, due to the mathematical difficulties for theoretical analysis. In this study, a simple but comprehensive enough ecohydrological model with the pulsed atmospheric forcing was developed from the process analysis perspective. The model was then utilized to analyze the non-trivial dynamic behaviors in a coupled ecohydrological system qualitatively and numerically. Our results confirm the existence of multiple stationary states discussed by many researchers. Furthermore, parameter bifurcation was studied and the phenomenon of mutation is found to be rather common. Also, the chaotic characteristic of the system state is obtained under some specific parameters. Parts of these behaviors were seldom reported through the deterministic dynamic analysis done previously.