Fuqiang Tian

From channelization to restoration: Sociohydrologic modeling with changing community preferences in the Kissimmee River Basin, Florida

The Kissimmee River Basin (Florida, USA) underwent river channelization in the 1960s and subsequent restoration in the 1990s, revealing a shift in management emphasis from flood protection to wetland health. In this paper, this shift is hypothesized to result from changing human values and preferences, and a power differential between the more numerous and affluent upstream urban residents (who prioritize wetland restoration) and downstream rural residents (who prioritize flood protection). We develop a conceptual sociohydrologic model to simulate the interactions between community interests and hydrology. The modeling results show that flood intensity decreased after channelization, which reduced concern about flooding. However, channelization also led to a decrease in wetland storage, which caused an increase of wetland concern, especially among the urban residents. Eventually, the community sensitivity switched from favoring flood protection to favoring wetlands, and subsequent management strategies switched from channelization to restoration. Using the model, we project that the wetlands will be recovering for the next 20 years and community sensitivity will slowly go back to a neutral state. However, possible rainfall intensification in the future could return the community sensitivity to favoring flood protection again. The preferential increase of upstream population growth will raise the communitys concern about wetlands and the preferential increase of downstream population growth will magnify concern about flooding. This study provides insight into the driving forces behind human-water interactions in the Kissimmee River Basin while simultaneously demonstrating the potential of sociohydrologic modeling to describe complex human-water coupled systems with simple concepts and equations.

Functional approach to exploring climatic and landscape controls of runoff generation: 1. Behavioral constraints on runoff volume†

Inspired by the Dunne diagram, the climatic and landscape controls on the partitioning of annual runoff into its various components (Hortonian and Dunne overland flow and subsurface stormflow) are assessed quantitatively, from a purely theoretical perspective. A simple distributed hydrologic model has been built sufficient to simulate the effects of different combinations of climate, soil, and topography on the runoff generation processes. The model is driven by a sequence of simple hypothetical precipitation events, for a large combination of climate and landscape properties, and hydrologic responses at the catchment scale are obtained through aggregation of grid-scale responses. It is found, first, that the water balance responses, including relative contributions of different runoff generation mechanisms, could be related to a small set of dimensionless similarity parameters. These capture the competition between the wetting, drying, storage, and drainage functions underlying the catchment responses, and in this way, provide a quantitative approximation of the conceptual Dunne diagram. Second, only a subset of all hypothetical catchment/climate combinations is found to be “behavioral,” in terms of falling sufficiently close to the Budyko curve, describing mean annual runoff as a function of climate aridity. Furthermore, these behavioral combinations are mostly consistent with the qualitative picture presented in the Dunne diagram, indicating clearly the commonality between the Budyko curve and the Dunne diagram. These analyses also suggest clear interrelationships amongst the “behavioral” climate, soil, and topography parameter combinations, implying these catchment properties may be constrained to be codependent in order to satisfy the Budyko curve.

A numerical model for water and heat transport in freezing soils with nonequilibrium ice‐water interfaces

A one-dimensional numerical model of heat and water transport in freezing soils is developed by assuming that ice-water interfaces are not necessarily in equilibrium. The Clapeyron equation, which is derived from a static ice-water interface using the thermal equilibrium theory, cannot be readily applied to a dynamic system, such as freezing soils. Therefore, we handled the redistribution of liquid water with the Richards equation. In this application, the sink term is replaced by the freezing rate of pore water, which is proportional to the extent of super-cooling and available water content for freezing by a coefficient, β. Three short-term laboratory column simulations show reasonable agreement with observations, with standard error of simulation on water content ranging between 0.007 cm3cm−3 and 0.011 cm3cm−3, showing improved accuracy over other models that assume equilibrium ice-water interfaces. Simulation results suggest that when the freezing front is fixed at a specific depth, deviation of the ice-water interface from equilibrium, at this location, will increase with time. However, this deviation tends to weaken when the freezing front slowly penetrates to a greater depth, accompanied with thinner soils of significant deviation. The coefficient, β, plays an important role in the simulation of heat and water transport. A smaller β results in a larger deviation in the ice-water interface from equilibrium, and backward estimation of the freezing front. It also leads to an underestimation of water content in soils that were previously frozen by a rapid freezing rate, and an overestimation of water content in the rest of the soils. This article is protected by copyright. All rights reserved.

Comparing different methods for determining forest evapotranspiration and its components at multiple temporal scales

Accurately estimating forest evapotranspiration and its components is of great importance for hydrology, ecology, and meteorology. In this study, a comparison of methods for determining forest evapotranspiration and its components at annual, monthly, daily, and diurnal scales was conducted based on in situ measurements in the subhumid mountainous forest of North China. The goal of the study was to evaluate the accuracies and reliabilities of the different methods. The results indicate the following: (1) The sap flow upscaling procedure, taking into account diversities in forest types and tree species, produced component-based forest evapotranspiration estimate that agreed with eddy covariance-based estimate at the temporal scales of year, month, and day, while soil water budget-based forest evapotranspiration estimate was also qualitatively consistent with eddy covariance-based estimate at the daily scale; (2) At the annual scale, catchment water balance-based forest evapotranspiration estimate was significantly higher than eddy covariance-based estimate, which might probably result from non-negligible subsurface runoff caused by the widely distributed regolith and fractured bedrock under the ground; (3) At the sub-daily scale, the diurnal course of sap flow based-canopy transpiration estimate lagged significantly behind eddy covariance-based forest evapotranspiration estimate, which might physiologically be due to stem water storage and stem hydraulic conductivity. The results in this region may have much referential significance for forest evapotranspiration estimation and method evaluation in regions with similar environmental conditions.

Divergence of stable isotopes in tap water across China

Stable isotopes in water (e.g., δ2H and δ18O) are important indicators of hydrological and ecological patterns and processes. Tap water can reflect integrated features of regional hydrological processes and human activities. China is a large country with significant meteorological and geographical variations. This report presents the first national-scale survey of Stable Isotopes in Tap Water (SITW) across China. 780 tap water samples have been collected from 95 cities across China from December 2014 to December 2015. (1) Results yielded the Tap Water Line in China is δ2H = 7.72 δ18O + 6.57 (r2 = 0.95). (2) SITW spatial distribution presents typical “continental effect”. (3) SITW seasonal variations indicate clearly regional patterns but no trends at the national level. (4) SITW can be correlated in some parts with geographic or meteorological factors. This work presents the first SITW map in China, which sets up a benchmark for further stable isotopes research across China. This is a critical step toward monitoring and investigating water resources in climate-sensitive regions, so the human-hydrological system. These findings could be used in the future to establish water management strategies at a national or regional scale.