资源环境科技发展态势分析平台

The water balance dynamics in lowland watersheds are influenced not only by local hydroclimatic controls on energy and water availability, but also by imports of water from the upstream watershed. These imports result in a stochastic extent of inundation in lowland watersheds that is determined by the local flood regime, watershed topography, and the rate of loss processes such as drainage and evaporation. Thus, lowland watershed water balances depend on two stochastic processesrainfall and local inundation dynamics. Lowlands are high productivity environments that are disproportionately associated with urbanization, high productivity agriculture, biodiversity, and flood risk. Consequently, they are being rapidly altered by human developmentgenerally with clear economic and social motivationbut also with significant trade-offs in ecosystem services provision, directly related to changes in the components and variability of the lowland water balance. We present a stochastic framework to assess the lowland water balance and its sensitivity to two common human interventionsreplacement of native vegetation with alternative land uses, and construction of local flood protection levees. By providing analytical solutions for the mean and PDF of the water balance components, the proposed framework provides a mechanism to connect human interventions to hydrologic outcomes, and, in conjunction with ecosystem service production estimates, to evaluate trade-offs associated with lowland watershed development.

Plain Language Summary The water balance is the fundamental partitioning of water between different inputs to a catchment, for example rainfall or snow, and processes that remove water from an areasuch as streamflow, evaporation, and deep recharge. The controls on the water balance have been well described in dryland areas. In lowland areaslike river deltas or floodplainsthe water balance is also influenced by water inputs from streams. Development of lowlands that alters these inputs can perturb the water balance in important ways. This study uses a theoretical approach to link the properties of the flow regime to flooding of lowland environments and water balance partitioning. It shows how building levees and changing land cover sets up trade-offs in terms of flood occurrence, flood duration, and total evaporation. These trade-offs impact the productivity and hazards associated with lowland areas. Being able to describe them analytically sets the stage for subsequent sociohydrologic assessment of lowland developments.