Rainfall interception - Localization of water storage and evapotranspiration in forests

降水截留对生态系统中水分的可利用性有重要影响。特别是在森林生态系统中，高达50%的降水通过截流蒸发，这是植物无法获得的。这一过程是高度可变的，模型还不能令人满意地描述。用于确定模型参数的统计方法，以及描述过程不完整的概念方法，在截获的量化中产生了很大的不确定性。特别是统计参数化和对植被结构和性质的考虑不足，阻碍了实验结果向其他地点的转移。然而，考虑到降雨模式和土地利用变化对未来水资源预算的影响，这是强制性的。拟议项目的目的是通过对该过程的小空间变异性进行调查和参数化，大大减少拦截评估和建模中的不确定性。已知低强度雨事件被林分外层拦截，其特征是强大气耦合和有效蒸发。相比之下，高强度的降雨事件超过了储存能力，也产生了湿层，干得很慢。由于对植被结构的考虑有限，这种非线性行为在拦截模型中仍然没有得到充分的考虑。在该项目中，将在详细测量（微气象、水文和激光扫描）的基础上研究冠层内的蓄水和截流机制，并将开发和测试新的方法，将植被结构的依赖关系参数化。森林截伐的标准估计是基于通过空间分布的降水计或大槽收集的穿透量和模型结果，而没有充分考虑林分的三维空间异质性。由此产生的参数误差和模型结果尚未被调查和量化。具有高时空分辨率的新建模方法将允许将模拟结果分配给单个穿透收集器，并与蒸散发的微气象测量进行比较。地面激光扫描提供了所需的详细植被模型。因此，将在一个非常适合的Fluxnet塔周围以1 m³和1分钟的时空分辨率在600 m × 600 m范围内进行拦截过程的模拟，该塔提供了一套独特的近20年微气象和水文测量数据。通过这种实验和建模的结合，预计将在理解拦截方面产生一个阶梯式的变化。

Interception of precipitation has a significant influence on the availability of water in ecosystems. Especially in forest ecosystems evaporates up to 50 % of precipitation via interception which is not available to plants. The process is highly variable and is not yet described by models satisfactorily. Statistical methods for the determination of model parameters, and conceptual approaches describing the processes incompletely, produce significant uncertainty in the quantification of interception. In particular the statistical parameterization and the weak consideration of the structure and properties of vegetation stands prevent the transfer of experimental findings to other sites. However, this is mandatory to account for effects of changing rainfall patterns and land use on the future water budget.The aim of the proposed project is the considerable reduction of uncertainties in interception assessment and modelling by investigation and parameterization of the small spatial variability of the process. It is known that rain events with low intensity are intercepted by the outer layers of forest stands which are characterized by strong atmospheric coupling and effective evaporation. In comparison, rain events with high intensity exceed the storage capacity and also produce wet layers, which dry very slowly. This nonlinear behavior is still not sufficiently included in interception models due to a limited consideration of the vegetation structure. In the project, the mechanisms of water storage and interception within the canopy shall be examined on the basis of detailed measurements (micrometeorological, hydrological and via laser scanning), and new approaches will be developed and tested which parameterize the dependencies with regard to vegetation structure. Standard interception estimates of forests are based on throughfall collected through spatially distributed precipitation gauges or large troughs and on model results without taking the three-dimensional spatial heterogeneity of the stands into account adequately. The resulting error in the parameters and model outcome has not been investigated and quantified yet. The new modeling approach with high spatiotemporal resolution will allow the assignment of the simulation results to individual throughfall collectors, as well as the comparison with micrometeorological measurements of evapotranspiration. The required detailed vegetation model is provided from terrestrial laser scanning. Therefore, the simulation of the interception process will be conducted with a spatial-temporal resolution of 1 m³ and 1 min in a range of 600 m × 600 m around a well suited Fluxnet tower, which provides a unique set of almost 20 years of micrometeorological and hydrological measurements. By this combination of experiments and modelling it is expected to generate a step-change in understanding of interception.