Tracing Trends and Changes of Drought in Hydrosystems (TrenDHy)

干旱对环境、社会和经济有着广泛的影响。干旱的现象、自然灾害及其在环境系统中的传播需要更多的基础研究。TrenDHy（追踪水文系统干旱趋势和变化）项目的总体目标是调查和量化耦合水文系统对气象干旱的恢复能力。如果气象干旱扩展到极低流量（也称为水文干旱），它可以对河流生态、供水和航运产生广泛的直接影响，并对一系列重要经济部门造成间接损害。其核心假设是，全球变化将增加为各种下游用水提供水源的水源系统发生干旱的风险。具体来说，该项目将调查两个特定的集水系统的长期变化，这两个系统可以在长期的气象干旱期间维持河流的流动：冰川和地下水。在方法上，TrenHy将采用区域方法，并将对每个系统的流量记录的大数据集进行统计趋势分析，并为每个系统开发基于模型的归因方法。统计分析将根据经验调查不同水文系统的区域特征、非线性定量水文变化轨迹，重点是它们对干旱期的响应（经验变化检测）。多模型方法将首先开发基于过程的模型，这些模型可以通过表示水文气候对不同系统在长时间干旱期间向流中储存和释放水的相互作用的直接和间接变化来解释这些变化（基于模型的归因）。最后，基于对系统功能、敏感性和恢复力（干旱灾害情景）的理解，这些模型将被应用于水文干旱灾害变化的预测。这些方法在方法上面临许多挑战，需要开发新的方法来进行非线性趋势分析、瞬态模型参数化和应用、情景开发及其在研究水源集水区区域气候敏感性表征中的应用。预期研究结果将增进对自然灾害过程的了解，预计未来在世界大部分地区自然灾害将变得更加频繁和严重，因此需要更好的风险评估和管理方法。

Drought has a wide range of impacts on environment, society and economy. The phenomenon and natural hazard of drought and its propagation through the environmental system requires more basic research. The overall objective of the project TrenDHy (Tracing Trends and Change of Drought in Hydrosystems) is the investigation and quantification of the resilience of coupled hydrological systems to meteorological drought. If a meteorological drought propagates into extreme low flows (also termed hydrological drought) it can have wide ranging direct impacts on river ecology, water supply, and navigation, as well as indirect damage potential for a range of economically important sectors. The central hypothesis is that global change will increase the risk of drought in headwater systems that supply water to a variety of downstream water uses as well. Specifically, the project will investigate long-term changes in two specific catchment systems that can sustain river flow during extended periods of meteorological drought: glaciers and groundwater. Methodologically, TrenHy will employ a regional approach and will combine statistical trend analysis of a large-n dataset of streamflow records for each system with the development of model-based attribution approaches for each system. The statistical analysis will investigate empirically the regionally characteristic, non-linear quantitative hydrological change trajectories for different hydrological systems with an emphasis on their response to dry periods (empirical change detection). The multi-modelling approach will first develop process-based models that can explain these changes through representation of the interacting direct and indirect changes that the hydro-climate has on the storage and release of water to streamflow during extended dry periods in different systems (model-based attribution). Finally, the models will be applied for the predictions of changes to the hydrological drought hazard based on the obtained understanding of system functioning, sensitivities and resilience (drought hazard scenarios). The approaches have a number of methodological challenges and require the developments of new methodology for the non-linear trend analysis, the transient model parameterization and application, and the scenario development and its use toward the characterization of a regional climate sensitivity of the studied headwater catchments. The results are expected to improve the understanding of the processes of a natural hazard that is expected to become more frequent and severe in the future in large parts of the world and therefore requires better risk assessment and management approaches.