Author(s): Laura E. Garza-Diaz; Samuel Sandoval-Solis

Linked Author(s):

Keywords: River basin; Regime shifts; Thresholds; Alternative regime; Resilience

Abstract: River basins are unique dynamic systems shaped by hydrologic variation patterns, a dominant control of ecological resilience and ecosystem health. As resilient systems, river basins can adapt and thrive to changes in hydrologic patterns over time, absorb disturbances, reorganize, and continue to perform their function —retaining their identity. Persistent forcing, either natural (e.g., extreme hydrologic events, climate change) or anthropogenic (e.g., impoundments, land-use change, increasing water demand), can bring the system to a critical threshold or limit, causing undesirable regime shifts or ecosystem switching to an alternative state. How ecosystems react to perturbations is a central question in ecology today because these can cause catastrophic, undesirable, and even irreversible changes in natural systems. This study addresses how much forcing a river basin can take until the system undergoes a regime shift and into an alternative state? As a representative case, the transboundary Rio Grande Bravo basin, shared between the United States and Mexico, is selected given that it is subject to a wide range of environmental, socioeconomic, and climatic challenges under a complex political climate. From a combination of highly variable climatic conditions and increased anthropogenic pressure, the RGB basin is considered one of the world's most stressed and impacted rivers. Resilient indicators for quantitatively assessing resilience require long-term records sampled as temporal and spatial scales. For instance, this study analyzes 110 years of daily natural flows in six control points from 1900 to 2010. First, the hydrologic variability of a river basin is analyzed to describe the hydrologic states or basins of attraction of the naturalized system compared to a regulated system using the Streamflow Drought Index (SDI). Second, the detection of regime shifts is captured by the quantitative indicator Fisher information, followed by quantifying anthropogenic pressures that have caused the shift. Third, the probability density of the SDI hydrologic states is used to compute a hypothetical stability landscape representation of resilience and its approximate shapes of basins of attractions. Preliminary results indicate that a resilience threshold was surpassed, and a regime shift occurred in the control point of the Rio Conchos subbasin after three substantial anthropogenic perturbations occurred by 1948. Additionally, the analysis of the naturalized streamflow data exhibits a warning for an upcoming regime shift, given that the instability of the system is increasing. The final results will be presented and discussed. Understanding the conditions under which a river basin is likely to cross a threshold and the mechanisms that underlie a regime shift behavior is critical for environmental management, in addition to broadening our conceptualization of river basin ecosystem dynamics, resilience, and regime shifts.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221682

Year: 2022