Fig. 1: Schematic diagrams of Z score and ecosystem water needs assessments.
From: Establishing ecological thresholds and targets for groundwater management
a, Landscape schematic diagram illustrating how normalized difference vegetation index (NDVI) and depth-to-groundwater (DTG) fluctuations can vary temporally and spatially across the landscape depending on land surface elevation and landscape positioning. Groundwater depths and associated NDVI values are site specific and provided here for illustrative purposes. Most vegetation are adapted to natural fluctuations in DTG (for example, within −1 to +1 standard deviation (σ) over a baseline period), but if DTG exceeds these natural fluctuations, vegetation can become adversely impacted. b, DTG naturally fluctuates over time, but drought events and intensive groundwater pumping can cause groundwater levels to extend far below the natural range of variability observed over time. c, Z scores can be used to standardize groundwater levels as an alternative metric for quantifying ecological thresholds and targets across environments with variable local conditions.
