Mean annual soil water stress index

The monthly water stress is the percentage of actual to potential evapotranspiration. Adapted from the index by (Hackett 1988). Actual evapotranspiration is an output of a water balance model, and potential evapotranspiration is the pan evaporation (free-water surface) adjusted by the coefficient of potential evapotranspiration (PETCF). A constant PETCF value of 0.9 was used for all months which assumes constant leaf area index.

月度水分胁迫为实际蒸散发（actual evapotranspiration）与潜在蒸散发（potential evapotranspiration）的百分比比值。该指标改编自Hackett于1988年提出的相关指数。其中，实际蒸散发为水平衡模型（water balance model）的输出结果；潜在蒸散发则为经潜在蒸散发系数（PETCF）校正后的自由水面蒸发皿蒸发量。所有月份均采用恒定为0.9的PETCF值，该取值假设叶面积指数保持恒定。