A new landscape leakiness index based on remotely sensed ground-cover data

A new continuous, cover-based, directional leakiness index, CDLI, is described that has a number of advantages over a binary-based, directional leakiness index, DLI, previously described in this journal. These indices are monitoring tools aimed to indicate the potential for gently sloping, arid and semi-arid landscapes to retain, not leak, resources, such as soils. To compute DLI, pixels in remotely sensed images had to be classified as being either vegetation patches or open interpatches. This simple binary classification procedure is unrealistic for images with relatively large pixels (e.g., 30-m pixel Landsat), where a single pixel is likely to be a mix of denser vegetation patches and more open interspaces. This mix of patch and interpatch within a pixel can be represented as proportional ground-cover. Because CDLI is based on these ground-cover data, which can vary continuously between 0–100%, it is an index of landscape leakiness that is applicable to larger scale, remotely sensed imagery. Using Landsat imagery, we illustrate how CDLI is useful for comparing the potential leakiness of four Australian arid and semi-arid sites differing in rangeland condition. When imagery is available for specific landscape sites through time, CDLI can be used to monitor changes in the potential leakiness of these sites. However, both CDLI and DLI assume that resource flows are one-directional, which restricts their application to images acquired from relatively gentle, uniform landscapes. A leakiness index applicable to landscapes with hilly terrain is being developed.