Ecosystem Viltality Drainage Basin Condition (DBC) Land Cover Naturalness (LCN)

The Land Cover Naturalness Index (LCN) describes the state and trend of land use/land cover (LULC) within the basin, according to the amount of human-induced transformation present. A basin in its undisturbed state, with intact forests and wetlands, generally maintains a sufficient quantity and quality of water to support indigenous flora and fauna. Naturalness exists on a gradient from completely natural to completely artificial or human dominated (Angermeier, 2000). Human conversion of lands and waterways are associated with increases in pollutant loads (non-point source from agriculture, point-source from urban and industrial), changes to infiltration and runoff regimes, and losses of regulating services (flood mitigation, erosion prevention, water purification). The Naturalness Index is, therefore, a proxy indicator for the degree to which these naturally-occurring functions are preserved within the basin. It is based on similar efforts to categorize and quantify this gradient over landscapes, such as Machado’s (2004) index of naturalness and the hemeroby hvb scale (Sukopp, 2004; Paracchini and Capitani, 2011; Walz and Stein 2014). More detailed investigations of specific LULC types, such as forest conversion to agriculture, may be warranted as a secondary step and can be calculated using the same data.

Data Preparation:

1. Review and revise naturalness weights:

The Degree of Naturalness classification table (Deg_of_N.csv) below contains descriptions of LULC types as well as cultural practices (e.g., irrigation) that correspond to “naturalness” weighted on a 0-100 gradient. Sub-classifications are suggested based on three factors:

1. Management of the water cycle: manually altering the flow and/or use of water to maintain a particular land-use type

2. Pollution: chemical and physical pollutants entering the local water cycle due to human practices, such as fertilizer and pesticide use, and increased soil runoff from croplands as well as urban runoff and point-source wastewater loads from urban and industrial lands

3. Vegetation characteristics: degree of native vegetation and permanence of vegetative cover

   The proposed weighting includes ranges of values to help highlight transitions from “natural” to “transformed” systems, i.e., from forests and wetlands to cultivated lands or from cultivated lands to urban areas (see Table below). It is strongly recommended that the default weights in the classification table be reviewed and, based on expert judgment, adjusted to be compatible with local conditions. For example, in some regions, flooded rice paddies may be considered to have a higher degree of naturalness than other irrigated crops, due to their ability to mimic some aspects of wetlands (which they may have replaced). In this case, a different classification and higher relative weight may be appropriate. Similarly, local or region-specific land use datasets may include highly detailed and differentiated classes of land use that will require expert judgment on their relative weight.

Table. Proposed “naturalness” characteristics and weights

Calculation in FHI Toolbox:

1. GIS processing

Intersect buffer polygon with land-cover data to generate table of land cover.

2. Classification (User-input)

For each land-cover type identified, assign weight based on decision-matrix above

3. Aggregation

Scores within a sub-basin can be calculated as:

$$ LCN = \left( \ \frac{\sum_{i = 1}^{m}{N_{i}\text{LCN}_{i}}}{\text{TN}} \right)*100 $$

where, TN is the total number of raster cells in buffer polygon of m type, Ni is the number of cells of land cover type ith, and LCNi is the appropriate score from the table directly above for that land-cover.