The Environmental Reporting Act 2015 creates a joint obligation on MfE and Statistics NZ for regular national reporting on New Zealand’s environment through synthesis and domain reports. To date, reporting of wetlands has simply compared extent in 2008 with pre-human extent (Environment Aotearoa 2015). To improve the currency of wetland reporting, MfE has contracted Landcare Research to produce an analysis of wetland loss for the period 2005−2016, reported by region. This is a desktop solution involved a visual comparison of the WONI wetlands, as mapped for 2001/02 from Landsat imagery, against 2016 Sentinel-2 satellite imagery. Although this visual inspection was insufficient to capture deterioration in the condition of wetlands, it was sufficient to detect disappearance of wetlands and reduction in their extent with reasonable confidence. Supplementary comments were also made if wetland polygons were seen to be inaccurate or erroneous. Seventy-six percent of the wetlands, comprising a little over half the total national area identified by WONI as wetlands, were recorded as unchanged. Only 214 wetlands (1.5% of the national total) were no longer present. However, 746 (5%) of the WONI wetlands were recorded as partially lost. Six percent of the wetland polygons appeared to be errors. In addition, 11.5% were flagged as correct but in need of improvements in the polygon line work.
Wetland outer boundaries (as depicted by WONI (Ausseil et.al. 2008)) were generated by dissolving internal differentiation arising from evidential and classification data to simply depict wetland outlines, attributed as Wetland = 'yes'
Wetlands outlines (of nominally 2003 date) were visually compared with summer 2015/2016 Sentinal 2 imagery and tagged according to whether there has been no loss, partial loss, or complete loss of area, or whether the polygons were either poorly delineated or original error.
This layer was finally intersected with 2017 Regional Council boundaries for analysis and reporting.