Land cover change study may lead to future impact studies

Data derived from a recent land cover change project on Saipan can be used to address other questions like the impact of human activities on water quality, watershed management, and sustainable development on Saipan, according Dr. Yuming Wen of the Water and Environmental Research Institute of the Western Pacific University of Guam in his report on the project.

In an interview, Wen, who led the project, noted significant urban development in the Kagman watershed as examples of some of the data collected during this year’s project.

He pointed to most change occurring in Kagman, the southern part of Saipan, some development on the west coast, but not a significant amount on the northeast coast of the island.

Over 30 years of land cover change were assessed by the project, according to Wen.

Land cover information was derived from Landsat MSS imagery of Oct. 17 and Dec. 10, 1978.

Wen said the two shots were needed, as one did not cover the whole island. There were problems with some of images due to cloud and shadow cover. Also, programs like the ArcGIS Desktop and ERDAS Imagine were used to correct displaced parts of the image. In the end, according to Wen, the two images were mosaicked to create one image.

In his report, the image was processed to collect land cover classification, and five general classes were detected: forest, grassland, urban, water, and cloud or shadow.

The 1978 image was then compared with two images from an ASTER satellite taken in 2009. These were also mosaicked as well as one shot did not include part of northern Saipan.

While the images had faults, they were the “best data he could get” from the U.S. Geological Survey for the project, according to Wen.

Comparing the two data sets, Wen found that Saipan was mainly covered by forest and grassland both in 1978 and 2009.

Forest area increased 47.4 percent or about 2,765 hectares from 1978 to 2009. Grasslands decreased by about 2,765 hectares, or about 54 percent, according to the report.

“Built-up/urban area” increased about 908 hectares or 63.7 percent during the same period, according the to the report.

Most of these increased urban areas occurred in forest and grassland.

Of the 11 watersheds on Saipan, Kagman Watershed was noted for its “many development activities” from 1978 to 2009.

Urban area about doubled, increasing about 191 hectares, according to the report.

Forest area increased by about 151 hectares, or 20 percent, and grassland decreased by about 333 hectares or about 54.2 percent.

Wen said the “next step” after this project would be to look at water quality in wells, for example. He said that more people moving into a watershed area might affect the water quality there.

WERI may possibly look if there is a relationship between water quality and human activity in the studied areas in a project next year, according to Wen.

If water quality is found to poorly affect communities, the island may need to find ways to reduce human activity, he said.

“We are dependent on underground water resources. We need to protect water quality on Saipan,” he said.

Also ongoing under WERI is the development of a geographic information system model for groundwater quality on Saipan. The project should be completed next February, according to Wen.