GIS-Based Ecosystem Service Analysis of Green Infrastructure
International Journal of Innovative Research in Science Engineering and Technology
To restore and sustain urban stream or river water quality, many cities have been devoting to a green infrastructure, and federal agencies have started collaborating to help the community invest in green roof, roadside rain gardens and increased tree canopies. The objective ofthis study is toanalyze the ecosystem benefit of the green stromwaterinfrastructurethat applies to managing stormwaterquantity and quality.Using an ArcGIS-based modelling tool, we quantitatively analyzedthe ecosystem
... the ecosystem service of green roofs. The results show that constructing green roofs on the rooftops of 2% of the impervious areas or building can reduce up to 166% and 32% storm water runoff in Rock Creek and Anacostia River sub-watersheds in Washington DC, respectively. This can save up to $21.4 million in building storage tanks to store total runoff volume. Improving green roof and tree canopy areas can significantly reduce the negative impact of urban storm water runoff and therebyimprove urban-stream water quality. III. STUDY SITE To conduct ecosystem service analysis of green infrastructure in DC, we considered Rock Creek and Anacostia River watershed. The Anacostia River is relatively a slow moving water body that is significantly affected by the tide. In contrary, Rock Creek is a free-flowing stream and unaffected by the tide for the majority of its length. Based on ArcGIS and land cover map of 2006( Fig. 2) , about 40% of the land cover in the Rock Creek park is impervious surface, including roads, buildings and other pavements, whereas about 60% of the area is covered by pervious layer, including tree canopies, grass/shrubs and bare earth. The urban ecosystem analysiswas conducted using CITYgreen® software inArcGIS  . The CITYgreen ® software uses the raster data land cover classification from the high-resolution imagery for the analysis. In this software three sub-models are integrated, such as stormwater runoff and water quality model, both were developed by U.S. Natural Resource Conservation (NRC), and urban forest effects model developed by the USDA. Forest Service for assessing air pollution model  is integrated with the water quality model. Air quality model is not the scope of this study, but the water quality model estimates the change in the concentration of the pollutants in a runoff during a typical storm event given the change in the land cover from existing trees to a no tree condition. This model estimates the event mean concentrations of nitrogen, phosphorus, suspended solids, zinc, lead, cadmium, chromium, chemical oxygen demand (COD), and biological oxygen demand (BOD). Pollutant values are expressed as a percentage of change, which depends on the areal coverage of the green infrastructure. Fig.2.DC Land cover in 2006 Rock Creek Anacostia River Fig.5.Effect of 2% increase of green roof area on storm water storage, water quality contaminant load reduction in Rock Creek. Fig. 8.Effect of 2% increase of Green roof area on storm water runoff and water quality in Anacostia River watershed in DC. V. CONCLUSION Based on the scenario analysis, one can conclude that increase of green roofs area by 2% can reduce peak flow rate. This is logical as green roof is mainly designed to slow down and reduce the peak flow rate of runoff during storm events. The overall study of this project shows the usefulness of integrating the GIS based quantitative ecosystem service analysis in the decision making process for sustainable water resources management. The results of the proposed GIS based ecosystem services analysis have the following benefits: Quantify the stormwater, water quality ecosystem service of the existing green infrastructure of the District of Columbia. Calculate the effects of future land cover change before those changes are made. Analyze the changed of green area of the city over time, by comparing land cover maps from earlier periods, such as 10 or 20 years ago, depending on the available data. Assist environmental managers as a tool for mitigating carbon emission and reduce its effect on climate. Community awareness of ecological and economic value of green infrastructure creates incentives for the landowner to consider planting trees and urban gardening. Quantify the costs of parts of the green area if lost to the residence. Can be used to educate future scientists, including school children, and thereby improve the wellbeing of our community.