Analysis of environmental protection priority zones and their impacts on urban planning in small- and medium-sized cities of Indonesia

Urbanization in small- and medium-sized cities has often been overlooked in urban studies. Research on urbanization has predominantly focused on large metropolitan cities; however, urbanization in small- and medium-sized cities also contributes to the acceleration of urban sprawl. Urban growth boundary (UGB) is an ecological approach designed to limit urban development. This study aimed to analyze environmental protection priority zones by combining ecological quality and sensitivity indices to identify the areas suitable for UGB implementation. Tegal City and its surrounding areas (including Tegal and Brebes regencies) of Indonesia were selected as the study area. The ecological quality index was calculated using the normalized difference vegetation index, humidity index, land surface temperature, and normalized difference bare soil index. These indices were subsequently subjected to principal component analysis (PCA) to extract orthogonal factors, which were summed to derive the final index value. In parallel, we mapped and evaluated ecological sensitivity based on spatial planning policies and regulations. The results revealed that ecological quality in Tegal and Brebes regencies was predominantly categorized as good and very good ecological quality, whereas Tegal City exhibited moderate and poor ecological quality. Additionally, over 45.00% of the area in Tegal and Brebes regencies demonstrated very high ecological sensitivity. Consequently, more than 50.00% of the area in Tegal and Brebes regencies, along with 27.00% of Tegal City, were classified as ecological constraint zone, making them potential regions for UGB development. The UGB is expected to curtail urban expansion, promote compact city planning, and preserve ecosystem services to achieve urban sustainability. This study implies that planning small- and medium-sized cities is important to prevent urban sprawl and maintain environmental health. Designing UGB to limit urban expansion should be enhanced by better knowledge about its ecological functions in supporting urban sustainability.