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PROCESSES MIGRATION SPACE build up sediment and biomass natu- rally, and “migrate” inland into higher areas. The total area of migration space has to do mainly with the slope of the land immediately adjacent to the Estuary. The space is widest across broad, gently sloping valleys and plains. CONTEXT Scientists project a 2-5 foot rise in the level of the sea within the next century due to climate change. As the ocean moves increasingly into the Bay and Delta, and floods lower elevation shorelines, urban development continues to encroach on these same zones. While many wetlands, wildlife habitats, and parklands in these zones are protected from development, the buffer zones around them may not be, leading scien- tists concerned with sea level rise impacts on estuary health to evaluate “migration space” for shoreline habitats 50% and sensitive species. Arbitrary Target = Migration space is the upland area between the present-day shoreline of the Estuary and a higher, future shoreline resulting from sea lev- el rise. In rough terms, this area offers space for lower, outer wetlands, for example, to Access to this zone of natural transition from estuarine habitats to terrestrial hab- itats is critically important for the health of the Estuary. Shallow estuarine habitats help protect the shore against erosion and flooding due to storm surges or erosive waves generated by high winds. Without protected, undeveloped migration space, the Estuary will rise against the developed landscape, compressing the natural shore into a narrow band of vulnerable habitats with minimal cultural, economic, or ecologi- cal value. M I G R AT I O N S PAC E % O F TOTA L 80 60 % Area Undeveloped for 2 ft SLR % Area Undeveloped & Protected for 2 ft SLR % Area Undeveloped for 5 ft SLR % Area Undeveloped & Protected for 5 ft SLR 40 20 0 South Bay Central Bay North Bay Suisun Bay North Delta Central Delta M I G R AT I O N S PAC E FROM RISING SEAS ESTUARY . . S TAT U S . . Poor . . . .T R E N D . . . . No data .....BENCHMARK..... Half of space undeveloped, and 75% of that protected INDICATOR This indicator DETAILS 100% 63 TRANSITIONS South Delta evaluates two alternative migra- tion spaces — one for a two-foot and one for a five-foot rise in sea level — in seven sub-regions of the Bay and Delta. It measures the current percentage of undevel- oped space, and the percentage of that space that is protected from development. For the pur- poses of this evaluation, migration space excludes all existing tidal areas, as well as any reclaimed areas, such as salt ponds in South San Francisco Bay or diked farmlands in the Delta that would be flooded without their dikes or levees. However, migration space does include all areas of landfill within the historical limits of the Estuary that are above the future shorelines. Benchmarks for migration space, as a new mea- sure of Estuary health in the face of future sea level rise, have no reference point yet. However, for the purposes of this evaluation, scientists have set the benchmark at 50% of the total mi- gration space in each sub-region being undevel- oped, and 75% of that undeveloped space being protected.