HAMPTON, Va. — A pair of nor’easters in early 1998, and Hurricane Isabel in 2003, awoke this low-lying Chesapeake Bay town to the impact of rising waters caused by climate change. A few years later, as Hurricane Katrina swamped New Orleans, and Hurricane Sandy raked the New Jersey-New York coastline, scientists warned that Hampton and its neighbors could be next. So this small city embarked on studies of what was happening and what it could do. Six years later, the city has changed its building codes, razed some houses and elevated others, and is finalizing a plan to address the oft-flooded Newmarket Creek in its densely developed center.