Cook clam juice and 3 cups water in a medium saucepan over medium-low, undisturbed, until steaming, about 10 minutes. Reduce heat to medium-low, and keep warm.

Meanwhile, heat oil in a large saucepan over medium-high. Add onion, carrot, and celery; cook, stirring often, until slightly softened, about 5 minutes. Add rice and saffron; cook, stirring constantly, until rice is toasted, about 1 minute. Add wine; cook, stirring often, until almost absorbed, 30 seconds to 1 minute. Reduce heat to medium.

Add 1 cup hot clam juice mixture to rice mixture; cook, stirring often, until almost absorbed, 2 to 3 minutes. Continue adding clam juice mixture, 1/2 cup at a time, stirring until clam juice mixture is almost absorbed after each addition, until rice is al dente and mixture is creamy, 15 to 20 minutes.

Remove rice mixture from heat; gently stir in lobster, salt, and pepper. Gradually stir in Parmesan cheese. Stir in additional clam juice mixture, a splash at a time, to loosen risotto, if needed. Discard remaining clam juice mixture. Divide risotto evenly among 4 bowls; garnish with chives