London needs to plant more trees, use less water, slash carbon emissions, and improve drainage to prevent and cope with climate change, Mayor Boris Johnson said. With 15 percent of the city at high risk of flooding, Johnson announced a climate-crisis plan that includes planting trees to soak up carbon and excess rainwater while also cooling the overheated city. Overhauling the Victorian drainage system is also a priority. Even as warmer, wetter winters pose a flood risk, London — which has less water per capita than Morocco — is facing more summer heat waves and droughts. Johnson’s plan, claimed as a first for a major world city, calls for reducing water consumption through metering, efficient building construction, and more harvesting of rainwater. His plan furthers ex-Mayor Ken Livingstone’s goal of cutting carbon by 60 percent by 2025.