青藏高原城市洪涝缓解能力评估

通过耦合FUTURES城市扩张模拟模型和城市洪涝缓解能力评估模型，综合不同气候变化和城市扩张情景对拉萨市洪涝缓解能力的历史及未来变化进行了定量评估．结果发现:1）2000—2015年，拉萨市各区洪涝缓解能力平均降低了5.34%．其中城关区和堆龙德庆区分别降低了4.63%和8.55%，仅达孜区的缓解能力提高了1.13%．2）城关区未来洪涝缓解能力在RCP4.5和RCP8.5情景下分别平均降低了15.01%和29.52%，堆龙德庆区则分别降低了16.16%和31.95%．3）城关区和堆龙德庆区的新增城镇用地造成其缓解能力比原自然地表降低50%以上，在城市扩张中采取保护水体措施，能够有效减少缓解能力的退化．4）未来城市扩张造成拉萨市未来洪涝缓解能力的大幅降低，而气候变化进一步扩大了其退化程度．因此，拉萨市在未来应该遏制城市建设向水体、草地扩张的趋势，提高城市土地利用效率．并且应当加强城市内部绿色基础设施的建设，适度提高防洪排水设施标准，以应对气候变化可能造成的极端降水事件． 

Assessment of urban flood mitigation capacity on the Qinghai-Tibet Plateau: the case of Lhasa City

Precipitation on the Qinghai-Tibet Plateau has shown an overall increasing trend in recent years, both the intensity and frequency of extreme precipitation events have increased．Continued expansion of plateau cities have affected hydrological cycles, this coupling effect exacerbates the risk of urban flooding．Historical and future changes in flood mitigation capacity of Lhasa city were quantitatively assessed here, by coupling FUTURES urban expansion simulation model and urban flood mitigation capacity assessment model, to integrate different climate change and urban expansion scenarios．It was found that from 2000 to 2015 overall flood mitigation capacity of Lhasa city had decreased by 42.70%．In particular, Chengguan and Dulongdeqing districts each decreased 4.63% and 8.55%, respectively, but mitigation capacity of Dazi district increased 1.13%．Future flood mitigation capacity in Chengguan District was found to have decreased by an average of 15.01% and 29.52% under RCP4.5 and RCP8.5 scenarios, while in Duilongdeqing District it decreased by 16.16% and 31.95%．The new urban land in Chengguan and Duilongdeqing districts has had their mitigation capacity reduced by more than 50% compared to original natural surface．Measures to protect water bodies in urban expansion will likely reduce further degradation of mitigation capacity．Future urban expansion will lead to significant reduction in future flood mitigation capacity in Lhasa city, while climate change will further amplifies its degradation．In Lhasa city the trend of urban construction to expand into water bodies and grasslands must be curbed in the future, and urban land use efficiency must be improved．Construction of green infrastructure within the city will need to be strengthened, standard of flood control and drainage facilities will need to be improved to cope with possible extreme precipitation events due to climate change．