低径流量条件下海平面上升对长江口淡水资源的影响

Impact of Sea-Level Rise on Saltwater Intrusion in the Changjiang Estuary in the Low River Discharge Cases

基于长江口水动力及盐水入侵三维数值模式ECOM—si，统筹考虑气候变化导致流域极端低径流最的前提下，研究在未来（2030、2050和2100年）海平面上升过程中，长江口淡水资源分布及总量变化过程，探讨河口三大重要水库取水活动对海平面上升的响应，对防范未来可能出现的盐水入侵危害具有重要作用，也为长江口水源地建设与水库取水调度提供理论依据和技术支持。1999年冬季、2006年秋季和2011年春季期间长江径流量均为自1980年以来的同期最低，且长江口均发生了极为严重、影响巨大的盐水入侵，考虑到径流量的季节变化特点，选取上述3个时期的径流量作为上游边界条件。结果表明，长江口淡水资源在1999年冬季径流量条件下随海平面上升而减少，至2100年大、小潮期间淡水总量相比于2012年分别减少42％和41％，水库最长不宜取水天数增加70％以上；在2006年秋季径流量条件下，淡水资源随海平面上升而减少，但在海平面上升至2050年情况下，河道水位抬升使进入北支的径流量增加，削弱盐水倒灌，水库最长不宜取水天数减少40％-50％；在2011年春季径流量条件下，淡水资源在海平面上升至2100年后火、小潮期间分别减少43％和20％，水库最长不宜取水天数增加1-3d。

A 3-D numerical model ECOM-si was used to assess the distribution and variation process of freshwater volume as well as the responses of major reservoirs to the sea-level rise in 2030, 2050 and 2100 in condition of low river discharge. The study concentrates on water intake in reservoirs and against the risk by saltwater intrusion. Considering seasonal variation of river discharge, we chose three cases as the runoff boundary condition, including winter in 1999, autumn in 2006 and spring in 2011, which were all the lowest river discharge in the past 30 years over the same seasons, and saltwater intrusion made great harm in those periods. The results showed that the freshwater resources decrease when sea level rises in condition of river discharge in 1999 winter, and the volume drop by 42% and 41% in spring and neap tides relatively in 2100 sea-level rise scenario, together with the 70% increase in duration periods that are unsuitable for water intake. In condition of spring in 2011, the freshwater volume decreases by 43% and 20% in spring and neap tides relatively under 2100 sea-level rise, and the duration periods that are unsuitable for water intake increase by 1-3 days. In condition of autumn in 2006, freshwater resources decrease except in 2050 sea-level rise scenario, in which the duration periods that are unsuitable for water intake decrease by 40%-50% because of the weakened saltwater intrusion caused by the diluted saltwater from the North Branch.