江苏沿海地区的相对海平面上升及其灾害性影响研究

RELATIVE SEALEVEL RISE AND ITS UNFAVORABLE IMPACTS IN JIANGSU COASTAL PLAIN

江苏海岸是全国潮滩最集中分布区，其面积约占全国的１／４，沿海地区地势低平，相对海平面上升幅度较大，是全国少数几个受海平面上升危害最严重的地区之一。初步估算，２１世纪前半期该地区不同岸段相对海平面上升速率将可能达到４．５～９．５ｍｍ／ａ，约为同期全球平均上升速率的２～３倍。其灾害性影响主要集中在：①造成堤外潮滩湿地资源损失，相对海平面上升５０ｃｍ，因直接淹没、侵蚀加剧和淤涨减缓造成的潮滩损失面积将超过５×１０４ｈｍ２，湿地损失面积达２．４×１０４ｈｍ２；②降低海堤防御标准、危及海堤自身和受保护地区安全，相对海平面上升５０ｃｍ，该地区现有海堤防御标准将由现状５０～１００年一遇降为２０～５０年一遇；遇５０年一遇风暴高潮位，全区受潮水漫溢的海堤长度将比现状增加１７３ｋｍ以上，占海堤总长的１／４；③阻碍低洼地的洪水排泄、加剧洪涝灾害损失，相对海平面上升４０ｃｍ，苏北里下河和苏南太湖湖东两片洼地的自然排水能力将可能分别下降约２５％和２０％，若两洼地分别重现１９９１年型和１９５４年型洪水。

Jiangsu coastal plain is the most concentrative distributed area of tidal flat in China,the area of tidal flat in this area makes up approximately 25 percent of the whole country.In there,the relief is low flat and the rate of relative sea level rise is high,so it will become one of the regions most vulnerable to future sea level rise in China,the rate of relative sea level rise in the different coastal sections will reach 4.5～9.5 mm/a during the first half part of the 21st century,2-3 times of the global mean value.Accelerated relative sea level rise will lose a large number of tidal flat and coastal wetlands due to direct inundation,coastal erosion exacerbating and accretion decreasing,decrease the defensive standard of seawall and threaten the safety of seawall and protected areas;as well as impede the drainage of floodwater of coastal lowlands and aggravate flood and waterlogging disaster in this area.It is estimated that,if relative sea level rises 50 cm,tidal flat and coastal wetlands will lose 5×10 4 hm 2 and 2.4×10 4 hm 2 respectively,the defensive standard of seawall will decrease from withstanding a storm surge level with a probability of occurrence of 1/50～1/100 today to 1/20～1/50 in the future,if the storm surge level with a probability of occurrence of 1/50 occurs,the length of seawall overflowed by seawater will increase 173 km,representing 25 precent of the total length of seawall.If relative sea level rises 40 cm,the natural drainage capacity of Lixiahe lowland in North Jiangsu and the eastern lowland in South Jiangsu,two the largest low lying regions of Jiangsu province,will decrease 25 percent and 20 percent respectively,if the regions are hit by the floods of 1991 type and 1954 type respectively again,the submerged area increased by sea level rise will exceed 4×10 4 hm 2.