Hydrological characteristics and changes in the Nu-Salween River basin revealed with model-based reconstructed data

The Nu-Salween River(NSR),the longest free-flow river in Southeast Asia,plays an irreplaceable role in social development and ecological protection.The lower NSR region is particularly valuable as it is inhabited by approximately 6.7 million people.The basin has limited hydraulic conservancy infrastructure and insufficient ability to cope with climate change risks.Studying the hydrological characteristics and changes in the basin provides the scientific basis for rational protection and development of the basin.However,owing to the limitation of observation data,previous studies have focused on the local area and neglected the study of the lower reaches,which is not enough to reflect the spatial characteristics of the entire basin.In this study,the ECMWF 5th generation reanalysis data(ERA5)and Multi-Source Weighted-Ensemble Precipitation(MSWEP)were applied to develop a geomorphology-based hydrological model(GBHM)for reconstructing hydrological datasets(i.e.GBHM-ERA5 and GBHM-MSWEP).The reconstructed datasets covering the complete basin were verified against the gauge observation and compared with other commonly used streamflow products,including Global Flood Awareness System v2.1,GloFAS-Reanalysis dataset v3.0,and linear optimal runoff aggregate(LORA).The comparison results revealed that GBHM-ERA5 is significantly better than the other four datasets and provides a good reproduction of the hydrological characteristics and trends of the NSR.Detailed analysis of GBHM-ERA5 revealed that:(1)A multi-year mean surface runoff represented 39%of precipitation over the basin during 1980–2018,which had low surface runoff in the upstream,while areas around the Three Parallel Rivers Area and the estuary had abundant surface runoff.(2)The surface runoff and discharge coefficient of variations in spring were larger than those in other seasons,and the inter-annual variation in the downstream was smaller than that in the upstream and midstream regions.(3)More than 70%of the basin areas showed a decreasing trend in the surface runoff,except for parts of Nagqu,south of Shan State in Myanmar,and Thailand,where surface runoff has an increasing trend.(4)The downstream discharge has dropped significantly at a rate of approximately 680 million cubic metresper year,and the decline rate is greater than that of upstream and midstream,especially in summer.This study provides a data basis for subsequent studies in the NSR basin and further elucidates the impact of climate change on the basin,which is beneficial to river planning and promotes international cooperation on the water-and eco-security of the basin.

云南怒江高原鳅属鱼类一新种记述

20 0 0年 7月和 2 0 0 4年 7月 ,分别在云南省怒江傈僳族自治州和保山市怒江干流采集到一批高原鳅标本。经鉴定 ,为高原鳅属Triplophysa一未经发表的新种。新种怒江高原鳅Triplophysa (Triplophysa)nujiangen sasp nov 在形态特征和食性方面与唐古拉高原鳅、斯氏高原鳅、粗唇高原鳅和细尾高原鳅较为相似。本新种身体相对短圆 ,头部近圆筒形 ,吻端钝圆 ,颊部正常 ,吻部在鼻孔之前明显向下倾斜 ,下颌铲状 ,边缘锐利而水平 ,上唇缘无突起 ,下唇中央中断 ,后部无突起 ,眼间隔稍隆起 ,眼间距为尾柄高 0 6～ 0 8倍 ,第一鳃弓内侧鳃耙 10～ 19,肠绕折 3个环 ,前背长为体长 71 1%～ 77 2 % ,体长为头长 4 6～ 5 5倍 ,偶鳍短圆 ,背鳍分枝鳍条 8根 ,胸鳍分枝鳍条 10～ 11根 ,腹鳍末端不达肛门 ,尾鳍高度向尾鳍方向不明显降低 ,尾柄起点处的宽小于该处的高 ,尾柄长为尾柄高 1 6～ 2 8倍 ,胸鳍长为胸腹鳍起点间距 4 7 5 %～ 6 3 5 % ,尾鳍内凹。本文列出了中国高原鳅属 5种铲状下颌种类的检索表 ,本新种可藉之与这些相似种相区别。

怒江干旱河谷灌溉定额变化趋势分析

利用福贡、潞江坝、孟定等3个站1960～2000年逐月气象数据及作物种植、农业耕作等资料,采用Mann-Kendal法和R/S分析法研究了怒江干旱河谷区近40年来的干湿变化及农业灌溉定额的转折变化趋势。结果表明,怒江河谷内降水增多、气温下降、年ET0有增有减,但整个河谷朝湿润化演变;水稻灌溉定额和农业综合灌溉定额大多呈减少趋势,只有潞江坝的水稻例外。怒江河谷内气象因子、干湿指数的转折点在20世纪70～90年代初都出现过,但ET0、水稻灌溉定额、农业综合灌溉定额没有转折变化。进一步分析发现了福贡、潞江坝站ET0变化的"蒸发悖论"现象,反映出西南纵向岭谷区受特殊地理环境的作用下,呈现气候环境和灌溉定额变化趋势的复杂性。