Analysis of the impact of conservation measures on stream flow regime in catchments of the Loess Plateau,China

Catchments in the Loess Plateau have been under the influence of human activities for centuries. In the last four decades, soil conservation measures have accelerated and intensified. These measures were designed to reduce soil erosion, improve agricultural productivity, and enhance environmental quality. It is important to evaluate the effects of these measures on hydrology in order to develop sustainable catchment management plans in the region. This study evaluated changes in stream flow data for four selected catchments in the Loess Plateau following large‐scale soil conservation measures. The non‐parametric Mann–Kendall test was used to identify trends in annual stream flow and the results showed significant downward trends in three of the four catchments. The Pettitt test indicated that a change point occurred in 1978 in these three catchments. Annual precipitation in all the catchments showed no significant trend during the period of record. Comparison of daily flow duration curves for two 20‐year periods (1957–1978) and (1979–2003) showed significant changes in stream flow regime. Reduction in most percentile flows varied between 20 and 45%, and the reduction in low flows was greatest. Overall, the reductions in daily flow were increasing with time, with significant changes occurring in the 1990s. However, it is not clear whether these catchments have seen the full effects of the soil conservation measures, so the results of this study might underestimate the final impact of soil conservation on stream flow regime. Copyright © 2007 John Wiley & Sons, Ltd.     

青海高原地区近250 a来年平均气温变化及突变分析

用多条树轮重建的青海高原近250 a平均气温序列,利用线性趋势、小波变换分析和突变检测等方法对近250 a青海高原年平均气温的年际变化及突变特征进行了综合分析,结果表明:250多a来青海高原年平均气温波动明显,30 a滑动平均表现出1779～1811年和1934～2006年年平均气温偏高,其中年平均气温最高出现在1998年为1.3℃,1741～1778年和1812～1933年年平均气温偏低,其中年平均气温最低出现在1823年为-1.5℃,年气温总体呈上升趋势;在20 a以上相对大尺度上,年平均气温冷、暖交替的特征明显,经历了7个冷、暖交替阶段,在2～3 a,28 a左右,48 a和110 a时间尺度上的周期变化都比较明显。     

Soil erosion and sediment interception by check dams in a watershed for an extreme rainstorm on the Loess Plateau,China

The magnitude of soil erosion and sediment load reduction efficiency of check dams under extreme rainstorms is a long-standing concern. The current paper aims to use check dams to deduce the amount of soil erosion under extreme rainstorms in a watershed and to identify the difference in sediment interception efficiency of different types of check dams. Based on the sediment deposition at 12 check dams with 100% sediment interception efficiency and sub-catchment clustering by taking 12 dam-controlled catchments as clustering criteria, the amount of soil erosion resulting from an extreme rainstorm event on July 26, 2017 (named “7·26” extreme rainstorm) was estimated in the Chabagou watershed in the hill and gully region of the Loess Plateau. The differences in the sediment interception efficiency among the check dams in the watershed were analyzed according to field observations at 17 check dams. The results show that the average erosion intensity under the “7–26” extreme rainstorm was approximately 2.03 × 10⁴ t/km², which was 5 times that in the second largest erosive rainfall in 2017 (4.15 × 10³ t/km²) and 11–384 times that for storms in 2018 (0.53 × 10² t/km² - 1.81 × 10³ t/km²). Under the “7–26” extreme rainstorm, the amount of soil erosion in the Chabagou watershed above the Caoping hydrological station was 4.20 × 10⁶ t. The sediment interception efficiency of the check dams with drainage canals (including the destroyed check dams) and with drainage culverts was 6.48 and 39.49%, respectively. The total actual sediment amount trapped by the check dams was 1.11 × 10⁶ t, accounting for 26.36% of the total amount of soil erosion. In contrast, 3.09 × 10⁶ t of sediment were input to the downstream channel, and the sediment deposition in the channel was 2.23 × 10⁶ t, accounting for 53.15% of the total amount of soil erosion. The amount of sediment transport at the hydrological station was 8.60 × 10⁵ t. The Sediment Delivery Ratio (SDR) under the “7·26” extreme rainstorm was 0.21. The results indicated that the amount of soil erosion was huge, and the sediment interception efficiency of the check dams was greatly reduced under extreme rainstorms. It is necessary to strengthen the management and construction technology standards of check dams to improve the sediment interception efficiency and flood safety in the watershed.     

Florogeography of mire plants in southern part of qinghai-xizang plateau and its adjacent areas

ＦＬＯＲＯＧＥＯＧＲＡＰＨＹＯＦＭＩＲＥＰＬＡＮＴＳＩＮＳＯＵＴＨＥＲＮＰＡＲＴＯＦＱＩＮＧＨＡＩＸＩＺＡＮＧＰＬＡＴＥＡＵＡＮＤＩＴＳＡＤＪＡＣＥＮＴＡＲＥＡＳＺｈａｏＫｕｉｙｉ（赵魁义）ＣｈａｎｇｃｈｕｎＩｎｓｔｉｔｕｔｅｏｆＧｅｏｇｒａｐｈｙ...     

非线性惯性重力内波的特征及天气意义

对大气非线性惯笥重力内波方程组,利用相平面分析法导出了相应的ＫｄＶ方程。采用直接积分法求出两类有意义的孤立波解,讨论了波解的基本特征,并着重分析了一类奇异孤立波与某些天气系统（如青藏高原５００ｈＰａ低涡）的可能联系。     

黄土高原稳定同位素与古环境研究

黄土高原黄土地层已被证明是大陆上最完好的记录了过去环境信息的载体。通过黄土地层的碳,氧同位素作为气候替代指标研究古植被,降雨量,古环境温度及古季风演化方面取得了长足的进展,本文拟就主要研究成果作一综述,并对今后的研究方向做一前瞻。     

青藏高原雪盖对亚洲季风影响研究进展

资料分析和数值模拟均表明,青藏高原作为一个特殊的抬高了的下垫面,其上雪盖面积和积雪日数等的异常均与亚洲夏季风的强弱及起讫有关．雪盖面积大、积雪日数多的年份,亚洲季风弱且爆发迟,推进慢;雪盖面积小、积雪日数少的年份,亚洲季风强且爆发早,推进快．但也存在不同的看法     

Magnetostratigraphy and palaeoclimatic significance of Late Tertiary aeolian sequences in the Chinese Loess Plateau

The aeolian Red Clay sequence in the central part of the Chinese Loess Plateau was investigated in an attempt to obtain magnetostratigraphic and palaeoclimatic records. From the results, we deduce that aeolian dust accumulation and the related East Asia palaeomonsoon system began at least 7.6  Myr ago, and that the Tibetan Plateau had reached a significant elevation by that time. The Late Tertiary palaeoclimatic history of the Red Clay as reflected by magnetic susceptibility is reconstructed for the time period 7.6–2.5  Ma. Increases in aeolian dust accumulation for the last 7.6  Myr appear to have a close relation with the uplift processes of the Tibetan Plateau. The remarkable increase of aeolian dust accumulation beginning at 3.2  Ma appears to reflect the influence of an increasing global ice volume on the East Asian monsoon and aeolian dust accumulation.     

Geochemical Evolution and Environmental Changes of Qinghai—Xizang Plateau Since Late Cenozoic

Long-and short-term climatic curves were preliminarily established based on the comprehensive analysis of geochemical information since the Late Cenozoic in the Qinghai Xizang(Qinghai-Tibet)Plateau.The curves show that the climate in the plateau was alternatively dry-warm and cold-wet during the period of 30-3.4 Ma when the plateau was not uplifted to an enough altitude and the monsoon was not completely formed either,In the period of 3.4-0.73 Ma.the climate fluctuated between dry-cold and wet-warm when the plateau was rapidly uplifted and the Asian monsoon was consequently formed.Since 0.73 Ma.the climate became even drier when the plateau continuously rose.In the Holocene period.the climate alternatively changed with a complex model of being cool-dry,warm-wet and cold-wet.