Invasion of natural grasslands by exotic trees increases flood risks in mountainous landscapes in South India
Invasion of natural grasslands by exotic trees increases flood risks in mountainous landscapes in South India
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外来树木对天然草原的入侵增加了印度南部山区的洪水风险
DOI：
10.1016/j.jhydrol.2022.128944
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发表时间：
2023
影响因子：
6.4
通讯作者：
Nayak R
中科院分区：
文献类型：
--
作者：
Nayak R
世界各地集水区的入侵树木由于其水文和生态影响而引起关注。大量的研究集中在它们对旱季河流流量的影响，由于增加蒸腾作用。由于气候变化，极端降雨事件越来越频繁，入侵树木对河流流量和洪水风险的影响尚未得到充分解决。我们研究了土地覆盖，冠层覆盖，和其他流域的形态特征流流量在丘陵集水区在轻，重，极端降雨事件的影响。2014年1月至2016年12月期间，在印度南部尼尔吉里斯的11个邻近山区集水区收集了三年的径流观测数据。每个集水区有一个独特的土地覆盖，即shola森林，山地草原，集水区入侵的荆（黑荆树）。每小时降雨强度之间的25-90，90-95和95以上分别归类为轻，重和极端，并用于研究每小时峰值流量响应。比较了天然草地流域和灌木入侵草地流域的径流量。对汇水区的排放率进行了修正。我们发现，土地覆盖和冠层覆盖影响水文响应极端降雨事件。以洪水事件为响应变量的回归模型表明，随着冠层覆盖的增加，径流响应增加。在参考草原集水区（0.00098 mm s−1）中观察到的最大小时流量低于在低密度（0.00529 mm s−1）和高密度（0.00497 mm s−1）的荆树集水区中观察到的最大流量。在较高的排放量，洪水的规模在金合欢入侵集水区是远远大于在草地集水区为一个给定的洪水频率-这表明更高的风险，严重的洪水在金合欢为主的集水区。我们的属性增强洪水流量蔓延的荆树根的影响，增强快速，浅的次表面流入侵集水区。以浅层地下水流为主的集水区，由于降雨强度大，蓄水时间缩短。前期的水分条件和排水密度是影响当地降雨径流关系的其他因素。在西高止山脉和印度其他地区的草原上种植了外来的木本树木，有些已经成为入侵。我们的研究表明，在景观尺度上用木本植物取代草地，可能会影响水文过程，并可能增加季风期间的洪水风险，特别是在山区。通过调节荆树和恢复半天然草地来管理被入侵的集水区，再加上在这些受影响地区安装预警系统，将有助于减少气候变化下极端降雨期间的洪水风险。
Invasive trees in catchments around the world are a source of concern due to their hydrological and ecological impacts. A large number of studies have focused on their impact on dry-season stream discharge due to enhanced transpiration. The impact of invasive trees on stream discharge and flood risk during extreme rain events, which are becoming more frequent due to climate change, has not been addressed adequately. We examined the influence of land-cover, canopy cover, and other catchment morphological characteristics on stream discharges in hilly catchments during light, heavy, and extreme rain events. Three years of rainfall-runoff observations, between January 2014 and December 2016, were collected in eleven neighbouring mountainous catchments in Nilgiris, South India. Each catchment had a distinct land cover, namely shola forests, montane grasslands, and catchments invaded by wattle (Acacia mearnsii). Hourly rain intensities between the percentiles 25–90, 90–95 and over 95 were categorised as light, heavy and extreme respectively, and were used to study hourly peak stream discharge responses. We compared discharge between native grassland catchments and grassland catchments invaded by wattle. Discharge rates were corrected for the catchment area. We found that land cover and canopy-cover influenced the hydrologic response to extreme rain events. Regression models with flood event as the response variable suggested an increase in rainfall-runoff response with an increase in canopy cover. The maximum hourly discharge observed in the reference grassland catchment (0.00098 mm s−1) was lower than the maximum discharge observed in low density (0.00529 mm s−1) and high density (0.00497 mm s−1) wattle catchments. At higher discharges, the flood magnitude in wattle invaded catchments was much greater than that in the grassland catchment for a given flood frequency – indicating a higher risk of severe flooding in wattle-dominated catchments. We attribute the enhanced flood discharges to the effects of spreading wattle roots on the enhancement of rapid, shallow sub-surface flows in invaded catchments. Catchments dominated by shallow sub-surface flows are known to have reduced water retention times in response to high rain intensities. Antecedent moisture conditions and drainage density were other factors that influenced the local rainfall-runoff relationships. In the Western Ghats and other parts of India grasslands have been planted with exotic woody trees, and some have become invasive. Our study indicates that replacing grasslands with woody plants at landscape scales, could affect hydrological processes and could increase flood risks during the monsoon, especially in mountainous regions. Management of invaded catchments by regulation of wattle and restoration of semi-natural grassland, combined with the installation of early warning systems in these impacted areas will help reduce flood risk during extreme rain under climate change.
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DOI：
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