River flow is critical for vegetation dynamics: Lessons from multi-scale analysis in a hyper-arid endorheic basin.

Knowledge of the spatio-temporal responses of vegetation dynamics to hydro-climatic factors is important to assess ecological restoration efforts in arid and semiarid areas. In this study, the vegetation dynamics during 2000-2015 were investigated in the downstream area of the Heihe River Basin (HRB) in Northwest China where an ecological water diversion project (EWDP) commenced in 2000. The spatio-temporal relationships between vegetation cover and climatic factors (precipitation and temperature) and available water resources (river flow and groundwater) were determined. The results indicated that the mean growing season NDVI increased significantly during the period of 2000-2015, and the area of East Juyan Lake (EJL) enlarged to 36.4km2 in 2010. The scale effect of the relationships between NDVI and hydro-climatic factors was obvious. At the catchment scale, changes of NDVI were not significantly correlated with climatic factors, but significantly related with the antecedent 1-year river flow. River flow played an important role in vegetation growth within approximately 2000m distance from the river bank. At the pixel scale, the changes of NDVI were significantly positive with temperature and river flow in 17.40% and 7.14% of the study area, respectively, whereas significant relationship between NDVI and precipitation occurred in only 0.65% of study area. The suitable water table depth for vegetation growth was between 1.8 and 3.5m. The increased river flow and recovered groundwater due to the EWDP were critical for the improvement of vegetation cover, whereas the riparian vegetation degraded along some parts of the river bank. It is important to improve integrated watershed management with consideration of spatio-temporal lagged hydro-ecological connections in the study area.

[1]  C. King.  Living with environmental change in the endorheic oasis systems of the Northern Sahara , 2011 .

[2]  Yi-chi Zhang,et al.  Interpreting the groundwater attributes influencing the distribution patterns of groundwater‐dependent vegetation in northwestern China , 2012 .

[3]  C. Tucker,et al.  Climate-Driven Increases in Global Terrestrial Net Primary Production from 1982 to 1999 , 2003, Science.

[4]  Guobin Fu,et al.  Vegetation dynamics induced by groundwater fluctuations in the lower Heihe River Basin, northwestern China , 2011 .

[5]  Jiali Xie,et al.  Assessing vegetation dynamics in the Three-North Shelter Forest region of China using AVHRR NDVI data , 2011 .

[6]  C. Tucker,et al.  Response of terrestrial ecosystems to recent Northern Hemispheric drought , 2005 .

[7]  Edward B. Barbier,et al.  Upstream dams and downstream water allocation: The case of the Hadejia‐Jama'are floodplain, northern Nigeria , 2003 .

[8]  Chansheng He,et al.  Evaluating the coupling effects of climate aridity and vegetation restoration on soil erosion over the Loess Plateau in China. , 2016, The Science of the total environment.

[9]  Chunyan Zhao,et al.  Inland river terminal lake preservation: determining basin scale and the ecological water requirement , 2015, Environmental Earth Sciences.

[10]  Chansheng He,et al.  Streamflow allocation in arid watersheds: a case study in Northwestern China , 2012 .

[11]  Qi Feng,et al.  Environmental changes after ecological water conveyance in the lower reaches of Heihe River, northwest China , 2009 .

[12]  G. Sun,et al.  Combined effects of climate and land management on watershed vegetation dynamics in an arid environment. , 2017, The Science of the total environment.

[13]  C. Tucker,et al.  Northern hemisphere photosynthetic trends 1982–99 , 2003 .

[14]  J. A. Schell,et al.  Monitoring vegetation systems in the great plains with ERTS , 1973 .

[15]  Lei Zhang,et al.  Object-based approach to national land cover mapping using HJ satellite imagery , 2014 .

[16]  Maja Schlüter,et al.  Optimizing long-term water allocation in the Amudarya River delta: a water management model for ecological impact assessment , 2005, Environ. Model. Softw..

[17]  Yapeng Chen,et al.  Groundwater fluctuations induced by ecological water conveyance in the lower Tarim River, Xinjiang, China , 2009 .

[18]  Michael E. Schaepman,et al.  Correlation Between Annual Runoff in the Heihe River to the Vegetation Cover in the Ejina Oasis (China) , 2010 .

[19]  Wenzhi Zhao,et al.  Ecosystem restoration and conservation in the arid inland river basins of Northwest China: Problems and strategies , 2016 .

[20]  Osbert Jianxin Sun,et al.  Changes in vegetation and landscape patterns with altered river water-flow in arid West China. , 2009 .

[21]  R. B. Jackson,et al.  Water subsidies from mountains to deserts: their role in sustaining groundwater-fed oases in a sandy landscape. , 2011, Ecological applications : a publication of the Ecological Society of America.

[22]  A. Shrestha,et al.  Upstream-downstream linkages of hydrological processes in the Himalayan region , 2014, Ecological Processes.

[23]  Honglang Xiao,et al.  Integrated study of the water–ecosystem–economy in the Heihe River Basin , 2014 .

[24]  Zhaoxia Ye,et al.  Desert riparian vegetation and groundwater in the lower reaches of the Tarim River basin , 2014, Environmental Earth Sciences.

[25]  Jeremy J. James,et al.  A systems approach to restoring degraded drylands , 2013 .

[26]  D. Patten.  Riparian ecosytems of semi-arid North America: Diversity and human impacts , 1998, Wetlands.

[27]  Kazuhito Ichii,et al.  Global monitoring of interannual changes in vegetation activities using NDVI and its relationships to temperature and precipitation , 2001 .

[28]  N. Thevs,et al.  Vegetation, fauna, and biodiversity of the Ile Delta and southern Lake Balkhash — A review , 2015 .

[29]  Ping Wang,et al.  Vegetation responses to integrated water management in the Ejina basin, northwest China , 2011 .

[30]  Yongping Wei,et al.  Downstream ecosystem responses to middle reach regulation of river discharge in the Heihe River Basin, China , 2016 .

[31]  M. T. Ferreira,et al.  Riparian responses to extreme climate and land-use change scenarios. , 2016, The Science of the total environment.