The 3rd International Symposium on Watershed Geographic Sciences (ISWSGS2020)

  ISWSGS2020 (the 3rd International Symposium on Watershed Geographic Sciences) will be held online from October 17 to 18, 2020. This symposium is organized by the Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences. The theme of the symposium is “Watershed geography and interdisciplinary sciences”. This symposium aims to provide a forum for the exchange of the latest research achievements on watershed geography and other related sciences. World leading scientists are invited to present keynotes covering the latest advances in soil and water processes, human geography, remote sensing and watershed management.
  Topics include
  1. Observation and monitoring at multiple scales
  2. Integrated watershed modeling of multi-processes
  3. Watershed soil and water processes and their environmental impacts
  4. Human activities, processes and driving mechanism in watersheds
  5. Sustainable development and watershed planning
  6. Watershed integrated management and spatial optimization
  7. Other topics relevant to watershed geography
  October 17 2020 for local participants’ arrival
  October 18 2020 for keynote speeches online
  Information and contacts
  Tel: +86 25 8688 2083
  Fax: +86 25 5771 4759
  Add: 73 East Beijing Road, Nanjing, China
  General enquiry:

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Climate changes of northern China during the “5000-year” Chinese History
The Chinese civilization is the oldest and most enduring in the world. During its long lasting “5000-year” history, China has experienced a series of centennial-scale rise and fall of dynasties, unifications and divisions, war and peace and south-north migration of northern nomads. Climate changes have long been proposed as an important driver of these historical cultural changes through affecting phenology and land productions, especially for China as a traditional farming civilized society. As early as the 1970s, Chu, (1972) first reported the temperature history of China over the past “5000-year” based on phenological documents and pioneered the study of climate and dynasty transitions. Over the past few decades, many efforts have been taken to reconstruct the climate records, but mostly qualitatively. Lack of high-resolution, quantitative climate records, especially for the heartland of ancient Chinese culture, limits a comprehensive examination of the relation between climate and culture changes in Chinese history. A scientific research group, composed of Nanjing Institute of Geography and Limnology, Institute of Tibetan Plateau Research, Nanjing University and other institutions, presents well-dated, high resolution, quantitative warm-season temperature and annual mean precipitation records and provides a high-quality climate background for the entire “5000-year” Chinese history. Results suggest that changes in temperature and precipitation are incomplete coupled in terms of both long-term trend and centennial-scale variability before ~1000 CE (Common era). The temperature displays a slight decrease of ~0.5oC before ~200 CE and a rapid cooling of ~4oC afterwards, superimposed with four 1-2oC centennial-scale cold events. The precipitation shows high value before ~1000 BCE and a gradual decrease of ~250 mm with two distinct ~100 mm centennial scale dry intervals after ~1000 CE. Climate changes in dynastic China indicate that the Three Sovereigns and Five Emperors began in a relatively warm and wet climate, and the moderate conditions lasted until Shang Dynasty followed by a gradually cold and dry climate with large fluctuations afterward. Specifically, we find cold-dry conditions in the late Tang, Five Dynasties and Ten Kingdoms (5D&10K), late Song, Yuan, late Ming Dynasty, and only cold conditions during the period of the Spring and Autumn and Warring States (SAWS), the period of Wei, Jin and Southern and Northern Dynasties (WJSN). It shows the three long-term and large-scale social unrests (5D&10K, SAWS, WJSN) in Chinese history have experienced large climate fluctuations. Comparison of climate changes and other social factors reveals some centennial-scale cold and/or dry oscillations are also accompanied by an increase of war frequency, a sharp decline of population size and a southward migration of northern nomads during three large-scale social unrests of SAWS, WJSN and 5D&10K, and nomadic dynasties (Yuan and Qing Dynasty) when northern nomads ruled the central plains. Thus, climate fluctuations likely played an important role in affecting cultural changes in the “5000-year” Chinese history. Dynasty transitions may also be influenced by other sociocultural factors and administrative efficiency such as class struggle, peasant uprising, economic collapses and misgovernment. For example, the end of some dynasties such as Xia, Shang and Qin Dynasty occurred under a background of stable climate, and ~70 years of cold event at ~750 CE did not lead to the end of the prosperous Tang Dynasty although it likely corresponds to the famous An-Shi Rebellion. Climate change may be not a decisive factor of dynastic transitions, although it has an important impact on Chinese historical cultural changes. Therefore, we must avoid falling into the trap of “geographical determinism” when discussing the relation between both. Our high-resolution quantitative climate records just provide crucial climate context to test the hypothesis of climatic impact on historical culture changes.
  Quantitatively reconstructed temperature (a) and precipitation (b). Frequency of wars in China (c). Population size of China (d). South limit of nomadic national regime with boundary the GreatWall in Inner Mongolia (e). 
  Paper link:
A Special Section in JGR Atmospheres: ater-Soil-Air-Plant-Human Nexus: Modeling and Observing Complex Land Surface Systems at River Basin

  A Special Section in JGR Atmospheres called Water-Soil-Air-Plant-Human Nexus: Modeling and Observing Complex Land Surface Systems at River Basin, reviews the latest progress in the watershed system models and observation methods. Here, some articles published in the special section are liested below.
  Vision of a watershed system model (Source: Li et al. [2018], Figure 1)
  A High‐Resolution Land Model With Groundwater Lateral Flow, Water Use, and Soil Freeze‐Thaw Front Dynamics and its Applications in an Endorheic Basin
  Human water regulation, groundwater lateral flow, and the movement of frost and thaw fronts (FTFs) affect soil water and thermal processes, as well as energy and water exchanges between the land surface and atmosphere. Reasonable representation of these processes in land surface models is very important to improving the understanding of land‐atmosphere interactions. In this study, mathematical descriptions of groundwater lateral flow, human water regulation, and FTFs were synchronously incorporated into a high‐resolution community land model, which is then named the Land Surface Model for Chinese Academy of Sciences (CAS‐LSM). With a series of atmospheric forcings and high‐resolution land surface data from the Heihe Watershed Allied Telemetry Experimental Research (HiWATER) program, numerical simulations of the period 1981–2013 using CAS‐LSM with 1‐km resolution were conducted for an endorheic basin, the Heihe River Basin in China. Compared with observations, CAS‐LSM reproduced the distributions of groundwater, evapotranspiration, and permafrost reasonably and well matched the temporal changes in ground temperature, heat fluxes, and FTFs. Results illuminate the temporal and spatial characteristics of frozen soil and the changes in the land‐atmosphere exchange of carbon, water, and energy. The permafrost and seasonally frozen soil were distinguished. In the seasonally frozen areas, the maximum soil frost depth increased by 0.65 mm/year within natural areas and decreased by 2.12 mm/year in human‐dominated areas. The active layer thickness increased 8.63 mm/year for permafrost. In the permafrost zone evapotranspiration and latent heat flux increased, and the sensible heat flux declined. In the human‐dominated areas water use raised the latent heat flux and reduced the sensible heat flux, net ecosystem exchange, and streamflow recharging to the eco‐fragile region in the lower reaches. Results suggested that the land surface model CAS‐LSM is a potential tool for studying land surface processes, especially in cold and arid regions experiencing human interventions.
  Intercomparison of Six Upscaling Evapotranspiration Methods: From Site to the Satellite Pixel
  Land surface evapotranspiration (ET) is an important component of the surface energy budget and water cycle. To solve the problem of the spatial‐scale mismatch between in situ observations and remotely sensed ET, it is necessary to find the most appropriate upscaling approach for acquiring ground truth ET data at the satellite pixel scale. Based on a data set from two flux observation matrices in the middle stream and downstream of the Heihe River Basin, six upscaling methods were intercompared via direct validation and cross validation. The results showed that the area‐weighted method performed better than the other five upscaling methods introducing auxiliary variables (the integrated Priestley‐Taylor equation, weighted area‐to‐area regression kriging [WATARK], artificial neural network, random forest [RF], and deep belief network methods) over homogeneous underlying surfaces. Over moderately heterogeneous underlying surfaces, the WATARK method performed better. However, the RF method performed better over highly heterogeneous underlying surfaces. A combined method (using the area‐weighted and WATARK methods for homogeneous and moderately heterogeneous underlying surfaces, respectively, and using the RF method for highly heterogeneous underlying surfaces) was proposed to acquire the daily ground truth ET data at the satellite pixel scale, and the errors in the ground truth ET data were evaluated. The Dual Temperature Difference (DTD) and ETMonitor were validated using ground truth ET data, which solve the problem of the spatial‐scale mismatch and quantify uncertainties in the validation process.
  Evaluating Different Machine Learning Methods for Upscaling Evapotranspiration from Flux Towers to the Regional Scale
  Evapotranspiration (ET) is a vital variable for land‐atmosphere interactions that links surface energy balance, water, and carbon cycles. The in situ techniques can measure ET accurately but the observations have limited spatial and temporal coverage. Modeling approaches have been used to estimate ET at broad spatial and temporal scales, while accurately simulating ET at regional scales remains a major challenge. In this study, we upscale ET from eddy covariance flux tower sites to the regional scale with machine learning algorithms. Five machine learning algorithms are employed for ET upscaling including artificial neural network, Cubist, deep belief network, random forest, and support vector machine. The machine learning methods are trained and tested at 36 flux towers sites (65 site years) across the Heihe River Basin and are then applied to estimate ET for each grid cell (1 km × 1 km) within the watershed and for each day over the period 2012–2016. The artificial neural network, Cubist, random forest, and support vector machine algorithms have almost identical performance in estimating ET and have slightly lower root‐mean‐square error than deep belief network at the site scale. The random forest algorithm has slightly lower relative uncertainty at the regional scale than other methods based on three‐cornered hat method. Additionally, the machine learning methods perform better over densely vegetated conditions than barren land or sparsely vegetated conditions. The regional ET generated from the machine learning approaches captured the spatial and temporal patterns of ET at the regional scale.
  Hydrological Cycle in the Heihe River Basin and Its Implication for Water Resource Management in Endorheic Basins
  Endorheic basins around the world are suffering from water and ecosystem crisis. To pursue sustainable development, quantifying the hydrological cycle is fundamentally important. However, knowledge gaps exist in how climate change and human activities influence the hydrological cycle in endorheic basins. We used an integrated ecohydrological model, in combination with systematic observations, to analyze the hydrological cycle in the Heihe River Basin, a typical endorheic basin in arid region of China. The water budget was closed for different landscapes, river channel sections, and irrigation districts of the basin from 2001 to 2012. The results showed that climate warming, which has led to greater precipitation, snowmelt, glacier melt, and runoff, is a favorable factor in alleviating water scarcity. Human activities, including ecological water diversion, cropland expansion, and groundwater overexploitation, have both positive and negative effects. The natural oasis ecosystem has been restored considerably, but the overuse of water in midstream and the use of environmental flow for agriculture in downstream have exacerbated the water stress, resulting in unfavorable changes in surface‐ground water interactions and raising concerns regarding how to fairly allocate water resources. Our results suggest that the water resource management in the region should be adjusted to adapt to a changing hydrological cycle, cropland area must be reduced, and the abstraction of groundwater must be controlled. To foster long‐term benefits, water conflicts should be handled from a broad socioeconomic perspective. The findings can provide useful information on endorheic basins to policy makers and stakeholders around the world.
  Large Hydrological Processes Changes in the Transboundary Rivers of Central Asia
  Central Asia, which is one of the most complex regions in the world, is crisscrossed with transboundary rivers shared by several countries. This paper analyzes the effects of climate change and human activities on hydrological processes and water resources in these transboundary rivers over the past half century. The results show that the average temperature in the Tienshan Mountains experienced “sharp” increases in 1998, with the average temperature after 1998 being 1.0°C higher than that during 1960–1998. This rapid warming has accelerated glacier shrinkage and decreases in snow cover. These changes influenced the hydrological processes, causing an earlier runoff peak and aggravated extreme hydrological events. Changes in mountainous hydrological processes affected regional water availability and intensified future water crisis in Central Asia. The mismatched spatial distributions of water and land resources, along with the intense human activities (e.g., overexploitation of water resources), have ultimately led to the present water crisis in Central Asia's river basins. This is the main reason for ongoing water conflicts in the region's transboundary rivers and the ecological disaster of the Aral Sea.
Prof. ZHANG Ganlin was selected as the top 2% scientists in the world

  Stanford University recently released the latest 2020 World's Top 2% Scientists. Prof. Zhang Ganlin of our institute was selected in the field of Agronomy & Agriculture.
  Prof. Zhang Ganlin has long been engaged in soil geography research. He has published more than 300 papers on soil genesis, soil classification, soil mapping, soil resource information system & evaluation, urban soil, etc. He is the winner the Distinguished Young Scholar of the National Natural Science Foundation of China. He also serves as the editor of many famous domestic and foreign journals such as Geoderma and National Science Review.
  The World's Top 2% Scientists was published by the team of Professor John P.A. Ioannidis of Stanford University. The top 2% scientists in the world were selected by the team from nearly 7 million scientists, based on citations, h-index, co-authorship adjusted hm-index, citations to papers in different authorship positions and a composite indicator. The ranking list was divided into 22 fields and 176 sub-fields, including a total of about 160,000 famous scientists from various fields.
   Source:Ioannidis JPA, Boyack KW, Baas J, Updated science-wide author databases of standardized citation indicators. PLoS Biol. 2020, 18(10): e3000918.

Int’l Cooperation News

Tackling harmful cyanobacterial blooms with Chinese colleagues: we’re all in the same boat

  Harmful cyanobacterial blooms (CyanoHABs) are a rapidly proliferating global problem, threatening the use and sustainability of our freshwater resources. In recent decades, the United States, China, and other developed and developing countries threatened by CyanoHAB expansion have established collaborative efforts aimed at mitigating and managing this environmental and human health problem. However, an escalating negative political climate and restrictive policies on scientific exchange threaten these efforts. In this Perspective, I point to progress that has been made to counter the CyanoHAB problem on U.S.–Chinese fronts through our collaborations, which have been mutually beneficial from research and academic perspectives. Much like global efforts now needed to control pandemics, we are all “in the same boat” when to comes to countering the threat CyanoHABs pose for drinkable, swimmable, and fishable freshwater supplies and human health.
   FIG. (A) Hans Paerl collecting surface algal bloom sample at Lake Taihu, China. (B) Prof. Guangwei Xu and Hans Paerl collecting plankton samples at Lake Erhai, Yunnan Province, China. (C) Prof. Guangwei Xu and Hans Paerl, preparing nutrient addition bioassays near Lake Taihu. (D) Chinese Graduate Students and Hans Paerl filling bioassays with lake Taihu water. (E and F) U.S. and Chinese students working at the experimental mesocosm site located on the shore of Lake Taihu. (G) Hans Paerl and collaborators at the International Society of Limnology (SIL) meetings, held in Nanjing, China, August, 2018. (H) Prof, Yiping Li and Hans Paerl at a Graduate Student Symposium, Hohai University, Nanjing.
  Hans W. Paerl. 2020. JOURNAL OF PHYCOLOGY.DOI: 10.1111/jpy.13058
Radiation dimming and decreasing water clarity fuel underwater darkening in lakes

  Long-term decreases in the incident total radiation and water clarity might substantially affect the underwater light environment in aquatic ecosystems. However, the underlying mechanism and relative contributions of radiation dimming and decreasing water clarity to the underwater light environment on a national or global scale remains largely unknown. Here, we present a comprehensive dataset of unprecedented scale in China’s lakes to address the combined effects of radiation dimming and decreasing water clarity on underwater darkening. Long-term total radiation and sunshine duration showed 5.8% and 7.9% decreases, respectively, after 2000 compared to 1961–1970, resulting in net radiation dimming. An in situ Secchi disk depth (SDD) dataset in 170 lakes showed that the mean SDD significantly decreased from 1.80 ± 2.19 m before 1995 to 1.28 ± 1.82 m after 2005. SDD remote sensing estimations for 641 lakes with areas ≥ 10 km2 showed that SDD markedly decreased from 1.26 ± 0.62 m during 1985–1990 to 1.14 ± 0.66 m during 2005–2010. Radiation dimming and decreasing water clarity jointly caused an approximately 10% decrease in the average available photosynthetically active radiation (PAR) in the euphotic layer. Our results revealed a more important role of decreasing water clarity in underwater darkening than radiation dimming. A meta-analysis of long-term SDD observation data from 61 various waters further elucidated a global extensive underwater darkening. Underwater darkening implies a decrease in water quality for potable water supplies, recession in macrophytes and benthic algae, and decreases in benthic primary production, fishery production, and biodiversity.
  Spatial distribution of SDD differences during 2005–2016 compared to the 1960s–1995 (a), comparison of SDDs before 1995 to after 2005 according to the five geographic lake zones and the Hu Huanyong Line (b and c) for the dataset of 170 lakes.
  All: all lakes; EPL: Eastern Plain Lake zone; YGPL; Yunnan-Guizhou Plateau Lake zone; NPL: Northeast Plain Lake zone; IMXL: Inner Mongolia-Xinjiang Lake zone; TPL: Tibetan Plateau Lake zone; NW and SE represent results for lakes in the northwestern and southeastern regions of the Hu Huanyong Line.
  Yunlin Zhang, Boqiang Qin, Kun Shi, Yibo Zhang, Jianming Deng, Martin Wild et al., 2020. Science Bulletin. DOI:
Climate mediates continental scale patterns of stream microbial functional diversity

  Understanding the large-scale patterns of microbial functional diversity is essential for anticipating climate change impacts on ecosystems worldwide. However, studies of functional biogeography remain scarce for microorganisms, especially in freshwater ecosystems. Here we study 15,289 functional genes of stream biofilm microbes along three elevational gradients in Norway, Spain and China.
  We find that alpha diversity declines towards high elevations and assemblage composition shows increasing turnover with greater elevational distances. These elevational patterns are highly consistent across mountains, kingdoms and functional categories and exhibit the strongest trends in China due to its largest environmental gradients. Across mountains, functional gene assemblages differ in alpha diversity and composition between the mountains in Europe and Asia. Climate, such as mean temperature of the warmest quarter or mean precipitation of the coldest quarter, is the best predictor of alpha diversity and assemblage composition at both mountain and continental scales, with local non-climatic predictors gaining more importance at mountain scale. Under future climate, we project substantial variations in alpha diversity and assemblage composition across the Eurasian river network, primarily occurring in northern and central regions, respectively.
  We conclude that climate controls microbial functional gene diversity in streams at large spatial scales; therefore, the underlying ecosystem processes are highly sensitive to climate variations, especially at high latitudes. This biogeographical framework for microbial functional diversity serves as a baseline to anticipate ecosystem responses and biogeochemical feedback to ongoing climate change.
  Félix Picazo, Annika Vilmi, Juha Aalto, Janne Soininen, Emilio O. Casamayor, Yongqin Liu, Qinglong Wu, Lijuan Ren, Jizhong Zhou, Ji Shen & Jianjun Wang*. Microbiome. 2020. DOI:10.1186/s40168-020-00873-2
China's inland water dynamics: The significance of water body types

  The recent paper by Feng et al. analyzes the changes of China’s inland water bodies (WBs) between 1985-1999 and 2000-2015 based on the Global Surface Water Dataset (GSWD). They quantify the area and number of changes of WBs in different hydrological regions of China, and discuss the possible driving factors. Although this study provides a synoptic view of China’s WB dynamics at basin scales, we here convey a caveat that their basin-scale statistics aggregate the changes in various types of WBs, and, consequently, mask divergent changing patterns among the WB types that are critical for attributing causality.
  An explicit consideration of WB types is essential for understanding large-scale water dynamics. This is especially true for China, a vastly diverse country that descends from the “Roof of the World” to coastal deltas, and is a global hotspot of booming dam construction. In such a complex setting, WB types provide indispensable insight on sorting out water change mechanisms. To elucidate our point, we categorized China’s WBs larger than 1 km2 (~123,150 km2) into saline lakes (42%), freshwater lakes (35%), and artificial reservoirs (23%) based on national lake/reservoir surveys, and reexplored their area changes between the two 15-y epochs using GSWD. 
  China at a national scale, as reported in ref. 1, owned more WB area during this century than previously. Nevertheless, the increased WB area mainly stems from a net expansion of saline lakes (5,572.0 km2) and the reservoirs (3,925.8 km2). In contrast, China’s natural freshwater lakes underwent a net shrinkage of 324.8 km2. Most of the expanded saline lakes are distributed in remote endorheic regions such as the Changtang Plateau, indicating a dominant contribution of climate change. The shrinkage of freshwater lakes, however, mainly occurred in densely populated regions such as the Yangtze River basin (YZR) and the Hai River basin, due to extensive impoldering and rising human water consumption. This contrast implicates an aggravated unevenness of China’s natural freshwater accessibility despite a net national WB gain.
  At least 3,665 reservoirs (≥1 km2) have been added to mitigate freshwater stress in populated basins. About one-third of the newly impounded area (1,219.5 km2) occurred in the upper YZR, largely owing to the construction of monumental reservoirs such as the Three Gorges Reservoir and the Xiluodo Reservoir. Newly impounded reservoirs contribute over half of the total freshwater increase in several major basins such as YZR, the Pearl River basin, and the Yellow River basin, suggesting that human water regulation, rather than increased precipitation, was the first-order driver of the recent WB increase in China’s populated basins.
  Reporting aggregated water changes, as in ref. 1, is an important initiative, but we have to ask, Can the implemented analysis better address the ultimate purposes of WB monitoring, such as understanding causations? Unequivocally, WB variations of different types are driven by different mechanisms. Without an explicit consideration of WB types, regional aggregates not only obscure a thorough attribution of the spatially variable water dynamics but may lead to misinterpreted ramifications to water resource management.
  Fig 1. China's inland WBs (salt lakes, freshwater lakes, and reservoirs) and their area changes during 1985–2015.
  (A) Distribution of natural freshwater and saline lakes, with 1° latitude/longitude histograms of “absolutely increased (AI) area” and “absolutely decreased (AD) area.” AI and AD areas are referred to in Feng et al., which indicates water occurrence change intensity of 100% and ?100%, respectively. Saline lakes were identified from the Second China Lake Survey.
  (B) Distribution of natural freshwater lakes and artificial reservoirs, with 1° latitude/longitude histograms of AI and AD areas. Reservoirs were identified from the Global Reservoir and Dam Database and Almanac of China’s water power.
  (C) WB area changes in the same 11 basins/regions as defined in Feng et al.
  作者:Jingying Zhu, Chunqiao Song et al. PNAS. 2020. DOI: 10.1073/pnas.2005584117