Vegetation dynamics and their response to freshwater inflow and climate variables in the Yellow River Delta, China

Based on SPOT Vegetation NDVI data, streamflow data and meteorological data, the variation of vegetation cover, measured by the Normalized Difference Vegetation Index (NDVI), and its response to freshwater inflow, precipitation and temperature in the Yellow River Delta and its buffer zones have been investigated for the period 1998-2009. The results show that NDVI has a remarkable regional and seasonal difference. The farther from the Yellow River Channel and the nearer to the Bohai Sea Coastline, the smaller the NDVI value, as influenced by the interaction between freshwater and saltwater on vegetation. Seasonally, high NDVI values appear in summer (August) and low in spring (April). From 1998 to 2009, growing season NDVI significantly increases in the Yellow River Delta. Summer and autumn NDVI have a similar trend pattern to growing season NDVI, while spring NDVI significantly decreases. NDVI shows different strengths of correlation with freshwater inflow, precipitation and temperature respectively and these correlations vary in different seasons and months. Freshwater inflow is a key factor for vegetation dynamics and NDVI variation. Climate features play a dominant role in seasonal variation in vegetation cover. However, the impacts of freshwater inflow and climate variables on vegetation have been greatly modified by a range of human activities such as land use pattern and land use change as well as water diversion from the Yellow River. Overall, the results of this study can be helpful for decision-making of regional ecological protection and economic development. (C) 2012 Elsevier Ltd and INQUA. All rights reserved.Based on SPOT Vegetation NDVI data, streamflow data and meteorological data, the variation of vegetation cover, measured by the Normalized Difference Vegetation Index (NDVI), and its response to freshwater inflow, precipitation and temperature in the Yellow River Delta and its buffer zones have been investigated for the period 1998-2009. The results show that NDVI has a remarkable regional and seasonal difference. The farther from the Yellow River Channel and the nearer to the Bohai Sea Coastline, the smaller the NDVI value, as influenced by the interaction between freshwater and saltwater on vegetation. Seasonally, high NDVI values appear in summer (August) and low in spring (April). From 1998 to 2009, growing season NDVI significantly increases in the Yellow River Delta. Summer and autumn NDVI have a similar trend pattern to growing season NDVI, while spring NDVI significantly decreases. NDVI shows different strengths of correlation with freshwater inflow, precipitation and temperature respectively and these correlations vary in different seasons and months. Freshwater inflow is a key factor for vegetation dynamics and NDVI variation. Climate features play a dominant role in seasonal variation in vegetation cover. However, the impacts of freshwater inflow and climate variables on vegetation have been greatly modified by a range of human activities such as land use pattern and land use change as well as water diversion from the Yellow River. Overall, the results of this study can be helpful for decision-making of regional ecological protection and economic development. (C) 2012 Elsevier Ltd and INQUA. All rights reserved

Simulated runoff responses to land use in the middle and upstream reaches of Taoerhe River basin, Northeast China, in wet, average and dry years

Study on runoff variations and responses can lay a foundation for flood control, water allocation and integrated river basin management. This study applied the Soil and Water Assessment Tool model to simulate the effects of land use on annual and monthly runoff in the Middle and Upstream Reaches of Taoerhe River basin, Northeast China, under the wet, average and dry climate conditions through scenario analysis. The results showed that from the early 1970s to 2000, land use change with an increase in farmland (17.0%) and decreases in forest (10.6%), grassland (4.6%) and water body (3.1%) caused increases in annual and monthly runoff. This effect was more distinct in the wet season or in the wet year, suggesting that land use change from the early 1970s to 2000 may increase the flood potential in the wet season. Increases in precipitation and air temperature from the average to wet year led to annual and monthly (March and from June to December) runoff increases, while a decrease in precipitation and an increase in air temperature from the average to dry year induced decreases in annual and monthly (all months except March) runoff, and moreover, these effects were more remarkable in the wet season than those in the dry season. Due to the integrated effects of changing land use and climate conditions, the annual runoff increased (decreased) by 70.1mm (25.2mm) or 197.4% (71.0%) from the average to wet (dry) year. In conclusion, climate conditions, especially precipitation, played an important role in runoff variations while land use change was secondary over the study area, and furthermore, the effects of changes in land use and/or climate conditions on monthly runoff were larger in the wet season. Copyright (c) 2012 John Wiley & Sons, Ltd.Study on runoff variations and responses can lay a foundation for flood control, water allocation and integrated river basin management. This study applied the Soil and Water Assessment Tool model to simulate the effects of land use on annual and monthly runoff in the Middle and Upstream Reaches of Taoerhe River basin, Northeast China, under the wet, average and dry climate conditions through scenario analysis. The results showed that from the early 1970s to 2000, land use change with an increase in farmland (17.0%) and decreases in forest (10.6%), grassland (4.6%) and water body (3.1%) caused increases in annual and monthly runoff. This effect was more distinct in the wet season or in the wet year, suggesting that land use change from the early 1970s to 2000 may increase the flood potential in the wet season. Increases in precipitation and air temperature from the average to wet year led to annual and monthly (March and from June to December) runoff increases, while a decrease in precipitation and an increase in air temperature from the average to dry year induced decreases in annual and monthly (all months except March) runoff, and moreover, these effects were more remarkable in the wet season than those in the dry season. Due to the integrated effects of changing land use and climate conditions, the annual runoff increased (decreased) by 70.1mm (25.2mm) or 197.4% (71.0%) from the average to wet (dry) year. In conclusion, climate conditions, especially precipitation, played an important role in runoff variations while land use change was secondary over the study area, and furthermore, the effects of changes in land use and/or climate conditions on monthly runoff were larger in the wet season. Copyright (c) 2012 John Wiley & Sons, Ltd

The Role of Satellite-Based Remote Sensing in Improving Simulated Streamflow: A Review

A hydrological model is a useful tool to study the effects of human activities and climate change on hydrology. Accordingly, the performance of hydrological modeling is vitally significant for hydrologic predictions. In watersheds with intense human activities, there are difficulties and uncertainties in model calibration and simulation. Alternative approaches, such as machine learning techniques and coupled models, can be used for streamflow predictions. However, these models also suffer from their respective limitations, especially when data are unavailable. Satellite-based remote sensing may provide a valuable contribution for hydrological predictions due to its wide coverage and increasing tempo-spatial resolutions. In this review, we provide an overview of the role of satellite-based remote sensing in streamflow simulation. First, difficulties in hydrological modeling over highly regulated basins are further discussed. Next, the performance of satellite-based remote sensing (e.g., remotely sensed data for precipitation, evapotranspiration, soil moisture, snow properties, terrestrial water storage change, land surface temperature, river width, etc.) in improving simulated streamflow is summarized. Then, the application of data assimilation for merging satellite-based remote sensing with a hydrological model is explored. Finally, a framework, using remotely sensed observations to improve streamflow predictions in highly regulated basins, is proposed for future studies. This review can be helpful to understand the effect of applying satellite-based remote sensing on hydrological modeling

Trends in temperature and precipitation extremes over Circum-Bohai-Sea region, China

Trends in temperature and precipitation extremes from 1961 to 2008 have been investigated over Circum-Bohai-Sea region, China using daily temperature and precipitation data of 63 meteorological stations. The results show that at most stations, there is a significant increase in the annual frequency of warm days and warm nights, as well as a significant decrease in the annual frequency of cold days, cold nights, frost days, and annual diurnal temperature range (DTR). Their regional averaged changes are 2.06 d/10yr, 3.95 d/10yr, -1.88 d/10yr, -4.27 d/10yr, -4.21 d/10yr and -0.20A degrees C/10yr, respectively. Seasonal changes display similar patterns to the annual results, but there is a large seasonal difference. A significant warming trend is detected at both annual and seasonal scales, which is more contributed by changes of indices defined by daily minimum temperature than those defined by daily maximum temperature. For precipitation indices, the regional annual extreme precipitation displays a weak decrease in terms of magnitude and frequency, i.e. extreme precipitation days (RD95p), intensity (RINTEN), proportion (RPROP) and maximum consecutive wet days (CWD), but a slight increase in the maximum consecutive dry days (CDD), which are consistent with changes of annual total precipitation (PRCPTOT). Seasonally, PRCPTOT and RD95p both exhibit an increase in spring and a decrease in other seasons with the largest decrease in summer, but generally not significant. In summary, this study shows a pronounced warming tendency at the less rainy period over Circum-Bohai-Sea region, which may affect regional economic development and ecological protection to some extent.Trends in temperature and precipitation extremes from 1961 to 2008 have been investigated over Circum-Bohai-Sea region, China using daily temperature and precipitation data of 63 meteorological stations. The results show that at most stations, there is a significant increase in the annual frequency of warm days and warm nights, as well as a significant decrease in the annual frequency of cold days, cold nights, frost days, and annual diurnal temperature range (DTR). Their regional averaged changes are 2.06 d/10yr, 3.95 d/10yr, -1.88 d/10yr, -4.27 d/10yr, -4.21 d/10yr and -0.20A degrees C/10yr, respectively. Seasonal changes display similar patterns to the annual results, but there is a large seasonal difference. A significant warming trend is detected at both annual and seasonal scales, which is more contributed by changes of indices defined by daily minimum temperature than those defined by daily maximum temperature. For precipitation indices, the regional annual extreme precipitation displays a weak decrease in terms of magnitude and frequency, i.e. extreme precipitation days (RD95p), intensity (RINTEN), proportion (RPROP) and maximum consecutive wet days (CWD), but a slight increase in the maximum consecutive dry days (CDD), which are consistent with changes of annual total precipitation (PRCPTOT). Seasonally, PRCPTOT and RD95p both exhibit an increase in spring and a decrease in other seasons with the largest decrease in summer, but generally not significant. In summary, this study shows a pronounced warming tendency at the less rainy period over Circum-Bohai-Sea region, which may affect regional economic development and ecological protection to some extent

River damming and drought affect water cycle dynamics in an ephemeral river based on stable isotopes: The Dagu River of North China

The flow regime and biogeochemical cycles are greatly affected by river damming and drought, especially in ephemeral rivers. However, the combined effects have been rarely considered. This study, taking the Dagu River in Jiaodong Peninsula of North China as an example, investigated the dynamic changes in water cycle related to river damming and drought using stable water isotopes for the period 2018-2019. The results indicated that riverwater isotopes significantly varied temporally and spatially. The temporal variations in riverwater isotopes appeared to be linked with those in precipitation, but the relationship between river water and precipitation isotopes was greatly affected by river damming, river water-groundwater exchange and potential water pollution. Spatially, a single dam exhibited no significant effect on riverwater isotopes, but the accumulative impacts of cascade dams resulted in the enrichment of heavy isotopes in river water towards the downstream through increasing hydraulic residence time and water evaporation largely. The inter-annual variations in river water isotopes with increased evaporative fractionationwere highlighted by their strong response to the drought in 2019. The combined effects of cascade dams and drought greatly changed water cycle dynamics and further exacerbated water shortage, which should thus be fully considered for water resource management, especially for regions with water-limited but heavily-regulated rivers. (C) 2020 Elsevier B.V. All rights reserved

Variability of extreme summer precipitation over Circum-Bohai-Sea region during 1961-2008

The variability of extreme summer precipitation over Circum-Bohai-Sea region during 1961-2008 was investigated based on the daily precipitation data of 63 meteorological stations using the linear regression method, the non-parametric Mann-Kendall test, and the continuous wavelet transform method. The results showed that there were large spatial differences in the trends of extreme summer precipitation indices. Decreasing trends were found in summer total precipitation, extreme precipitation frequency, intensity and proportion, the maximum consecutive wet days (CWD), and the maximum 1- and 5-day precipitation, and the largest decrease was observed in the central coast area (except CWD), although the trends were not statistically significant at the 5% level at most places. Inversely, the maximum consecutive dry days exhibited non-significant increasing trends. Additionally, the significant 2-4-year periods were detected for eight indices, showing the significant interannual variability of extreme summer precipitation. Overall, the results of this study indicated that in the last 48 years, there was severe water stress over Circum-Bohai-Sea region, especially in the central coast area, which exerted negative effects on economic development and natural ecosystems.The variability of extreme summer precipitation over Circum-Bohai-Sea region during 1961-2008 was investigated based on the daily precipitation data of 63 meteorological stations using the linear regression method, the non-parametric Mann-Kendall test, and the continuous wavelet transform method. The results showed that there were large spatial differences in the trends of extreme summer precipitation indices. Decreasing trends were found in summer total precipitation, extreme precipitation frequency, intensity and proportion, the maximum consecutive wet days (CWD), and the maximum 1- and 5-day precipitation, and the largest decrease was observed in the central coast area (except CWD), although the trends were not statistically significant at the 5% level at most places. Inversely, the maximum consecutive dry days exhibited non-significant increasing trends. Additionally, the significant 2-4-year periods were detected for eight indices, showing the significant interannual variability of extreme summer precipitation. Overall, the results of this study indicated that in the last 48 years, there was severe water stress over Circum-Bohai-Sea region, especially in the central coast area, which exerted negative effects on economic development and natural ecosystems

Ridge cultured rice integrated with fish farming in trenches, Anhui Province

Meeting: National Rice Fish Farming Systems Symposium, 4-8 Oct. 1988, Wuxi, CNIn IDL-1614

Combined effects of damming and drought on nitrogen dynamics in an ephemeral river of North China

Damming and drought have dramatically altered water cycle dynamics in rivers, which further affects nitrogen biogeochemical cycles; however, their combined effects have rarely been studied, especially for ephemeral rivers with variable water flows. Taking the Dagu River of North China as the study area, we examined the spatiotemporal variability of nitrogen in river water and its relation to damming and drought. The total nitrogen (TN), dissolved inorganic nitrogen (DIN) and NO3- concentrations varied significantly in space and time, but the NH4+ and NO2- concentrations changed little. Spatially, compared with the upper reaches, the TN, DIN and NO3- concentrations in the lower reaches decreased by 71%, 81% and 85%, respectively, which was concurrent with the isotopic enrichment of nitrate. Temporally, their concentrations in dry seasons were more than twice of wet seasons, and increased from 2018 (normal year) to 2019 (dry year). The cascade dams may promote the NO3- removal towards the lower reaches through assimilation, which combined with nitrification and strong evaporation to enhance delta O-18-NO3- enrichment and disproportionate delta N-15-NO3-/delta O-18-NO3- ratio. Further, the damming effects can be aggravated by droughts because of no flow, extended nitrogen residence time and increased groundwater discharge with higher nitrogen contents, which jointly elevated the nitrogen level. Hence, the combined effects of damming and drought should be fully considered for management of water environment and resources in regions with ephemeral rivers