Yuzhou Luo

Recent changes in pan-evaporation dynamics in China

[1] Pan‐evaporation (Epan) as the indicator of atmospheric evaporative demand has decreased worldwide with climate change in the last decades, which is called “Pan Evaporation Paradox”. This study investigates the recent changes in Epan dynamics in China using the observed Epan records for the period 1960–2007. The records show that Epan decreased in China from 1960 to 1991 by �5.4 mm yr �2 . The attribution results show that the significant decreases (P 0.1). The results show that increasing air temperature dominated the change in Epan, which offset the effect of wind speed and led to the increase in Epan. Citation: Liu, X., Y. Luo, D. Zhang, M. Zhang, and C. Liu (2011), Recent changes in pan‐evaporation dynamics in China, Geophys. Res. Lett., 38, L13404, doi:10.1029/2011GL047929.

Assessment of climate change impacts on hydrology and water quality with a watershed modeling approach

The assessment of hydrologic responses to climate change is required in watershed management and planning to protect water resources and environmental quality. This study is designed to evaluate and enhance watershed modeling approach in characterizing climate change impacts on water supply and ecosystem stressors. Soil and Water Assessment Tool (SWAT) was selected as a base model, and improved for the CO2 dependence of potential evapotranspiration and stream temperature prediction. The updated model was applied to quantify the impacts of projected 21st century climate change in the northern Coastal Ranges and western Sierra Nevada, which are important water source areas and aquatic habitats of California. Evapotranspiration response to CO2 concentration varied with vegetation type. For the forest-dominated watersheds in this study, only moderate (1-3%) reductions on evapotranspiration were predicted by solely elevating CO2 concentration under emission scenarios A2 and B1. Modeling results suggested increases in annual average stream temperature proportional to the projected increases in air temperature. Although no temporal trend was confirmed for annual precipitation in California, increases of precipitation and streamflow during winter months and decreases in summers were predicted. Decreased streamflow during summertime, together with the higher projected air temperature in summer than in winter, would increase stream temperature during those months and result in unfavorable conditions for cold-water species. Compared to the present-day conditions, 30-60 more days per year were predicted with average stream temperature >20°C during 2090s. Overall, the hydrologic cycle and water quality of headwater drainage basins of California, especially their seasonality, are very sensitive to projected climate change.

Dynamic modeling of organophosphate pesticide load in surface water in the northern San Joaquin Valley watershed of California

The hydrology, sediment, and pesticide transport components of the Soil and Water Assessment Tool (SWAT) were evaluated on the northern San Joaquin Valley watershed of California. The Nash-Sutcliffe coefficients for monthly stream flow and sediment load ranged from 0.49 to 0.99 over the watershed during the study period of 1992-2005. The calibrated SWAT model was applied to simulate fate and transport processes of two organophosphate pesticides of diazinon and chlorpyrifos at watershed scale. The model generated satisfactory predictions of dissolved pesticide loads relative to the monitoring data. The model also showed great success in capturing spatial patterns of dissolved diazinon and chlorpyrifos loads according to the soil properties and landscape morphology over the large agricultural watershed. This study indicated that curve number was the major factor influencing the hydrology while pesticide fate and transport were mainly affected by surface runoff and pesticide application and in the study area.

Dramatic decrease in streamflow from the headwater source in the central route of China's water diversion project: Climatic variation or human influence?

The Danjiangkou Reservoir is the headwater source of the central route of Chinas South to North Water Diversion Project (SNWDP). Average annual streamflow into the Reservoir was 40.97 km(3) from 1951 to 1989, while it was 31.64 km(3) from 1990 to 2006. Between the two periods, the average annual streamflow was reduced by 9.33 km(3), accounting for 71.8% of the proposed amount of water diversion of the central route (13 km3 per year). The sharply decreasing streamflow would inevitably have negative impacts on the implementation of the SNWDP. The reasons for the decrease in streamflow should be investigated before developing any adaption strategies. In this study, the impacts of climatic variation and human activities on streamflow were evaluated by a climate elasticity method. The results show that the impact of climatic variation (indicated by precipitation and potential evapotranspiration) was responsible for 84.1-90.1% of the streamflow reduction, while human activities or other indentified uncertainties contributed 9.9-15.9% of the streamflow reduction. The observed 69.89 mm decrease in average annual precipitation contributed 81.6-87.3% of the decrease in streamflow. According to the observed data during the study period, the planned water diversion could lead to an ecological disaster of the downstream area of the Danjiangkou Reservoir in certain years. We suggest that the water diversion from the Danjiangkou Reservoir should be conducted in an adaptive manner to avoid such an adverse consequence, instead of the current plan of a fixed annual amount of water.

Sensitivity of agricultural runoff loads to rising levels of CO2 and climate change in the San Joaquin Valley watershed of California

The Soil and Water Assessment Tool (SWAT) was used to assess the impact of climate change on sediment, nitrate, phosphorus and pesticide (diazinon and chlorpyrifos) runoff in the San Joaquin watershed in California. This study used modeling techniques that include variations of CO(2), temperature, and precipitation to quantify these responses. Precipitation had a greater impact on agricultural runoff compared to changes in either CO(2) concentration or temperature. Increase of precipitation by +/-10% and +/-20% generally changed agricultural runoff proportionally. Solely increasing CO(2) concentration resulted in an increase in nitrate, phosphorus, and chlorpyrifos yield by 4.2, 7.8, and 6.4%, respectively, and a decrease in sediment and diazinon yield by 6.3 and 5.3%, respectively, in comparison to the present-day reference scenario. Only increasing temperature reduced yields of all agricultural runoff components. The results suggest that agricultural runoff in the San Joaquin watershed is sensitive to precipitation, temperature, and CO(2) concentration changes.

Atmospheric deposition of nitrogen along the Connecticut coastline of Long Island Sound: a decade of measurements

Four monitoring stations were established along the Connecticut coastline to study the atmospheric deposition of nitrogen into the Long Island Sound (LIS). Two stations at Bridgeport and Hammonasset were set up in 1991. Two additional ones have been in full operation since 1997 at Old Greenwich and Avery Point. Measurements were taken continuously from 1991 through 1994, and from 1997 through 1999. Nitrogen species including (nitrate/nitrite), ammonium, nitric acid gas and total nitrogen (since 1997) in air and precipitation were collected and used to infer ambient concentrations and dry and wet deposition flux densities, with independently collected meteorological data. Statistical procedures were employed to analyze the spatial and temporal variations of the weekly data and quarterly means for the two sampling periods of 1991–1994 and 1997–1999. The deposition flux densities of total nitrogen during 1991–1994 were 6.80 and 24.36 mg N m � 2 wk � 1 , respectively, for dry and wet forms averaged over the two sites of Bridgeport and Hammonasset. During 1997–1999, the overall mean weekly wet and dry depositions of total nitrogen over the four sites were 4.28 and 23.64 mg N m � 2 wk � 1 , respectively. In dry deposition, nitric acid gas was predominant and explained more than 70% of the total dry flux, while in wet deposition nitrate/nitrite was the major contributor (40–60%). Most of the collected nitrogen quantities were higher during warm months, especially from June through September, indicating higher emission rate, scavenging efficiency, and surface uptaking at warmer temperature. The ambient concentration and dry deposition peaked at Bridgeport, and the maximal wet deposition was observed at Old Greenwich. The spatial variation of the dry deposition quantities was affected by potential local emission sources, while the geographic gradient of the wet deposition was largely attributed to the proximities of the sites to the New York–New Jersey metropolitan area. Comparisons of nitrogen quantities between the two sampling periods revealed that the dry and total depositions at Hammonasset decreased, while there were no discernible changes at Bridgeport. r 2002 Elsevier Science Ltd. All rights reserved.

Management-oriented sensitivity analysis for pesticide transport in watershed-scale water quality modeling using SWAT

The Soil and Water Assessment Tool (SWAT) was calibrated for hydrology conditions in an agricultural watershed of Orestimba Creek, California, and applied to simulate fate and transport of two organophosphate pesticides chlorpyrifos and diazinon. The model showed capability in evaluating pesticide fate and transport processes in agricultural fields and instream network. Management-oriented sensitivity analysis was conducted by applied stochastic SWAT simulations for pesticide distribution. Results of sensitivity analysis identified the governing processes in pesticide outputs as surface runoff, soil erosion, and sedimentation in the study area. By incorporating sensitive parameters in pesticide transport simulation, effects of structural best management practices (BMPs) in improving surface water quality were demonstrated by SWAT modeling. This study also recommends conservation practices designed to reduce field yield and in-stream transport capacity of sediment, such as filter strip, grassed waterway, crop residue management, and tailwater pond to be implemented in the Orestimba Creek watershed.

Multimedia transport and risk assessment of organophosphate pesticides and a case study in the northern San Joaquin Valley of California.

This paper presents a framework for cumulative risk characterization of human exposure to pesticides through multiple exposure pathways. This framework is illustrated through a case study of selected organophosphate (OP) pesticides in the northern San Joaquin Valley of California. Chemical concentrations in environmental media were simulated using a multimedia environmental fate model, and converted to contamination levels in exposure media. The risk characterization in this study was based on a residential-scale exposure to residues of multiple pesticides through everyday activities. Doses from a mixture of OP pesticides that share a common mechanism of toxicity were estimated following US Environmental Protection Agency guidelines for cumulative risk analysis. Uncertainty in the human exposure parameters was included in the Monte Carlo simulation in order to perform stochastic calculations for intakes and corresponding risks of OP pesticides. Risk of brain acetylcholinesterase inhibition was reported as margins of exposure (MOEs) of the 99.9th population percentile for two age groups living in the northern San Joaquin Valley during 1992-2005. Diet was identified as the dominant exposure pathway in cumulative exposure and risk, while the temporal trend and spatial variation in total MOE levels were associated with exposures to contaminated drinking water and ambient air. Uniformly higher risks were observed for children because of their greater inhalation and ingestion rates per body weight, relative to adults. The results indicated that exposures for children were about twice of those estimated for adults. Concerns over childrens exposure to OP pesticide through food and water ingestion were suggested based on the spatiotemporal variations predicted for the subchronic MOEs at the 99.9th percentile of exposure in the study area.

Evaluation of water quality in an agricultural watershed as affected by almond pest management practices

In the last decade, the detection of organophosphate (OP) pesticides in the San Joaquin River watershed has raised concerns about water quality. This study examined the influences of almond pest management practices (PMPs) on water quality. The Soil and Water Assessment Tool (SWAT) model was employed to simulate pesticide concentration in water as affected by different PMPs. California Pesticide Use Reporting (PUR) data were used to investigate PMP use trends. Stepwise regression analysis was performed to test the correlation between specific PMP use and pesticide concentrations in surface water and sediment. Our results showed an increasing use of reduced risk pesticides and pyrethroids on almonds. SWAT simulation over the period of 1992-2005 showed decreases in OP concentrations in surface water. High OP and pyrethroid use in dormant sprays was associated with high pesticide concentrations in water and sediment. Almond pesticide use was proved to have significant impacts on the pesticide load in the San Joaquin River watershed. The PMP which combines the use of reduced risk pesticides with no dormant spray was recommended for almond orchard use. This paper presented a novel method of studying the environmental impacts of different agricultural PMPs. By combining pesticide use surveys with watershed modeling, we provided a quantitative foundation for the selection of PMPs to reduce pesticide pollution in surface water.

Investigation of the probability of concurrent drought events between the water source and destination regions of China's water diversion project

In this study, we investigate the concurrent drought probability between the water source and destination regions of the central route of Chinas South to North Water Diversion Project. We find that both regions have been drying from 1960 to 2013. The estimated return period of concurrent drought events in both regions is 11years. However, since 1997, these regions have experienced 5years of simultaneous drought. The projection results of global climate models show that the probability of concurrent drought events is highly likely to increase during 2020 to 2050. The increasing concurrent drought events will challenge the success of the water diversion project, which is a strategic attempt to resolve the water crisis of North China Plain. The data suggest great urgency in preparing adaptive measures to ensure the long-term sustainable operation of the water diversion project.