[1] We develop a stream temperature model within the Soil and Water Assessment Tool (SWAT) that reflects the combined influence of meteorological (air temperature) and hydrological conditions (streamflow, snowmelt, groundwater, surface runoff, and lateral soil flow) on water temperature within a watershed. SWAT currently uses a linear air-stream temperature relationship to determine stream temperature, without consideration of watershed hydrology. As SWAT uses stream temperature to model various in-stream biological and water quality processes, an improvement of the stream temperature model will result in improved accuracy in modeling these processes. The new stream temperature model is tested on seven coastal and mountainous streams throughout the western United States for which high quality flow and water temperature data were available. The new routine does not require input data beyond that already supplied to the model, can be calibrated with a limited number of calibration parameters, and achieves improved representation of observed daily stream temperature. For the watersheds modeled, the Nash-Sutcliffe (NS) coefficient and mean error (ME) for the new stream temperature model averaged 0.81 and À0.69 C, respectively, for the calibration period and 0.82 and À0.63 C for the validation period. The original SWAT stream temperature model averaged a NS of À0.27 and ME of 3.21 C for the calibration period and a NS of À0.26 and ME of 3.02 C for the validation period. Sensitivity analyses suggest that the new stream temperature model calibration parameters are physically reasonable and the model is better able to capture stream temperature changes resulting from changes in hydroclimatological conditions.

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[1] Pan-evaporation (E pan ) 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 E pan dynamics in China using the observed E pan records for the period 1960-2007. The records show that E pan decreased in China from 1960 to 1991 by −5.4 mm yr −2 . The attribution results show that the significant decreases (P < 0.001) in wind speed and solar radiation offset the effect of increasing air temperature and led to the decrease in E pan . However, the observed E pan has increased since 1992 by 7.9 mm yr −2 . From 1992 to 2007, the amplitude of increase in air temperature rose seriously, while the amplitude of decrease in wind speed declined and solar radiation even increased insignificantly (P > 0.1). The results show that increasing air temperature dominated the change in E pan , which offset the effect of wind speed and led to the increase in E pan . Citation:

.[1] The Danjiangkou Reservoir is the headwater source of the central route of China's 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 km 3 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.Citation: Liu, X., C. Liu, Y. Luo, M. Zhang, and J. Xia (2012), Dramatic decrease in streamflow from the headwater source in the central route of China's water diversion project: Climatic variation or human influence?,

A novel model named random-forest-spatiotemporal-kriging (RF-STK) was developed to estimate the daily ambient NO concentrations across China during 2013-2016 based on the satellite retrievals and geographic covariates. The RF-STK model showed good prediction performance, with cross-validation R = 0.62 (RMSE = 13.3 μg/m) for daily and R = 0.73 (RMSE = 6.5 μg/m) for spatial predictions. The nationwide population-weighted multiyear average of NO was predicted to be 30.9 ± 11.7 μg/m (mean ± standard deviation), with a slowly but significantly decreasing trend at a rate of -0.88 ± 0.38 μg/m/year. Among the main economic zones of China, the Pearl River Delta showed the fastest decreasing rate of -1.37 μg/m/year, while the Beijing-Tianjin Metro did not show a temporal trend ( P = 0.32). The population-weighted NO was predicted to be the highest in North China (40.3 ± 10.3 μg/m) and lowest in Southwest China (24.9 ± 9.4 μg/m). Approximately 25% of the population lived in nonattainment areas with annual-average NO > 40 μg/m. A piecewise linear function with an abrupt point around 100 people/km characterized the relationship between the population density and the NO, indicating a threshold of aggravated NO pollution due to urbanization. Leveraging the ground-level NO observations, this study fills the gap of statistically modeling nationwide NO in China, and provides essential data for epidemiological research and air quality management.