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During 1961–2012, the regional average annual potential evapotranspiration (PET) of Southwest China (SWC) and the four subregions (named as SR1, SR2, SR3, and SR4) showed different decreases (excluding SR3); while the breakpoint analysis suggested that PET changes (i.e., sign and magnitude) have shifted. Based on a group of sensitivity experiments with Penman‐Monteith equation and a new separating method, the contributions of each climate factor alone (i.e., net radiation, Rn; mean temperature, Tave; wind speed, Wnd; and vapor pressure deficit, Vpd) to PET changes were calculated. Results showed that declined Wnd in SR1, reduced Rn in SR2, SR4, and SWC, and increased Vpd in SR3 were responsible for the PET changes during 1961–2012. However, the determinant factor for each subregion and SWC varied in different segmented periods, which were identified using the breakpoint analysis. The impacts of PET shifts on SWC dryness/wetness (reflected by the 3 month Standardized Precipitation‐Evapotranspiration index, SPEI‐3) during 1961–2012 were then quantified. Briefly, SPEI‐3 changes in SR3, SR4, and SWC had the determinant factor of PET in the first one or two period(s), and precipitation in the last period; while they were attributed to PET (precipitation) in SR1 (SR2) for each segmented period. It is found that PET and precipitation had comparable contributions to the variations in SWC dryness/wetness. Our findings have suggested that more attentions should be paid to the impacts of PET changes and shifts in future studies of dryness/wetness or drought.

Abstract. Lack of reliable long-term precipitation record from the northern Tibetan Plateau has constrained our understanding of precipitation variations in this region. We drilled an ice core on the Puruogangri Ice Field in the central Tibetan Plateau in 2000 to reveal the precipitation variations. The well dated part of the core extends back to AD 1600, allowing us to construct a 400-year annual accumulation record. This record shows that the central Tibetan plateau experienced a drier period with an average annual precipitation of ~300 mm in the 19th century, compared to ~450 mm in the wetter periods during 1700–1780 and the 20th century. This pattern agrees with precipitation reconstructions from the Dunde and Guliya ice cores on the northern Plateau but differs from that found in the Dasuopu ice cores from the southern Plateau The north-south contrasts in precipitation reconstruction reveals difference in moisture origin between the south Tibetan Plateau dominated by the Asian monsoon and the north Tibetan Plateau dominated by the continental recycling and the westerlies.

Symptoms of eutrophication (including biodiversity loss, harmful algal blooms, and hypoxia) are an increasing problem in Chinese seas. Nutrient enrichment is primarily caused by accelerated human activities that cause nutrient pollution of the aquatic environment. In this study, the Integrated Model to Assess the Global Environment-Global Nutrient Model (IMAGE-GNM) was used to estimate nitrogen inputs from river discharge, submarine fresh groundwater discharge, and mariculture, and TM5-FAst Scenario Screening Tool (TM5-FASST) for atmospheric nitrogen deposition to the three Large Marine Ecosystems (LMEs, i.e., Yellow Sea/Bohai Sea, YS/BS; East China Sea, ECS; South China Sea, SCS) bordered by China and several other countries for the period 1970-2010. China's river nitrogen export was the largest nitrogen source in YS/BS and ECS. In SCS, however, China and other countries contributed equally and although decreasing, the proportion of natural sources remain considerable. The total nitrogen inputs to YS/BS (1.0 to 4.1 Tg year −1), ECS (1.3 to 5.5 Tg year −1), and SCS (2.1 to 5.8 Tg year −1) increased rapidly during 1970-2010. River export is dominated by agriculture; nitrogen inputs from atmospheric deposition and mariculture have been increasing rapidly in recent years. Considering only the coastal zone of the three LMEs, our results show that the total nitrogen inputs are strongly concentrated spatially in areas close to river mouths and those confined regions with mariculture production. To sustain the food production and economic growth in the coming decades, nitrogen inputs may increase further, depending on future eutrophication mitigation policies. Plain Language Summary Nitrogen is a limiting nutrient for plant production. Excessive nitrogen use in agriculture and discharge from wastewater is the primary causes of eutrophication in aquatic environments. Symptoms of eutrophication (including biodiversity loss, harmful algal blooms (HABs), and hypoxia) are an increasing problem in Chinese seas. Here we quantified the nitrogen inputs from river export, atmospheric deposition, submarine fresh groundwater discharge, and mariculture to the Yellow Sea/Bohai Sea (YS/BS), East China Sea (ECS), and South China Sea (SCS) bordered by China and other countries for the period 1970-2010. Nitrogen inputs increased rapidly, mainly due to increasing land-based sources (river export and atmospheric deposition), while nitrogen from mariculture started to increase recently. River export is dominated by agriculture with growing proportions of sewage and freshwater aquaculture. Nitrogen inputs were spatially concentrated and increased faster in Chinese coastal waters than in other countries. China's contribution to nitrogen pollution exceeded that of other countries in YS/BS and ECS, while China and other countries contributed equally in SCS. Nitrogen concentrations and HAB frequency in the seas seem to be correlated as both increased substantially since 1970s. Mitigation of nitrogen pollution is therefore urgent because human ac...

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The three large marine ecosystems (LMEs) bordering China (Yellow Sea/Bohai Sea, East China Sea, and South China Sea) have received excess nitrogen (N) and phosphorus (P) in the past decades with detrimental consequences for ecosystem functioning, such as increased productivity, loss of biodiversity, and proliferation of harmful algal blooms (HABs). N loading increased much faster than that of P. Here, we show that HABs in the three LMEs started to proliferate after the N:P molar ratio exceeded the threshold value of 25 in the 1980s. The mismatch of N and P inputs is not only related to differences in loads but also inherent to the differences in their biogeochemical cycles which more efficiently filter P than N in land- and waterscapes. Future Shared Socioeconomic Pathways show that high N:P ratios will persist for decades to come, even worsening in a future oriented toward sustainability, and indicate that HABs may be a persisting problem in China’s coastal waters. While efforts in agricultural systems are governed by the agronomic crop requirements and are not easy to manage with respect to N:P ratios, the separate collection of urine in urban and rural areas could contribute to decreases in both total nutrient loads and N:P ratios.

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