The quantitative attribution of climate change to runoff increase over the Qinghai-Tibetan Plateau.

Runoff from the Qinghai-Tibetan Plateau, a major global water tower, is crucial to regional hydrological processes and the availability of water for a large population living downstream. Climate change, especially changes in precipitation and temperature, directly impacts hydrological processes and exacerbates shifts in the cryosphere, such as glacier and snow melt, leading to changes in runoff. Although there is a consensus on increased runoff due to climate change, it is still unclear to what extent precipitation and temperature contribute to runoff variations. This lack of understanding is one of the primary sources of uncertainty when assessing the hydrological impacts of climate change. In this study, a large-scale, high-resolution, and well-calibrated distributed hydrological model was employed to quantify the long-term runoff of the Qinghai-Tibetan Plateau, and the changes in runoff and runoff coefficient were analyzed. Furthermore, the impacts of precipitation and temperature on runoff variation were quantitatively estimated. The results found that runoff and runoff coefficient decreased from southeast to northwest, with mean values of 184.77 mm and 0.37, respectively. Notably, the runoff coefficient exhibited a significant increasing trend of 1.27 %/10 yr (P < 0.001), while the southeastern and northern regions of the plateau showed a declining tendency. We further showed that the warming and humidification of the Qinghai-Tibetan Plateau led to an increase in the runoff by 9.13 mm/10 yr (P < 0.001). And precipitation is a more important contributor than temperature across the plateau, contributing 72.08 % and 27.92 % to the runoff increase, respectively. At the basin scale, the influence of precipitation and temperature on runoff varies among basins, with the Daduhe basin and the Inner basin being the most and least influenced by precipitation, respectively. This research analyses historical runoff changes on the Qinghai-Tibetan Plateau and provides insights into the contributions of climate change to runoff.

Improving global gross primary productivity estimation by fusing multi-source data products.

A reliable estimate of the gross primary productivity (GPP) of terrestrial vegetation is essential for both making decisions to address global climate change and understanding the global carbon balance. The lack of consistency in global terrestrial GPP estimates across various products leads to great uncertainty. In this study, we improve the quantification of global gross primary productivity by integrating multiple source GPP products without using any prior knowledge through the Bayesian-based Three-Cornered Hat (BTCH) method to generate a new weighted GPP data set. The fusion results demonstrate the superiority of weighted GPP, which greatly reduces the random error of individual datasets and fully takes advantage of the characteristics of multi-source data products. The weighted dataset can largely reproduce the interannual variation of regional GPP. Overall, the merging scheme based on the BTCH method can effectively generate a new GPP dataset that integrates information from multiple products and provides new ideas for GPP estimation on a global scale.

Would the obtainable gross primary productivity (GPP) products stand up? A critical assessment of 45 global GPP products.

Gross primary productivity (GPP) is a vital variable of the global carbon cycle, but the quantification of global GPP is subject to significant uncertainty due to the lack of direct observations at a global scale. Here, we evaluated and compared 45 GPP products in terms of their applicability to different vegetation types at various spatiotemporal scales. The results show that 44 GPP products and obsGPP (Model Tree Ensemble GPP derived from observations and named obsGPP) have similar global patterns with correlation coefficients greater than 0.8 except for NGT, where GOSIF, RS, and BESS are prominent. GPP products have the greatest variation in Suriname, with a mean 75th and 25th percentile difference value of 0.4748 (normalized), and we recommend RS, SDGVM and LPJ-wsl as they provide GPP estimates close to the average GPP. In terms of seasonal estimations, considerable disagreement occurs among the GPP products in winter, with a range from 118.76 to 314.95 gC/m2/season, among which JULES has the closest GPP value to the average GPP estimation. For studies concerning vegetation types preference is given to the LUE average GPP. The 45 GPP products are more consistent on grasslands but, have obvious differences for savannas. All GPP products have their own specific spatiotemporal scales, such as global or national scales or different seasons and different vegetation types (forest, grasslands, etc.). This study provides guidelines for selecting GPP products.

An estimate of human and natural contributions to changes in water resources in the upper reaches of the Minjiang River.

Climate change and human activities have changed the spatial-temporal distribution of water resources, especially in a fragile ecological area such as the upper reaches of the Minjiang River (UMR) basin, where they have had a more profound effect. The average of double-mass curve (DMC) and Distributed Time-Variant Gain Hydrological Model (DTVGM) are applied to distinguish between the impacts of climate change and human activities on water resources in this paper. Results indicated that water resources decreased over nearly 50 years in the UMR. At the annual scale, contributions of human activities and climate change to changes in discharge were -77% and 23%, respectively. In general, human activities decreased the availability of water resources, whereas climate change increased the availability of water resources. However, the impacts of human activities and climate change on water resources availability were distinctly different on annual versus seasonal scales, and they showed more inconsistency in summer and autumn. The main causes of decreasing water resources are reservoir regulation, and water use increases due to population growth. The results of this study can provide support for water resource management and sustainable development in the UMR basin.

2015-16 floods and droughts in China, and its response to the strong El Niño.

The features of hydro-climate anomalies in China in 2015-2016 were analyzed in great detail, together with possible responses to the super 2015-16 El Niño event. The 2015-16 El Niño is characterized as a "strong" event in terms of the duration, intensity, and coverage of warming sea surface temperature (SST) in the central and east-central equatorial Pacific in comparison to the 1982-83 and 1997-98 events. The floods and droughts frequency were incidence of floods and droughts per year, respectively. The results show several significant anomalies in China: 1) About 9%-173% of precipitation variance in 2015-16 can be attributed to this El Niño; 2) There was significant inconformity between hydro-climate anomalies and the occurrence of floods and droughts; 3) Flood frequency has increased, especially over Southeast China and the Yangtze River in the summer of 2016; 4) Drought frequency has also increased, especially over Northeast China in summer of 2015, Northwest China in spring of 2016, and most parts in winter of 2015. The response of China hydro-climate anomalies to the 2015-16 El Niño was significant via El Niño and warm Indian Ocean induced circulation anomalies, which were characterized by stronger and more westward-extending western Pacific subtropical high and anomalous water vapor transport. Knowledge of the response of hydro-climate extremes to El Niño can provide valuable information to improve flood and drought forecasting in China.

Inclusion of soil carbon lateral movement alters terrestrial carbon budget in China.

The lateral movement of soil carbon has a profound effect on the carbon budget of terrestrial ecosystems; however, it has never been quantified in China, which is one of the strongest soil erosion areas in the world. In this study, we estimated that the overall soil erosion in China varies from 11.27 to 18.17 Pg yr(-1) from 1982 to 2011, accounting for 7-21% of total soil erosion globally. Soil erosion induces a substantial lateral redistribution of soil organic carbon ranging from 0.64 to 1.04 Pg C yr(-1). The erosion-induced carbon flux ranges from a 0.19 Pg C yr(-1) carbon source to a 0.24 Pg C yr(-1) carbon sink in the terrestrial ecosystem, which is potentially comparable in magnitude to previously estimated total carbon budget of China (0.19 to 0.26 Pg yr(-1)). Our results showed that the lateral movement of soil carbon strongly alters the carbon budget in China, and highlighted the urgent need to integrate the processes of soil erosion into the regional or global carbon cycle estimates.

Variations in global temperature and precipitation for the period of 1948 to 2010.

Climate change has impacts on both natural and human systems. Accurate information regarding variations in precipitation and temperature is essential for identifying and understanding these potential impacts. This research applied Mann-Kendall, rescaled range analysis and wave transform methods to analyze the trends and periodic properties of global and regional surface air temperature (SAT) and precipitation (PR) over the period of 1948 to 2010. The results show that 65.34% of the area studied exhibits significant warming trends (p < 0.05) while only 3.18% of the area exhibits significant cooling trends. The greatest warming trends are observed in Antarctica (0.32 °C per decade) and Middle Africa (0.21 °C per decade). Notably, 62.26% of the area became wetter, while 22.01% of the area shows drying trends. Northern Europe shows the largest precipitation increase, 12.49 mm per decade. Western Africa shows the fastest drying, -21.05 mm per decade. The rescaled range analysis reveals large areas that show persistent warming trends; this behavior in SAT is more obvious than that in PR. Wave transform results show that a 1-year period of SAT variation dominates in all regions, while inconsistent 0.5-year bands are observed in East Asia, Middle Africa, and Southeast Asia. In PR, significant power in the wavelet power spectrum at a 1-year period was observed in 17 regions, i.e., in all regions studied except Western Europe, where precipitation is instead characterized by 0.5-year and 0.25-year periods. Overall, the variations in SAT and PR can be consistent with the combined impacts of natural and anthropogenic factors, such as atmospheric concentrations of greenhouse gases, the internal variability of climate system, and volcanic eruptions.