• Energy Research
• 6. Clean water close

China is the world's most populous country and a major emitter of greenhouse gases. Consequently, much research has focused on China's influence on climate change but somewhat less has been written about the impact of climate change on China. China experienced explosive economic growth in recent decades, but with only 7% of the world's arable land available to feed 22% of the world's population, China's economy may be vulnerable to climate change itself. We find, however, that notwithstanding the clear warming that has occurred in China in recent decades, current understanding does not allow a clear assessment of the impact of anthropogenic climate change on China's water resources and agriculture and therefore China's ability to feed its people. To reach a more definitive conclusion, future work must improve regional climate simulations-especially of precipitation-and develop a better understanding of the managed and unmanaged responses of crops to changes in climate, diseases, pests and atmospheric constituents.

AbstractDynamics of global wetlands are closely linked to biodiversity conservation, hydrology, and greenhouse gas emissions. However, long-term time series of global wetland products are still lacking. Using a diagnostic model based on the TOPography-based hydrological MODEL (TOPMODEL), this study produced an ensemble of 28 gridded maps of monthly global/regional wetland extents (with more reliable estimates at mid-low latitudes) for 1980–2020 at 0.25° × 0.25° spatial resolution, calibrated with a combination of four observation-based wetland data and seven gridded soil moisture reanalysis datasets. The gridded dynamic maps of wetlands capture the spatial distributions, seasonal cycles, and interannual variabilities of observed wetland extent well, and also show a good agreement with independent satellite-based terrestrial water storage estimates over wetland areas. The long temporal coverage extending beyond the era of satellite datasets, the global coverage, and the opportunity to provide real-time updates from ongoing soil moisture data make these products helpful for various applications such as analyzing the wetland-related methane emission.

La sécheresse est l'un des problèmes les plus importants mais les moins bien compris dans les changements environnementaux mondiaux. La diminution de l'humidité du sol est un indicateur de la sécheresse. Ici, nous analysons les données de mesure de l'humidité du sol en été (juin-août) sur 50 sites en Chine afin d'étudier le lien entre le changement climatique et la sécheresse. À l'échelle du pays, une diminution significative de l'humidité du sol en été dans les 50 premiers cm a été observée entre 1981 et 2002, résultant principalement de la baisse de l'humidité du sol dans le nord de la Chine. Les analyses statistiques suggèrent que les changements dans la fréquence des précipitations ont une incidence significative conséquences sur la dynamique de l'humidité du sol, mais notre capacité à utiliser les changements de fréquence des précipitations pour expliquer la variation de l'humidité du sol dépend des critères discriminants des événements de précipitations. Parmi cinq critères (0, 5, 10, 15 et 20 mm jour -1 ), le coefficient maximal de corrélation entre l'humidité du sol d'été dans les 50 premiers cm et la fréquence des précipitations se produit lorsque l'on considère le nombre de jours où la quantité quotidienne de précipitations est supérieure à 10 mm (PF10) .Spatialement, la corrélation entre l'humidité du sol dans les 50 premiers cm et PF10 est faible pour les sols très secs et très humides et est beaucoup plus forte pour les valeurs intermédiaires. La sequía es uno de los problemas más importantes pero menos comprendidos en los cambios ambientales globales. La disminución de la humedad del suelo es un indicador de la sequía. Aquí, analizamos los datos de medición de la humedad del suelo en verano (junio-agosto) en 50 sitios en China para investigar el vínculo entre el cambio climático y la sequía. A escala del país, se observó una disminución significativa de la humedad del suelo en verano en los 50 cm superiores durante 1981-2002, como resultado principalmente de la disminución de la humedad del suelo en el norte de China. Los análisis estadísticos sugieren que los cambios en la frecuencia de las precipitaciones tienen consecuencias para la dinámica de la humedad del suelo, pero nuestra capacidad de utilizar los cambios de frecuencia de precipitación para explicar la variación de la humedad del suelo depende de los criterios discriminatorios de los eventos de precipitación. Entre cinco criterios (0, 5, 10, 15 y 20 mm día -1 ), el coeficiente máximo de correlación entre la humedad del suelo de verano en los 50 cm superiores y la frecuencia de precipitación se produce al considerar el número de días en que la cantidad de precipitación diaria es mayor que 10 mm (PF10). Espacialmente, la correlación entre la humedad del suelo en los 50 superiores cm y PF10 es débil para suelos muy secos y muy húmedos y es mucho más fuerte para valores intermedios. Drought is one of the most important but least understood issues in global environmental changes.Decrease in soil moisture is an indicator of drought.Here, we analyze summer (June-August) soil moisture measurement data across 50 sites in China in order to investigate the linkage between climate change and drought.At the country scale, a significant decrease in summer soil moisture in the top 50 cm was observed during 1981-2002, resulting mainly from the decline in soil moisture in North China.Statistical analyses suggest that changes in precipitation frequency have significant consequences for soil moisture dynamics, but our ability to use precipitation frequency changes to explain the variation of soil moisture depends on the discriminating criteria of precipitation events.Among five criteria (0, 5, 10, 15, and 20 mm day -1 ), the maximum coefficient of correlation between summer soil moisture in the top 50 cm and precipitation frequency occurs when considering the number of days on which the daily precipitation amount is larger than 10 mm (PF10).Spatially, the correlation between soil moisture in the top 50 cm and PF10 is weak for very dry and very wet soils and is much stronger for intermediate values. الجفاف هو واحد من أهم القضايا ولكن أقلها فهمًا في التغيرات البيئية العالمية. انخفاض رطوبة التربة هو مؤشر على الجفاف. هنا، نقوم بتحليل بيانات قياس رطوبة التربة في الصيف (يونيو- أغسطس) عبر 50 موقعًا في الصين من أجل التحقيق في العلاقة بين تغير المناخ والجفاف. على مستوى البلاد، لوحظ انخفاض كبير في رطوبة التربة في الصيف في أعلى 50 سم خلال الفترة 1981-2002، ويرجع ذلك أساسًا إلى انخفاض رطوبة التربة في شمال الصين. تشير التحليلات الإحصائية إلى أن التغيرات في تواتر هطول الأمطار لها تأثير كبير عواقب على ديناميكيات رطوبة التربة، ولكن قدرتنا على استخدام تغيرات تردد هطول الأمطار لشرح تباين رطوبة التربة تعتمد على المعايير التمييزية لأحداث هطول الأمطار. من بين خمسة معايير (0، 5، 10، 15، و 20 مم يوم -1 )، يحدث الحد الأقصى لمعامل الارتباط بين رطوبة التربة الصيفية في أعلى 50 سم وتردد هطول الأمطار عند النظر في عدد الأيام التي تكون فيها كمية هطول الأمطار اليومية أكبر من 10 مم (PF10). على المستوى المكاني، يحدث الارتباط بين رطوبة التربة في أعلى 50 سم و PF10 ضعيف للتربة الجافة جدًا والرطبة جدًا وأقوى بكثير للقيم المتوسطة.

Wetlands play a critical role in global hydrological and biogeochemical cycles. Regulating the regional climate is one of the most important ecosystem services of natural wetlands. However, the impact of wetlands on local temperature on the global scale and the attribution is still unclear. This study utilizes the satellite-based products (land surface temperature (LST), albedo, and evapotranspiration (ET)) to evaluate the difference in LST between wetlands and their adjacent landcover types and the possible drivers. Here we show that on average for the whole year, wetlands have a cooling effect in tropical regions, but have a warming effect in boreal regions. The impacts of wetlands on LST show great seasonality in the boreal regions; i.e., the wetlands have a warming effect in winter but a cooling effect in summer. The difference in albedo and ET between wetlands and the other landcover types only interprets 30% of temporal variation of the difference in LST. Due to the large water storage in wetlands, the ground heat flux (G) may interpret the rest of the impact, absorbing energy in summer and releasing energy in winter in wetlands, which has often been neglected in previous studies. Our results indicate that it is critical to comprehensively consider the effects of wetland restoration in different regions to realize potential climatic benefits in the future.

The frequency and intensity of droughts have increased over the decades, leading to increased forest decline. The response of forest to drought can be evaluated by both its sensitivity to drought (resistance) and its post-drought recovery rate (resilience). However, it remains uncertain how drought resistance and resilience of forests change over time under climate change. We assessed the spatiotemporal dynamics of forest resistance and resilience to drought over the past century (1901-2015) with global tree ring data records from 2,935 sites, in conjunction with plant trait data. We found that gymnosperms and angiosperms showed different spatial patterns of drought resistance and resilience, driven by variations in eco-physiological traits. Resistance and resilience also varied with drought seasonal timing. Surprisingly, we found that the trade-off between resistance and resilience for gymnosperms, previously reported only spatially, also occurred at the temporal scale. In particular, drought resilience markedly increased, but resistance decreased, for gymnosperms between 1950-1969 and 1990-2009, indicating that previous model simulations assuming invariant resistance may have underestimated the impacts of drought on gymnosperm-dominated forests under future climate change.

AbstractThe positive response of wetland methane (CH4) emissions to climate change is an important yet uncertain Earth-system feedback that amplifies atmospheric CH4 concentrations. Here, using a wetland model, we report intensified wetland CH4 emissions during 2000–2021, corresponding with 2020 and 2021 being exceptional years of growth. Our results highlight the need for sustained monitoring and observations of global wetland CH4 fluxes to document emerging trends, variability and underlying drivers.