• Energy Research

The Arctic has warmed more than twice the rate of the entire globe. To quantify possible climate change effects, we calculate wind energy potentials from a multi-model ensemble of Arctic-CORDEX. For this, we analyze future changes of wind power density (WPD) using an eleven-member multi-model ensemble. Impacts are estimated for two periods (2020–2049 and 2070–2099) of the 21st century under a high emission scenario (RCP8.5). The multi-model mean reveals an increase of seasonal WPD over the Arctic in the future decades. WPD variability across a range of temporal scales is projected to increase over the Arctic. The signal amplifies by the end of 21st century. Future changes in the frequency of wind speeds at 100 m not useable for wind energy production (wind speeds below 4 m/s or above 25 m/s) has been analyzed. The RCM ensemble simulates a more frequent occurrence of 100 m non-usable wind speeds for the wind-turbines over Scandinavia and selected land areas in Alaska, northern Russia and Canada. In contrast, non-usable wind speeds decrease over large parts of Eastern Siberia and in northern Alaska. Thus, our results indicate increased potential of the Arctic for the development and production of wind energy. Bias corrected and not corrected near-surface wind speed and WPD changes have been compared with each other. It has been found that both show the same sign of future change, but differ in magnitude of these changes. The role of sea-ice retreat and vegetation expansion in the Arctic in future on near-surface wind speed variability has been also assessed. Surface roughness through sea-ice and vegetation changes may significantly impact on WPD variability in the Arctic. Future projections of wind energy potentials in the arctic for the 21st century under the RCP8.5 scenario from regional climate models (Arctic-CORDEX) submittedVersion

Le réchauffement rapide récent a eu des impacts inégaux sur la composition, la structure et le fonctionnement des écosystèmes nordiques. On ne sait toujours pas comment les facteurs climatiques contrôlent les tendances linéaires et non linéaires de la productivité des écosystèmes. Sur la base d'un produit d'indice de phénologie végétale (IPP) à une résolution spatiale de 0,05° sur 2000-2018, nous avons utilisé un schéma d'ajustement polynomial automatisé pour détecter et caractériser les types de tendances (c.-à-d. tendances polynomiales et non tendances) dans l'IPP annuel intégré (PPIINT) pour les écosystèmes nordiques (> 30°N) et leur dépendance aux facteurs climatiques et aux types d'écosystèmes. La pente moyenne pour les tendances linéaires (p < 0,05) de PPIINT était positive dans tous les écosystèmes, parmi lesquels les forêts de feuillus à feuilles larges et les forêts de feuillus à aiguilles (ENF) ont montré les pentes moyennes les plus élevées et les plus basses, respectivement. Plus de 50% des pixels dans les ENF, les arbustes arctiques et boréaux et les zones humides permanentes (PW) avaient des tendances linéaires. Une grande fraction de PW a également montré des tendances quadratiques et cubiques. Ces tendances concordent bien avec les estimations de la productivité globale de la végétation basées sur la fluorescence de la chlorophylle induite par le soleil. Dans tous les biomes, PPIINT dans les pixels avec des tendances linéaires a montré des valeurs moyennes plus faibles et des coefficients de corrélation partielle plus élevés avec la température ou les précipitations que dans les pixels sans tendances linéaires. Dans l'ensemble, notre étude a révélé l'émergence d'une convergence latitudinale et d'une divergence dans les contrôles climatiques sur les tendances linéaires et non linéaires de PPIINT, ce qui implique que les déplacements nordiques de la végétation et le changement climatique peuvent potentiellement augmenter la nature non linéaire des contrôles climatiques sur la productivité des écosystèmes. Ces résultats peuvent améliorer notre compréhension et notre prévision des changements induits par le climat dans la phénologie et la productivité des plantes et faciliter la gestion durable des écosystèmes en tenant compte de leur résilience et de leur vulnérabilité au changement climatique futur. El rápido calentamiento reciente ha causado impactos desiguales en la composición, estructura y funcionamiento de los ecosistemas del norte. Se desconoce cómo los impulsores climáticos controlan las tendencias lineales y no lineales en la productividad de los ecosistemas. Con base en un producto de índice de fenología vegetal (PPI) a una resolución espacial de 0.05° durante 2000-2018, utilizamos un esquema de ajuste polinómico automatizado para detectar y caracterizar los tipos de tendencias (es decir, tendencias polinómicas y no tendencias) en el PPI integrado anual (PPIINT) para los ecosistemas del norte (> 30°N) y su dependencia de los impulsores climáticos y los tipos de ecosistemas. La pendiente promedio para las tendencias lineales (p < 0.05) de PPIINT fue positiva en todos los ecosistemas, entre los cuales los bosques caducifolios de hoja ancha y los bosques perennifolios de hoja de aguja (ENF) mostraron las pendientes medias más altas y más bajas, respectivamente. Más del 50% de los píxeles en ENF, matorrales árticos y boreales y humedales permanentes (PW) tuvieron tendencias lineales. Una gran fracción de PW también mostró tendencias cuadráticas y cúbicas. Estos patrones de tendencia coincidieron bien con las estimaciones de la productividad global de la vegetación basadas en la fluorescencia de la clorofila inducida por el sol. En todos los biomas, PPIINT en píxeles con tendencias lineales mostró valores medios más bajos y coeficientes de correlación parcial más altos con la temperatura o la precipitación que en píxeles sin tendencias lineales. En general, nuestro estudio reveló la aparición de convergencia latitudinal y divergencia en los controles climáticos sobre las tendencias lineales y no lineales de PPIINT, lo que implica que los cambios septentrionales de la vegetación y el cambio climático pueden aumentar potencialmente la naturaleza no lineal de los controles climáticos sobre la productividad de los ecosistemas. Estos resultados pueden mejorar nuestra comprensión y predicción de los cambios inducidos por el clima en la fenología y la productividad de las plantas y facilitar la gestión sostenible de los ecosistemas al tener en cuenta su resiliencia y vulnerabilidad al cambio climático futuro. Recent rapid warming has caused uneven impacts on the composition, structure, and functioning of northern ecosystems. It remains unknown how climatic drivers control linear and non-linear trends in ecosystem productivity. Based on a plant phenology index (PPI) product at a spatial resolution of 0.05° over 2000-2018, we used an automated polynomial fitting scheme to detect and characterize trend types (i.e., polynomial trends and no-trends) in the yearly-integrated PPI (PPIINT) for northern (> 30°N) ecosystems and their dependence on climatic drivers and ecosystem types. The averaged slope for the linear trends (p < 0.05) of PPIINT was positive across all the ecosystems, among which deciduous broadleaved forests and evergreen needle-leaved forests (ENF) showed the highest and lowest mean slopes, respectively. More than 50% of the pixels in ENF, arctic and boreal shrublands, and permanent wetlands (PW) had linear trends. A large fraction of PW also showed quadratic and cubic trends. These trend patterns agreed well with estimates of global vegetation productivity based on solar-induced chlorophyll fluorescence. Across all the biomes, PPIINT in pixels with linear trends showed lower mean values and higher partial correlation coefficients with temperature or precipitation than in pixels without linear trends. Overall, our study revealed the emergence of latitudinal convergence and divergence in climatic controls on the linear and non-linear trends of PPIINT, implying that northern shifts of vegetation and climate change may potentially increase the non-linear nature of climatic controls on ecosystem productivity. These results can improve our understanding and prediction of climate-induced changes in plant phenology and productivity and facilitate sustainable management of ecosystems by accounting for their resilience and vulnerability to future climate change. تسبب الاحترار السريع الأخير في تأثيرات غير متكافئة على تكوين وبنية وأداء النظم الإيكولوجية الشمالية. لا يزال من غير المعروف كيف تتحكم المحركات المناخية في الاتجاهات الخطية وغير الخطية في إنتاجية النظام البيئي. استنادًا إلى منتج مؤشر الفينولوجيا النباتية (PPI) بدقة مكانية تبلغ 0.05درجة خلال الفترة 2000-2018، استخدمنا مخططًا آليًا للتركيب متعدد الحدود لاكتشاف وتمييز أنواع الاتجاهات (أي الاتجاهات متعددة الحدود وعدم وجود اتجاهات) في مؤشر أسعار المنتجين السنوي المتكامل (PPIINT) للنظم الإيكولوجية الشمالية (> 30درجةشمالًا) واعتمادها على الدوافع المناخية وأنواع النظم الإيكولوجية. كان المنحدر المتوسط للاتجاهات الخطية (p < 0.05) لـ PPIINT إيجابيًا في جميع النظم الإيكولوجية، من بينها الغابات المتساقطة ذات الأوراق العريضة والغابات دائمة الخضرة ذات الأوراق الإبرية (ENF) التي أظهرت أعلى وأدنى المنحدرات المتوسطة، على التوالي. كان لأكثر من 50 ٪ من وحدات البكسل في ENF، والشجيرات القطبية والشمالية، والأراضي الرطبة الدائمة (PW) اتجاهات خطية. أظهر جزء كبير من المياه الصالحة للشرب أيضًا اتجاهات تربيعية ومكعبة. اتفقت أنماط الاتجاه هذه بشكل جيد مع تقديرات إنتاجية الغطاء النباتي العالمي بناءً على فلورة الكلوروفيل المستحثة بالطاقة الشمسية. في جميع المناطق الحيوية، أظهر PPIINT بالبكسل مع الاتجاهات الخطية قيمًا متوسطة أقل ومعاملات ارتباط جزئية أعلى مع درجة الحرارة أو هطول الأمطار مقارنة بالبكسل بدون اتجاهات خطية. بشكل عام، كشفت دراستنا عن ظهور تقارب وتباعد خطوط العرض في الضوابط المناخية على الاتجاهات الخطية وغير الخطية لـ PPIINT، مما يعني أن التحولات الشمالية للغطاء النباتي وتغير المناخ قد تزيد من الطبيعة غير الخطية للضوابط المناخية على إنتاجية النظام الإيكولوجي. يمكن أن تحسن هذه النتائج فهمنا وتنبؤنا بالتغيرات الناجمة عن المناخ في علم الظواهر النباتية والإنتاجية وتسهيل الإدارة المستدامة للنظم الإيكولوجية من خلال مراعاة مرونتها وقابليتها للتأثر بتغير المناخ في المستقبل.

Abstract Future Arctic tundra primary productivity and vegetation community composition will partly be determined by nitrogen (N) availability in a warmer climate. N mineralization rates are predicted to increase in winter and summer, but because N demand and –mobility varies across seasons, the fate of mineralized N remains uncertain. N mineralized in winter is released in a “pulse” upon snowmelt and soil thaw, with the potential for lateral redistribution in the landscape. In summer, the release is into an active rhizosphere with high local biological N demand. In this study, we investigated the ecosystem sensitivity to increased lateral N input and near-surface warming, respectively and in combination, with a numerical ecosystem model (CoupModel) parameterized to simulate ecosystem biogeochemistry for a tundra heath ecosystem in West Greenland. Both model and measurements indicated that plants were poor utilizers of increased early-season lateral N input, indicating that higher winter N mineralization rates may have limited influence on plant growth and carbon (C) sequestration for a hillslope ecosystem. The model further suggested that, although deciduous shrubs were the plant type with overall most lateral N gain, evergreen shrubs had a comparative advantage utilizing early-season N. In contrast, near-surface summer warming increased plant biomass and N uptake, moving N from soil to plant N pools, and offered an advantage to deciduous plants. Neither simulated high lateral N fluxes nor near-surface soil warming suggests that mesic tundra heaths will be important sources of N2O under warmer conditions. Our work highlights how winter and summer warming may play different roles in tundra ecosystem N and C budgets depending on plant community composition.

Understanding N budgets of tundra ecosystems is crucial for projecting future changes in plant community composition, greenhouse gas balances and soil N stocks. Winter warming can lead to higher tundra winter nitrogen (N) mineralization rates, while summer warming may increase both growing season N mineralization and plant N demand. The undulating tundra landscape is inter-connected through water and solute movement on top of and within near-surface soil, but the importance of lateral N fluxes for tundra N budgets is not well known. We studied the size of lateral N fluxes and the fate of lateral N input in the snowmelt period with a shallow thaw layer, and in the late growing season with a deeper thaw layer. We used 15N to trace inorganic lateral N movement in a Low-arctic mesic tundra heath slope in West Greenland and to quantify the fate of N in the receiving area. We found that half of the early-season lateral N input was retained by the receiving ecosystem, whereas half was transported downslope. Plants appear as poor utilizers of early-season N, indicating that higher winter N mineralization may influence plant growth and carbon (C) sequestration less than expected. Still, evergreen plants were better at utilizing early-season N, highlighting how changes in N availability may impact plant community composition. In contrast, later growing season lateral N input was deeper and offered an advantage to deeper-rooted deciduous plants. The measurements suggest that N input driven by future warming at the study site will have no significant impact on the overall N2O emissions. Our work underlines how tundra ecosystem N allocation, C budgets and plant community composition vary in their response to lateral N inputs, which may help us understand future responses in a warmer Arctic. (Less)

Abstract The northern hemisphere has experienced regional cooling, especially during the global warming hiatus (1998–2012) due to ocean energy redistribution. However, the lack of studies about the natural cooling effects hampers our understanding of vegetation responses to climate change. Using 15,125 ground phenological time series at 3,620 sites since the 1950s and 31-year satellite greenness observations (1982–2012) covering the warming hiatus period, we show a stronger response of leaf onset date (LOD) to natural cooling than to warming, i.e. the delay of LOD caused by 1°C cooling is larger than the advance of LOD with 1°C warming. This might be because cooling leads to larger chilling accumulation and heating requirements for leaf onset, but this non-symmetric LOD response is partially offset by warming-related drying. Moreover, spring greening magnitude, in terms of satellite-based greenness and productivity, is more sensitive to LOD changes in the warming area than in the cooling. These results highlight the importance of considering non-symmetric responses of spring greening to warming and cooling when predicting vegetation-climate feedbacks.

Globally, boreal forests act as important carbon sinks, however, drought and forest management could substantially alter the sink strength, though the controlling mechanisms of drought and management remain unclear. In this study, we combined the detailed process-based CoupModel with multiple measurements to study the impacts of recent drought and forest thinning on a boreal forest during 2018-2021. CoupModel after calibration showed high ability to represent the dynamics of long-term net ecosystem exchange and its responses to environmental changes. The model simulation showed that the canopy temperature exacerbated the dominant role in regulating the boreal forest growth during the 2018 extreme drought year with slight increase in the annual mean net carbon uptake by 76.65 g C/m2/yr compared to 2017. The posterior model simulations ensemble suggested that thinning of trees in 2019-2020 caused the boreal forest in 2020 to be a sink to slight source ([-229.95, 94.90] g C/m2/yr, 90 % confidence interval), while the observations depicted a small source (69.35 g C/m2/yr). Moreover, rapid recovery of the boreal forest to a carbon sink was found in 2021, though remaining smaller than the carbon sink in 2017. Overall, the negative impacts from drought and harvest (2018-2021) were found to have offset the positive impacts from climate by 8 % - 92 %, on the net carbon uptake. This study highlights the resilience of boreal forests as carbon sink and provides new insights into the boreal forests' responses to both climate change and management.

To mitigate the climate change-induced water shortage and realize the sustainable development of agriculture, drip irrigation, a more efficient water-saving irrigation method, has been intensively implemented in most arid agricultural regions in the world. However, compared to traditional border irrigation, how drip irrigation affects the biophysical conditions in the cropland and how crops physiologically respond to changes in biophysical conditions in terms of water, heat and carbon exchange remain largely unknown. In view of the above situation, to reveal the mechanism of drip irrigation in improving spring wheat water productivity, paired field experiments based on drip irrigation and border irrigation were conducted to extensively monitor water and heat fluxes at a typical spring wheat field (Triticum aestivum L.) in Northwest China during 2017–2020. The results showed that drip irrigation improved yield by 10.3 % and crop water productivity (i.e., yield-to-evapotranspiration-ratio) by 15.6 %, but reduced LAI by 16.9 % in contrast with border irrigation. Under drip irrigation, the lateral development of spring wheat roots was promoted by higher soil temperature combined with frequent dry-wet alternation in the shallow soil layer (0–20 cm), which was the basis for efficient absorption of water and fertilizer, as well as efficient formation of photosynthate. Meanwhile, drip irrigation increased net radiation and decreased latent heat flux by inhibiting leaf growth, thereby increased sensible heat, causing a higher soil temperature (+1.10 ℃) and canopy temperature (+1.11 ℃). Further analysis proved that soil temperature was the key factor affecting yield formation. Based on the above conditions, the decrease in leaf distribution coefficient (−0.030) led to the decrease in evapotranspiration (−5.7 %) and the increase in ear distribution coefficient (+0.029). Therefore, drip irrigation emphasized the role of soil moisture in the soil-plant-atmosphere continuum, enhanced crop activity by increasing field temperature, especially soil temperature, and finally improved yield and water productivity via carbon reallocation. The study revealed the mechanism of drip irrigation for improving spring wheat yield, and would contribute to improving Earth system models in representing agricultural cropland ecosystems with drip irrigation and predicting the subsequent biophysical and biogeochemical feedbacks to climate change.