• Energy Research

AbstractTropical montane forest ecosystems are pivotal for sustaining biodiversity and essential terrestrial ecosystem services, including the provision of high-quality fresh water. Nonetheless, the impact of montane deforestation and climate change on the capacity of forests to deliver ecosystem services is yet to be fully understood. In this study, we offer observational evidence demonstrating the response of air temperature and cloud base height to deforestation in African montane forests over the last two decades. Our findings reveal that approximately 18% (7.4 ± 0.5 million hectares) of Africa’s montane forests were lost between 2003 and 2022. This deforestation has led to a notable increase in maximum air temperature (1.37 ± 0.58 °C) and cloud base height (236 ± 87 metres), surpassing shifts attributed solely to climate change. Our results call for urgent attention to montane deforestation, as it poses serious threats to biodiversity, water supply, and ecosystem services in the tropics.

Monitoring lakes in high-latitude areas can provide a better understanding of freshwater systems sensitivity and accrete knowledge on climate change impacts. Phytoplankton are sensitive to various conditions: warmer temperatures, earlier ice-melt and changing nutrient sources. While satellite imagery can monitor phytoplankton biomass using chlorophyll a (Chl) as a proxy over large areas, detection of Chl in small lakes is hindered by the low spatial resolution of conventional ocean color satellites. The short time-series of the newest generation of space-borne sensors (e.g., Sentinel-2) is a bottleneck for assessing long-term trends. Although previous studies have evaluated the use of high-resolution sensors for assessing lakes’ Chl, it is still unclear how the spatial and temporal variability of Chl concentration affect the performance of satellite estimates. We discuss the suitability of Landsat (LT) 30 m resolution imagery to assess lakes’ Chl concentrations under varying trophic conditions, across extensive high-latitude areas in Finland. We use in situ data obtained from field campaigns in 19 lakes and generate remote sensing estimates of Chl, taking advantage of the long-time span of the LT-5 and LT-7 archives, from 1984 to 2017. Our results show that linear models based on LT data can explain approximately 50% of the Chl interannual variability. However, we demonstrate that the accuracy of the estimates is dependent on the lake’s trophic state, with models performing in average twice as better in lakes with higher Chl concentration (>20 µg/L) in comparison with less eutrophic lakes. Finally, we demonstrate that linear models based on LT data can achieve high accuracy (R2 = 0.9; p-value < 0.05) in determining lakes’ mean Chl concentration, allowing the mapping of the trophic state of lakes across large regions. Given the long time-series and high spatial resolution, LT-based estimates of Chl provide a tool for assessing the impacts of environmental change.

Water resources and land use are closely linked with each other and with regional climate, assembling a very complex system. The understanding of the interconnecting relations involved in this system is an essential step for elaborating public policies that can effectively lead to the sustainable use of water resources. In this study, an integrated modelling framework was assembled in order to investigate potential impacts of agricultural expansion and climate changes on Irrigation Water Requirements (IWR) in the Taita Hills, Kenya. The framework comprised a land use change simulation model, a reference evapotranspiration model and synthetic precipitation datasets generated through a Monte Carlo simulation. In order to generate plausible climate change scenarios, outputs from General Climate Models were used as reference to perturbing the Monte Carlo simulations. The results indicate that throughout the next 20 years the low availability of arable lands in the hills will drive agricultural expansion to areas with higher IWR in the foothills. If current trends persist, agricultural areas will occupy roughly 60% of the study area by 2030. This expansion will increase by approximately 40% the annual water volume necessary for irrigation. Climate change may slightly decrease crops' IWR in April and November by 2030, while in May a small increase will likely be observed. The integrated assessment of these environmental changes allowed a clear identification of priority regions for land use allocation policies and water resources management.

Abstract Precipitation extremes have a strong influence on the exchange of energy and water between the land surface and the atmosphere. Although the Horn of Africa has faced recurrent drought and flood events in recent decades, it is still unclear how these events impact energy exchange and surface temperature across different ecosystems. Here, we analyzed the impact of precipitation extremes on spectral albedo (total shortwave, visible, and near-infrared (NIR) broadband albedos), energy balance, and surface temperature in four natural vegetation types: forest, savanna, grassland, and shrubland. We used remotely sensed observations of surface biophysical properties and climate from 2001 to 2016. Our results showed that, in forests and savannas, precipitation extremes led to divergent spectral changes in visible and NIR albedos, which cancelled each other limiting shortwave albedo changes. An exception to this pattern was observed in shrublands and grasslands, where both visible and NIR albedo increased during drought events. Given that shrublands and grasslands occupy a large fraction of the Horn of Africa (52%), our results unveil the importance of these ecosystems in driving the magnitude of shortwave radiative forcing in the region. The average regional shortwave radiative forcing during drought events (−0.64 W m−2, SD 0.11) was around twice that of the extreme wet events (0.33 W m−2, SD 0.09). Such shortwave forcing, however, was too small to influence the surface–atmosphere coupling. In contrast, the surface feedback through turbulent flux changes was strong across vegetation types and had a significant (P

Forest canopy structural complexity (CSC) plays a crucial role in shaping forest ecosystem productivity and stability, but the precise nature of their relationships remains controversial. Here, we mapped the global distribution of forest CSC and revealed the factors influencing its distribution using worldwide light detection and ranging data. We find that forest CSC predominantly demonstrates significant positive relationships with forest ecosystem productivity and stability globally, although substantial variations exist among forest ecoregions. The effects of forest CSC on productivity and stability are the balanced results of biodiversity and resource availability, providing valuable insights for comprehending forest ecosystem functions. Managed forests are found to have lower CSC but more potent enhancing effects of forest CSC on ecosystem productivity and stability than intact forests, highlighting the urgent need to integrate forest CSC into the development of forest management plans for effective climate change mitigation.

Los impactos de la conversión de la cubierta terrestre se han estudiado bien desde el nivel superior del dosel utilizando observaciones satelitales. Sin embargo, los impactos de calentamiento o enfriamiento de la cobertura terrestre y el cambio de gestión (LCMC) desde el nivel por debajo del dosel siguen siendo menos explorados. Aquí, estudiamos el cambio de temperatura por debajo del dosel del campo al nivel del paisaje en múltiples LCMC en el sureste de Kenia. Para estudiar esto, se utilizaron sensores de microclima in situ, observaciones satelitales y enfoques de modelado de temperatura por debajo del dosel de alta resolución. Nuestros resultados muestran que, a escala de campo a paisaje, la conversión de bosque a tierras de cultivo, seguida del cambio de matorral a tierras de cultivo, genera un calentamiento de la temperatura de la superficie más alto que otros tipos de conversión. A escala de campo, la pérdida de árboles aumenta la temperatura media del suelo (medida a 6 cm bajo tierra) más que la temperatura media debajo de la superficie del dosel, pero su impacto en el rango de temperatura diurno fue mayor en la temperatura de la superficie que en la temperatura del suelo tanto en las conversiones de bosque a tierra de cultivo como de matorral a tierra de cultivo/pastizales. A escala de paisaje, en comparación con el calentamiento de la temperatura de la superficie terrestre de la parte superior del dosel, que se estimó en el tiempo de paso superior de Landsat (~10:30 a.m.), la conversión de bosque a tierras de cultivo genera ~3 ° C más de calentamiento de la temperatura de la superficie por debajo del dosel. El cambio en la gestión de la tierra, a través del cercado de las áreas de protección de la vida silvestre y la limitación de la movilidad de los megaexploradores, puede tener un impacto en la cobertura leñosa e inducir un mayor calentamiento de la temperatura de la superficie por debajo del dosel que la parte superior del dosel en comparación con las áreas que no son de protección. Estos resultados indican que los cambios en la tierra inducidos por el hombre pueden generar más calentamiento debajo del dosel que el inferido de las observaciones satelitales de la parte superior del dosel. En conjunto, los resultados resaltan la importancia de considerar los impactos climáticos de LCMC tanto desde el nivel superior del dosel como por debajo del dosel para la mitigación efectiva del calentamiento antropogénico de los cambios en la superficie terrestre. Les impacts de la conversion de la couverture terrestre ont été bien étudiés à partir du sommet de la canopée à l'aide d'observations par satellite. Pourtant, les impacts du réchauffement ou du refroidissement de la couverture terrestre et du changement de gestion (LCMC) en dessous du niveau de la canopée restent moins explorés. Ici, nous avons étudié le changement de température sous la canopée du champ au niveau du paysage à travers plusieurs LCMC dans le sud-est du Kenya. Pour étudier cela, des capteurs de microclimat in situ, des observations par satellite et des approches de modélisation de la température sous la voûte à haute résolution ont été utilisés. Nos résultats montrent que de l'échelle du champ au paysage, la conversion de la forêt en terre cultivée, suivie du changement de fourré en terre cultivée, génère un réchauffement de la température de surface plus élevé que les autres types de conversion. À l'échelle du champ, la perte d'arbres augmente la température moyenne du sol (mesurée à 6 cm sous terre) de plus que la température moyenne de surface sous la canopée, mais son impact sur la plage de températures diurnes était plus élevé sur la température de surface que la température du sol dans les conversions de la forêt en terres cultivées et du fourré en terres cultivées/prairies. À l'échelle du paysage, par rapport au réchauffement de la température à la surface de la terre au sommet de la canopée, qui a été estimé au temps de passage supérieur de Landsat (∼10h30), la conversion de la forêt en terre cultivée génère ∼3 °C de plus que le réchauffement de la température à la surface de la canopée. Le changement de gestion des terres, par le biais de la clôture des zones de conservation de la faune et de la limitation de la mobilité des méga-navigateurs, peut avoir un impact sur la couverture ligneuse et induire plus de réchauffement de la température de surface sous la canopée que le haut de la canopée par rapport aux zones de non-conservation. Ces résultats indiquent que les changements de terres induits par l'homme peuvent générer plus de réchauffement sous la canopée que ce qui est déduit des observations satellitaires du haut de la canopée. Ensemble, les résultats soulignent l'importance de prendre en compte les impacts climatiques du LCMC à partir du sommet de la canopée et du dessous de la canopée pour une atténuation efficace du réchauffement anthropique dû aux changements de surface des terres. Impacts of land cover conversion have been studied well from the top-of-canopy level using satellite observations. Yet, the warming or cooling impacts of land cover and management change (LCMC) from below-canopy level remain less explored. Here, we studied the below-canopy temperature change from field to landscape level across multiple LCMC in southeastern Kenya. To study this, in situ microclimate sensors, satellite observations, and high-resolution below-canopy temperature modelling approaches were used. Our results show that from field to landscape scale, forest to cropland conversion, followed by thicket to cropland change, generate higher surface temperature warming than other conversion types. At field scale, tree loss increases the mean soil temperature (measured at 6 cm below ground) more than the mean below-canopy surface temperature but its impact on the diurnal temperature range was higher on surface temperature than soil temperature in both forest to cropland and thicket to cropland/grassland conversions. At landscape scale, compared with top-of-canopy land surface temperature warming, which was estimated at Landsat overpass time (∼10:30 a.m.), forest to cropland conversion generates ∼3 °C higher below-canopy surface temperature warming. Land management change, through fencing of wildlife conservation areas and limiting mobility of mega browsers, can have an impact on woody cover and induce more below-canopy surface temperature warming than top-of-canopy in comparison with non-conservancy areas. These results indicate that human induced land changes can generate more below-canopy warming than inferred from top-of-canopy satellite observations. Together, the results highlight the importance of considering the climatic impacts of LCMC from both top-of-canopy and below-canopy level for effective mitigation of anthropogenic warming from land surface changes. تمت دراسة آثار تحويل الغطاء الأرضي بشكل جيد من أعلى مستوى المظلة باستخدام الملاحظات الساتلية. ومع ذلك، فإن آثار الاحترار أو التبريد للغطاء الأرضي وتغيير الإدارة (LCMC) من مستوى أقل من المظلة لا تزال أقل استكشافًا. هنا، درسنا تغير درجة الحرارة تحت المظلة من مستوى الحقل إلى مستوى المناظر الطبيعية عبر العديد من LCMC في جنوب شرق كينيا. لدراسة هذا، تم استخدام مستشعرات المناخ المحلي في الموقع، وملاحظات الأقمار الصناعية، ونُهج نمذجة درجة الحرارة تحت المظلة عالية الدقة. تظهر نتائجنا أنه من الحقل إلى مقياس المناظر الطبيعية، فإن تحويل الغابات إلى أراضي زراعية، متبوعًا بالغابة إلى تغيير الأراضي الزراعية، يولد ارتفاعًا في درجة حرارة السطح مقارنة بأنواع التحويل الأخرى. على نطاق الحقل، يزيد فقدان الأشجار من متوسط درجة حرارة التربة (المقاسة عند 6 سم تحت سطح الأرض) أكثر من متوسط درجة حرارة السطح تحت الظلة ولكن تأثيرها على نطاق درجة الحرارة النهارية كان أعلى على درجة حرارة السطح من درجة حرارة التربة في كل من الغابات إلى الأراضي الزراعية والغابة إلى تحويلات الأراضي الزراعية/الأراضي العشبية. على نطاق المناظر الطبيعية، مقارنة بارتفاع درجة حرارة سطح الأرض، والذي تم تقديره في وقت عبور لاندسات (10:30 صباحًا)، يولد تحويل الغابات إلى أراضٍ زراعية ارتفاعًا في درجة حرارة سطح الأرض بمقدار 3 درجات مئوية. يمكن أن يكون لتغيير إدارة الأراضي، من خلال تسييج مناطق الحفاظ على الحياة البرية والحد من حركة المتصفحات الضخمة، تأثير على الغطاء الخشبي ويؤدي إلى ارتفاع درجة حرارة السطح تحت المظلة أكثر من أعلى المظلة مقارنة بالمناطق غير المحمية. تشير هذه النتائج إلى أن تغيرات الأراضي التي يسببها الإنسان يمكن أن تولد المزيد من الاحترار تحت الظل أكثر مما يستدل عليه من ملاحظات الأقمار الصناعية فوق الظل. تسلط النتائج الضوء معًا على أهمية النظر في التأثيرات المناخية لـ LCMC من أعلى مستوى الظل وتحت مستوى الظل للتخفيف الفعال من الاحترار البشري الناتج عن تغيرات سطح الأرض.

High elevations are thought to be warming more rapidly than lower elevations, but there is a lack of air temperature observations in high mountains. This study compares instantaneous values of land surface temperature (1030/2230 and 0130/1330 local solar time) as measured by MODIS MOD11A2/MYD11A2 at 1 km resolution from the TERRA and AQUA platforms respectively with equivalent screen level air temperatures (in the same pixel). We use a transect of 22 in situ weather stations across Kilimanjaro ranging in elevation from 990 to 5803 m, one of the biggest elevational ranges in the world. There are substantial differences between LST and Tair, sometimes up to 20˚C. During the day/night LST tends to be higher/lower than Tair. LST-Tair differences (ΔT) show large variance, particularly during the daytime, and tend to increase with elevation, particularly on the NE slope which faces the morning sun. Differences are larger in the dry seasons (JF and JJAS), and reduce in cloudy seasons. Healthier vegetation (as measured by NDVI) and increased humidity lead to reduced daytime surface heating above air temperature and lower ΔT, but these relationships weaken with elevation. At high elevations transient snow cover cools LST more than Tair. The predictability of ΔT therefore reduces. It will therefore be challenging to use satellite data at high elevations as a proxy for in situ air temperatures in climate change assessments, especially for daytime Tmax. ΔT is smaller and more consistent at night, so it will be easier to use LST to monitor changes in Tmin.