Impact of rainfall extremes on energy exchange and surface temperature anomalies across biomes in the Horn of Africa

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http://hdl.handle.net/10138/310143

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Abera , T , Heiskanen , J , Pellikka , P & Maeda , E 2020 , ' Impact of rainfall extremes on energy exchange and surface temperature anomalies across biomes in the Horn of Africa ' , Agricultural and Forest Meteorology , vol. 280 , 107779 . https://doi.org/10.1016/j.agrformet.2019.107779

Title: Impact of rainfall extremes on energy exchange and surface temperature anomalies across biomes in the Horn of Africa
Author: Abera, Temesgen; Heiskanen, Janne; Pellikka, Petri; Maeda, Eduardo
Contributor: University of Helsinki, Department of Geosciences and Geography
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
University of Helsinki, Helsinki Institute of Sustainability Science (HELSUS)
University of Helsinki, TreeD lab - Terrestrial Ecosystem Dynamics
Date: 2020-01-15
Language: eng
Number of pages: 13
Belongs to series: Agricultural and Forest Meteorology
ISSN: 0168-1923
URI: http://hdl.handle.net/10138/310143
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 <0.05) impact on the surface temperature and net radiation anomalies, except in forests. The strongest energy exchange and surface temperature anomalies were observed over grassland and the smallest over forest, which was shown to be resilient to precipitation extremes. These results suggest that land management activities that support forest preservation, afforestation, and reforestation can help to mitigate the impact of drought through their role in modulating energy fluxes and surface temperature anomalies in the region.
Subject: 1171 Geosciences
Precipitation extremes
Albedo
Energy exchange
Land surface temperature
MODIS
CERES
SOIL-MOISTURE
DROUGHT
ALBEDO
CLIMATE
FEEDBACKS
WATER
CONVERGENCE
FORESTS
FLUXES
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