Carbon dioxide fluxes from contrasting ecosystems in the Sudanian Savanna in West Africa

Background: The terrestrial land surface in West Africa is made up of several types of savanna ecosystems differing in land use changes which modulate gas exchanges between their vegetation and the overlying atmosphere. This study compares diurnal and seasonal estimates of CO2 fluxes from three contrasting ecosystems, a grassland, a mixture of fallow and cropland, and nature reserve in the Sudanian Savanna and relate them to water availability and land use characteristics. Results: Over the study period, and for the three study sites, low soil moisture availability, high vapour pressure deficit and low ecosystem respiration were prevalent during the dry season (November to March), but the contrary occurred during the rainy season (May to October). Carbon uptake predominantly took place in the rainy season, while net carbon efflux occurred in the dry season as well as the dry to wet and wet to dry transition periods (AM and ND) respectively. Carbon uptake decreased in the order of the nature reserve, a mixture of fallow and cropland, and grassland. Only the nature reserve ecosystem at the Nazinga Park served as a net sink of CO2, mostly by virtue of a several times larger carbon uptake and ecosystem water use efficiency during the rainy season than at the other sites. These differences were influenced by albedo, LAI, EWUE, PPFD and climatology during the period of study. Conclusion: These results suggest that land use characteristics affect plant physiological processes that lead to flux exchanges over the Sudanian Savanna ecosystems. It affects the diurnal, seasonal and annual changes in NEE and its composite signals, GPP and RE. GPP and NEE were generally related as NEE scaled with photosynthesis with higher CO2 assimilation leading to higher GPP. However, CO2 effluxes over the study period suggest that besides biomass regrowth, other processes, most likely from the soil might have also contributed to the enhancement of ecosystem respiration. © 2015 Quansah et al

Trends of rainfall onset, cessation, and length of growing season in northern Ghana: comparing the rain gauge, satellite, and farmer's perceptions

Open Access Journal; Published: 13 Dec 2021Rainfall onset and cessation date greatly influence cropping calendar decisions in rain-fed agricultural systems. This paper examined trends of onsets, cessation, and the length of growing season over Northern Ghana using CHIRPS-v2, gauge, and farmers’ perceptions data between 1981 and 2019. Results from CHIRPS-v2 revealed that the three seasonal rainfall indices have substantial latitudinal variability. Significant late and early onsets were observed at the West and East of 1.5◦ W longitude, respectively. Significant late cessations and longer growing periods occurred across Northern Ghana. The ability of farmers’ perceptions and CHIRPS-v2 to capture rainfall onsets are time and location-dependent. A total of 71% of farmers rely on traditional knowledge to forecast rainfall onsets. Adaptation measures applied were not always consistent with the rainfall seasonality. More investment in modern climate information services is required to complement the existing local knowledge of forecasting rainfall seasonalit

Monitoring of Stratospheric O3 and NO2 Profiles with SCIAMACHY/ENVISAT

SCIAMACHY on ENVISAT offers with its limb solar backscatter, solar and lunar occultation measurement modes the opportunity to continue long term data sets of stratospheric O3 and NO2 profiles started with SAGE and HALOE. Data from SCIAMACHY is available since autumn 2002. Currently the mission will continue at least until 2010 and an extension until 2013 is currently under investigation at ESA. Stratospheric profiles derived from occultation measurements have a good data quality, but are limited in their coverage. Stratospheric profiles from the limb measurement mode allow global coverage of the stratosphere within 3 days. Nevertheless, until 2007 the limb data products of SCIAMACHY were heavily affected in their quality by large uncertainties in the knowledge of the tangent height. This was substantially improved in 2007 by implementing improved mis-alignment parameters in the operational processing chain at ESA. Consequently, the error in the limb data products is no longer dominated by the impact of the tangent height error and algorithms and the products are systematically improving