Historical climatology and dendroclimatology in the Blue Nile River basin, northern Ethiopia

The aim of this paper is to explore the feasibility of developing long-term dendroclimatological analyses in a climatically important area of Africa. Rainfall over the highlands of northern Ethiopia is highly seasonal and the main source of runoff to the Blue Nile and through it, the main determinant of variability in Main Nile discharge. The region is also climatically interesting due to its links with El Nino-Southern Oscillation events and Sahel rainfall. Tree-cores were taken from 180 trees at two different locations in northern Ethiopia and one in central Ethiopia. Cores were obtained from 18 different species, with most taken from two species considered to have the best ring definition: Juniperus procera and Ekebergia capensis. Many of the species showed no evidence of seasonal growth although some appeared to have good, but intermittent, examples of clear rings. Nearly all the cores, however, contained areas with unclear ring boundaries and false rings. Attempts to match up cores from the same tree were successful in one or two cases with J. procera but it was not possible to achieve the same degree of unequivocal cross-matching between different trees as is routinely possible in other (non-African) regions. Further work is required in two areas: first, more detailed analysis of the samples and second, an assessment of the distribution and quantity of mature J. procera and E. capensis in northern Ethiopia.
The aim of this paper is to explore the feasibility of developing long-term dendroclimatological analyses in a climatically important area of Africa. Rainfall over the highlands of northern Ethiopia is highly seasonal and the main source of runoff to the Blue Nile and through it, the main determinant of variability in Main Nile discharge. The region is also climatically interesting due to its links with El Nino-Southern Oscillation events and Sahel rainfall. Tree-cores were taken from 180 trees at two different locations in northern Ethiopia and one in central Ethiopia. Cores were obtained from 18 different species, with most taken from two species considered to have the best ring definition: Juniperus procera and Ekebergia capensis. Many of the species showed no evidence of seasonal growth although some appeared to have good, but intermittent, examples of clear rings. Nearly all the cores, however, contained areas with unclear ring boundaries and false rings. Attempts to match up cores from the same tree were successful in one or two cases with J. procera but it was not possible to achieve the same degree of unequivocal cross-matching between different trees as is routinely possible in other (non-African) regions. Further work is required in two areas: first, more detailed analysis of the samples and second, an assessment of the distribution and quantity of mature J. procera and E. capensis in northern Ethiopia.