the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Documents, Reanalysis, and Global Circulation Models: A New Method for Reconstructing Historical Climate Focusing on Present-day Inland Tanzania, 1856–1890
Melissa J. Lazenby
Michael R. Frogley
Cecile Dai
Wenqi Su
Abstract. This article proposes a novel methodology for reconstructing past climatic conditions in regions and time-periods for which there is limited evidence from documentary and natural proxy sources. Focusing on present-day inland Tanzania during the period 1856–1890, it integrates evidence from qualitative documentary sources with quantitative outputs from climate reanalysis and global circulation models (GCMs), which enables the creation of interdisciplinary seasonal time-series of rainfall variability for three distinct locales. It does so by indexing each dataset to the same 7-point scale and weighting each output according to a predefined level of confidence in the documentary data. This process challenges the subjectivity of nineteenth-century Europeans in Africa, whose reports form the basis of the documentary material, and adds evidence from the region, which is currently lacking from the latest reanalysis products and GCMs. The result is a more scientifically grounded interpretation of documentary materials and a more locally grounded estimation of rainfall that would otherwise be gained from referring to reanalysis or GCMs alone. The methodology is validated with reference to observed long-term trends gathered from (paleo)limnological studies, and it is shown to provide marked insights into four periods of environmental stress in the region’s late-nineteenth-century past. Future challenges may involve integrating evidence from oral traditions and adapting the methodology for other regions and time-periods.
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Philip Gooding et al.
Status: open (until 29 Oct 2023)
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RC1: 'Comment on egusphere-2023-992', David Nash, 05 Jul 2023
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General comments
This is a welcome paper addressing the thorny issue of how best to integrate historical and meteorological evidence to reconstruct climates of the past. It is clearly structured, generally very well written and makes persuasive arguments. However, as you will see from my specific comments below, it includes some statements that are problematic. These mainly relate to the way that the text falls into the “documentary evidence unreliable, instrumental data reliable” trope common to many climatological studies.
There are also some methodological issues that need addressing. These include the need for a clearer description of the way in which documentary index classes are derived. Explanation is also needed as to why – given that the goal of the study is to produce a time series that is “interoperable with Nicholson et al. (2012)” (line 167) – the method used to convert modelled rainfall levels from 20CR and GCMs is not the same as that used by Nicholson et al. (2012).
I’m very surprised that the authors do not cite the recent papers by Nash et al. (2018) and Mutua & Runguma (2020), which present 19th century documentary climate series for Malawi and Kenya respectively. I would have thought that these are essential for comparison with the results presented for Tanzania.
Mutua, T.M. and Runguma, S.N. (2020) Documentary driven chronologies of rainfall variability for Kenya, 1845–1976, Journal of Climatology and Weather Forecasting, 8, 255, available at: https://www.longdom.org/open-access/documentary-drivenchronologies-of-rainfall-variability-for-kenya–18451976.pdf
Nash, D.J. et al. (2018) Rainfall variability over Malawi during the late 19th century, International Journal of Climatology, 38 (Suppl. 1), e629–e642.
Specific comments
Lines 16-17, 60 and 507 – I’m not sure the wording “…a more scientifically grounded interpretation of documentary materials…” in the abstract and main text is ideal. This makes a value judgement about the validity of documentary evidence. Maybe ‘climatologically grounded’ rather than ‘more scientifically’ grounded would be better.
Line 38 (and throughout) – best to avoid the use of terms derived from ‘East Africa’ as this is a colonial construct. Academics that I have worked with from the region tend to prefer the term ‘eastern Africa’.
Line 45 – I don’t think Endfield & Nash (2002) used a term as strong as ‘distorted’ to describe European perceptions (and hence descriptions) of African climate. Rather, the descriptions made by Europeans were often framed relative to their ‘home’ climate (particularly during their early years of residence in Africa), so tend to over-emphasise drier conditions. As noted in section 2, they may also be shaped by imperial knowledge-making.
Lines 46-48 – this is a very strong statement – are you sure that absolutely no records made by Europeans describing climate in Tanzania exist between 1861 and 1868? I find that very hard to believe.
Lines 114-127 – this paragraph makes some valuable points. However, it paints the rather sweeping picture that all explorer and missionary descriptions of weather and climate were shaped by imperial agendas and are therefore unreliable. Some descriptions might well be ‘highly subjective’ – especially the broad overviews of climatic conditions in the more general explorer monographs – but other accounts of specific weather events and related phenomena (e.g. delays to the start of the rainy season, counts of rainy days, descriptions of flood events, descriptions of pasture conditions etc) will likely be reliable. I suggest that this paragraph be tweaked to provide greater nuance.
Lines 128-129 – the emphasis on describing extreme conditions is not unique to African documentary evidence and is well documented in historical climatology studies around the world – have a look at some of the excellent reviews by Christian Pfister or Rudolf Brazdil for further details and cite relevant methodological sources.
Lines 130-139 – these kinds of uncertainty surrounding ‘climatically indirect’ indicators of climate variability are routinely dealt with in historical climatology studies and there is a wide literature on this. Again, have a look at some of the reviews by Christian Pfister or Rudolf Brazdil for details. These include explicit guidance on how to handle an ‘absence of discussion’.
Lines 1444-148 – this is a very long sentence – suggest you fragment.
Lines 155-157 – on a more pragmatic note, it is also very likely that they were interested in weather conditions as they relied upon them to grow their own food.
Lines 169-178 – I’m slightly unclear over the methodology used here. Are you following directly the methodology used by Nicholson et al. (2012) whereby individual pieces of narrative evidence (i.e. individual quotes) are read and graded from 1-7 (and then averaged to give an annual picture), or the approach used in most other documentary-based climate reconstructions around the world where collections of quotes from specific months or seasons are read together and given a collective grade? This is important because, as Nash et al. (2021 – section 8.3) have discussed, the Nicholson method tends to lead to an over-representation of drier conditions in the resulting reconstruction. Figs 2-4 seem to suggest some sort of hybrid, which could be problematic if the authors are aiming to replicate Nicholson’s approach as they suggest.
Lines 199-203 – I would appreciate a little more explanation over the way in which individual diary entries are incorporated into Figs 2-4, particularly where they are merged with results from quotations in letters that could refer to conditions over periods of longer than a single day. In effect, you appear to be giving equal weight to (for example) a single daily diary entry describing drought and a letter documenting dry conditions that could span weeks or months. If you are following the Nicholson method described above this could lead to an over-representation of particular conditions, especially if these are isolated quotes from a personal diary rather than a ‘weather diary’ with daily weather-related entries.
Line 225 – there are many reasons for famine, not simply climatic. Do you have any contextual data from missionary sources that might explain the causes?
Lines 319-321 – this sounds like the approach used in the majority of historical climatology studies based on the European tradition, where monthly indices are summed and averaged. There is nothing new here methodologically, so you would do well to cite related sources – see section 8.1 in Nash et al. (2021) for more detail.
Lines 337-347 – I’m intrigued to know why you have adopted this approach when Nicholson has published her method for converting rain gauge data into 7-point index values based on standard deviations from the long-term mean (see section 8.3 in Nash et al. 2021 for a summary). If, as suggested earlier by the authors, they are trying to make results that are interoperable with those of Nicholson, then surely the same method needs to be used in this study?
Lines 513-517 – these sentences again oversimplify the apparent subjectivity of European observers. If you are going to make statements that European observers “regularly misunderstood the climatic and environmental contexts they reported on”, then you need supporting evidence. I would suggest softening of these two sentences. There is as much evidence in the literature supporting the idea that European observers provided reliable eye-witness testimonies of climatic conditions in Africa as there is that their observations were unreliable.
Lines 522-525 – in light of the work by Mutua and Runguma (2020), this sentence requires revision.
Citation: https://doi.org/10.5194/egusphere-2023-992-RC1 -
AC1: 'Reply on RC1', Philip Gooding, 09 Aug 2023
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See attachment.
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AC1: 'Reply on RC1', Philip Gooding, 09 Aug 2023
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Philip Gooding et al.
Data sets
Data for: Documents, Reanalysis, and Global Circulation Models: A New Method for Reconstructing Historical Climate Focusing on Present-day Inland Tanzania, 1856–1890 Philip Gooding, Melissa J. Lazenby, Michael R. Frogley, Cecile Dai, and Wenqi Su https://doi.org/10.5683/SP3/LDODGI
Philip Gooding et al.
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