More variable tropical climates have a slower demographic growth

Abstract

A classical approach to assess the amplitude of rainfall variations is based on the coefficient of variation. Using worldwide station data for the twentieth century, an alternative method, involving the development of a polynomial fit, was shown to be more relevant to semi-arid climates. The results singularised the tropical and subtropical regions, whose amplitude of interannual rainfall variability was larger than that of the extra-tropical regions, for a given mean rainfall value. However, the tropical belt also showed large contrasts between highly variable climates -corresponding mainly to regions where the sea-surface temperature forcing is strongest -and more steady climates. A separate analysis documented the relationship between the amplitude of rainfall variations and human demography. Population densities did not show any systematic decline with increasing variability. However, in the tropics, there was often a coincidence between reduced demographic growth and high rainfall variability. This smaller demographic growth may result from both reduced natural growth (especially enhanced mortality) and out-migration from regions affected by strong rainfall variations, as evidenced from a number of African cases studies. In contrast, tropical regions with a fast-growing population had on average a lower rainfall variability.

Climate of Eastern Africa

“…Given the semi-arid conditions which prevail over much of the region, the generally low incomes and the dependence to water resources which account for a high vulnerability, these variations have dramatic effects on the economy and the living of local communities. Figure 13 recalls that the tropics, except for very wet months and locations, shows much larger interannual rainfall variations than the extratropics (Camberlin, 2010). Equatorial East Africa (mainly Kenya and southern Somalia) adhere to this feature, and many of its wetter locations (above 150 mm/month) even exhibit larger interannual rainfall variations than in other parts of the tropics.…”

Climatic gradients along the windward slopes of Mount Kenya and their implication for crop risks. Part 1: climate variability

“…There are substantial interannual variations of seasonal rainfall over East Africa, particularly for the Short Rains (Hastenrath et al , ; Nicholson, ; Black et al , ; Camberlin, ). Over the Mount Kenya area, the interannual variability is also large, and absolute variability tends to increase with the mean rainfall amounts (i.e.…”

Ethnographic context and spatial coherence of climate indicators for farming communities – A multi-regional comparative assessment

“…In these countries, climatic vulnerability (Turner et al, 2003;Adger, 2006;Gallopin, 2006) is mostly related to rainfall variations and is often very high in semi-arid areas, where low-income populations strongly depend on very scarce and variable water resources (Camberlin, 2010). In that context, seasonal rainfall forecasts (Goddard et al, 2001(Goddard et al, , 2003Barnston et al, 2010) are a potential tool for farmers to reduce risks and to optimize gains (Glantz, 1977;Dilley, 2000;Luseno et al, 2003;Meinke and Stone, 2005;Hansen et al, 2006Hansen et al, , 2009Challinor, 2009;Sultan et al, 2010a,b;Roudier et al, 2011Roudier et al, , 2014, even though several issues (e.g.…”