Theme RAINFALL AND LAND DEGRADATION IN GUINEABISSAU IMPACTS

Theme: RAINFALL AND LAND DEGRADATION IN GUINEA-BISSAU IMPACTS ON CLIMATE CHANGES Superior Technical in Meteorological Instruments- Luís Cá E-mail: luis. ca 19@yahoo. fr - General Direction of Meteorology - July/2010

PRESENTATION PLAN I. ABSTRACT II. INTRODUCTION III. LAND DEGRATATION IV. RAINFALL ANALYSIS FOR LAND DEGRADATION ASSESSMENT V. APPLICATION OF THE ANNUAL SCALE: FTRENDS AND PROBABILITIES

I. ABSTRACT Among the components of land degradation are desertification, soil degradation and erosion. In any discussion of land degradation there are four spatial-temporal scalesthat should be distinguished: regional, watershed, field and point. At each scale, one may use different proxies for land degradation. In order to study land degradation at multiple scales it is also necessary to study rainfall at multiple scales. Rainfall can be analysed for land degradation at four different scales: from the “small” annual scale to the “large” minute scale. Besides scales one may also distinguish between average values and temporal and spatial variations. In this paper, one of more examples of rainfall data are presented for each scale and interpreted with respect to land degradation. At the annual scale, trend analysis and rainfall probabilities are important. The decadal(10 – days) scale is especially suitable for calculating the varying lengths of the growing season. At the scale of one day, the size classes of showers, return period (design storm), hydrological and agronomic modelling and dry spell analysis are discussed.

ABSTRACT – (Cont. ) • The concepts of land degradation mitigation are derived from the rainwater balance. After drawing a number of conclusions, it is suggested how we could improve our understanding of land degradation by improving the availability of rainfall data at multiple scales.

II. INTRODUTION • Rainfall is the most important climatic factor in determinig areas at risk of land degradation and potential desertification. Rainfall plays a vital role in the developpment and distribution of plant life, but the variability and extremes of rainfall can lead to soil erosion and land degradation. If unchecked for a period of time, this land degradation can lead to desertification. The interaction of human activity on the distribution of vegetation though land management practices and seemingly benign rainfall events can make land more vulnerable to degradation. These vulnerabilities become more acute when the prospect of climate change is introduced. • Land is the complex of soil, water and the natural flora and fauna in a landscape, above and below the soil surface. Land degradation is the decline in the extent too which land yields products useful to local livelihoods(Scoones and Toulmin 1999) or, in more recent terminology, in the decline in “ecosystem services”(MEA 2005). The complexity of the notions “land” and “land degradation” and their scale features lead to many different definitions.

INTRODUTION (CONT. ) • A special form of land degradation is desertification, land degradation in the arid, semi-arid and dry sub-humid areas most vunerable to land degradation. The previous UN Secretary-General Kofi Annan has called desertification one of the world´s most alarming processes of environmental degradation. Under the scenario of climate change it is often claimed that the droughts, flash floods, dust storms, famine, migration and forest fires associated with desertification are bound to increase, leading to loss in human well-being and bringing high socio-economic costs. That long-term food productivity is threatened by land degradation is of major significance and concern, since this has serious impact on global food security.

III. LAND DEGRATATION • • Definition land degradation All current land degradation definitions refer to loss in productivity of the land (Blaikie and Brookfield 1987). This implies that one of the possible proxies for land degradation is a decline in productivity of the land. Soil degradation, being a component of land degradation, comprises erosion and the decline in soil qualities: chemical changes due to leaching or salinisation, physical changes due to compaction or crusting, and biological changes due to the loss of soil organic matter or micro-organisms. With respect to erosion, it is useful to distinguish between on-site and off-site erosion. Recently a new definition has been proposed, based on the concept of ecosystem services(MEA 2005). Furthermore, many have taken on board the notion expressed by Warren(2002) that land degradation is contextual and cannot be judged independently of its spatial, temporal, economic, environmental and cultural context. So, at present there are too many definitions for land degradation. In fact it may be questioned whether changes in land or land qualities that result from deliberate changes in land use, for instance due to economic development, may be called land degradation.

IV. RAINFALL ANALYSIS FOR LAND DEGRADATION ASSESSMENT • In order to study land degradation at multiple scales it is necessary to study rainfall at multiple scales too. Rainfall can be analysed for land degradation at four different scales: from the “small” annual scale to the “large” minute scale. Each scale has its specific application(s). Besides scales, one may also distinguish between average values and temporal and spatial variations. A few examples of rainfall data for each of the scales are presented below and interpreted with respect to land degradation.

V. APPLICATION OF THE ANNUAL SCALE: TRENDS AND PROBABILITIES • Trends of annual rainfall are used to assess changes in rainfall that affect land degradation mainly through changes in vegetation cover. Conway et al. (2004), analysing 100 years of rainfall in Addis Ababa, conclude that there was no major shift or trend in annual and seasonal rainfall during the period 1898 – 2002. Wellknown drought years in northern and northeastern Ethiopia are not picked out in the Addis Ababa rainfall record, suggesting that the series should not be used as a proxy for inter-annual rainfall variability in these parts of the Ethiopian highlands. • The annual rainfall of the 3 major stations in Guinea. Bissau with a long-term record. The result is shown in Figures.