Estimated impacts of soil degradation on the African water balance and climate

Abstract

This study uses a well-established water balance methodology, the Thornthwaite-Mather approach, to evaluate the effects of soil water holding capacity assumptions on estimates of African evapotranspiration rates, moisture deficit, and moisture surplus conditions. Under constant climate conditions, the model tests the impact of using a constant 150 mm soil water holding capacity compared to using a newly derived soil water holding capacity data set (the Dunne-Willmott data set). The study also uses a worldwide survey of soil degradation between 1950 and 1980 (GLASOD: Global Assessment of Soil Degradation) to evaluate the impacts of human-induced soil degradation on local water balances. The GLASOD data are used to alter local soil water holding capacities based on the DunneWillmott data to simulate human soil degradation patterns in Africa. Results indicate that the use of simplified soil water holding capacities can lead to significant errors in estimated evapotranspiration rates and water surplus and deficit conditions in Africa. Regions most affected are those with seasonal wet and dry climates, which are also those locations with the greatest climate variability. Because these are often the climates most studied to detect and model environmental change, it is important that accurate soil moisture estimates be used to simulate climate conditions in these regions. Results also indicate that soil degradation occurring over a 30 yr period (1950 to 1980) has had a significant impact on local water resources. The greatest impacts of these changes are in some of the more productive agricultural areas in the wetter sub-humid climates. Changes include increased runoff during wet seasons and an extended drought period during the dry seasons. Given that these agricultural systems have less flexibility to respond to long-term desiccation as compared to pastoral systems, this could lead to significant changes in local growing seasons and perhaps overall productivity in the future.

Assessment of uncertainties in the response of the African monsoon precipitation to land use change simulated by a regional model

“…Land degradation in the African Sahel has also resulted in soil texture change. Feddema (1998) has shown that variations in soil water holding capacity associated with land degradation can have important effects on evapotranspiration and local water balances. The relative contributions of LULC change and soil texture change and the degree to which uncertainty in model response to these change feeds back to the monsoon dynamics is a subject of future study.…”

Intervalo hídrico ótimo para avaliação da degradação física do solo

“…Como consequência dessa degradação, ocorrem alterações em propriedades do solo que controlam os processos fundamentais relacionados com a dinâmica de água, ar e calor (Topp et al, 1994;Feddema, 1998) e crescimento das raízes. Assim, a quantificação dos impactos do manejo sobre a qualidade física do solo deveria ser realizada por meio de atributos que determinam os processos físicos que interferem em aspectos fisiológicos ligados ao crescimento e desenvolvimento das plantas.…”

“…Em geral, a perda da qualidade física do solo está associada com modificações dos arranjos de agregados e poros do solo, reduzindo a disponibilidade de ar, água e nutrientes necessários à produção de biomassa (Six et al, 2004;Omuto, 2008). Essas mudanças interferem nas características da superfície do solo, resultando na compactação do solo (Lanzanova et al, 2007); nas mudanças na distribuição e no tamanho de poros (Dexter, 2004); na diminuição da taxa de infiltração de água no solo (Sobrinho et al, 2003); na diminuição da água disponível (Dexter, 2004); na perda de matéria orgânica (Álvaro-Fuentes et al, 2008); na redução da diversidade e atividade de microrganismos (Six et al, 2004); e no aumento da suscetibilidade à erosão do solo (Feddema, 1998;Lal, 2000;Richard et al, 2001). …”

Atributos físicos e carbono orgânico em latossolo vermelho sob diferentes sistemas de uso e manejo

“…A degradação física é um dos componentes do processo de degradação do solo, geralmente associado às perdas de matéria orgânica e da integridade estrutural dos solos. Como consequência da degradação física, há alterações em propriedades do solo que controlam processos fundamentais relacionados com a dinâmica de água, ar e calor (Feddema, 1998).…”