Baring High-Albedo Soils by Overgrazing: A Hypothesized Desertification Mechanism

Abstract

Observations are reported of high-albedo soils denuded by overgrazing which appear bright, in high contrast to regions covered by natural vegetation. Measurements and modeling show that the denuded surfaces are cooler, when compared under sunlit conditions. This observed "thermal depression" eflect should, on theoretical grounds, result in a decreased lifting of air necessary for cloud formation and precipitation, and thus lead to regional climatic desertification.

Why Large-Scale Afforestation Efforts in China Have Failed To Solve the Desertification Problem

“…ing (2), and monoculture planting of forests (often to prioritize wood production) in China has led to the disappearance of many natural forests and to large increases in desertification (3). Currently, desertification is concentrated in the northwestern, northern, and northeastern parts of the country (the so-called Three Norths): an estimated 3.3 million km 2 have been affected by desertification, accounting for 34% of China's total land area (4).…”

“…Currently, desertification is concentrated in the northwestern, northern, and northeastern parts of the country (the so-called Three Norths): an estimated 3.3 million km 2 have been affected by desertification, accounting for 34% of China's total land area (4).…”

L'évolution des idées sur la variabilité interannuelle récente du cycle de l'eau atmosphérique en Afrique de l'ouest

“…Ceci entraîne un refroidissement de la colonne d'air en altitude compensé adiabadquement par une accentuation de la subsidence et donc par une ditninution de la convection accentuant la diminution initiale des précipitations, toutes choses égales par ailleurs. Ce méca-nistne a été proposé dans une atmosphère de polémique (Otterman, 1974;Jackson et Idso, 1975) au sujet de la variation des températures de surface induites par la désertification. En effet une augmentation d'albédo entraîne une diminution de la chaleur absorbée par le sol, donc de la température de surface et, en l'absence totale de végétation et/ou d'humidité, favorise la diminution de H (puisque qu'alors LE=0) et celle de la température de l'air en contact.…”

Late Quaternary vegetation-climate feedbacks

“…Claussen and Gayler explain the positive feedback by an interaction between high albedo of Saharan sand deserts and tropical atmospheric circulation. This desert-albedo feedback was originally proposed by Otterman (1974) and described in a model by Charney (1975) to explain the opposite process of desertification in the Sahel region. Charney (1975) hypothesizes that the high albedo over subtropical deserts causes a radiative cooling above deserts because the sum of incoming solar radiation, reflected solar radiation and outgoing long-wave radiation is negative at the top of the atmosphere: more radiation leaves than enters the atmosphere above a subtropical desert.…”