Contrasting conditions of surface water balance in wet years and dry years as a possible land surface-atmosphere feedback mechanism in the West African Sahel

Journal Article · Sun May 01 04:00:00 EDT 1994 · Journal of Climate; (United States)

DOI:https://doi.org/10.1175/1520-0442(1994)007<0653:CCOSWB>2.0.CO;2· OSTI ID:7011386

Lare, A R; Nicholson, S E ^[1]

---

1. Florida State Univ., Tallahassee, FL (United States)

the climate of West Africa, in particular the Sahel, is characterized by multiyear persistence of anomalously wet or dry conditions. Its Southern Hemisphere counterpart, the Kalahari, lacks the persistence that is evident in the Sahel even though both regions are subject to similar large-scale forcing. It has been suggested that land surface-atmosphere feedback contributes to this persistence and to the severity of drought. In this study, surface energy and water balance are quantified for nine stations along a latitudinal transect that extends from the Sahara to the Guinea coast. In the wetter regions of West Africa, the difference between wet and dry years is primarily reflected in the magnitude of runoff. For the Sahel and drier locations, evapotranspiration and soil moisture are more sensitive to rainfall anomalies. The increase in evapotranspiration, and hence latent heating, over the Sahel in wet years alters the thermal structure and gradients of the overlying atmosphere and thus the strength of the African easterly jet (AEJ) at 700 mb. The difference between dry and wet Augusts corresponds to a decrease in magnitude of the AEJ at 15[degrees]N on the order of 2.6 m s[sup [minus]1], which is consistent with previous studies of observed winds. Spatial patterns were also developed for surface water balance parameters for both West Africa and southern Africa. Over southern Africa, the patterns are not as spatially homogeneous as those over West Africa and are lower in magnitude, thus supporting the suggestion that the persistence of rainfall anomalies in the Sahel might be due, at least in part, to land-atmosphere feedback, and that the absence of such persistence in the Kalahari is a consequence of less significant changes in surface water and energy balance. 38 refs., 10 figs. 2 tabs.

• OSTI ID: 7011386
• Journal Information: Journal of Climate; (United States), Journal Name: Journal of Climate; (United States) Vol. 7:5; ISSN JLCLEL; ISSN 0894-8755
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540110*
AFRICA
ANNUAL VARIATIONS
ATMOSPHERIC PRECIPITATIONS
DROUGHTS
EARTH ATMOSPHERE
FORCING FUNCTIONS
VARIATIONS