Anthropogenic impact on the albedo of the earth

Otterman, J.

doi:10.1007/bf01884408

Cited by 95 publications

(45 citation statements)

References 18 publications

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“…These results suggested a positive feedback mechanism by which droughts could be self-accelerating, or could perhaps even be produced. This paper was followed up by several general circulation model (GCM) experiments that drew conclusions consistent with Charney's original hypothesis (e.g., Charney et al 1975, 1977, Sud & Fennessy 1982, Sud & Molod 1988, Xue & Shukla 1993, Dirmeyer & Shukla 1994, Lofgren 1995a.…”

Section: The Albedo Issuementioning

confidence: 85%

“…Few measurements have been carried out, but 3 case studies are worth noting: a study of 'protected' and 'unprotected' grazing areas in Tunisia and studies that surveyed grazed and ungrazed sides of international borders in the Sinai/Negev and the Sonoran Desert of the US and Mexico. Satellite photos (Otterman 1977(Otterman , 1981 indicate that the soil in the overgrazed Sinai has an albedo of 0.4 in the visible and 0.53 in the infrared; in the protected area of the Negev, the visible and infrared albedos were 0.12 and 0.24 respectively, but in most of the region the albedo averaged about 0.25. In Tunisia the albedo of protected versus unprotected sites was 0.35 versus 0.39 in one case and 0.26 versus 0.36 in another, while oases had albedos on the order of 0.10 to 0.23 (Wendler & Eaton 1983).…”

Section: The Albedo Issuementioning

confidence: 99%

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Climatic and environmental change in Africa during the last two centuries

Nicholson¹

2001

Clim. Res.

439

262

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Climatic and environmental changes in Africa during the last 2 centuries have been examined, using both systematic rainfall records and proxy information concerning lakes and rivers and the occurrence of famine and drought. The rainfall records provide excellent detail for the 20th century. The proxy data have been used to produce a semi-quantitative data set spanning most of the continent and having an annual time resolution. These provide an overview of conditions during the 19th century. Various issues related to the causes of these 2 centuries of variability are also considered: atmospheric and oceanic processes, desertification, surface albedo, mineral dust and hydrological feedbacks. The most significant climatic change that has occurred has been a long-term reduction in rainfall in the semi-arid regions of West Africa. This was on the order of 20 to 40% in parts of the Sahel. There have been 3 decades of protracted aridity. Nearly all of Africa has been affected by increased aridity, particularly since the 1980s. Few changes in temperature have been demonstrated. These have occurred on a much smaller scale and are of considerably lower magnitude than those over the continents. The rainfall conditions over Africa during the last 2 to 3 decades are not unprecedented. A similar dry episode prevailed during most of the first half of the 19th century. By mid-century, conditions more typical of the 'normal' for the current century again prevailed. Thus, the 3 decades of dry conditions evidenced in the Sahel are not in themselves evidence of irreversible global change. On the other hand, the processes controlling rainfall over most of the continent are now reasonably well understood. One of the most important factors, particularly in the Sahel, is sea-surface temperatures. It has been hypothesized that anthropogenic changes in the land surface, particularly land use change and desertification, have contributed significantly to the decline in rainfall. Current evidence suggests that if changes in the land surface (e.g., vegetation cover, surface albedo, soil moisture) signficantly impact climate, they are much more strongly controlled by natural climate variations, such as the recent decline in rainfall, than by human-induced land-use change or degradation. Unfortunately, we still do not have any accurate large-scale assessments of the extent, nature and degree of such changes. The dreaded 'desertification' process appears to be confined to relatively small scales. However, there is still cause for concern because the net effect of the various feedback processes involved in land degradation appears to be destabilization of ecosystems. Thus, a priority must be large-scale monitoring of the land surface and estimates of the degree of change. KEY WORDS: Africa · Climate · Rainfall · EnvironmentResale or republication not permitted without written consent of the publisher

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Section: The Albedo Issuementioning

confidence: 85%

Section: The Albedo Issuementioning

confidence: 99%

Climatic and environmental change in Africa during the last two centuries

Nicholson¹

2001

Clim. Res.

439

262

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“…The surface cooling reduces emission of surface long wave radiation, while water vapor in the upper air can absorb and release more long wave radiation to the surface (Boucher et al 2004;Kueppers and Snyder 2012). Irrigation can also increase net solar radiation at the surface due to the decreased albedo of the wet soil (Otterman 1977). Irrigation increases local and regional precipitation in regions where the atmosphere and soil moisture are highly coupled.…”

Section: Introductionmentioning

confidence: 99%

Crop growth and irrigation interact to influence surface fluxes in a regional climate-cropland model (WRF3.3-CLM4crop)

2015

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spaceAbstract In this study, we coupled Version 4.0 of the Community Land Model that includes crop growth and man-agement (CLM4crop) into the Weather Research and Fore-casting (WRF) model Version 3.3 to better represent inter-actions between climate and agriculture. We evaluated the performance of the coupled model (WRF3.3-CLM4crop) by comparing simulated crop growth and surface climate to multiple observational datasets across the continental United States. The results showed that although the model with dynamic crop growth overestimated leaf area index (LAI) and growing season length, interannual variability in peak LAI was improved relative to a model with prescribed crop LAI and growth period, which has no environmental sensi-tivity. Adding irrigation largely improved daily minimum temperature but the RMSE is still higher over irrigated land than nonirrigated land. Improvements in climate variables were limited by an overall model dry bias. However, with addition of an irrigation scheme, soil moisture and surface energy flux partitioning were largely improved at irrigated sites. Irrigation effects were sensitive to crop growth: the spacecase with prescribed crop growth underestimated irrigation water use and effects on temperature and overestimated soil evaporation relative to the case with dynamic crop growth in moderately irrigated regions. We conclude that studies exam-ining irrigation effects on weather and climate using coupled climate-land surface models should include dynamic crop growth and realistic irrigation schemes to better capture land surface effects in agricultural regions.

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“…1, this region is characterized by a sharp contrast between the bright reflectance from the Egyptian side (Sinai) and the dark one from the Israeli side (Negev) . The contrast was interpreted as being caused by different land surface cover structures under different land use policies (Otterman, 1974(Otterman, , 1977(Otterman, , 1981Warren & Harrison, 1984;Tsoar & Mller, 1986). The Egyptian side has lower vegetation cover and much more bare sand surface.…”

Section: Introductionmentioning

confidence: 99%