Trend assessment of sunshine duration, cloudiness, and reference evapotranspiration for exploring global dimming/brightening in Tehran
- 238 Downloads
Recent studies have shown global warming as a deterministic phenomenon, while assessment of changes in specific variables such as sunshine duration, cloud cover and the amount of solar radiation at ground level increase uncertainties about this phenomenon in response to increasing greenhouse gases. Assessment studies of the mentioned variables have suggested the existence of a global dimming/brightening phenomenon in recent decades. In order to further research to investigate the global dimming/brightening phenomenon, the use of climatic variables such as sunshine duration used as a proxy for solar radiation variable is essential. Thus, this study used the cloudiness and residual sunshine duration time series after removal of the effect of cloud cover to study how the trend of changes in this phenomenon and its impact on reference evapotranspiration. In this regard, daily sunshine duration and cloudiness data measured at Mehrabad synoptic station of Tehran during the period 1951–2008 was used. Since the direct impact of this phenomenon will be on receiving solar radiation and subsequently on evapotranspiration, in this study, the trend of seasonal and annual variations of reference evapotranspiration and its trend accordance with mentioned factors was examined. The results showed that the existence trends in seasonal and annual sunshine duration and cloud cover time series in Mehrabad station are in accordance with global dimming/brightening trend, and it represents the overall occurrence of this phenomenon on a global scale.
KeywordsReference evapotranspiration Sunshine duration Cloudiness Global dimming/brightening Trend Tehran
The authors acknowledge the I.R. of Iran Meteorological Organization for providing the meteorological data. The authors also thank the anonymous reviewers for useful comments, which improved the quality of the paper.
- Allen RG, Pereira Raes LSD, Smith M (1998) Crop evapotranspiration: guidelines for computing crop water requirements-FAO irrigation and drainage paper 56. FAO, Rome, 300(9): p D05109Google Scholar
- Brutsaert W (2006) Indications of increasing land surface evaporation during the second half of the 20th century. Geophys Res Lett 33(20). doi: 10.1029/2006GL027532
- Chiacchio M, Wild M (2010) Influence of NAO and clouds on long-term seasonal variations of surface solar radiation in Europe. Geophys Res Atmos 115(D10). doi: 10.1029/2009JD012182.
- Emberlin JC, Norris-Hill J (1996) The influence of wind speed on the ambient concentrations of pollen from Graminae, Platanus and Betula in the air of London, England. In: M. Muilenberg and H. Burge (eds.). Aerobiology, pp. 27–38. CRC press. Lewis Pubishers, Boca RatonGoogle Scholar
- Papaioannou G, Kitsara G, Athanasatos S (2011) Impact of global dimming and brightening on reference evapotranspiration in Greece. J Geophys Res 116(D9). doi: 10.1029/2010JD015525
- Roderick ML, Farquhar GD (2002) The cause of decreased pan evaporation over the past 50 years. Science 298(5597):1410–1411Google Scholar
- Roderick ML, Rotstayn LD, Farquhar GD, Hobbins MT (2007) On the attribution of changing pan evaporation. Geophys Res Lett 34(17). doi: 10.1029/2007GL031166
- Sanchez-Lorenzo A, Brunetti M, Calbó J, Martin-Vide J (2007) Recent spatial and temporal variability and trends of sunshine duration over the Iberian Peninsula from a homogenized data set. J Geophys Res 112(D20). doi: 10.1029/2007JD008677
- Sanchez-Lorenzo A, Brunetti M, Calbó J, Deser C (2009) Dimming/Brightening over the Iberian Peninsula: trends in sunshine duration and cloud cover and their relations with atmospheric circulation. J Geophys Res 114(D10). doi: 10.1029/2008JD011394
- Stanhill G, Cohen S (2001) Global dimming: a review of the evidence for a widespread and significant reduction in global radiation with discussion of its probable causes and possible agricultural consequences. Agric For Meteorol 107(4):255–278. doi: 10.1016/s0168-1923(00)00241 CrossRefGoogle Scholar
- Streets DG, Wu Y, Chin M (2006) Two-decadal aerosol trends as a likely explanation of the global dimming/brightening transition. Geophys Res Lett 33(15). doi: 10.1029/2006GL026471
- Wild M (2009) Global dimming and brightening: a review. J Geophys Res 114(D10). doi: 10.1029/JD011470
- Wild M, Liepert B (2010) The Earth radiation balance as driver of the global hydrological cycle. Environ Res Lett 5(2). doi: 10.1088/1748-9326/5/02/0225003