Enhancement of Cloudless Skies Frequency over a Large Tropical Reservoir in Brazil

André R Gonçalves,Arcilan T Assireu,Silvia V Pereira,Robson B Passos,Enio B Pereira,Madeleine S G Casagrande,Francisco J L Lima,Enrique V Mattos,Fernando R Martins,Marcelo P Pes,Rodrigo S Costa

doi:10.3390/rs12172793

Abstract

Several studies show the effects of lake breezes on cloudiness over natural lakes and large rivers, but only few contain information regarding large flooded areas of hydroelectric dams. Most Brazilian hydropower plants have large water reservoirs that may induce significant changes in the local environment. In this work, we describe the prevailing breeze mechanism in a Brazilian tropical hydropower reservoir to assess its impacts on local cloudiness and incoming surface solar irradiation. GOES-16 visible imagery, ISCCP database products, and ground measurement sites operated by INMET and LABREN/INPE provided data for the statistical analysis. We evaluate the cloudiness frequency assuming two distinct perspectives: spatial distribution by comparing cloudiness over the water surface and areas nearby its shores, and time analysis by comparing cloudiness prior and after reservoir completion. We also evaluated the solar irradiance enhancement over the water surface compared to the border and land areas surrounding the hydropower reservoir. The results pointed out daily average cloudiness increases moving away from the reservoir in any of the four cardinal directions. When looking at the afternoon-only cloudiness (14 h to 16 h local time), 4% fewer clouds were observed over the flooded area during summer (DJF). This difference reaches 8% during autumn (MAM) and spring (SON). Consequently, the irradiance enhancement at the water surface compared to external areas was around 1.75% for daily average and 4.59% for the afternoon-only average. Our results suggest that floating solar PV power plants in hydropower reservoirs can be an excellent option to integrate both renewable energy resources into a hybrid power generation due to the high solar irradiance in Brazilian territory combined with the prevailing breeze mechanism in large tropical water reservoirs.

Highlights

Lake breeze circulation is one of the most well-known thermally-induced phenomena in mesoscale meteorology
Our results suggest that floating solar PV power plants in hydropower reservoirs can be an excellent option to integrate both renewable energy resources into a hybrid power generation due to the high solar irradiance in Brazilian territory combined with the prevailing breeze mechanism in large tropical water reservoirs
This work evaluated the formation of the lake breeze in the Serra da Mesa Reservoir, located in the Central region of Brazil, and its impacts on the regional cloudiness climate

Summary

Introduction

Lake breeze circulation is one of the most well-known thermally-induced phenomena in mesoscale meteorology. Segal et al [3] evaluated the lake breeze phenomena in Florida (USA) using modeling and observational approaches. They reported that the atmospheric forcing induced by subsidence and suppression of the cumulus cloud mutually contribute to the increase in the cloudless frequency over the lakes. Iakunin et al [5] have shown that the lake breeze for the Alqueva reservoir (southeast of Portugal) could be detected at a distance of more than 6 km away from the shores and at altitudes up to 300 m above the water surface based on observation and model. It is a consensus among researchers that factors like the sensible heat flux, synoptic wind, atmospheric stability, watershed dimensions, terrain slope, and roughness affect lake breeze occurrence

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