The use of remote sensing for reliable estimation of net radiation and its components: a case-study for contrasting land covers in an agricultural hotspot of the Brazilian semiarid region

This study aims to ascertain the uncertainties related to the spatiotemporal estimation of net radiation, and its components, using remote sensing data. Geographical focus is an irrigated agricultural hotspot of the Brazilian semiarid region, for which we also investigate the impact that contrasting land-cover types have on the upwelling radiation balance components, and hence on net radiation. Instantaneous (Rn) and daily (Rn,24) values of net radiation were estimated based on OLI/TIRS-Landsat-8 images and key weather variables. In addition, we evaluated two models for downwelling shortwave (Rsw), ten models for downwelling longwave radiation (Rlw), and two models for derivation of Rn,24. The accuracy of each model was evaluated with radiation measurements obtained from research quality sensors installed in micrometeorological towers. The best performances were found for the Allen model, Duarte model, and De Bruin model for Rsw, Rlw, and Rn,24, respectively. The contrasting land-use types exhibited substantial differences in the biophysical variables and radiative properties that affect Rn. The albedo for the irrigated crops has average absolute values that are 0.01–0.03 larger than those found for the pristine caatinga, whereas the land surface temperature, LST, is 3–5 degrees smaller. However, Rn for these two distinctly different surface types was similar, as a result of a considerably lower surface emissivity in the caatinga. For rangeland, the albedo, LST, and hence the upwelling radiation had greater values than those found for the caatinga, which caused reduced values of Rn. The urban areas exhibited the lowest values of Rn, mainly as a consequence of their high albedo values. We show that when in-situ net radiation data are not available, remote sensing data combined with more readily available in-situ weather data can be used to derive spatiotemporal estimates of Rn. This facilitates the identification of anthropogenic impacts on the radiation at the land-surface and ultimately the energy balance, including the short-term seasonal and long-term effects

Riscos e vulnerabilidades: teoria e prática no contexto Luso-Brasileiro

O livro apresenta os resultados mais relevantes das atividades realizadas dentro do Programa de Pesquisa sobre Mudanças Climáticas Globais, patrocinado pela Fapesp e relacionado a estudos de impactos, vulnerabilidades e variabilidades nas mudanças do clima no estado de São Paulo e região sudeste do Brasil. Tais experiências têm sido discutidas e desenvolvidas com grupos de pesquisa de Portugal, que dão ao trabalho um caráter mais abrangente e internacional. O Brasil vem estudando já há algum tempo impactos das mudanças no clima que possam servir como base para estratégias de adaptação e para análises de vulnerabilidade diante das ameaças climáticas. O projeto da Fapesp tem, especificamente, a missão de produzir estudos de detecção e traçar cenários climáticos futuros, com metodologias que possam ser aplicadas em todo o Brasil. Essa metodologia leva em conta uma combinação de dados do clima (observações e projeções derivadas de modelos climáticos) com base em informações ambientais, geográficas, geofísicas e sociais. A ênfase está nos extremos climáticos e nos seus impactos sobre os recursos hídricos, assim como no planejamento com vista a minimizar os desastres naturais de origem meteorológica, que de alguns anos para cá têm se disseminado pelo paí