Over the past 350 years, the eastern half of the United States experienced extensive land cover changes. These began with land clearing in the 1600s, continued with widespread deforestation, wetland drainage, and intensive land use by 1920, Reforestation of eastern U.S. forests began with efforts to promote forest regrowth in support of environmental conservation movements that began in the 1880s, motivated by concerns about the negative consequences of land use change, specifically land and water resource degradation associated with deforestation and poor farming practices. The reforestation of the eastern United States, however, was also characterized by land cover transformation that included growing urbanization and other land use changes leading to increasing landscape fragmentation. Bythe late 1990s reforestation in the eastern United States had reached its peak, with slow but steady declines in forest cover during the last two decades. This natural experimentation in land use modification, occurring concurrently with climate change, raises a question regarding how the PBL and, more specifically, BLcu have responded. Fortunately, we now have an extensive data base of long-term surface-based cloud observations to interrogate—the Automated Surface Observing System (ASOS) network established by the Federal Aviation Administration and the National Oceanic and Atmospheric Administration National Weather Service over two decades ago.
Using twenty years of 5-minute ASOS observations, we present preliminary results of what the effects of real world afforestation/deforestation, combined with a changing climate, have had on the frequency and distribution of BLcu. Included in the analysis is the current climatology, trends, and inter-annual and seasonal variability of BLcu over the eastern United States.
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