Search for: All records

Small stream dams and their reservoirs are ubiquitous in Brazil but mostly unmapped in existing datasets. Often used for cattle watering, farm-scale hydropower, irrigation, and/or fish aqua-culture, these reservoirs can have immense cumulative impacts on aquatic habitats, down-stream water quality, greenhouse gas emissions, and water balances. By applying deep learning to data from Landsat and Sentinel satellites, we created the first comprehensive datasets on small surface-water reservoirs in Brazil, including annual maps from 1984 to 2023. Then, we synthesized these maps with land-use data, property information, and semi-structured inter-views conducted in Mato Grosso state to elucidate the drivers and impacts of reservoir creation and persistence. First, we used high-resolution Sentinel-1 and -2 satellite data from 2021 to map over 1 million in-stream reservoirs smaller than 1 km2, a massive increase from existing datasets. Using weather data and climate models, we estimated that these reservoirs lose approximately 11.7 km3yr-1 to surface evaporation, a number projected to increase by 3-13% as climate change drives warmer and drier weather. Next, we showed that these reservoirs can be consistently and accurately mapped over time using Landsat 5, 7, and 8 data with only a slight de-crease in performance compared to Sentinel. From 1984 to 2023, the number of reservoirs in Brazil increased dramatically from 265,617 to 1,040,754 and the total surface area increased from 3526 km2 to 8629 km2. Then, we drew on interviews and MapBiomas land-use data to demonstrate that creation typically accompanied clearing of forest and savanna for cattle pasture in the first-waves settlement in the so-called hollow frontier of Mato Grosso. In many cases, these reservoirs were obsolete legacies of the hollow frontier, left over after intensified crop agriculture replaced dispersed cattle ranching. However, others are still critical and flexible sources of water, particularly for small-scale dairy, beef, fruit, and vegetable producers. Finally, we analyzed how the overarching discourse of resource abundance in eastern Mato Grosso obscures daily experiences of water scarcity, showing that the abundances of land, capital, and infrastructure contribute to and intersect with water inequality to favor large, export-oriented crop farms over small-scale producers. Applying an interdisciplinary approach to synthesize deep learning and remote sensing with political ecologies of water and agriculture, we highlight the important role of these reservoirs in agricultural expansion and intensification in Brazil and especially Mato Grosso state. Although they have widespread negative environmental impacts, reservoirs are also a critical form of water infrastructure for many. As climate change and the adoption of irrigation alter agricultural water use across Brazil, our results can inform water management decisions that balance the positive and negative social, environmental, and economic effects of stream damming. 

Wildfire frequency and extent is increasing throughout the boreal forest-tundra ecotone as climate warms. Understanding the impacts of wildfire throughout this ecotone is required to make predictions of the rate and magnitude of changes in boreal-tundra landcover, its future flammability, and associated feedbacks to the global carbon (C) cycle and climate. We studied 48 sites spanning a gradient from tundra to low-density spruce stands that were burned in an extensive 2013 wildfire on the north slope of the Alaska Range in Denali National Park and Preserve, central Alaska. We assessed wildfire severity and C emissions, and determined the impacts of severity on understory vegetation composition, conifer tree recruitment, and active layer thickness (ALT). We also assessed conifer seed rain and used a seeding experiment to determine factors controlling post-fire tree regeneration. We found that an average of 2.18 ± 1.13 Kg C m -2 was emitted from this fire, almost 95% of which came from burning of the organic soil. On average, burn depth of the organic soil was 10.6 ± 4.5 cm and both burn depth and total C combusted increased with pre-fire conifer density. Sites with higher pre-fire conifer density were also located at warmer and drier landscape positions and associated with increased ALT post-fire, greater changes in pre- and post-fire understory vegetation communities, and higher post-fire boreal tree recruitment. Our seed rain observations and seeding experiment indicate that the recruitment potential of conifer trees is limited by seed availability in this forest-tundra ecotone. We conclude that the expected climate-induced forest infilling (i.e. increased density) at the forest-tundra ecotone could increase fire severity, but this infilling is unlikely to occur without increases in the availability of viable seed.