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Department of Geography

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This series is automatically populated with publications deposited by UCLA Department of Geography researchers in accordance with the University of California’s open access policies. For more information see Open Access Policy Deposits and the UC Publication Management System.

Soil moisture-atmosphere feedbacks mitigate declining water availability in drylands

(2022)

Global warming alters surface water availability (precipitation minus evapotranspiration, P-E) and hence freshwater resources. However, the influence of land-atmosphere feedbacks on future P-E changes and the underlying mechanisms remain unclear. Here we demonstrate that soil moisture (SM) strongly impacts future P-E changes, especially in drylands, by regulating evapotranspiration and atmospheric moisture inflow. Using modeling and empirical approaches, we find a consistent negative SM feedback on P-E, which may offset ~60% of the decline in dryland P-E otherwise expected in the absence of SM feedbacks. The negative feedback is not caused by atmospheric thermodynamic responses to declining SM, but rather reduced SM, in addition to limiting evapotranspiration, regulates atmospheric circulation and vertical ascent to enhance moisture transport into drylands. This SM effect is a large source of uncertainty in projected dryland P-E changes, underscoring the need to better constrain future SM changes and improve representation of SM-atmosphere processes in models.

Global field observations of tree die-off reveal hotter-drought fingerprint for Earth's forests.

(2022)

Earth's forests face grave challenges in the Anthropocene, including hotter droughts increasingly associated with widespread forest die-off events. But despite the vital importance of forests to global ecosystem services, their fates in a warming world remain highly uncertain. Lacking is quantitative determination of commonality in climate anomalies associated with pulses of tree mortality-from published, field-documented mortality events-required for understanding the role of extreme climate events in overall global tree die-off patterns. Here we established a geo-referenced global database documenting climate-induced mortality events spanning all tree-supporting biomes and continents, from 154 peer-reviewed studies since 1970. Our analysis quantifies a global "hotter-drought fingerprint" from these tree-mortality sites-effectively a hotter and drier climate signal for tree mortality-across 675 locations encompassing 1,303 plots. Frequency of these observed mortality-year climate conditions strongly increases nonlinearly under projected warming. Our database also provides initial footing for further community-developed, quantitative, ground-based monitoring of global tree mortality.

Cover page of Speculating on land, property and peri/urban futures: A conjunctural approach to intra-metropolitan comparison

Speculating on land, property and peri/urban futures: A conjunctural approach to intra-metropolitan comparison

(2022)

This article explores a conjunctural approach to comparison as a means to capture the complexity of the processes shaping metropolitan land transformations in a city of the global South, comparing the co-implicated actions of developers and local residents across central and peri-urban Jabodetabek. A conjunctural approach shares with some other forms of comparison the ambition to build new theories and challenge existing knowledge. Rather than controlling for the characteristics of units of analysis as in conventional comparison, a conjunctural approach attends to the broader spatio-temporal conjuncture. It involves highlighting unexpected or overlooked starting points for comparison, attending to inter-place, inter-scalar and inter-temporal relationalities in order to identify shared general tendencies as well as particularities and to chart their mutual constitution. Grounding this comparison iteratively puts local knowledge and observations in conversation with already existing theories. Deploying these principles in a socio-spatial intra-metropolitan comparison, we show that economic speculation on land and property is complexly entangled with actors’ socio-cultural speculations, as they seek also to realise aspirations for distinct peri/urban futures. Economic speculation deepens already existing inequalities in wealth and power differentials between and among developers and kampung residents. The erasure of informal settlements and displacement of their residents is supplemented by the ability of other kampungs and select residents to take advantage of spillover opportunities from the formal developments built on former kampung land. Distinct central city and peri-urban landscapes are emerging, shaped by differences in the social ecology of land and local governance and planning regimes.

Large Divergence in Tropical Hydrological Projections Caused by Model Spread in Vegetation Responses to Elevated CO2

(2022)

Increasing atmospheric CO2 and associated global warming are expected to alter the global hydrological cycle, thereby posing widespread threats to freshwater availability. However, future hydrological projections differ greatly between models, particularly over the tropical regions. The large difference between model projections directly limits policy planning efforts, and the responsible modeling processes remain unclear. Here, we identify the primary processes accounting for model differences in tropical hydrological changes using multiple CO2 sensitivity experiments in the Coupled Model Intercomparison Project. We show that differences in projected changes to tropical evapotranspiration, precipitation, and surface water availability mainly arise from model representations of vegetation cover and stomatal conductance responses to elevated CO2 and associated changes in atmospheric moisture and circulation. Atmospheric responses to sea surface warming contribute additionally to the divergence in hydrological projections. Given the importance of vegetation responses to elevated CO2 and associated atmosphere feedbacks, our results underscore the need to improve representations of the vegetation physiological response to rising CO2 and its coupling to the atmosphere, to provide reliable tropical hydrological projections.

Cover page of Geography and the present conjuncture

Geography and the present conjuncture

(2022)

Anthropogenic global heating is accelerating, with dramatic implications for the long-term prospects of humans and many other species, underwritten by the logics of Euro-centric capitalism compounded by the colonialism, racism, patriarchy, and commodification of nature that has accompanied it. Nationalism is re-emerging, as are socio-cultural divisions within national societal assemblages. Global capitalism faces a series of crises stemming from the consequences of these relations. Critics are quick to argue that non-capitalist alternatives can advance socio-ecological justice, but how? Geography is ideally suited to making sense of this conjuncture, critiquing the processes facilitating its emergence, and realizing alternatives. Yet we are far from achieving our potential, caught up in our own philosophical, ideological, and substantive silos. I argue that five priorities must be taken up if geographical thinking is to be suited for the present moment. We must be more historical in our thinking (integrating the temporal with the spatial). We must pay more attention to the macro-scale: to how local events are complexly bound-up in spatially differentiated planetary processes? We must be socio-ecological: incentivizing productive collaboration across earth science, social science, and humanities sub-fields. We must deconstruct our disabling quantitative–qualitative methodological divide, incentivizing training in multi-methods. We must work harder to diversify the perspectives and socio-spatial positionalities incorporated into geographical thinking to decenter White male, Anglophone, and settler geographies. Excitingly, the potential for all this exists within Geography today.

Rapid Growth of Large Forest Fires Drives the Exponential Response of Annual Forest-Fire Area to Aridity in the Western United States

(2022)

Annual forest area burned (AFAB) in the western United States (US) has increased as a positive exponential function of rising aridity in recent decades. This non-linear response has important implications for AFAB in a changing climate, yet the cause of the exponential AFAB-aridity relationship has not been given rigorous attention. We investigated the exponential AFAB-aridity relationship in western US forests using a new 1984–2019 database of fire events and 2001–2020 satellite-based records of daily fire growth. While forest-fire frequency and duration grow linearly with aridity, the exponential AFAB-aridity relationship results from the exponential growth rates of individual fires. Larger fires generally have more potential for growth due to more extensive firelines. Thus, forces that promote fire growth, such as aridification, have more potent effects on larger fires. As aridity increases linearly, the potential for growth of large fires accelerates, leading to exponential increases in AFAB.

Plant-water sensitivity regulates wildfire vulnerability.

(2022)

Extreme wildfires extensively impact human health and the environment. Increasing vapour pressure deficit (VPD) has led to a chronic increase in wildfire area in the western United States, yet some regions have been more affected than others. Here we show that for the same increase in VPD, burned area increases more in regions where vegetation moisture shows greater sensitivity to water limitation (plant-water sensitivity; R2 = 0.71). This has led to rapid increases in human exposure to wildfire risk, both because the population living in areas with high plant-water sensitivity grew 50% faster during 1990-2010 than in other wildland-urban interfaces and because VPD has risen most rapidly in these vulnerable areas. As plant-water sensitivity is strongly linked to wildfire vulnerability, accounting for ecophysiological controls should improve wildfire forecasts. If recent trends in VPD and demographic shifts continue, human wildfire risk will probably continue to increase.