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David M. Meko
,
Franco Biondi
,
Alan H. Taylor
,
Irina P. Panyushkina
,
Richard D. Thaxton
,
Alexander A. Prusevich
,
Alexander I Shiklomanov
,
Richard B. Lammers
, and
Stanley Glidden

Abstract

Regional warming and associated changes in hydrologic systems pose challenges to water supply management in river basins of the western United States, and call for improved understanding of the spatial and temporal variability of runoff. We apply a network of total-width, subannual width and delta blue intensity tree-ring chronologies in combination with a monthly water balance model to identify droughts and their associated precipitation (P) and temperature (T) footprints in the Truckee-Carson River basin (TCRB). Stepwise regression gave reasonably accurate reconstructions, from 1688 to 1999, of seasonal P and T (e.g., R 2 = 0.50 for May-Sept T). These were disaggregated to monthly values, which were then routed through a water balance model to generate “indirectly” reconstructed runoff. Reconstructed and observed annual runoff correlate highly (r = 0.80) from 1906 to 1999. The extended runoff record shows that 20th century droughts are unmatched in severity in a 300-year context. Our water balance modeling reconstruction advances the conventional regression-based dendrochronological methods as it allows for multiple hydrologic components (evapotranspiration, snowmelt, etc.) to be evaluated. We found that imposed warming (3 °C and 6 °C) generally exacerbated the runoff deficits in past droughts but that the impact could be lessened and sometimes even reversed in some years by compensating factors, including changes in snow regime. Our results underscore the value of combining multi-proxy tree-ring data with water balance modelling to place past hydrologic droughts in the context of climate change.

Open access
Yujun Wang
,
Hongbo Yang
,
Vanessa Hull
,
Jindong Zhang
,
Xiaodong Chen
,
Xiang Li
,
Zejun Zhang
,
Cheng Li
,
Fang Wang
,
Zhiqiang Zhao
,
Ying Tang
, and
Jianguo Liu

Abstract

The effects of various strategies aimed at simultaneously promoting environmental conservation and human development are closely related to sustainable development regionally and globally. However, although the effects of many such strategies have been evaluated by ecologists and sociologists separately, their ability to simultaneously meet these two anticipated goals (i.e., environmental conservation and human development) at the fine spatial scale remains unclear. To answer this fundamental but crucial question, incorporating household and forest change data, we concurrently estimated the ecological and socioeconomic effects of two world-renowned Payment for Ecosystem Services (PES) programs (i.e., the Nature Forest Conservation Program, the Grain to Green Program) and nature-based tourism in 30 protected areas across 8 provinces in China. Here we showed a trade-off between the ecological and economic effects of two PES programs, while synergistic effects exist in the ecological and economic benefits of tourism. Attributes of household and protected areas significantly influenced economic and environmental benefits as well. Our research provides new insights into the complex effects of PES programs and tourism, and crucial information to support their adequate and sustainable implementation in China and the rest of the world.

Significance Statement

This work answers a fundamental but crucial question, that is, whether the policies commonly advocated to incorporate environmental conservation and human development can yield positive effects both for conservation and economic development. Our evaluation is also timely to inform some shortness (i.e., negligible economic effects, or the lack of expected positive economic benefits) and provides new insights (e.g., the implication of households and protected-areas attributes in conservation and economic outcomes) of Payment for Ecosystem Services (PES) programs and the complex effects of instruments in the context of multiple policies, particularly given the upcoming 2030 deadline for achieving the Sustainable Development goals (SDGs). We expected that implications in this study can provide important lessons for these two instruments, other PES programs, and other conservation and development instruments to support their adequate and sustainable implementation in China and beyond and to contribute to the achievement of relevant SDGs in the remaining years.

Open access
Free access
D. Yvette Wiley
and
Renee A. McPherson

Abstract

Harmful algae and cyanobacteria blooms are increasing in frequency and intensity in freshwater systems due to anthropogenic impacts such as nutrient loading in watersheds and engineered alterations of natural waterways. There are multiple physical factors that affect the conditions in a freshwater system that contribute to optimal habitats for harmful algae and toxin-producing cyanobacteria. A growing body of research shows that climate change stressors also are impacting water-body conditions that favor harmful algae and cyanobacteria species over other phytoplankton. The overgrowth of these organisms, or a “bloom,” increases the opportunity for exposure to toxins by humans, companion animals, livestock, and wildlife. As waters warm and precipitation patterns change over time, exposure to these blooms is projected to increase. Hence, it is important that states and tribes develop monitoring and reporting strategies as well as align governmental policies to protect their citizens and ecosystems within their jurisdiction. Currently, the policies and approaches taken to monitor and report on harmful algae and cyanobacteria blooms vary widely among states, and it is undetermined if any tribes have specific policies on harmful algae blooms. This paper synthesizes research on algal blooms in inland freshwater systems of the United States. This review examines how climate change contributes to trends in bloom frequency or severity and outlines approaches that states and tribes may use to monitor, report, and respond to harmful algae and cyanobacteria blooms.

Significance Statement

Inland bodies of freshwater supply drinking water for humans and animals, water for irrigating crops, habitats for aquatic species, places of cultural significance for Indigenous peoples, and other important functions. Many of these bodies of water have been polluted with runoff from industry, including agriculture, and already support harmful algal blooms during warm conditions. Hot extremes associated with climate change are expected to increase the occurrence and duration of harmful algal blooms, and in some places, initiate blooms where none have been recorded previously. These toxic blooms are harmful to people, companion animals, livestock, and wildlife. It is important to review the interconnections among biological, climate, and water systems to monitor blooms and alert the public about their toxin production.

Open access
Jonathan B. Butcher
,
Mark Fernandez
,
Thomas E. Johnson
,
Afshin Shabani
, and
Sylvia S. Lee

Abstract

Cyanobacteria blooms are an increasing concern in U.S. freshwaters. Such blooms can produce nuisance conditions, deplete oxygen, and alter the food chain, and in some cases they may produce potent toxins, although many factors may modulate the relationships between biomass and toxin production. Cyanobacterial blooms are in turn associated with nutrient enrichment and warm water temperatures. Climate change is expected to increase water temperatures and, in many areas, surface runoff that can transport nutrient loads to lakes. While some progress has been made in short-term prediction of cyanobacterial bloom and toxin risk, the long-term projections of which lakes will become more vulnerable to such events as a result of climate change is less clear because of the complex interaction of multiple factors that affect bloom probability. We address this question by reviewing the literature to identify risk factors that increase lake vulnerability to cyanobacterial blooms and evaluating how climate change may alter these factors across the sample of conterminous U.S. lakes contained in the 2007 National Lakes Assessment. Results provide a national-scale assessment of where and in which types of lakes climate change will likely increase the overall risk of cyanobacterial blooms, rather than finer-scale prediction of expected cyanobacterial and toxin levels in individual lakes. This information can be used to guide climate change adaptation planning, including monitoring and management efforts to minimize the effects of increased cyanobacterial prevalence.

Significance Statement

Cyanobacteria blooms and associated algal toxins are an increasing problem in U.S. freshwater lakes and reservoirs. Climate change may further increase bloom frequency and severity. We survey the literature on relationships between bloom formation and climate. These relationships are combined with projections of future climate and lake response to develop indices of where and in what types of lakes such blooms are most likely to increase relative to current conditions. The results can help to focus monitoring and management measures to mitigate potential impacts on human health, wildlife, and aquatic biota.

Open access
Amy S. Hendricks
,
Uma S. Bhatt
,
Gerald V. Frost
,
Donald A. Walker
,
Peter A. Bieniek
,
Martha K. Raynolds
,
Rick T. Lader
,
Howard E. Epstein
,
Jorge E. Pinzon
,
Compton J. Tucker
, and
Josefino C. Comiso

Abstract

Rapidly warming temperatures in the Arctic are driving increasing tundra vegetation productivity, evidenced in both the satellite derived normalized difference vegetation index (NDVI) imagery and field studies. These trends, however, are not uniformly positive across the circumpolar Arctic. One notable region of negative linear NDVI trends that have persisted over the last 15 years is southwest Alaska’s Yukon–Kuskokwim Delta (YKD). Negative NDVI trends in the YKD region appear inconsistent with our understanding since tundra vegetation is temperature-limited and air temperatures have increased on the YKD. Analysis over a 40-yr record from 1982 to 2021 reveals distinct decadal variability in the NDVI time series, which continues to produce negative linear trends. Similar decadal variability is also evident in summer warmth and 100-km coastal zone spring sea ice concentrations. This suggests that decadal climate variations can dominate the trends of NDVI through their influence on the drivers of tundra vegetation, namely, coastal sea ice concentrations and summer warmth. The relationships among sea ice, summer warmth, and NDVI have changed over the 40-yr record. Seasonality analysis since 1982 shows declining sea ice concentration in spring is followed by trends of increasing temperatures, but weakly declining NDVI during the growing season. An additional key finding is that since early 2010s, the relationships between sea ice concentration and summer warmth, and sea ice concentration and NDVI have strengthened, while the relationship between NDVI and summer warmth has weakened, indicating that temperature may no longer be the primary limiting factor for Arctic tundra vegetation on the YKD.

Significance Statement

This paper addresses a curiosity of regional Arctic climate change, which is that despite increasing temperatures, spatially and temporally declining trends of vegetation productivity on the Yukon–Kuskokwim Delta appear in satellite data. This study bridges our understanding of Arctic climate relationships at varying scales and informs questions about how these relationships may change in the future.

Open access
Douglas Schuster
and
Michael Friedman
Open access
Natalya Kilifarska
,
Tsvetelina Velichkova
, and
Antonia Mokreva

Abstract

Analyses of the Northern Hemisphere’s sea level pressure, air surface temperature, and lower-stratospheric ozone during the period 1900–2019 reveal an existing coherence in their temporal variability. The coherence is heterogeneously distributed over the globe, and the patterns of ozone impact on the pressure and temperature are different. More specifically, the strongest ozone influence on the sea level pressure is found in the main “centers of action”—that is, the Aleutian low and the region of NAO formation. The ozone influence is localized mainly in the latitudinal belt 40°–75°N, where the ozone mixing ratio at 70 hPa is reduced during most of the twentieth century (relative to the first decade of the twenty-first century). This peculiarity of ozone spatial distribution we attribute to the energetic particles trapped in Earth’s radiation belts, activating ion-molecular reactions of ozone production in the region of Regener–Pfotzer ionization maximum. Consequently, the spatial–temporal variations of the lower-atmospheric ionization could be a good explanation for irregularly distributed ozone and its regionally specified impact on the climatic variables.

Significance Statement

We tried to understand the regional character of the Northern Hemisphere’s winter weather conditions. The latter is usually attributed to the North Atlantic Oscillation (NAO), but we actually do not know the factors impacting the NAO variability itself. We found that, at multiannual time scales, the surface pressure is only weakly related to the temperature variations, whereas its correlation with the ozone at 70 hPa is unexpectedly strong—especially in the active regions of the weather phenomena formation. We attribute the ozone variability itself to the variable intensity of energetic particles precipitating in the lower atmosphere—where they activate ion-molecular reactions producing ozone. This finding opens new horizons for understanding the regionality of atmospheric variation at different time scales.

Open access
Greta E. M. Shum
,
Marysa M. Laguë
,
Stephanie S. Rushley
, and
Abigail L. S. Swann

Abstract

We explore the possible role of plant–atmosphere feedbacks in accelerating forest expansion using a simple example of forest establishment. We use an unconventional experimental design to simulate an initial forest establishment and the subsequent response of climate and nearby vegetation. We find that the forest’s existence produces favorable nearby growing-season conditions that would promote forest expansion. Specifically, we consider a hypothetical region of forest expansion in modern Alaska. We find that the forest acts as a source of heat and moisture for plants to the west, leading them to experience earlier springtime temperatures, snowmelt, and growth. Summertime cooling and cloud formation over the forest also drive a circulation change that reduces summertime cloud cover south of the forest, increasing solar radiation reaching plants there and driving warming. By isolating these vegetation–atmosphere interactions as the mechanisms of increased growth, we demonstrate the potential for forest expansion to be accelerated in a way that has not been highlighted before. These simulations illuminate two separate mechanisms that lead to increased plant growth nearby: 1) springtime heat advection and 2) summertime cloud feedbacks and circulation changes; both have implications for our understanding of past changes in forest cover and the predictability of biophysical impacts from afforestation projects and climate change–driven forest-cover changes. By examining these feedbacks, we seek to gain a more comprehensive understanding of past and potential future land–atmosphere interactions.

Significance Statement

This study investigates whether the emergence of a high-latitude forest could influence the way water and energy are exchanged between the land and atmosphere in a way that impacts nearby growing conditions and subsequent forest expansion. We use a computer model to simulate a climate with and without forest establishment in the high latitudes and test the response of plants surrounding the forest to the two different climates. We find that a forest is indeed able to spur neighboring plant growth by modifying regional climate and producing more favorable growing conditions for surrounding vegetation. Specifically, forest establishment can bring better growing conditions to plants adjacent to it by warming the air and altering nearby circulation and cloud cover.

Open access
Felicia Chiang
,
Benjamin I. Cook
, and
Sonali McDermid

Abstract

The moderating influence of irrigation on dry heat extremes is well established, but the effect of irrigation on humid heat is more uncertain. Here, we study the impact of modern irrigation on both dry and humid heat-wave occurrences during the boreal summer using the NASA GISS Earth System Model (ModelE) with and without present-day irrigation. We show that the presence of modern irrigation reduces the total number of dry heat waves in most land areas, especially in arid and temperate regions. In contrast, humid heat waves occur more frequently under modern irrigation, especially in the Mediterranean Sea region, northern Africa, southern Africa, and the Middle East. Present-day irrigation reduces dry heat extremes by favoring latent heating over sensible heating and lowering surface solar radiation by increasing total cloud cover. Meanwhile, modern irrigation drives increases in humid heat through increases in specific humidity and precipitation. Notably, the reduction in dry heat is mostly localized over irrigated grid cells while humid heat increases both in locally irrigated areas and remote (nonirrigated) regions because of widespread increases in humidity associated with irrigation. Our results suggest that irrigation may amplify humid heat, even in nonirrigated areas, highlighting the importance of improving our understanding of both local and remote effects of the irrigation forcing on climate hazards.

Open access