Climate research must sharpen its view

Potential dynamic changes of single-season rice planting suitability across China

As an important food crop in China, changes in suitable areas for rice planting are critical to agricultural production. In this study, the maximum entropy model (MaxEnt) was utilized to pick the main climatic factors affecting single-season rice planting distribution and project the potential changes under RCP4.5 and RCP8.5 scenarios. It was clear that rice planting distribution was significantly affected by annual total precipitation, the accumulated temperature during a period in which daily temperature was ≥ 10 °C, the moisture index, total precipitation during April-September, and continuous days during the period of daily temperature ≥ 18 °C, with their contribution being 97.6%. There was a continuous decrease in the area of good and high suitability for rice planting projected from 2021-2040 to 2061-2080, with a respective value ranging from 1.49 × 10⁶ km² to 0.93 × 10⁶ km² under the RCP4.5 scenario and from 1.42 × 10⁶ km² to 0.66 × 10⁶ km² under RCP8.5 scenarios. In 2081-2100, there was a bit increase in the area of good and high suitability under the RCP4.5 scenario. The most significant increases in good and high suitability were detected in Northeast China, while obvious decreases were demonstrated in the Yangtze River Basin which might be exposed to extreme temperature threat. The spatial potential planting center was characterized by the largest planting area in 25°N-37°N and 98°E-134°E. The north boundary and center of rice cultivation arose to 53.5°N and 37.52°N, respectively. These potential distributions for single-season rice under future climate change can provide a theoretical basis for optimizing rice planting layout, improving cultivation, and adjusting variety and management systems in response to climate change.

Climate change impact on major crop yield and water footprint under CMIP6 climate projections in repeated drought and flood areas in Thailand

Understanding crop yield and water requirements in response to the future climate at the local scale is essential to develop more precise and appropriate adaptation strategies. From this perspective, repeated drought and flood events in the lower north of Thailand were investigated. The objectives of the study were to evaluate the impact of climate change on major crop yields and the water footprint (WF). Five global circulation model datasets from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), known as Shared Socioeconomic Pathways (SSPs), were selected. Three future periods: near (2015-2039), mid (2040-2069), and far future (2070-2100) under SSP245 and SSP585 scenarios were used to predict the major crop yields and WF changes in the future. The precipitation and maximum and minimum temperatures were projected to increase in all periods under both scenarios. Rice yields in irrigated areas were predicted to rise gradually over the three projection periods under SSP245 but decline in mid and far-future periods under SSP585. There was a predicted reduction of first and second rice crop yields by -6.0% to -17.7% under SSP585. Fortunately, those rice yields were expected to increase in the near-future period under SSP245 by 3.0% to 4.3%. Growing maize, soybean, or mung bean instead of a second rice crop will have a less negative impact on future climate change. Changing from growing rice to be planting maize twice per year and growing cassava had increased favorability in rain-fed areas. The WF changes in the future were associated with future crop yield changes; therefore, the decrease in WFs was due to an increase in crop yield and vice-versa. The total WFs of maize, soybean, mung bean, and cassava production were roughly half that of rice production, indicating that these crops are suitable alternatives in the dry season.

Climate change: what we know and what not

There is ample scientific knowledge about climate change which is assessed at a frequency of about once every seven years by large, international groups of scientists in the comprehensive reports of the Intergovernmental Panel on Climate Change (IPCC). This presentation attempts a short and digestible summary of the certainties and uncertainties existing about the physics of climate change. For my summary, I strongly rely on the contribution of IPCC’s working group 1 to the most recent IPCC assessment report that was published in 2021. To set the stage, I first present some basics about climate and climate modeling before summarizing the current state of knowledge and then providing a few personal conclusions.

Quantifying uncertainty in aggregated climate change risk assessments

High-level assessments of climate change impacts aggregate multiple perils into a common framework. This requires incorporating multiple dimensions of uncertainty. Here we propose a methodology to transparently assess these uncertainties within the 'Reasons for Concern' framework, using extreme heat as a case study. We quantitatively discriminate multiple dimensions of uncertainty, including future vulnerability and exposure to changing climate hazards. High risks from extreme heat materialise after 1.5-2 °C and very high risks between 2-3.5 °C of warming. Risks emerge earlier if global assessments were based on national risk thresholds, underscoring the need for stringent mitigation to limit future extreme heat risks.

Radial variations in xylem sap flux in a temperate red pine plantation forest

BACKGROUND

Scaling sap flux measurements to whole-tree water use or stand-level transpiration is often done using measurements conducted at a single point in the sapwood of the tree and has the potential to cause significant errors. Previous studies have shown that much of this uncertainty is related to (i) measurement of sapwood area and (ii) variations in sap flow at different depths within the tree sapwood.

RESULTS

This study measured sap flux density at three depth intervals in the sapwood of 88-year-old red pine (Pinus resinosa) trees to more accurately estimate water-use at the tree- and stand-level in a plantation forest near Lake Erie in Southern Ontario, Canada. Results showed that most of the water transport (65%) occurred in the outermost sapwood, while only 26% and 9% of water was transported in the middle and innermost depths of sapwood, respectively.

CONCLUSIONS

These results suggest that failing to consider radial variations in sap flux density within trees can lead to an overestimation of transpiration by as much as 81%, which may cause large uncertainties in water budgets at the ecosystem and catchment scale. This study will help to improve our understanding of water use dynamics and reduce uncertainties in sap flow measurements in the temperate pine forest ecosystems in the Great Lakes region and help in protecting these forests in the face of climate change.

Spatial co-localisation of extreme weather events: a clear and present danger

Extreme weather events have become a dominant feature of the narrative surrounding changes in global climate with large impacts on ecosystem stability, functioning and resilience; however, understanding of their risk of co-occurrence at the regional scale is lacking. Based on the UK Met Office's long-term temperature and rainfall records, we present the first evidence demonstrating significant increases in the magnitude, direction of change and spatial co-localisation of extreme weather events since 1961. Combining this new understanding with land-use data sets allowed us to assess the likely consequences on future agricultural production and conservation priority areas. All land-uses are impacted by the increasing risk of at least one extreme event and conservation areas were identified as the hotspots of risk for the co-occurrence of multiple event types. Our findings provide a basis to regionally guide land-use optimisation, land management practices and regulatory actions preserving ecosystem services against multiple climate threats.

Coral reef islands can accrete vertically in response to sea level rise

Increased flooding due to sea level rise (SLR) is expected to render reef islands, defined as sandy or gravel islands on top of coral reef platforms, uninhabitable within decades. Such projections generally assume that reef islands are geologically inert landforms unable to adjust morphologically. We present numerical modeling results that show reef islands composed of gravel material are morphodynamically resilient landforms that evolve under SLR by accreting to maintain positive freeboard while retreating lagoonward. Such island adjustment is driven by wave overtopping processes transferring sediment from the beachface to the island surface. Our results indicate that such natural adaptation of reef islands may provide an alternative future trajectory that can potentially support near-term habitability on some islands, albeit with additional management challenges. Full characterization of SLR vulnerability at a given reef island should combine morphodynamic models with assessments of climate-related impacts on freshwater supplies, carbonate sediment supply, and future wave regimes.

The scientific challenge of understanding and estimating climate change

Given the slow unfolding of what may become catastrophic changes to Earth's climate, many are understandably distraught by failures of public policy to rise to the magnitude of the challenge. Few in the science community would think to question the scientific response to the unfolding changes. However, is the science community continuing to do its part to the best of its ability? In the domains where we can have the greatest influence, is the scientific community articulating a vision commensurate with the challenges posed by climate change? We think not.

On the need to integrate uncertainty into U.S. water resource planning

A changing climate is expected to introduce uncertainty into water resource management decision making. We examined the latest publicly-available, state-level guidance regarding the management of water supplies and demands concerning risks associated with drought, flooding, and climate change. We found state-level guidance supplementing the federally-backed flood mitigation program to be updated most regularly (54% in the last 5 years; 84% in the last decade). Yet, the underlying floodplain mapping data these local planning efforts rely on are acknowledged by the Federal Emergency Management Agency (FEMA) to be chronically outdated. Drought planning guidance was found to be most outdated (16% last updated in the last 5 years; 18% almost two decades ago), and across the U.S., almost universally (94%) reactive (emergency response) rather than proactive (mitigation or management). Although 79-94% of states provide some level of guidance regarding water supply and demand, the projections themselves may significantly predate the guidance. Many (70%) U.S. states still lack climate change impact guidance, particularly non-coastal states and those impacted by increased water scarcity rather than flooding. Strategies are rare (4%) for addressing the impacts of increased variability and uncertainty to meet inelastic demands with finite supplies. We conclude significant gaps exist in planning to address known or projected risks of climate-related impacts. Specific recommendations, including the implementation of a nationwide water census, are provided to improve both the data and knowledge base of water management and reduce current vulnerabilities.

Causal Reasoning: Towards Dynamic Predictive Models for Runoff Temporal Behavior of High Dependence Rivers

Nowadays, a noteworthy temporal alteration of traditional hydrological patterns is being observed, producing a higher variability and more unpredictable extreme events worldwide. This is largely due to global warming, which is generating a growing uncertainty over water system behavior, especially river runoff. Understanding these modifications is a crucial and not trivial challenge that requires new analytical strategies like Causality, addressed by Causal Reasoning. Through Causality over runoff series, the hydrological memory and its logical time-dependency structure have been dynamically/stochastically discovered and characterized. This is done in terms of the runoff dependence strength over time. This has allowed determining and quantifying two opposite temporal-fractions within runoff: Temporally Conditioned/Non-conditioned Runoff (TCR/TNCR). Finally, a successful predictive model is proposed and applied to an unregulated stretch, Mijares river catchment (Jucar river basin, Spain), with a very high time-dependency behavior. This research may have important implications over the knowledge of historical rivers´ behavior and their adaptation. Furthermore, it lays the foundations for reaching an optimum reservoir dimensioning through the building of predictive models of runoff behavior. Regarding reservoir capacity, this research would imply substantial economic/environmental savings. Also, a more sustainable management of river basins through more reliable control reservoirs’ operation is expected to be achieved.

Predicting the variable ocean carbon sink

Strong decadal variations in the oceanic uptake of carbon dioxide (CO₂) observed over the past three decades challenge our ability to predict the strength of the ocean carbon sink. By assimilating atmospheric and oceanic observational data products into an Earth system model-based decadal prediction system, we can reproduce the observed variations of the ocean carbon uptake globally. We find that variations of the ocean CO₂ uptake are predictable up to 2 years in advance globally, albeit there is evidence for a higher predictive skill up to 5 years regionally. We further suggest that while temperature variations largely determine shorter-term (<3 years) predictability, nonthermal drivers are responsible for longer-term (>3 years) predictability, especially at high latitudes.

Twentieth century redistribution in climatic drivers of global tree growth

Energy and water limitations of tree growth remain insufficiently understood at large spatiotemporal scales, hindering model representation of interannual or longer-term ecosystem processes. By assessing and statistically scaling the climatic drivers from 2710 tree-ring sites, we identified the boreal and temperate land areas where tree growth during 1930-1960 CE responded positively to temperature (20.8 ± 3.7 Mio km²; 25.9 ± 4.6%), precipitation (77.5 ± 3.3 Mio km²; 96.4 ± 4.1%), and other parameters. The spatial manifestation of this climate response is determined by latitudinal and altitudinal temperature gradients, indicating that warming leads to geographic shifts in growth limitations. We observed a significant (P < 0.001) decrease in temperature response at cold-dry sites between 1930-1960 and 1960-1990 CE, and the total temperature-limited area shrunk by -8.7 ± 0.6 Mio km². Simultaneously, trees became more limited by atmospheric water demand almost worldwide. These changes occurred under mild warming, and we expect that continued climate change will trigger a major redistribution in growth responses to climate.

Flood Hazard Assessment Supported by Reduced Cost Aerial Precision Photogrammetry

Increasing flood hazards worldwide due to the intensification of hydrological events and the development of adaptation-mitigation strategies are key challenges that society must address. To minimize flood damages, one of the crucial factors is the identification of flood prone areas through fluvial hydraulic modelling in which a detailed knowledge of the terrain plays an important role for reliable results. Recent studies have demonstrated the suitability of the Reduced Cost Aerial Precision Photogrammetry (RC-APP) technique for fluvial applications by accurate-detailed-reliable Digital Terrain Models (DTMs, up to: ≈100 point/m2; vertical-uncertainty: ±0.06 m). This work aims to provide an optimal relationship between point densities and vertical-uncertainties to generate more reliable fluvial hazard maps by fluvial-DTMs. This is performed through hydraulic models supported by geometric models that are obtained from a joint strategy based on Structure from Motion and Cloth Simulation Filtering algorithms. Furthermore, to evaluate vertical-DTM, uncertainty is proposed as an alternative approach based on the method of robust estimators. This offers an error dispersion value analogous to the concept of standard deviation of a Gaussian distribution without requiring normality tests. This paper reinforces the suitability of new geomatic solutions as a reliable-competitive source of accurate DTMs at the service of a flood hazard assessment.

Patterns of island change and persistence offer alternate adaptation pathways for atoll nations

Sea-level rise and climatic change threaten the existence of atoll nations. Inundation and erosion are expected to render islands uninhabitable over the next century, forcing human migration. Here we present analysis of shoreline change in all 101 islands in the Pacific atoll nation of Tuvalu. Using remotely sensed data, change is analysed over the past four decades, a period when local sea level has risen at twice the global average (~3.90 ± 0.4 mm.yr-1). Results highlight a net increase in land area in Tuvalu of 73.5 ha (2.9%), despite sea-level rise, and land area increase in eight of nine atolls. Island change has lacked uniformity with 74% increasing and 27% decreasing in size. Results challenge perceptions of island loss, showing islands are dynamic features that will persist as sites for habitation over the next century, presenting alternate opportunities for adaptation that embrace the heterogeneity of island types and their dynamics.

The Potential Impacts of Climate Change on Biodiversity in Flowing Freshwater Systems

Ongoing increases in air temperature and changing precipitation patterns are altering water temperatures and flow regimes in lotic freshwater systems, and these changes are expected to continue in the coming century. Freshwater taxa are responding to these changes at all levels of biological organization. The generation of appropriate hydrologic and water temperature projections is critical to accurately predict the impacts of climate change on freshwater systems in the coming decade. The goal of this review is to provide an overview of how changes in climate affect hydrologic processes and how climate-induced changes in freshwater habitat can impact the life histories and traits of individuals, and the distributions of freshwater populations and biodiversity. Projections of biological responses during the coming century will depend on accurately representing the spatially varying sensitivity of physical systems to changes in climate, as well as acknowledging the spatially varying sensitivity of freshwater taxa to changes in environmental conditions.