Land System Model Research Articles

Landsystem analysis of temperate non‐surging glaciers on the Mýrdalsjökull Ice Cap, southern Iceland

Glacial deposits are important sources of palaeoclimatic information but not all deposits are formed by processes that reflect the overall climatic conditions of a region; surge‐type glaciers undergo periodic episodes of rapid ice movement, often unrelated to ambient climatic conditions. This study examines the glacier forefields of Öldufellsjökull and western Sléttjökull, two outlet glaciers of the Mýrdalsjökull Ice Cap in southern Iceland, to identify landform characteristics indicative of past episodes of fast flow. Previous studies suggest episodes of fast flow at these glaciers in the past century. Remotely sensed data and field investigations were combined to complete a landsystem analysis of the forefields of these glaciers and an uncrewed aerial vehicle was used to collect high‐resolution imagery of areas of particular interest. Two assemblages of landsystems are identified on each forefield, which pass from streamlined landforms containing abundant flutes close to the glacier to spatially restricted bands of arcuate moraines with associated glaciofluvial and glaciolacustrine deposits more distally. This distribution of landsystem tracts has limited similarity to the current surge‐type glacier landsystem model, suggesting that other processes are controlling the development of landform–sediment assemblages. Using a high‐resolution digital elevation model of an area within the 1984 ice margin, two distinct landform types were identified that were not apparent on the coarse resolution imagery: hummocky moraine and a circular feature hypothesized to have formed as a result of water escape caused by changing hydrological regimes. The forefields of Öldufellsjökull and western Sléttjökull lack many of the characteristics typical of surge‐type landsystems and instead are more similar to the active temperate landsystem common in Iceland.

Optimization of land use to accommodate nutritional transformation of food systems: a case study from the Beijing–Tianjin–Hebei region

The transformation and reconstruction of China’s food system not only faces many risks, such as the unceasing growth of food consumption on the demand side and the structural imbalance of dietary nutrition, but also must address serious challenges, such as constraints of resources, environment, and production capacity on the supply side. The optimal allocation of land use structure is an important method to realizing a transformation of sustainable food systems, achieving the goal of nutrition security, and guiding coordinated spatial development. This study takes the Beijing–Tianjin–Hebei region as an example, analyzing the development trends of the region’s dietary nutrition structure clarifies the objectives for improving dietary nutrition. This study uses comprehensive optimization model and dynamic land system model, exploring land use optimization schemes under different nutritional goals and development scenarios. The result show that the dietary structure in the Beijing–Tianjin–Hebei region is transitioning from “food based” to “intake balance” and gradually evolved to “intake diversity,” with the main objectives being to maintain stable calorie intake while moderately increasing protein intake and reducing fat intake. Achieving this goal will gradually increase demand for cultivated land and intensify spatial competition for land use. However, by optimizing land use allocation, it is possible to free up more spatial resources to balance economic development and ecological protection and reduce land use fragmentation, thereby significantly enhancing regional economic benefits and the value of ecosystem services based on improvements in dietary nutrition.

Bioenergy in Europe is unlikely to make a timely contribution to climate change targets

Increasing bioenergy production is a significant component of European efforts to mitigate climate change, but has contested potential for reducing emissions. We use an integrated land system model to explore the effects of large-scale bioenergy production within the European Union on carbon balances. We find that increased bioenergy crop production is likely to cause substantial deforestation and a commensurate loss of associated carbon stocks largely due to displacement of food production from other areas. Deforestation would occur either within the EU if European forests were not protected, or in other parts of the world arising from indirect land use change if European forests were protected. The net carbon benefit of bioenergy production is largely negative, or uncertain, even under the most optimistic levels of fossil fuel replacement, and will not offset initial carbon losses over the coming 50 yr. The growth of intensive agriculture required to satisfy the demand for bioenergy and food will have negative impacts on crucial ecosystem services. Overall, we identify substantial disadvantages to increasing bioenergy production relative to freeing land for natural succession. At best, large-scale bioenergy production is likely to be irrelevant to time-sensitive climate targets.

Heat waves related to Quasi-Biweekly variability over Southern China in the FGOALS-g3 model

In the present study, we focused on the heat waves (HW) associated with the quasi-biweekly (QBW, 10–20-day period) variability (QBW-HW) over Southern China (SC, 102º–120ºE, 21º–30ºN) in the Flexible Global Ocean–Atmosphere–Land System Model, GridPoint version 3 (FGOALS-g3), and the HW-associated structures and surface air temperature budget investigated by using model outputs from historical experiment of Coupled Model Intercomparison Project Phase 6 (CMIP6). We found that the anomalous circulations related to the QBW-HW events over SC are closely linked to the southeastward propagation of the wave train from mid-high latitudes and the northwestward-propagating disturbances from the tropics. The results also showed that adiabatic and diabatic heating play a key role in the QBW-HW over SC. These results are in good agreement with observations from previous studies. In addition, QBW-HWs are dry in the FGOALS-g3 model, while observed humid HWs occur over SC. The difference is mainly due to the new boundary layer scheme incorporated in the FGOALS-g3 model, which overestimates the entrainment process at the top of the boundary layer during the QBW-HW over SC, resulting in more and drier air into the boundary layer, and thus less moisture. It implies that the entrainment equation at the top of the boundary layer in the FGOALS-g3 model does need to be improved to be suitable for humid HW processes, although the boundary layer scheme can improve the model precipitation and radiative forcing.

Past glaciation of temperate‐continental mountains: A model for a debris‐charged plateau icefield/cirque glacier landsystem in the Southern Carpathians, Romania

AbstractReconstructing the extent, style, timing and drivers of past mountain glaciation is crucial in both understanding past atmospheric circulation and predicting future climate change. Unlike in high‐elevation mountains situated in maritime and continental climates, less is known of past glaciation in mid‐altitude mountains, located in transitional climates, such as the Southern Carpathians of Romania. Despite these mountains harbouring a rich glacial geomorphology, this has never been systematically mapped according to well‐established morphological criteria, nor confidently related to former styles of glaciation. Therefore, filling this gap is important for not only accurately identifying glacial extents but also for establishing past glaciation styles and relating them to past ice dynamics and climate. Here, we devise the first glacial landsystem model for the Southern Carpathians, to enhance our understanding of the glaciation style and dynamics of past mountain glaciers in temperate‐continental climates. We present a geomorphological map, from which we infer the spatial and temporal evolution of glacial, periglacial and paraglacial landforms. We then assess the links between the mountain geomorphology and glaciation style and dynamics to construct a glacial landsystem model for debris‐charged plateau icefields and cirque glaciers in temperate‐continental mountain settings.

Mapping the shared socio-economic pathways onto the Nature Futures Framework at the global scale

AbstractThe Nature Futures Framework (NFF) was developed for the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) to explore scenarios that represent a diversity of positive relationships between humans and nature. Widely used in global environmental assessments, the shared socio-economic pathways (SSPs) in combination with the representative concentration pathways (RCPs) were developed for climate change assessments. However, the relationship at a global level between the SSP–RCP scenario outcomes and the framing of the NFF around three value perspectives—Nature for Nature, Nature for Society, and Nature as Culture—has not been established. Here, we demonstrate a method to map onto the NFF value perspectives results from alternative SSP scenarios, each paired with an RCP consistent with the SSP storyline. For each of the NFF value perspectives, multiple elements were identified, each represented by one or more nature-focused indicators. Values for these indicators, for the different SSP scenario outcomes, were derived from an existing application of a global land system model, LandSyMM. A score for each indicator is estimated by comparing the indicator values against a normative target range. We find that only SSP1 provides greater benefits for Nature as Culture and Nature for Society relative to a 2010 baseline. Overall, the SSP scenarios provide fewer benefits for Nature for Nature, consistent with a bias towards the provision of material over non-material ecosystem services. The results demonstrate that the SSP–RCP scenario framing captures some, but not all, of the dimensions of nature and that alternative scenario framings, such as the NFF, are needed to study a broader range of biodiversity and ecosystem related questions as well as exploring positive futures.

Uncertainty in land-use adaptation persists despite crop model projections showing lower impacts under high warming

Climate change is expected to impact crop yields and alter resource availability. However, the understanding of the potential of agricultural land-use adaptation and its costs under climate warming is limited. Here, we use a global land system model to assess land-use-based adaptation and its cost under a set of crop model projections, including CO2 fertilization, based on climate model outputs. In our simulations of a low-emissions scenario, the land system responds through slight changes in cropland area in 2100, with costs close to zero. For a high emissions scenario and impacts uncertainty, the response tends toward cropland area changes and investments in technology, with average adaptation costs between −1.5 and +19 US$05 per ton of dry matter per year. Land-use adaptation can reduce adverse climate effects and use favorable changes, like local gains in crop yields. However, variance among high-emissions impact projections creates challenges for effective adaptation planning.

Structural succession of land resources under the influence of different policies: A case study for Shanxi Province, China

The increased focus on land resources is a result of global climate change. For human life and progress, land resources provide a key foundation. Using land resources under sensible regulations can enable sustainable development in order to better adapt to climate change. In this study, we used the Malmquist index to compute the outcomes and spatial distribution of land use efficiency in Shanxi Province during 2006–2019. According to the findings, ecologically vulnerable areas have less efficient land use than areas with rapid economic growth. Therefore, to more effectively resolve the tensions between economic development and ecological conservation and to provide scientific guidance to decision makers, we need to model future land use in Shanxi Province driven by socio-economic systems. To predict future land use demand and its spatial distribution under the influence of socio-economic and government policies, this study combines the Computable General Equilibrium of Land Use Change (CGELUC) model and Dynamics of Land System (DLS) model. Under the green development scenario, the reduction rates of forest land and grassland are 2.09 % and 1.65 %, respectively, which is the slowest reduction of ecological land among the three scenarios. Development of ecological land such as forests and grasslands are severely prohibited by government regulations. The lowest carbon sequestration reduction rate of 1.62 % is registered in Shanxi Province under the green development scenario. Construction land increases more quickly under the economic priority development scenario, with a growth rate of 33.02 %. Ecological land, including grasslands and forests, is declining. Under the scenario of economic development priority, the ecological land in Shanxi Province will inevitably be sacrificed. Therefore, the government should strive to actively overcome barriers to the development of land resources for ecological protection as this is a key region for that purpose.

Assessing the quality of land system models: moving from valibration to evaludation

Assessing the quality of land system models: moving from valibration to evaludation

Hybrid forecasting: blending climate predictions with AI models

Abstract. Hybrid hydroclimatic forecasting systems employ data-driven (statistical or machine learning) methods to harness and integrate a broad variety of predictions from dynamical, physics-based models – such as numerical weather prediction, climate, land, hydrology, and Earth system models – into a final prediction product. They are recognized as a promising way of enhancing the prediction skill of meteorological and hydroclimatic variables and events, including rainfall, temperature, streamflow, floods, droughts, tropical cyclones, or atmospheric rivers. Hybrid forecasting methods are now receiving growing attention due to advances in weather and climate prediction systems at subseasonal to decadal scales, a better appreciation of the strengths of AI, and expanding access to computational resources and methods. Such systems are attractive because they may avoid the need to run a computationally expensive offline land model, can minimize the effect of biases that exist within dynamical outputs, benefit from the strengths of machine learning, and can learn from large datasets, while combining different sources of predictability with varying time horizons. Here we review recent developments in hybrid hydroclimatic forecasting and outline key challenges and opportunities for further research. These include obtaining physically explainable results, assimilating human influences from novel data sources, integrating new ensemble techniques to improve predictive skill, creating seamless prediction schemes that merge short to long lead times, incorporating initial land surface and ocean/ice conditions, acknowledging spatial variability in landscape and atmospheric forcing, and increasing the operational uptake of hybrid prediction schemes.

Role of Ocean Initialization in Skillful Prediction of Sahel Rainfall on the Decadal Time Scale

Abstract Sahel summer rainfall has undergone persistent drought from the 1970s to 1980s, causing severe human life and economic losses. Many studies pointed out that the decadal variations of Sahel rainfall are mainly modulated by low-frequency sea surface temperature (SST) variations in different ocean basins. However, how this modulation contributes to the decadal prediction skill of Sahel rainfall remains unknown. This study provided an affirmative response using the decadal hindcasts initialized by a dimensional-reduced projection four-dimensional variational (DRP-4DVar) data assimilation method to incorporate only ocean analysis data into the gridpoint version 2 of the Flexible Global Ocean–Atmosphere–Land System Model (FGOALS-g2). The hindcasts reveal the benefits of the DRP-4DVar approach for improving the Sahel rainfall decadal prediction skill measured by the anomaly correlation coefficient (ACC), root-mean-square error, ACC difference, and mean square skill score. The decadal variations of SSTs in the Atlantic, Mediterranean Sea, Indian Ocean, and Pacific as well as correct representations of the associated Sahel rainfall–SST relationships are well predicted, thus leading to skillful predictions of Sahel rainfall. In particular, the initialization of SSTs in the Atlantic and Mediterranean Sea plays a more important role in skillful Sahel rainfall predictions than in the other basins. The prediction skill of Sahel rainfall by the FGOALS-g2 prediction system is significantly higher than those by most phase 5 and 6 of the Coupled Model Intercomparison Project (CMIP5&6) prediction systems initialized only with ocean analysis data. This result is likely attributed to a more accurate relationship between Sahel rainfall and SST by the FGOALS-g2 prediction system than by the CMIP5&6 prediction systems. Significance Statement Previous studies have shown limited success in predicting Sahel rainfall. By using an advanced coupled data assimilation method constrained only by ocean observational data, we achieve a high decadal prediction skill for Sahel rainfall. The successful prediction is attributed to accurately predicted decadal variations of sea surface temperatures in the Atlantic, Mediterranean Sea, Indian Ocean, and Pacific as well as their relationships with Sahel rainfall. Our results can provide references for future decadal predictions of Sahel rainfall and motivate the need to evaluate the contributions of the initialization of the ocean versus the other climate components (e.g., atmosphere or land) to Sahel rainfall predictions.

Exploring the effects of protected area networks on the European land system

The European Union's Biodiversity Strategy for 2030 seeks to protect 30% of land, with 10% under strict protection, while building a transnational nature network. We explore the effects of the Biodiversity Strategy targets for land use and ecosystem services across the European land system. To do so, we propose a novel approach, combining a methodological framework for improving green network connectivity with an EU-wide land system model. We identify an improved network of EU protected areas consistent with the 2030 targets, and explore its effects under different levels of protection and in a range of paired climatic and socio-economic scenarios. The existing network of protected areas is highly fragmented, with more than one third of its nodes being isolated. We find that prioritizing connectivity when implementing new protected areas could achieve the strategy's targets without compromising the future provision of ecosystem services, including food production, in Europe. However, we also find that EU-wide distributions of land uses and ecosystem services are influenced by the protected area network, and that this influence manifests differently in different climatic and socio-economic scenarios. Varying the strength of protection of the network had limited effects. Extractive services (food and timber production) decreased in protected areas, but non-extractive services increased, with compensatory changes occurring outside the network. Changes were small where competition for land was low and scenario conditions were benign, but became far larger and more extensive where competition was high and scenario conditions were challenging. Our findings highlight the apparent achievability of the EU's protected area targets, but also the need to account for adaptation in the wider land system and its consequences for spatial and temporal patterns of ecosystem services provision now and in the future.

UniFHy v0.1.1: a community modelling framework for the terrestrial water cycle in Python

Abstract. The land surface, hydrological, and groundwater modelling communities all have expertise in simulating the hydrological processes at play in the terrestrial component of the Earth system. However, these communities, and the wider Earth system modelling community, have largely remained distinct with limited collaboration between disciplines, hindering progress in the representation of hydrological processes in the land component of Earth system models (ESMs). In order to address key societal questions regarding the future availability of water resources and the intensity of extreme events such as floods and droughts in a changing climate, these communities must come together and build on the strengths of one another to produce next-generation land system models that are able to adequately simulate the terrestrial water cycle under change. The development of a common modelling infrastructure can contribute to stimulating cross-fertilisation by structuring and standardising the interactions. This paper presents such an infrastructure, a land system framework, which targets an intermediate level of complexity and constrains interfaces between components (and communities) and, in doing so, aims to facilitate an easier pipeline between the development of (sub-)community models and their integration, both for standalone use and for use in ESMs. This paper first outlines the conceptual design and technical capabilities of the framework; thereafter, its usage and useful characteristics are demonstrated through case studies. The main innovations presented here are (1) the interfacing constraints themselves; (2) the implementation in Python (the Unified Framework for Hydrology, unifhy); and (3) the demonstration of standalone use cases using the framework. The existing framework does not yet meet all our goals, in particular, of directly supporting integration into larger ESMs, so we conclude with the remaining limitations of the current framework and necessary future developments.

Valuation of Land-Use/Land-Cover-Based Ecosystem Services in Afghanistan—An Assessment of the Past and Future

Being one of the weakest economies in the world, livelihoods in Afghanistan remain highly dependent on local ecosystem services. However, the risk of ecosystem services degradation in Afghanistan over the past two decades has significantly increased, mainly due to rapid changes in land-use and land-cover (LULC). As such, policy makers must be able to estimate the impact of LULC changes on various ecosystem services. By utilizing GlobeLand30 land cover products for 2000, 2010 and 2020, and by adopting the value transfer method, this study assessed the ecosystem services value (ESV) changes in response to the changes of LULC in Afghanistan. Additionally, the dynamics of the land system (DLS) model was innovatively coupled with linear programming to predict likely scenarios of ESV changes by 2030. The predicted results were also validated against actual land cover and achieved a Kappa value of 0.78. The results showed that over the 20-year period, ecologically important LULC categories such as forest, water bodies and grassland were severely unstable and rapidly decreasing in scope. These LULC types were being threatened by agricultural, built-up and unused lands. During this period, we estimated a decrease in the total ESV from 161 billion USD in 2000 to 152.27 billion USD in 2020. About 92% of this decrease was shared by supporting and provisioning services. The simulated scenarios also showed that ESV will likely further decrease under Business-As-Usual (BAU), and Rapid Economic Development (RED) scenarios. Positively, an Environmental Protection (ENP) scenario is predicted, with a 4.5% increase in ESV by 2030. However, achieving this scenario requires the enforcement of strict environmental protection measures.

Evaluation of the interannual variability in the East Asian summer monsoon in AMIP and historical experiments of CAS FGOALS-f3-L

The evaluation of East Asian summer monsoon (EASM) simulations could improve our understanding of Asian monsoon dynamics and climate simulations. In this study, by using Phase 6 of the Coupled Model Intercomparison Project (CMIP6) experiments of the Atmospheric Model Intercomparison Project (AMIP) and historical runs of the Chinese Academy of Sciences (CAS) Flexible Global Ocean–Atmosphere–Land System (FGOALS-f3-L) model, the model simulation skill for the interannual variability in the EASM was determined. According to multivariate empirical orthogonal function (MV-EOF) analysis, the major mode of the EASM mainly emerged as a Pacific-Japan pattern in the western Pacific accompanied by a local anticyclonic anomaly with a total variance of 24.6%. The historical experiment could suitably reproduce this spatial pattern and attained a closer total variance than that attained by the AMIP experiment. The historical experiment could also better simulate the time frequency of the EASM variability than the AMIP experiment. However, the phase of principal component 1 (PC1) was not suitably reproduced in the historical experiment since no initialization procedure was applied at the beginning of the integration in the historical simulation process, whereas the sea surface temperature (SST) was preset in the AMIP experiment. Further analysis revealed that air–sea interactions in the Indian Ocean and tropical western Pacific were important for the model to provide satisfactory EASM simulations, while El Niño–Southern Oscillation (ENSO) simulation was possibly related to the climate variability in the EASM simulations, which should be further analyzed.摘要对东亚夏季季风(EASM)模拟的评估可以提高我们对亚洲季风动力和气候模拟的理解. 在这项研究中, 通过使用中国科学院(CAS)全球海洋-大气-陆地系统(FGOALS-f3-L)模式参加的第六次耦合模式相互比较计划(CMIP6)中的大气模式相互比较计划(AMIP)和历史(historical)试验, 明确了EASM的年际变率的模拟能力. 通过多变量经验正交函数(MV-EOF)分析发现, 观测的EASM的主导模态为西太平洋上的太平洋-日本模态, 并伴有局部反气旋异常. 主导模态的方差贡献率为24.6%. 历史(historical)试验可以基本再现这种空间模态, 其方差贡献率较AMIP试验更接近于观测. 与AMIP试验相比, 历史(historical)试验还能更好地模拟EASM变率的时间频率. 然而, 由于历史(historical)模拟没有在积分开始时应用初始化过程, 而AMIP试验受到海表面温度(SST)的约束, 因此主成分(PC1)的位相在历史(historical)试验中没有得到较好地再现. 进一步分析发现, 印度洋和西太平洋热带地区的海气相互作用对EASM的模拟非常重要, 而EASM气候变率的模拟可能与厄尔尼诺-南方涛动(ENSO)的模拟能力有关, 这值得进一步分析.

Land use change and carbon emissions of a transformation to timber cities

Using engineered wood for construction has been discussed for climate change mitigation. It remains unclear where and in which way the additional demand for wooden construction material shall be fulfilled. Here we assess the global and regional impacts of increased demand for engineered wood on land use and associated CO2 emissions until 2100 using an open-source land system model. We show that if 90% of the new urban population would be housed in newly built urban mid-rise buildings with wooden constructions, 106 Gt of additional CO2 could be saved by 2100. Forest plantations would need to expand by up to 149 Mha by 2100 and harvests from unprotected natural forests would increase. Our results indicate that expansion of timber plantations for wooden buildings is possible without major repercussions on agricultural production. Strong governance and careful planning are required to ensure a sustainable transition to timber cities even if frontier forests and biodiversity hotspots are protected.

Geomorphic and sedimentary signatures of catastrophic glacier detachments: A first assessment from Flat Creek, Alaska

Large-volume detachments of low-angle mountain glaciers involve the sudden mobilization of large amounts of glacier ice and lithic material in long-runout mass flows. Scientific investigations of these events have only recently brought to light their global occurrence and the similarities in the conditions under which they occur. While this recent research suggests that glacier detachments may become more frequent in a warming climate, a long-term record is largely lacking. Knowledge of the geomorphic signatures of glacier detachments could help establish such a record. Here, we present the first geomorphic and sedimentary assessment of a glacier detachment deposit. We investigate the landscape impacts of the Flat Creek glacier detachments in Alaska's St. Elias mountains through a combination of remote sensing analyses, field observations, Electrical Resistivity Tomography, and grain size and grain orientation analyses. From these data, we outline a land-system model that may help identify past glacier detachments elsewhere. Some of the most distinguishing features we documented were large bodies of buried ice-conglomerates, a rapid response of the remnant glacier ice, clusters of small-scale thermokarst ponds, countless molards, parallel striations etched into the hillslope and individual clasts, and a very long runout distance. We assess these features in terms of their longevity in the landscape and compare them to what has been described at glacier detachment sites elsewhere. Finally, we discuss to what extent glacier detachment deposits can be distinguished from deposits left by rock(−ice) avalanches, debris flows, and surging glaciers, and show that a differentiation is possible if detailed field investigations are undertaken.

Reforming China’s fertilizer policies: implications for nitrogen pollution reduction and food security

Reactive nitrogen (N) is a requisite nutrient for agricultural production, but results in greenhouse gas and air and water pollution. The environmental and economic impacts of N fertilizer use in China are particularly relevant, as China consumes the largest amount of N fertilizer in the world to meet its soaring food demand. Here, we use an agro-economic land system model (MAgPIE) in combination with a difference-in-differences econometric model to provide a forward-looking assessment of China’s fertilizer policies in terms of removing fertilizer manufacturing subsidies and implementing measures to improve agricultural nutrient management efficiency. Our model results indicate that enhancing soil N uptake efficiency and manure recycled to soil alongside fertilizer subsidy removal can largely reduce N fertilizer use and N losses and abate N pollution in the short and long term, while food security remains largely unaffected. Enhancing soil N uptake efficiency appears to be decisive to achieving China’s national strategic target of zero growth in N fertilizer use. This study also finds that improving agricultural nutrient management efficiency contributes to higher land productivity and less cropland expansion, with substantial benefits for the environment and food security.

Dynamic and Thermal Effects of the Tibetan and Iranian Plateaus on the Northward-Propagating Intraseasonal Oscillation during Boreal Summer

Abstract This study investigates the dynamic and thermal effects of the Tibetan and Iranian Plateaus (TIP) on the characteristics of the northward-propagating boreal summer intraseasonal oscillation (BSISO) and reveals associated physical mechanisms. The relative importance of the Tibetan Plateau (TP) and Iranian Plateau (IP) to the northward propagation of BSISO is also detected. The findings are based on comparative analyses of the control run and six sensitivity experiments using the atmospheric model component of CAS FGOALS-f3-L (the low-resolution version of the Chinese Academy of Sciences Flexible Global Ocean–Atmosphere–Land System model, finite-volume version 3). It is demonstrated that the absence of TIP surface sensible heat or terrain restricts the occurrence of upper-level easterly and lower-level westerly anomalies, as well as moisture convergence over the Asian summer monsoon (ASM) region, which leads to a weakened easterly vertical wind shear with a narrowed range and the generation of a negative meridional specific humidity gradient in the northern Bay of Bengal. These mean-state changes are not conducive to the formation of positive barotropic vorticity together with planetary boundary layer moisture convergence to the north of the convective center, thus impeding the northward propagation of the BSISO. Results indicate that the combined TIP area, via its dynamic and thermal effects, modulates the northward-propagating BSISO by directly affecting the vertical wind shear and meridional moisture gradient in the northern Indian Ocean. By contrast, the TP plays a decisive role in the BSISO northward propagation due to the limited dynamic and thermal effects of IP on the background circulation and water vapor convergence over the ASM region.

Evaluating the Nature and Extent of Changes to Climate Sensitivity Between FGOALS‐g2 and FGOALS‐g3

AbstractEquilibrium climate sensitivity (ECS) and its related feedbacks are important metrics that can be used to measure the global mean surface temperature change in future climate projections, and the cloud feedback (CF) is considered to be the main contributor to ECS uncertainties. However, the use of different CF methods significantly affects the CF amplitudes, and the sign of the CF may also change. Combining the radiative kernel approach with a simplified CF method, the differences in the ECS and associated feedbacks between two versions of the Flexible Global Ocean–Atmosphere–Land System model (i.e., FGOALS‐g2 and FGOALS‐g3) were analyzed. Results show that the ECS of FGOALS‐g3 is smaller than that of FGOALS‐g2 (2.8 vs. 3.3 K). The main feedback processes that contribute to the ECS change in FGOALS‐g3 are the weaker surface albedo feedback and stronger negative shortwave CF. The reduced surface albedo feedback in FGOALS‐g3 can be attributed mainly to the differences in the simulations of sea ice area, surface temperature, and the Atlantic Meridional Overturning Circulation, as well as their interactions, compared with FGOALS‐g2. The enhanced negative shortwave CF in FGOALS‐g3 is directly related to the strengthened feedback of cloud area fraction and liquid water path. Furthermore, these changes can be traced back to the different atmospheric moist processes, parameter tuning, ocean grid, and external forcings used in FGOALS‐g3, as these all affect the mean climate state of the model.