Tropical Land Research Articles

Contrasting Response of Mesoscale Convective Systems Occurrence Over Tropical Land and Ocean to Increased Sea Surface Temperature

AbstractMesoscale convective systems (MCSs) are pivotal in global energy/water cycles and typically produce extreme weather events. Despite their importance, our understanding of their future change remains limited, largely due to inadequate representation in current climate models. Here, using a global storm‐resolving model that accurately simulates MCSs, we conclude contrasting responses to increased SST in their occurrence, that is, notable decreases over land but increases over ocean. This land‐ocean contrast is attributed to the changes in convective available potential energy (CAPE) and convective inhibition (CIN). Over land, notable rises in CIN alongside moderate increases in CAPE effectively suppress (favor) weak to moderate (intense) MCSs, resulting in an overall reduction in MCS occurrences. In contrast, substantial increases in CAPE with minimal changes in CIN over ocean contribute to a significant rise in MCS occurrences. The divergent response in MCS occurrence has profound impacts on both mean and extreme precipitation.

The detrimental effect of rainforest conversion to rubber plantations on soil dissolved organic carbon and C: N stoichiometry, mediated by altered soil biogeochemistry

Rainforest conversion into rubber (Hevea brasiliensis) plantations (RP) alters global carbon cycling and contributes to climate change. However, the impact of this widespread tropical land use change on various elements of the carbon cycle is poorly understood. Here, we aimed to investigate the impact of rainforest conversion into RP on soil-dissolved organic carbon (DOC), one of the most mobile organic matter (OM) in the terrestrial ecosystem that causes the transformation and migration of C. We also explored the underlying edaphic factors regulating soil DOC changes. Our study sites were rubber monoculture, mixed-rubber plantations (H. brasiliensis, Ficus langkokensis, and Actinodaphne henryi), and a reference rainforest. We found that soil DOC concentration was 150-200% higher in RP than in rainforests, with an unchanged pattern across the seasons (dry and rainy) and plantation type. These results were concomitant with degradation in main soil properties, markedly including lower pH, electrical conductivity, SOC, available nitrogen, available phosphorus, total nitrogen (TN), and total phosphorus (TP), following the RP establishment and explicitly having a significant negative correlation with DOC. Our fitted structure equation model (SEM) highlights that RP caused accelerated DOC production and a higher DOC/DN ratio by decreasing SOC (38.5%) and nutrients (TN and TP). Further, the SEM revealed a significant negative correlation between microbial biomass C (MBC) and N (MBN) and the DOC/DN ratio, implying limited microbial degradation of DOC under RP. This is further supported by our findings of 81.1% lower MBC per unit DOC and 37.1% lower MBN per unit DN under RP compared to rainforests, indicating poor transformation of DOC to microbial biomass under RP. Collectively, our findings suggest that RP with high nutrient demands and altered soil properties lead to increased leaching of DOC due to its limited utilization by microbes. These findings underscore the importance of robust and sustainable soil management (such as optimizing plant density and legume intercropping) in RP to improve soil health and minimize DOC leaching and its potential environmental consequences.

Reducing the Uncertainty in the Tropical Precipitation through a Multi‐Criteria Decision‐Making Approach

ABSTRACTThe inherent model uncertainty in precipitation projections is found to be more dominant over tropical regions thereby reducing the reliability of using them in climate change impact assessment studies. To address such issues, a subset of well performing global climate models (GCMs) can provide narrow range of possible future outcomes, which can be helpful in formulating mitigation and adaptation strategies that are more targeted and efficient. In this study, climate models are selected based on their performance in simulating relative humidity and vertical velocity since these variables play an important role in precipitation simulation and significantly contribute toward the intermodel spread. The models are evaluated by using various statistical performance measures and ranked using multi‐criteria decision‐making approaches. Finally, based on Jenks natural breaks optimization algorithm, subset of GCMs consisting of ACCESS1.0, ACCESS1.3 and INM‐CM4 models, are considered as the best possible subset for precipitation simulation over tropical land regions. Two observational precipitation datasets are further considered to investigate the effectiveness of the proposed framework. The proposed methodology is validated to be effective in identifying the best climate models since the resulting subset is capable of both capturing observed precipitation and minimizing the uncertainty in future projections. Hence, this methodology can be utilized further for performance evaluation of GCMs focusing different geography and climatic drivers.

The decline in tropical land carbon sink drives high atmospheric CO2 growth rate in 2023

Abstract Atmospheric CO2 growth rate (CGR), reflecting the carbon balance between anthropogenic emissions and net uptake from land and ocean, largely determines the magnitude and speed of global warming. CGR at Mauna Loa Baseline Observatory reached record high in 2023. Here we quantified major components of global carbon balance for 2023, by developing a framework which integrated fossil fuel CO2 emissions data, an atmospheric inversion from Global ObservatioN-based system for monitoring Greenhouse GAses (GONGGA) with two artificial intelligence (AI) models derived from dynamic global vegetation models. We attributed the record high CGR increase in 2023 compared to 2022 primarily to the large decline in land carbon sink (1803 ± 197 TgC year−1), with minor contributions from a small reduction in ocean carbon sink (184 TgC year−1) and a slight increase in fossil fuel emissions (24 TgC year−1). At least 78% of the global decline in land carbon sink was contributed by the decline in tropical sink, with GONGGA inversion (1354 TgC year−1) and AI simulations (1578 ± 666 TgC year−1) showing similar declines in the tropics. We further linked this tropical decline to the detrimental impact of El Niño-induced anomalous warming and drying on vegetation productivity in water-limited Sahel and southern Africa. Our successful attribution of CGR increase within the framework combining atmospheric inversion with AI simulations enabled near-real-time tracking of the global carbon budget which had a one-year reporting lag.

Two Perspectives on Amplified Warming over Tropical Land Examined in CMIP6 Models

Abstract Climate change projections show amplified warming associated with dry conditions over tropical land. We compare two perspectives explaining this amplified warming: one based on tropical atmospheric dynamics and the other focusing on soil moisture and surface fluxes. We first compare the full spatiotemporal distribution of changes in key variables in the two perspectives under a quadrupling of CO2 using daily output from the CMIP6 simulations. Both perspectives center around the partitioning of the total energy/energy flux into the temperature and humidity components. We examine the contribution of this temperature/humidity partitioning in the base climate and its change under warming to rising temperatures by deriving a diagnostic linearized perturbation model that relates the magnitude of warming to 1) changes in the total energy/energy flux, 2) the base-climate temperature/humidity partitioning, and 3) changes in the partitioning under warming. We show that the spatiotemporal structure of warming in CMIP6 models is well predicted by the inverse of the base-climate partition factor, which we term the base-climate sensitivity: conditions that are drier in the base climate have a higher base-climate sensitivity and experience more warming. On top of this relationship, changes in the partition factor under intermediate (between wet and dry) surface conditions further enhance or dampen the warming. We discuss the mechanistic link between the two perspectives by illustrating the strong relationships between lower-tropospheric temperature lapse rates, a key variable for the atmospheric perspective, and surface fluxes, a key component of the land surface perspective. Significance Statement Understanding what conditions give rise to the largest magnitude of warming in response to rising CO2 concentrations is not only scientifically important but also critical from a climate impact standpoint. Two main perspectives, one focusing on atmospheric dynamics and the other focusing on land surface processes, have been proposed to explain the stronger warming associated with drier conditions in the tropics. Here, we compare and contrast these two perspectives. We demonstrate that amplified warming in CMIP6 models can largely be predicted from base-climate dryness alone in both perspectives but is further modified based on changes in the partitioning of energy between temperature and moisture. We highlight the spatiotemporal conditions where assumptions in the two perspectives hold and where deviations occur within CMIP6 climate models.

Reduced productivity and carbon drawdown of tropical forests from ground-level ozone exposure

AbstractElevated ground-level ozone, a result of human activity, is known to reduce plant productivity, but its influence on tropical forests remains unclear. Here we estimate how increased ozone exposure has affected tropical-forest productivity and the global carbon cycle. We experimentally measure the ozone susceptibility of various tropical tree species, and then incorporate these data into a dynamic global vegetation model. We find that current anthropogenic-derived ozone results in a substantial decline in annual net primary productivity (NPP) across all tropical forests, with some areas being particularly impacted. For example, Asia sees losses of 10.9% (7.2–19.7%) NPP. We calculate that this productivity decline has resulted in a cumulative loss in carbon drawdown of 0.29 PgC per year since 2000, equating to ~17% of the tropical contemporary annual land carbon sink in the twenty-first century. We also find that areas of current and future forest restoration are disproportionately affected by elevated ozone. Future socioeconomic pathways that reduce ozone formation in the tropics will incur benefits to the global carbon budget by relieving the current ozone impacts seen across both intact forest and areas of forest restoration, which are critical terrestrial regions for mitigation of rising atmospheric carbon dioxide.

INFLUENCE OF MINERAL NUTRITION ON THE SOIL HEALTH AND PRODUCTIVITY OF COCONUT PALMS (Cocos nucifera L.) IN TROPICAL LAND USE SYSTEMS

Perennial plantation crops, such as coconut trees require the systematic addition of nutrients for sustained growth and productivity. This study aimed to understand plant and soil nutrient dynamics, root health and soil biological properties upon addition of specific nutrients in tropical land use systems. Field experiments in randomised block design were conducted in Agro-Ecological Unit-3 (AEU-3) and Agro-Ecological Unit-9 (AEU-9) from 2014 to 2020. Treatments were T1 (site-specific nutrient management practices (SSNM), T2 (SSNM without sodium chloride); T3 (SSNM without gypsum); T4 (SSNM along with the 50 g microbial formulation Kera Probio); T5 (Farming practice without any amendments or nutrients). Root health parameters, cumulative nut yield and nutrient dynamics in soil and leaf samples were estimated at the beginning and the end of the study. Systematic provision of all the essential nutrients resulted in significant increase content of N (1.39%), P (0.164%), K (1.71%), Ca (0.406%) and Mg (0.175%) in index leaves of coconut trees in sandy soils. Foliar nutrient levels of coconut trees grown in laterite soils were 1.21% N, 0.142% P, 1.27% K, 0.504% Ca and 0.146% Mg. In AEU-3, treatment that received all amendments and nutrients showed highest organic carbon content at the three depths as 6.79 g kg-1soil, 5.39 g kg-1 soil and 3.82 g kg-1, soil, respectively. In AEU-3, 61% increase in yield was observed, while in AEU-9,40% increase was recorded. Application of gypsum resulted in downward displacement of K and Mg indicating that gypsum is required for the amelioration of sub soil acidity in sandy soils. However, the displacement effect was less pronounced in laterite soils and beneficial effect of gypsum was evident with the enhancement of exchangeable Ca. Hence sandy soils require application of inputs as per T3 (T1 without gypsum), with external organic inputs and palm residues whereas in laterite soils application of treatments as per T1 is required with in situ palm residue recycling. Key words: coconut, leaf nutrients, sandy soil, laterite soil, root health, dehydrogenase.

Does the diversity of vegetation and diatoms correlate with soil and water factors in a tropical cloud forest's complex land use/land cover scenario?

Soil and water characteristics in micro basins with different land uses/land cover (LULC) can influence riparian vegetation diversity, stream water quality, and benthic diatom diversity. We analyzed 18 streams in the upper part of the La Antigua River basin, México, surrounded by cloud forests, livestock pastures, and coffee plantations. Concentrations of P, C, and N were elevated in the humus of forested streams compared to other land uses. In contrast, cations, ammonium, and total suspended solids (TSS) of water streams were higher in pastures and coffee plantations. These results indicate that LULC affects stream chemistry differently across land uses. Vegetation richness was highest (86-133 spp.) in forest streams and lowest in pastures (46-102), whereas pasture streams had the greatest richness of diatoms (9-24), likely due to higher light and temperatures. Some soil and water characteristics correlated with both true diversity and taxonomic diversity; soil carbon exchange capacity (CEC) correlated with vegetation diversity (r = 0.60), while water temperature correlated negatively (r = - 0.68). Diatom diversity was related to soil aluminum (r = - 0.59), magnesium (r = 0.57), water phosphorus (r = 0.88), and chlorophyll (r = 0.75). These findings suggest that land use affects riparian vegetation, while physical and chemical changes influence diatom diversity in stream water and soil. The lack of correlation between vegetation and diatom diversity indicates that one cannot predict the other. This research is an essential first step in understanding how land use changes impact vegetation and diatom diversity in mountain landscapes, providing valuable insights for environmental monitoring and conservation efforts in tropical cloud forests.

Author Correction: Amplified warming of extreme temperatures over tropical land

Author Correction: Amplified warming of extreme temperatures over tropical land

Precipitation enhancement over tropical land through the lens of the moisture–precipitation relationship

AbstractTropical precipitation has been found to be related to column relative humidity by a simple relationship known as the moisture–precipitation relationship . Based on one decade of daily ERA5 reanalysis data, we test whether is able to reproduce the tropical land–ocean precipitation contrast measured by , the ratio between mean precipitation over land and ocean. We find that captures the mean seasonal cycle of as long as we account for the fact that is distinct over land and ocean, and that it varies seasonally. Typical values of above 0.86 imply that precipitation is enhanced over land, relative to the ocean. We therefore investigate next whether this enhancement is due to the differences in and/or in the humidity distribution between land and ocean. We show that, rather than enhancing precipitation, the presence of land modifies in such a way that precipitation over land is disfavored compared to over ocean. Precipitation enhancement over land is instead explained by the modified terrestrial humidity distribution that features a more pronounced tail towards high values compared to the one over ocean. All results rest on an accurate construction of from the underlying data. Simple fit models such as an exponential function that were proposed by previous studies are unable to capture the seasonal cycle of and fail to explain land–ocean differences in precipitation.

Developing sustainable dairy farms in the tropics: From policy to practice

CONTEXTSustainable dairy production is included in the policy agenda of many countries in the tropics to address, among others, their commitment to the Paris Agreement. To the best of our knowledge, however, a study to assess the impact of the proposed interventions for sustainable dairy production is still lacking for most of those countries. Using policy goals as entry points to develop scenarios can provide insight into the impact of policy interventions on dairy farming practices. OBJECTIVEThis study aimed to evaluate the implication of interventions towards sustainable dairy development identified by the governments of Indonesia and Costa Rica. METHODSInformation about current farming practices (i.e. the baseline) were collected on 32 smallholder dairy farms in Indonesia and 24 dairy farms in Costa Rica. Scenarios were designed based on policy goals for dairy development and climate change mitigation in each country. The scenarios for Indonesia encompassed relocation of the dairy sector to Sumatra to allow coupling of livestock to land combined with a restriction on manure production to ensure all manure to be applied to grow forage, and a restriction on the amount of purchased feeds, at two levels: maximally 100% and 50% of the baseline. The scenarios for Costa Rica included a silvopastoral system and a reduction in the amount of purchased feeds, at two levels: 50% and 80% lower than the baseline. We estimated greenhouse gas (GHG) emissions at chain level and carbon (C) stocks at farm level. RESULTS AND CONCLUSIONSThe scenarios for Indonesia increased herd size and milk output by 240–360%, and GHG emissions per farm by 269–455%, while decreased GHG emissions per kg milk by 1–10%, compared to the baseline. C stocks per farm were higher in the scenarios than in the baseline, but compared to natural vegetation much more C is lost under the scenarios because more land is being used. The scenarios for Costa Rica reduced herd size and milk output by 5–25% and GHG emissions per farm by 17–35%, while GHG emissions per kg milk decreased by 10%, compared to the baseline. C stocks per farm were comparable. SIGNIFICANCETo achieve the multiple policy goals for sustainable dairy development, the governments need to consider the trade-off between increasing milk production and reducing GHG emissions. In Indonesia, relocation of the dairy sector needs a strict policy to avoid the expansion of dairy farms into tropical forest land. Furthermore, the Costa Rican government needs to incentivise dairy farmers to implement a silvopastoral system to reduce GHG emissions and land use. This, however, will be at the expense of milk output.

Uncontrolled deforestation and population growth threaten a tropical island's water and land resources in only 10 years.

Rapid demographic growth in tropical islands can exacerbate conflicts and pressures on natural resources, as illustrated by the French island of Mayotte where resources are limited. In only 10 years, uncontrolled migration and population growth (+80% of population between 2002 and 2021) have led to a pronounced 3600% increase in deforestation rates (2010-2014) and an intensification of agricultural practices, escalating conflicts over limited land, water, and biodiversity resources. Implementing an original multi-proxy approach to sediment cores, our study reveals a staggering 300% acceleration in erosion during the first wave of migration (2011-2015), followed by a further 190% increase (2019-2021) under sustained migratory and demographic pressures. Sedimentary DNA analysis provided insights into increased connectivity and community changes. By 2050, the population of this region will increase by 74 and 103%, in Comoros and Madagascar islands, respectively. Urgent conservation measures are needed to avoid major socio-environmental crises and to protect resources for future generations.

Fourteen-year field experiment reveals neutral effects of N and P deposition on abundance and stoichiometric traits of the earthworm Pontoscolex corethrurus in tropical plantations

The afforestation of tropical forests plays an important role in mitigating climate change. Exploring the impacts of nitrogen (N) and phosphorus (P) deposition on earthworm communities is significant for understanding the contributions of tropical forests to global change. A 14-year field experiment simulating N and P deposition at a station with 50-year-old tropical plantations was conducted. We found that the pantropical widespread exotic earthworm species Pontoscolex corethrurus was dominant, and it did not respond to exogenous N input. Moreover, P addition only increased the abundance of P. corethrurus after 14 years. Similarly, neither N addition nor P addition changed the stoichiometric traits of P. corethrurus. However, over the past decade, the abundance, biomass, and carbon (C), N, and P concentrations in the tissues of P. corethrurus have increased. A strong positive correlation between P. corethrurus population size and soil gram-negative (G−) bacteria biomass was observed, suggesting that P. corethrurus may benefit from the soil bacterial channel. This study ascertained that non-natural tropical lands may be resistant to N and P deposition in terms of earthworm related belowground processes, which would be helpful for fully understanding plant-soil biota feedback and their contributions to tropical plantation development and the mitigation of global climate change.

Changes in soil microbial metabolic limitations after half-century forest restoration in degraded tropical lands

Due to increasing anthropogenic pressure, over half of the world’s tropical forests are reforested or afforested secondary forests or plantations. The recovery pace and potential of these forests depend largely on soil microbially-mediated biogeochemical cycling. Here we measured soil extracellular enzyme activities and quantified microbial metabolic limitations using a vector analysis in a bare land (BL, representing the original state before restoration), two afforested sites [i.e. a restored secondary forest (MF) and a managed Eucalyptus exserta plantation (EP)] and a nearby undisturbed forest (UF) in south China. Results showed that soil microbial metabolisms were co-limited by carbon (C) and phosphorus (P) across the four forests. Both microbial C and P limitations were higher in BL than UF. Microbial C limitation significantly reduced after restoration only in MF when compared to BL, but it was still higher than that in UF. Interestingly, microbial P limitation significantly enhanced after restoration in both EP and MF when compared to BL, and it did not differ between the two restored forests. Structural equation modeling (SEM) showed that microbial C limitation was primarily attributed to microbial C use efficiency, while microbial P limitation was co-driven by plant biomass, microbial C use efficiency and soil P availability. These findings suggest microbial C limitation could be gradually recovered after forest restoration in southern China, which would facilitate soil organic carbon accumulation. However, the enhanced microbial P limitation after forest restoration underlines the necessity to develop optimal P management in these restored forests.

No constraint on long-term tropical land carbon-climate feedback uncertainties from interannual variability

Unraveling drivers of the interannual variability of tropical land carbon cycle is critical for understanding land carbon-climate feedbacks. Here we utilize two generations of factorial model experiments to show that interannual variability of tropical land carbon uptake under both present and future climate is consistently dominated by terrestrial water availability variations in Earth system models. The magnitude of this interannual sensitivity of tropical land carbon uptake to water availability variations under future climate shows a large spread across the latest 16 models (2.3 ± 1.5 PgC/yr/Tt H2O), which is constrained to 1.3 ± 0.8 PgC/yr/Tt H2O using observations and the emergent constraint methodology. However, the long-term tropical land carbon-climate feedback uncertainties in the latest models can no longer be directly constrained by interannual variability compared with previous models, given that additional important processes are not well reflected in interannual variability but could determine long-term land carbon storage. Our results highlight the limited implication of interannual variability for long-term tropical land carbon-climate feedbacks and help isolate remaining uncertainties with respect to water limitations on tropical land carbon sink in Earth system models.

Asymmetric impacts of forest gain and loss on tropical land surface temperature

Asymmetric impacts of forest gain and loss on tropical land surface temperature

Forecasting Tropical Annual Maximum Wet‐Bulb Temperatures Months in Advance From the Current State of ENSO

AbstractHumid heatwaves, characterized by high temperature and humidity combinations, challenge tropical societies. Extreme wet‐bulb temperatures (TW) over tropical land are coupled to the warmest sea surface temperatures by atmospheric convection and wave dynamics. Here, we harness this coupling for seasonal forecasts of the annual maximum of daily maximum TW (TWmax). We develop a multiple linear regression model that explains 80% of variance in tropical mean TWmax and significant regional TWmax variances. The model considers warming trends and El Niño and Southern Oscillation indices. Looking ahead, the strong‐to‐very‐strong El Niño at the end of 2023, with an Oceanic Niño Index of ∼2.0, suggests a 2024 tropical land mean TWmax of 26.2°C (25.9–26.4°C), and a 68% chance (24%–94%) of breaking existing records. This method also predicts regional TWmax in specific areas.

Satellite-observed precipitation and total column water vapor

This study explores the relationship between water vapor and rainfall intensities over three tropical lands (Amazon Basin, Sahel, southern South America) and three tropical ocean regions (Atlantic Ocean, Indian Ocean, Niño 4). We utilized daily total column water vapor (TCWV) data from the Atmospheric Infrared Sounder (AIRS) and daily precipitation records from the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation. Over tropical land, precipitation shows higher sensitivity to changes in water vapor, with a well-sorted pattern of an increased occurrence of higher daily precipitation as TCWV increases. Precipitation intensity over the Sahel, in particular, is extremely responsive to TCWV change. Over tropical oceans, the precipitation intensity is less sensitive to water vapor, particularly in the Indian Ocean and Niño 4 where precipitation intensities above the 40th percentile are no longer responding to the increasing TCWV. Quantifying water vapor and precipitation intensity aids in forecasting the occurrence of precipitation between tropical land and oceans.

Response of the Current Climate to Land‐Ocean Contrasts in Parameterized Cumulus Entrainment

AbstractCumulus entrainment substantially regulates the earth's climate but remains poorly constrained in global climate models. Recent studies have shown that cumulus bulk entrainment (or dilution) is particularly sensitive to continentality, with the entrainment rate in simulated maritime cumuli nearly double that of continental cumuli. This study examines the impacts of such land–ocean entrainment contrasts on the current climate using 21‐year simulations with the Geophysical Fluid Dynamics Laboratory's High‐Resolution Atmospheric Model (HIRAM). In response to a 25% reduction in the HIRAM entrainment parameter c0 over land, precipitation over tropical land regions increases by up to 40%. Along with directly facilitating enhanced convective precipitation, this c0 reduction induces an increase in soil moisture, which may contribute to a further enhancement of convective precipitation over land. A 25% c0 reduction over the oceans leads to more widespread modifications of convection patterns, with the strongest signal in the tropical Pacific. Deep convection shifts upstream (eastward) there, inducing enhanced large‐scale ascent over the central Pacific with compensating subsidence and reduced humidity and precipitation over the western Pacific (WP). Land–ocean variations in c0 project onto the Pacific Walker circulation, with the 25% land reduction strengthening it by 4% and the 25% ocean reduction weakening it by 14%. These changes are driven by variations in convective and large‐scale stratiform heating over the Pacific. While reduced c0 over land enhances diabatic heating in the Maritime Continent to strengthen the Walker circulation, reduced c0 over the oceans decreases diabatic heating in the WP to weaken the Walker circulation.

Oceanic Influence and Lapse Rate Changes Dominate the Recent Amplified Saharan Warming

AbstractThe surface air temperature (SAT) over the Sahara Desert has increased at a much faster rate than average tropical land in recent decades. This study examines the relative roles of anthropogenic greenhouse gas (GHG) forcing and sea surface temperature (SST) change in the observed Saharan temperature increase during boreal warm season from 1979 to 2020 using atmospheric general circulation model simulations. It is found that the SST forcing dominates the observed Saharan warming. Further analysis shows that the warming ocean forces the Saharan SAT increase by moving more energy to the Sahara Desert, while the water vapor feedback plays a secondary role. The reason for the stronger Saharan warming than the average tropical land given the same SST forcing is also explored. We found that the largest contributor to the warming contrast is the lapse‐rate feedback, which is attributable to the difference in the vertical warming profile.