Low Interannual Variability Research Articles

The emergent past: past natural and human disturbances of trees can reduce their present resistance to drought stress

Forest tree growth is primarily explained, modelled, and predicted depending on current age or size, environmental conditions, and competitive status in the stand. The accumulated size is commonly used as a proxy for a tree's past development. However, recent studies suggest that antecedent conditions may impact present growth by epigenetic, transcriptional, proteomic, or metabolic changes alongside physiological and structural properties. Here, I analysed the ecological memory effect embedded in the xylem as a tree-ring structure. I used 35 mature Norway spruces (Picea abies (L.) H. Karst.) and 36 European beeches (Fagus sylvatica L.) of the Kranzberg Forest water retention experiment KROOF in South Germany to scrutinise how their past development determines the growth of control plots and plots with 5-year water retention. I hypothesised that the current size and growing conditions determine tree growth and drought stress resistance. Metrics quantifying the trees’ recent and past growth, and correlation and linear mixed models with random effects revealed the following ecological memory effects. (1) For both species, the progressive growth course, low inter-annual growth variation in the long term, and low growth deflections in the recent past increased the growth resistance to drought. (2) The correlation between the past growth metrics and current stress reactions revealed that legacy effects could reach back 5–30 years; I found short- and long-term ecological memory. (3) Parameters of model prediction of the basic model with only size as a predictor of tree growth could be improved. The results suggest differences in the internal stem structure and ring pattern cause-specific differences in the trees' functioning and growth. I conclude that a long-term progressive increase and low variation in ring width may improve water conduction and reduce embolism in both species. Annual growth variation and low growth events in the recent past may have primed the morphology and allocation of the Norway spruce to better resist drought. The strong reduction in current growth, drought resistance by irregular growth, and past growth disturbances reveal a memory effect embedded in the tree ring pattern, suggesting further exploration and consideration in tree monitoring, growth modelling, and silvicultural prescriptions.

Wave Energy Resource Harnessing Assessment in a Subtropical Coastal Region of the Pacific

Most wave energy converters (WECs) are designed to operate in high-latitude energetic seas, limiting their performance in regions usually dominated by milder conditions. The present study assesses the performance of complete test-stage WECs in farms that satisfy a decentralized energy scheme (DES) on the coast of Baja California, which is considered one of the most energetic regions along the Mexican Pacific. A high-resolution 11-year nearshore wave hindcast was performed and validated with Acoustic Doppler Current Profilers (ADCPs) data to characterize the wave energy resource in the study area. Two hotspots were identified from the wave power climatology. In these sites, the extractive capacities of seven well-known WEC technologies were determined based on their power matrices. Finally, the power extracted by small WEC farms, with the minimum number of devices required to satisfy a DES, was estimated. The studied region has moderate wave power availability with marked seasonality and low inter-annual variability. Out of all the evaluated devices, WaveDragon extracts the highest wave power; however, Pelamis has the best performance, with maximum monthly mean capacity factors up to 40%. Coupling WEC farms with storage modules or hybrid renewable systems are recommended to satisfy a continuous DES during the less energetic summer months.

Long-Term Variability in Ground Thermal State in Central Yakutia’s Tuymaada Valley

This paper presents the results of long-term temperature monitoring at the Yakutsk and Zeleny Lug stations, which are experimental sites, for the thermal state of valley permafrost landscapes under the conditions of modern climate warming. An analysis of the long-term data from meteorological stations in the region clearly showed one of the highest trends of increase in the mean annual air temperature in the north of Russia. Here, we established quantitative regularities in the long-term variability of the ground temperature at the bottom of the active layer and at zero amplitude. The dynamics of the ground temperature of the layer of zero amplitude during climate warming indicate the thermal stability of permafrost. The main regulating factor of the thermal state of grounds in permafrost landscapes is short-term fluctuations in the regime of snow accumulation. Active layer thickness is characterized by low interannual variability, weak climate warming responses, and insignificant trends. The results of studies of the thermal regime of soils can be extended to the same types of valley landscapes in the Lena River, and are a reliable basis for predicting heat transfer in natural and disturbed landscapes.

Short-Term Meteorological and Environmental Signals Recorded in a Firn Core from a High-Accumulation Site on Plateau Laclavere, Antarctic Peninsula

High-accumulation sites are crucial for understanding the patterns and mechanisms of climate and environmental change in Antarctica since they allow gaining high-resolution proxy records from firn and ice. Here, we present new glacio- and isotope-geochemical data at sub-annual resolution from a firn core retrieved from an ice cap on Plateau Laclavere (LCL), northern Antarctic Peninsula, covering the period 2012–2015. The signals of two volcanic eruptions and two forest fire events in South America could be identified in the non-sea-salt sulphur and black carbon records, respectively. Mean annual snow accumulation on LCL amounts to 2500 kg m−2 a−1 and exhibits low inter-annual variability. Time series of δ18O, δD and d excess show no seasonal cyclicity, which may result from (1) a reduced annual temperature amplitude due to the maritime climate and (2) post-depositional processes. The firn core stratigraphy indicates strong surface melt on LCL during austral summers 2013 and 2015, likely related to large-scale warm-air advection from lower latitudes and temporal variations in sea ice extent in the Bellingshausen-Amundsen Sea. The LCL ice cap is a highly valuable natural archive since it captures regional meteorological and environmental signals as well as their connection to the South American continent.

Interannual and Seasonal Drivers of Carbon Cycle Variability Represented by the Community Earth System Model (CESM2).

Earth system models are intended to make long‐term projections, but they can be evaluated at interannual and seasonal time scales. Although the Community Earth System Model (CESM2) showed improvements in a number of terrestrial carbon cycle benchmarks, relative to its predecessor, our analysis suggests that the interannual variability (IAV) in net terrestrial carbon fluxes did not show similar improvements. The model simulated low IAV of net ecosystem production (NEP), resulting in a weaker than observed sensitivity of the carbon cycle to climate variability. Low IAV in net fluxes likely resulted from low variability in gross primary productivity (GPP)—especially in the tropics—and a high covariation between GPP and ecosystem respiration. Although lower than observed, the IAV of NEP had significant climate sensitivities, with positive NEP anomalies associated with warmer and drier conditions in high latitudes, and with wetter and cooler conditions in mid and low latitudes. We identified two dominant modes of seasonal variability in carbon cycle flux anomalies in our fully coupled CESM2 simulations that are characterized by seasonal amplification and redistribution of ecosystem fluxes. Seasonal amplification of net and gross carbon fluxes showed climate sensitivities mirroring those of annual fluxes. Seasonal redistribution of carbon fluxes is initiated by springtime temperature anomalies, but subsequently negative feedbacks in soil moisture during the summer and fall result in net annual carbon losses from land. These modes of variability are also seen in satellite proxies of GPP, suggesting that CESM2 appropriately represents regional sensitivities of photosynthesis to climate variability on seasonal time scales.

Evapotranspiration and energy partitioning across a forest-shrub vegetation gradient in a subarctic, alpine catchment

As a result of altitude and latitude amplified climate change, widespread changes in vegetation composition, density and distribution have been observed across northern regions. Despite wide documentation of shrub proliferation and treeline advance, few field-based studies have evaluated the hydrological implications of these changes. Quantification of total evapotranspiration (ET) across a range of vegetation gradients is essential for predicting water yield, yet challenging in cold alpine catchments due to heterogeneous land cover, including both boreal forest and shrub taiga ecosystems. Here, we present six years of surface energy balance components and ET dynamics at three sites along an elevational gradient in a subarctic, alpine catchment near Whitehorse, Yukon Territory, Canada. These sites span a gradient of thermal and vegetation regimes, providing a space-for-time comparison for future ecosystem shifts: 1) a low-elevation boreal white spruce forest (~12–20 m), 2) a mid-elevation subalpine taiga comprised of tall, dense willow (Salix) and birch (Betula) shrubs (~1–3 m) and 3) a high-elevation subalpine taiga with short, sparse shrub cover (<0.75 m) and moss, lichen, and bare rock. Eddy covariance instrumentation ran year-round at the forest and during the growing season at the two shrub sites. Total ET decreased and interannual variability increased with elevation, with mean May to September ET totals of 349 (±3) mm at the forest, 249 (±10) mm at the tall, dense shrub site, and 240 (±26) mm at the short, sparse shrub site. Comparatively, over the same period, ET:R ratios were the highest and most variable at the forest (2.19 ± 0.37) and similar at the tall, dense shrub (1.22 ± 0.09) and short, sparse shrub (1.14 ± 0.05) sites. Our results suggest that advances in treeline will increase overall ET and lower interannual variability; however, the large growing season water deficit at the forest indicates strong reliance on soil moisture from late fall and snowmelt recharge. In contrast, ET was considerably less at the cooler higher elevation shrub sites, which exhibited similar ET losses over 6 years despite differences in shrub height and abundance. ET rates between the two shrub sites were similar throughout the year, except during the peak growing season. Greater interannual variability in ET at the short, sparse shrub site indicates the reduced influence of vegetation controls on ET. Results suggest that predicted changes in vegetation type and structure in northern regions will have a considerable impact on water partitioning and will vary in a complex way in response to changing precipitation timing, phase and magnitude, growing season length, and vegetation snow and rain interactions.

Towards a Future Scenario for Offshore Wind Energy in Chile: Breaking the Paradigm

Offshore wind energy continues to be a potential candidate for meeting the electricity consumption needs of the Chilean population for decades to come. However, the Chilean energy market is skeptical about exploiting offshore marine energy. At present, there are no offshore marine energy farms. This is probably attributable to the current legal framework, payback period, initial costs of inversions, and future wind speed trends. This work aims to break this paradigm by advancing knowledge regarding the main issues concerning offshore marine energy in Chile. To this end, we estimated the Levelized Cost of Energy (LCOE) from 2000 to 2054 using the CMIP RCP 4.5 and 8.5 climate projections. These projections were based on the estimations for a 608 MW offshore wind project located along the Chilean coast. A comprehensive analysis of the legal framework for implementing offshore marine energy is also presented. The results show that the LCOE ranges between 24 USD/MWh and 2000 USD/MWh. Up to 80% of the study area presents favorable results. Future climate scenarios did not affect the project’s economic viability and notably indicated two major zones with low interannual variability. In terms of legal frameworks, there is a gap in a Chilean trans-ministerial law that ends up causing several processes to be duplicated. Further research is needed to reduce the uncertainties associated with offshore wind energy generation on the Chilean coast. This study aims to further knowledge related to both the opportunities and challenges associated with offshore wind.

The upper homeostatic range for the temperature–yield response of irrigated US wheat down revised from a theoretical and experimental perspective

High temperature (HT) and drought (D) have detrimental effects on growth and phenology that result in reductions of the yields of agricultural crops. Nevertheless, homeostatic ranges of tolerance exist. Recent analysis of survey data and simulations suggest US wheat (Triticum aestivum L.) yields remain relatively stable under irrigation in the range of 35°– 40°C. Applying analogue statistical procedures on experimental data and simulations from the Hot Serial Cereal Experiment (HSC) we demonstrate that failed incorporation of the corresponding phenological acceleration due to HT and a low interannual temperature variability lead to this result. Here, we incorporate the phenological effect into the used binned temperature exposure yield model by rescaling (normalizing) the absolute seasonal temperature counts to a maximum season length. The application to observed and simulated HSC data with a wide temperature range reveals that the suggested upper homeostatic response limit of US wheat yields to HT requires a down–revision. HT stress can be reduced by transpirational cooling. However, the effect is currently not sufficient to expand the homeostatic range of irrigated wheat markedly beyond 25°C taking our analysis of the HSC experiment.

Faster decline and higher variability in the sea ice thickness of the marginal Arctic seas when accounting for dynamic snow cover

Abstract. Mean sea ice thickness is a sensitive indicator of Arctic climate change and is in long-term decline despite significant interannual variability. Current thickness estimations from satellite radar altimeters employ a snow climatology for converting range measurements to sea ice thickness, but this introduces unrealistically low interannual variability and trends. When the sea ice thickness in the period 2002–2018 is calculated using new snow data with more realistic variability and trends, we find mean sea ice thickness in four of the seven marginal seas to be declining between 60 %–100 % faster than when calculated with the conventional climatology. When analysed as an aggregate area, the mean sea ice thickness in the marginal seas is in statistically significant decline for 6 of 7 winter months. This is observed despite a 76 % increase in interannual variability between the methods in the same time period. On a seasonal timescale we find that snow data exert an increasingly strong control on thickness variability over the growth season, contributing 46 % in October but 70 % by April. Higher variability and faster decline in the sea ice thickness of the marginal seas has wide implications for our understanding of the polar climate system and our predictions for its change.

A 30 ‐Year Time Series of Transient Tracer‐Based Estimates of Anthropogenic Carbon in the Central Labrador Sea

AbstractWe use a 30‐year time series (1986–2016) of dichlorodifluoromethane (CFC‐12) concentrations with a refined transit time distribution (TTD) method, to estimate the temporal variation of anthropogenic carbon (Cant) in the Central Labrador Sea. We determined that the saturation of CFC‐12 and sulfur hexafluroide (SF6) in newly‐formed Labrador Sea Water had departed significantly from 100% and varied systematically with time. Multiple linear regression of the time‐varying saturation, with the tracer's atmospheric growth rate and the wintertime mixed layer depth as independent variables, allowed reconstruction of the saturation history of CFC‐12 and SF6 in wintertime surface waters, which was implemented in the TTD method. Use of the time‐varying saturation for CFC‐12 gave Cant concentrations ∼7 μmol kg−1 larger than estimates obtained assuming a constant saturation of 100%. The resulting Cant column inventories were ∼20% larger and displayed lower interannual variability compared to conventional TTD‐based estimates. The column inventory of Cant increased at an average rate of 1.8 mol m−2 y−1 over the 30‐year period. However, the accumulation rate of Cant was higher than this average in the early 1990s and since 2013, whereas inventories remained almost unchanged between 2003 and 2012. The variation in the Cant accumulation rate is shown to be linked to temporal variability in the relative layer thickness of the annually ventilated Labrador Sea Water and the underlying Deep Intermediate Water. The non‐steady Cant accumulation highlights the importance of sampling frequency, especially in regions of variable deep mixing and high carbon inventories, and potential misinterpretation of Cant dynamics.

Performance of a process-based model for predicting robusta coffee yield at the regional scale in Vietnam

Reliable and timely prediction of robusta coffee (Coffea canephora Pierre ex A. Froehner) yield is pivotal to the profitability of the coffee industry worldwide. In this study we assess the performance of a simple process-based model for simulating and predicting robusta coffee yield at the regional scale in Vietnam. The model includes the key processes of coffee growth and development and simulates its response to variation in climate and potential water requirements throughout the growing season. The model was built and evaluated for the major Vietnamese robusta coffee-producing provinces Dak Lak, Dak Nong, Gia Lai, Kon Tum, and Lam Dong, using official provincial coffee yield data and climate station data for the 2001–2014 period, and field data collected during a 10-year (2008–2017) survey. Overall, good agreements were found between the observed and predicted coffee yields. Root mean square error (RMSE) and mean absolute percentage error (MAPE) values ranged from 0.24 to 0.33 t ha−1, and 9% to 14%, respectively. Willmott's index of agreement (WI) was greater than or equal to 0.710 in model evaluation steps for three out of five provinces. The relatively low values of WI were found for provinces with relatively low inter-annual yield variability (i.e. Dak Lak and Dak Nong). Moreover, the model was successfully tested using remote sensing satellite and model-based gridded climate data: MAPE values were ≤ 12% and RMSE were ≤ 0.29 t ha−1. Such evaluation is important for long-term coffee productivity studies in these regions where long-term climate stations data are not readily available. The simple process-based model presented in this study could serve as a basis for developing an integrated seasonal climate-robusta coffee yield forecasting system, which would offer substantial benefits to coffee growers and industry through better supply chain management and preparedness for extreme climate events, and increased profitability.

Structure of the Freshened Surface Layer in the Kara Sea During Ice‐Free Periods

AbstractThis work is focused on the seasonal and interannual variability of the freshened surface layer (FSL) in the Kara Sea during ice‐free periods. The majority of annual freshwater runoff inflows to the Kara Sea during the freshet period in June–July. As a result, a large low‐salinity and strongly stratified FSL is formed in the central Kara Sea at the beginning of the ice‐free period. Initially, this layer is fresh with salinities of less than 15. Then, in August–October, river discharge steadily decreases, the fresh (&lt;15) and strongly stratified river plume remains limited to the inner part of the FSL adjacent to the Ob and Yenisei gulfs, which receives reduced freshwater discharge. The area of the fresh plume steadily decreases with decreasing of river discharge; in October, it remains only within the Ob and Yenisei gulfs. Area and position of the outer part of the FSL, on the opposite, remain stable until the end of ice‐free period. Salinities in the outer part steadily increase to 20–25, vertical salinity gradients at the boundary with the subjacent sea decrease, albeit remain prominent. Area and position of the FSL also have low interannual variability, because the volume of river runoff during freshet period in June–July is stable on interannual time scale. As a result, downward freshwater transport and the formation of the seasonal halocline occur in August–October at the stable area located in the central Kara Sea.

Sedimentology of the modern seasonal lower Ganges River with low inter-annual peak discharge variance, Bangladesh

The Ganges River, one of the largest rivers on Earth, is a typical monsoonal and flood-controlled system but has low inter-annual peak discharge variability. The seasonal discharge can reach 70 000 m 3 s −1 during the wet season but maintains a low base flow of 500–3000 m 3 s −1 during the dry season. However, the constancy in peak discharge every year categorizes the lower Ganges River as a river with low inter-annual peak discharge variability. This paper examines the modern lower Ganges River by conducting a detailed process-oriented investigation of the main channel, channel margin and overbank deposits, supplemented by satellite image observation and comparison with other modern fluvial systems. The channel and braid bar deposits show a dominance of small-scale to medium-scale cross-sets, with a variety of accretion processes constructing braid bars. The braid bar and channel deposits are typical of facies models of rivers with low inter-annual peak discharge variance. In contrast, the channel flank deposits are dominated by planar lamination, massive sand and mud couplets, and some ripple cross-lamination, with very little cross-bedding. Characteristic channel margin deposits represent sediments that accumulated by high-speed flows, multiple-surge and rapidly depositing flows, rapid or regular waning flows and hyperconcentrated flows. The overbank deposits predominantly comprise current ripples with long, thin bedforms and soft sediment deformation structures, which record flow transformation on the muddy flat topography and the processes of an unstable river bank. Our study shows that the channel margin and floodplain deposits are entirely different from those of the braid bar and channel. The bedform distribution of the fluvial deposits here (main channel, channel margin and overbank) may be an important tool in the identification of similar seasonal rivers with low inter-annual peak discharge variance and in the interpretation of fluvial processes. Supplementary material : The sediment texture and the depositional age is available at: https://doi.org/10.6084/m9.figshare.c.5144403

Inter-annual variability and skill of tropical rainfall and SST in APCC seasonal forecast models

The present study explored the performance of the current coupled models obtained from the Asia Pacific Economic Cooperation (APEC) Climate Centre (APCC) in representing the tropical Indo-Pacific sea surface temperature (SST) and rainfall during boreal summer season (June through September; JJAS). We have used the retrospective/hindcast runs for 28 years from 1983 to 2010 initialized in May. The mean SST bias in the tropical Indo-Pacific Oceans showed large diversity among the models in JJAS. In the case of the rainfall, most of the models displayed a strong dry bias over the major continental regions and wet biases over the tropical oceans. The majority of the models simulated the Inter-annual variability (IAV) of JJAS rainfall and SST reasonably well over the equatorial Pacific region, where the models are close to observed IAV and maximum signal to noise ratio (SNR). It is found that the models display, low IAV of rainfall and SST over the Indian Ocean with low SNR values, resulting in less predictive skill as compared to the tropical Pacific region. Similarly, all models showed a higher skill in summer rainfall prediction over the oceanic regions compared to the Asian land region, where SNR is very low. Further analysis suggested that the models have greater skill in predicting El Nino-Southern Oscillation (ENSO). The category wise analysis showed that models could predict 60–70% of the extreme ENSO events, but the normal events are represented only by 50%. It is noted that the models predict many false alarms for El Nino resulting in a higher frequency of El Nino occurrence. This is mainly responsible for stronger ENSO and the Asian Monsoon teleconnections in the models than in the observations. Meanwhile, the category wise rainfall skill for extended Indian monsoon region (EMR) displayed 50–60% accuracy for the extreme monsoon years and is around 50% for normal years. However, models such as CCSM3, CFSV2, and CANCM3 have displayed higher rainfall skills over EMR as compared to the other models possibly due to better representation of teleconnections spatial patterns between EMR rainfall and SST anomalies over Indo-Pacific Oceans.

Spatiotemporal variability and trends in rainfall and temperature in Alwero watershed, western Ethiopia

Climate analysis at relevant time scales is important for water resources management, agricultural planning, flood risk assessment, ecological modeling and climate change adaptation. This study analyses spatiotemporal variability and trends in rainfall and temperature in Alwero watershed, western Ethiopia. Our analysis is focused on describing spatial and temporal variability of rainfall in the study area including detection of trends, with no attempt at providing meteorological explanations to any of the patterns or trends. The study is based on gridded monthly rainfall and maximum and minimum temperature data series at a resolution of 4 × 4 km which were obtained from the National Meteorological Agency of Ethiopia for the period 1983–2016. The study area is represented by 558 points (each point representing 4 × 4 km area). Mean annual rainfall of the watershed is > 1600 mm. Annual, June–September (Kiremt), March–May (Belg) rainfall totals exhibit low inter-annual variability. Annual and October-February (Bega) rainfalls show statistically significant increasing trends at p = 0.01 level. May and November rainfall show statistically significant increasing trends at p = 0.01 level. March shows statistically significant decreasing trend at p = 0.1 level. The mean annual temperature of the watershed is 25 °C with standard deviation of 0.31 °C and coefficient of variation of 0.01 °C. Mean annual minimum and maximum temperatures show statistically non-significant decreasing trends. Bega season experienced statistically significant deceasing trend in the maximum temperature at p = 0.01 level. The year-to-year variability in the mean annual minimum and maximum temperatures showed that the 2000s is cooler than the preceding decades. Unlike our expectations, annual and seasonal rainfall totals showed increasing trends while maximum and minimum temperatures showed decreasing trends. Our results suggest that local level investigations such as this one are important in developing context-specific climate change adaptation and agricultural planning, instead of coarse-scale national level analysis guiding local level decisions.

Climatology and trends of reference evapotranspiration in Spain

AbstractThis study presents a climatology and trend analysis of reference crop evapotranspiration (ETo) over continental Spain and the Balearic Islands. Geographic features of the study region play a substantial role in the climatology of ETo. The highest values (in excess of 1,200 mm y−1) are found at lower elevations in the south, while the lowest values (less than 900 mm y−1) are found in the highest elevations in the north. A deep analysis reveals: (a) a low interannual variability; (b) summer accumulates more than 50% of annual values; and (c) the radiative component contribution is higher than 50%. A positive long‐term trend (1961–2014) has been detected for most of the study area, but showing contrasting situations when shorter periods (20–30 years) are analysed. A short initial period of negative trend was followed by a longer period of a positive trend. We argue that global dimming/brightening played a role in this process, as these two contrasting periods are clearly guided by the radiative component. A seasonal analysis of the trends reveals that spring and summer are the seasons showing the long‐term positive trends. Interestingly, a monthly analysis shows that spring trends are guided by March and April and summer trends are mostly guided by June, which is the month showing the highest relative changes. This could have important consequences for agriculture and natural ecosystems since this month represents the start of the summer (dry) period.

Trophically polymorphic loggerhead sea turtles show similar interannual variability in clutch frequencies: implications for estimating population size of iteroparous animals

AbstractWe investigated how trophic polymorphism observed at a loggerhead sea turtle (Caretta caretta) rookery affected the interannual variability of clutch frequency (the number of clutches laid by a female during a nesting season) and of the number of total located nests, based on comprehensive nighttime and daytime field surveys conducted at Yakushima Island, Japan, over a non‐consecutive eight‐year period. Taking into account the fact that lower trophic‐level sea turtles show greater variability in these parameters, we anticipated clutch frequency and the number of total located nests to vary more in low trophic‐level oceanic planktivores (secondary consumers) than in high trophic‐level neritic benthivores (tertiary consumers). Oceanic planktivores and neritic benthivores were classified by stable isotope ratios in egg yolks. Neritic foragers had higher clutch frequencies than oceanic foragers in any year. Contrary to our anticipation, however, both types of foragers showed similarly low interannual variability in clutch frequencies. No significant correlations were found between mean clutch frequencies and the estimated number of nests made by either oceanic or neritic foragers and the number of total located nests. Interannual fluctuations in the total number of nests made by loggerhead turtles, whether trophically monomorphic or polymorphic, seem to be driven more by the number of females than by clutch frequency; this suggests that the number of total located nests can be a good proxy for the population size of iteroparous animals at relatively high trophic levels.

Trend and Variability in Interannual Air Temperature Over South West Mau Forest, 1985 - 2015

The research is sponsored by Jomo Kenyatta University of Agriculture and Technology and National Commission for Science, Technology and Innovation Kenya. Abstract Globally high altitude forest regions are considered to be more prone to rapid warming. These regions have also shown great seasonal and inter annual temperatures variability. In Kenya mean annual temperatures increased by 1.0 0 C since 1960. Going by global trends it is plausible to argue that high altitude forest areas in Kenya might have shown great seasonal and inter annual temperatures variability over time. This study assessed interannual trend and variability as well as change point detection in average annual air temperature in South West Mau Forest, Kenya between 1985 and 2015. South West Mau Forest is an indigenous montane ecosystem with a tropical montane climate. Annual average air temperature over the South West Mau forest pointed towards climate warming of 0.0188 0 C per year (Kendall’s tau = 0.3677, p value = 0.0033) but with low interannual variability (CV= 0.11%). A shift in the annual average air temperature of 0.368 0 C at p= 0.0051 was detected between 1985-1998 and 1999- 2015. There was a weak positive anomaly in the annual average air temperature with a slope of 0.0192 and R 2 = 0.3074. Overall the region experienced climate warming. Keywords: Climate warming, Trend, Variability, Average temperature DOI: 10.7176/JNSR/11-16-04 Publication date: August 31 st 2020

Carbon Sequestration by the Above Ground Biomass Pool in the South West Mau Forest of Kenya, 1985 - 2015

Forests are important for regulation of the global carbon balance. Increase in forest biomass enhances atmospheric carbon sequestration while decrease in forest biomass contributes to carbon dioxide emissions. World over, forest biomass has been declining due to forest loss and degradation. The South West Mau has experienced significant forest loss since 1964. The decline is posited to have significant impacts on carbon sequestration, carbon storage, carbon dioxide emissions and status of atmospheric carbon dioxide. This study assessed interannual trend and variability as well as change point detection in carbon sequestration in South West Mau Forest, Kenya between 1985 and 2015. Above ground biomass carbon sequestration was quantified based on the Carnegie-Ames-Stanford Approach (CASA) and carbon fraction for tropical climate domain. Carbon sequestration dynamics were characterized by increase-decrease cycles of approximately 3 years and low interannual variability (CV= 9.13). It emerged that South West Mau Forest was a net carbon emitter with a carbon sequestration balance of -588.40 Kg/ha between 1985 and 2015. Keywords: Forest, Carbon sequestration, Carnegie-Ames-Stanford Approach, Above ground net primary production DOI: 10.7176/JEES/10-8-05 Publication date: August 31 st 2020

Characteristics of the Onset, Withdrawal, and Breaks of the Western North Pacific Summer Monsoon in the 1949–2014 Period

ABSTRACTThe western North Pacific summer monsoon (WNPSM) onset and withdrawal dates as well as its breaks have been determined throughout the 1949–2014 period by defining the monsoon daily directional index (MDDI). This index, developed exclusively with wind direction observations, is an upgrade of the monthly western North Pacific directional index. The onset date shows a high interannual variability, varying between early May and early August, whereas the WNPSM withdrawal shows a lower interannual variability, occurring between October and mid-November. The MDDI reflects the multibreak character of the WNPSM. Breaks, which tend to last a few weeks, are more likely to happen from mid-August to early September and from late June to mid-July. This bimodal distribution shows decadal variability. In addition, the monsoon dates determined by the MDDI show very good agreement with relationships previously described in literature, such as the influence of tropical Pacific SST on the monsoon onset/withdrawal and changes in tropical cyclone (TC) tracks related to monsoon breaks. The WNPSM tends to start earlier (later) and finish later (earlier) under eastern Pacific (EP) La Niña (El Niño) conditions, especially from the 1980s on. Central Pacific (CP) ENSO is also associated with the monsoon withdrawal, which is advanced (delayed) under CP El Niño (La Niña). TCs tend to move from the Philippine Sea to the South China Sea during active monsoon days whereas they tend to reach higher latitudes during inactive monsoon days, especially in August and July.