Changes In Season Length Research Articles

The Elusive "Switch Process" in Bipolar Disorder and Photoperiodism: A Hypothesis Centering on NADPH Oxidase-Generated Reactive Oxygen Species Within the Bed Nucleus of the Stria Terminalis.

One of the most striking and least understood aspects of mood disorders involves the “switch process” which drives the dramatic state changes characteristic of bipolar disorder. In this paper we explore the bipolar switch mechanism as deeply grounded in forms of seasonal switching (for example, from summer to winter phenotypes) displayed by many mammalian species. Thus we develop a new and unifying hypothesis that involves four specific claims, all converging to demonstrate a deeper affinity between the bipolar switch process and the light-sensitive (photoperiodic) nonhuman switch sequence than has been appreciated. First, we suggest that rapid eye movement (REM) sleep in both human and nonhuman plays a key role in probing for those seasonal changes in length of day that trigger the organism's characteristic involutional response (in certain animals, hibernation) to shorter days. Second, we claim that this general mammalian response requires the integrity of a neural circuit centering on the anterior bed nucleus of the stria terminalis. Third, we propose that a key molecular mediator of the switch process in both nonhumans and seasonal humans involves reactive oxygen species (ROS) of a particular provenance, namely those created by the enzyme NADPH oxidase (NOX). This position diverges from one currently prominent among students of bipolar disorder. In that tradition, the fact that patients afflicted with bipolar-spectrum disorders display indices of oxidative damage is marshaled to support the conclusion that ROS, escaping adventitiously from mitochondria, have a near-exclusive pathological role. Instead, we believe that ROS, originating instead in membrane-affiliated NOX enzymes upstream from mitochondria, take part in an eminently physiological signaling process at work to some degree in all mammals. Fourth and finally, we speculate that the diversion of ROS from that purposeful, genetically rooted seasonal switching task into the domain of human pathology represents a surprisingly recent phenomenon. It is one instigated mainly by anthropogenic modifications of the environment, especially “light pollution.”

Earlier green-up and senescence of temperate United States rangelands under future climate

Climate and vegetation phenology are closely linked, and climate change is already impacting phenology in many systems. These impacts are expected to progress in the future. We sought to forecast future shifts in rangeland growing season timing due to climate change, and interpret their importance for land management and ecosystem function. We trained a model on remotely sensed land surface phenology and climate data collected from 2001 to 2014 in temperate United States rangelands. We used this model to forecast annual growing season start dates, end dates, and season length through 2099 among six general circulation models and under RCP 4.5 and 8.5 scenarios. Growing season start was projected to shift earlier throughout our study area. In 2090–2099, start of season advanced by an average of 10 (RCP 4.5) to 17 (RCP 8.5) days. End of season also advanced by 12 (RCP 4.5) to 24 (RCP 8.5) days, but with greater heterogeneity. Start and end of season change mainly offset one another, so growing season length changes were lesser (2 days in RCP 4.5, and 7 in RCP 8.5). Some mountainous areas experienced both earlier start of season and later end of season, lengthening their growing season. Earlier phenology in rangelands would force adaptation in grazing and impact ecosystem function. Mountainous areas with earlier start and later end of season may become more viable for grazing, but most areas may experience slightly shortened growing seasons. Autumn phenology warrants greater research, and our finding of earlier autumn senescence contradicts some prior research.

Simulation evidence on Herfindahl-Hirschman measures of competitive balance in professional sports leagues

Measurement of the degree of competitive balance, how evenly teams are matched, is central to the analysis of professional sports leagues. A common problem with within-season competitive balance measures, however, is their sensitivity to the number of teams and the number of matches played by each team, i.e. season length. This paper uses simulation methods to examine the effects of changes in season length on the distributions of several widely used variants of the Herfindahl-Hirschman index applied to wins in a season. Accounting for both the lower and upper bounds of the index improves its robustness to variation in the numbers of teams or games played per season, but does not completely remove overestimation of imbalance associated with shorter season lengths. Overall, McGee’s balance measure significantly mitigates the dependence on the number of matches and, of the measures considered, is recommended as the most robust to variation in season length.

Competitive balance with unbalanced schedules

Abstract Many empirical studies on competitive balance (CB) use the ratio of the actual standard deviation to the idealized standard deviation of win percentages (RSD). This paper suggests that empirical studies that use RSD to compare CB among different leagues are invalid, but that RSD may be used for time-series analysis on CB in a league if there are no changes in season length. When schedules are unbalanced and/or include interleague games, the final winning percentage is a biased estimator of the true win probability. This paper takes a mathematical statistical approach to derive an unbiased estimator of within-season CB that can be applied to not only balanced but also unbalanced schedules. Simulations and empirical applications are also presented, which confirm that the debiasing strategy to obtain the unbiased estimator of within-season CB is still effective for unbalanced schedules.

Seasonal and Long-Term Changes to Pavement Life Caused by Rising Temperatures from Climate Change

Pavements are vulnerable to reduced life with climate-change-induced temperature rise. Greenhouse gas emissions have caused an increase in global temperatures since the mid-20th century and the warming is projected to accelerate. Many studies have characterized this risk with a top-down approach in which climate-change scenarios are chosen and applied to predict pavement-life reduction. This approach is useful in identifying possible pavement futures but may miss short-term or seasonal pavement-response trends that are essential for adaptation planning. A bottom-up approach focuses on a pavement’s response to incremental temperature change resulting in a more complete understanding of temperature-induced pavement damage. In this study, a hybrid bottom-up/top-down approach was used to quantify the impact of changing pavement seasons and temperatures on pavement life with incremental temperature rise from 0 to 5°C at a site in coastal New Hampshire. Changes in season length, seasonal average temperatures, and temperature-dependent resilient modulus were used in layered-elastic analysis to simulate the pavement’s response to temperature rise. Projected temperature rise from downscaled global climate models was then superimposed on the results to determine the timing of the effects. The winter pavement season is projected to end by mid-century, replaced by a lengthening fall season. Seasonal pavement damage, currently dominated by the late spring and summer seasons, is projected to be distributed more evenly throughout the year as temperatures rise. A 7% to 32% increase in the asphalt-layer thickness is recommended to protect the base and subgrade with rising temperatures from early century to late-mid-century.

Climate, forest growing season, and evapotranspiration changes in the central Appalachian Mountains, USA

We analyzed trends in climatologic, hydrologic, and growing season length variables, identified the important variables effecting growing season length changes, and evaluated the influence of a lengthened growing season on increasing evapotranspiration trends for the central Appalachian Mountains region of the United States. We generated three growing season length variables using remotely sensed GIMMS NDVI3g data, two variables from measured streamflow, and 13 climate parameters from gridded datasets. We included various climate, hydrology, and phenology explanatory variables in two applications of Principle Components Analysis to reduce dimensionality, then utilized the final variables in two Linear Mixed Effects models to evaluate the role of climate on growing season length and evapotranspiration. The results showed that growing season length has increased, on average, by ~22 days and evapotranspiration has increased up to ~12 mm throughout the region. The results also suggest that a suite of climatic variables including temperature, vapor pressure deficit, wind, and humidity are important in growing season length change. The climatic variables work synergistically to produce greater evaporative demand and atmospheric humidity, which is theoretically consistent with intensification of the water cycle and the Clausius-Clapeyron relation, which states that humidity increases nonlinearly by 7%/K. Optimization of the evapotranspiration model was increased by the inclusion of growing season length, suggesting that growing season length is partially responsible for variations in evapotranspiration over time. The results of this research imply that a longer growing season has the potential to increase forest water cycling and evaporative loss in temperate forests, which may lead to decreased freshwater provisioning from forests to downstream population centers. Additionally, results from this study provide important information for runoff and evapotranspiration modelling and forest water management under changing climate.

Gradients of season length and mortality risk cause shifts in body size, reserves and reproductive strategies of determinate growers

Abstract The theory of life‐history evolution investigates how growth‐reproduction trade‐offs drive evolution of body size in uni‐ and multivoltine (one or more generations per year) arthropods. Existing theory does not predict how the length of the feeding season (season length hereafter) affects body size in semivoltine (i.e., juvenile period longer than 1 year) determinate growers and usually ignores that uni‐ and semivoltine arthropods accumulate large reserves to cover costs of diapause and future reproduction. Here, we present how the trade‐offs between growth, storage and reproduction drive evolution of body mass and reproductive strategy in arthropods with determinate growth. Our life‐history model concerns high‐latitude marine copepods living in a strongly seasonal environment. We find that small changes in season length and mortality rate translate into abrupt shifts in lean body mass (a proxy for body size). Body size shifts are caused by a change from multi‐ to uni‐ and semivoltine life cycles with semivoltine life histories selected for in short seasons and only if background mortality is low. Shifts in the number of generations per year do not translate into shifts in the mass of lipid reserves. The model predicts less reserves the shorter the winter. Season length alone is not a sufficient predictor of the degree of capital breeding. Storing for reproduction is strongly selected for under short season but low mortality rate. Hence, capital breeding contributes to fitness in uni‐ and semivoltine organisms whereas multivoltines are income breeders. We also show that storing reserves for diapause and capital breeding trades off with adult size of determinately growing arthropods. Our results, in particular regarding optimal body size, reproductive strategy (income‐to‐capital breeding) and degree of storage are relevant to a number of determinate growers, including insects and crustaceans. A plain language summary is available for this article.

Projected climate change impacts on skiing and snowmobiling: A case study of the United States

Abstract We use a physically-based water and energy balance model to simulate natural snow accumulation at 247 winter recreation locations across the continental United States. We combine this model with projections of snowmaking conditions to determine downhill skiing, cross-country skiing, and snowmobiling season lengths under baseline and future climates, using data from five climate models and two emissions scenarios. Projected season lengths are combined with baseline estimates of winter recreation activity, entrance fee information, and potential changes in population to monetize impacts to the selected winter recreation activity categories for the years 2050 and 2090. Our results identify changes in winter recreation season lengths across the United States that vary by location, recreational activity type, and climate scenario. However, virtually all locations are projected to see reductions in winter recreation season lengths, exceeding 50% by 2050 and 80% in 2090 for some downhill skiing locations. We estimate these season length changes could result in millions to tens of millions of foregone recreational visits annually by 2050, with an annual monetized impact of hundreds of millions of dollars. Comparing results from the alternative emissions scenarios shows that limiting global greenhouse gas emissions could both delay and substantially reduce adverse impacts to the winter recreation industry.

Impacts of oak pollen on allergic asthma in the United States and potential influence of future climate change.

Future climate change is expected to lengthen and intensify pollen seasons in the U.S., potentially increasing incidence of allergic asthma. We developed a proof‐of‐concept approach for estimating asthma emergency department (ED) visits in the U.S. associated with present‐day and climate‐induced changes in oak pollen. We estimated oak pollen season length for moderate (Representative Concentration Pathway (RCP) 4.5) and severe climate change scenarios (RCP8.5) through 2090 using five climate models and published relationships between temperature, precipitation, and oak pollen season length. We calculated asthma ED visit counts associated with 1994–2010 average oak pollen concentrations and simulated future oak pollen season length changes using the Environmental Benefits Mapping and Analysis Program, driven by epidemiologically derived concentration‐response relationships. Oak pollen was associated with 21,200 (95% confidence interval, 10,000–35,200) asthma ED visits in the Northeast, Southeast, and Midwest U.S. in 2010, with damages valued at $10.4 million. Nearly 70% of these occurred among children age <18 years. Severe climate change could increase oak pollen season length and associated asthma ED visits by 5% and 10% on average in 2050 and 2090, with a marginal net present value through 2090 of $10.4 million (additional to the baseline value of $346.2 million). Moderate versus severe climate change could avoid >50% of the additional oak pollen‐related asthma ED visits in 2090. Despite several key uncertainties and limitations, these results suggest that aeroallergens pose a substantial U.S. public health burden, that climate change could increase U.S. allergic disease incidence, and that mitigating climate change may have benefits from avoided pollen‐related health impacts.

Impacts of oak pollen on allergic asthma in the USA and potential effect of future climate change: a modelling analysis

BackgroundFuture climate change is expected to lengthen and intensify pollen seasons in the USA, potentially increasing incidence of allergic asthma. We examined the health consequences of present day oak pollen levels and climate-induced changes in oak pollen on asthma emergency department visits in the USA. MethodsWe estimated oak pollen season length for moderate (RCP4.5) and severe climate change scenarios (RCP8.5) from 2010 through to 2090 using five climate models and published relationships between temperature, precipitation, and pollen season length. We calculated asthma emergency department visit counts associated with 1994–2010 average oak pollen concentrations and with simulated future oak pollen season length changes using the Environmental Benefits Mapping and Analysis Program (BenMAP-CE), driven by epidemiologically derived concentration-response relationships. FindingsOak pollen was associated with an estimated 7400, 8800, and 5000 asthma emergency department visits in the northeast, southeast, and midwest USA, respectively, in 2010, with substantial economic damages. Most of these visits (14 600) occurred among children age younger than 18 years. Severe climate change could increase oak pollen season length and associated asthma emergency departments visits in all regions examined in 2030, 2050, 2070, and 2090, resulting in millions of dollars in health-care costs in these US regions through to 2090. Moderate versus severe climate change could mitigate much of the additional burden of oak pollen-related asthma emergency department visits. InterpretationAlthough these results were restricted to one pollen type and one health outcome, these results suggest that aeroallergens pose a substantial US public health burden, that climate change could increase US allergic disease incidence, and that mitigating climate change might have benefits from avoided pollen-related health effects. However, wide confidence intervals and several key methodological limitations constrain the strength of these conclusions. As more studies quantify the effects of climate on pollen and pollen on health, this methodology can be applied to additional pollen types and health outcomes. FundingUS Environmental Protection Agency.

Seasonally Varying Predation Behavior and Climate Shifts Are Predicted to Affect Predator-Prey Cycles.

The functional response of some predator species changes from a pattern characteristic for a generalist to that for a specialist according to seasonally varying prey availability. Current theory does not address the dynamic consequences of this phenomenon. Since season length correlates strongly with altitude and latitude and is predicted to change under future climate scenarios, including this phenomenon in theoretical models seems essential for correct prediction of future ecosystem dynamics. We develop and analyze a two-season model for the great horned owl (Bubo virginialis) and snowshoe hare (Lepus americanus). These species form a predator-prey system in which the generalist to specialist shift in predation pattern has been documented empirically. We study the qualitative behavior of this predator-prey model community as summer season length changes. We find that relatively small changes in summer season length can have a profound impact on the system. In particular, when the predator has sufficient alternative resources available during the summer season, it can drive the prey to extinction, there can be coexisting stable states, and there can be stable large-amplitude limit cycles coexisting with a stable steady state. Our results illustrate that the impacts of global change on local ecosystems can be driven by internal system dynamics and can potentially have catastrophic consequences.

Reconsidering meteorological seasons in a changing climate

Traditional definitions of seasonality are insufficient to reflect changes associated with a swiftly changing climate. Regional changes in season onset and length using surface based metrics are well documented, but hemispheric assessments using tropospheric metrics has received little attention. The long-term average of six-hourly analyses of temperature on isobaric surfaces, provided by the Twentieth Century Reanalysis Project, is separated here into quartiles to determine climatologic seasonal end dates. Annual season end dates are defined as the date when the 5-day moving average rose above (winter and spring) or fell below (summer and fall) the long term mean. Climatic season end dates fall between meteorological and astronomical season end dates. The length of summer has increased by an average of 13 days and the length of winter has decreased by an average of 20 days, which are more substantial seasonal changes than previous studies. These changes in season length have occurred largely within the past 36 years, corresponding to most aggressive anthropogenic climate change. Results show that the planetary boundary layer is warming at nearly twice the rate of the free troposphere. The spatial distribution of warming suggests that topographically induced weather systems are collocated with maxima or minima in free tropospheric and boundary layer temperature slope. Furthermore, regions of greatest ensemble spread are not collocated with relative maxima or minima in free troposphere or boundary layer temperature slope. This improved assessment of seasonal transitions is useful to climatologists, agricultural land managers, and scientists interested in seasonally driven biology, hydrology and biogeochemical processes.

Constrained growth flips the direction of optimal phenological responses among annual plants.

Phenological changes among plants due to climate change are well documented, but often hard to interpret. In order to assess the adaptive value of observed changes, we study how annual plants with and without growth constraints should optimize their flowering time when productivity and season length changes. We consider growth constraints that depend on the plant's vegetative mass: self-shading, costs for nonphotosynthetic structural tissue and sibling competition. We derive the optimal flowering time from a dynamic energy allocation model using optimal control theory. We prove that an immediate switch (bang-bang control) from vegetative to reproductive growth is optimal with constrained growth and constant mortality. Increasing mean productivity, while keeping season length constant and growth unconstrained, delayed the optimal flowering time. When growth was constrained and productivity was relatively high, the optimal flowering time advanced instead. When the growth season was extended equally at both ends, the optimal flowering time was advanced under constrained growth and delayed under unconstrained growth. Our results suggests that growth constraints are key factors to consider when interpreting phenological flowering responses. It can help to explain phenological patterns along productivity gradients, and links empirical observations made on calendar scales with life-history theory.

Projected Twenty-First-Century Changes in the Length of the Tropical Cyclone Season

Abstract This study investigates projected changes in the length of the tropical cyclone season due to greenhouse gas increases. Two sets of simulations are analyzed, both of which capture the relevant features of the observed annual cycle of tropical cyclones in the recent historical record. Both sets use output from the general circulation models (GCMs) of either phase 3 or phase 5 of the CMIP suite (CMIP3 and CMIP5, respectively). In one set, downscaling is performed by randomly seeding incipient vortices into the large-scale atmospheric conditions simulated by each GCM and simulating the vortices’ evolution in an axisymmetric dynamical tropical cyclone model; in the other set, the GCMs’ sea surface temperature (SST) is used as the boundary condition for a high-resolution global atmospheric model (HiRAM). The downscaling model projects a longer season (in the late twenty-first century compared to the twentieth century) in most basins when using CMIP5 data but a slightly shorter season using CMIP3. HiRAM with either CMIP3 or CMIP5 SST anomalies projects a shorter tropical cyclone season in most basins. Season length is measured by the number of consecutive days that the mean cyclone count is greater than a fixed threshold, but other metrics give consistent results. The projected season length changes are also consistent with the large-scale changes, as measured by a genesis index of tropical cyclones. The season length changes are mostly explained by an idealized year-round multiplicative change in tropical cyclone frequency, but additional changes in the transition months also contribute.

Evaluating changes in season length, onset, and end dates across the United States (1948–2012)

ABSTRACTDiscussed in a global context, the issue of scale is important to consider as it relates to climate change. As climatological studies utilize temporally and spatially static definitions of seasonal definitions, the understanding of seasonal change may be limited by the way in which seasons are defined. This research serves as a challenge to this perspective by examining the changes in seasons by incorporating variability into the way in which seasons are defined. Temporally and spatially variable seasons were defined based on thresholds of apparent temperature and upper‐level circulation patterns for the period 1948–2012. Using 60 US surface stations, two apparent air temperature metrics were used to define seasons that vary spatially and temporally. Stations represented major cities found in the contiguous United States. A large‐scale circulation approach utilized synoptic categorizations based on 250‐mb geopotential heights from the NCEP‐NCAR reanalysis (NNR) as a metric of seasonal delineation. In this method, seasons varied temporally but not spatially. Despite the different methodological approaches, consistent trends were found. Since 1948, late starts of autumn and winter have been observed while earlier onsets of spring and summer have taken place. For the individual stations, the largest shifts occurred along coasts and in larger, more urbanized environments. Individual locations also showed increased variability in start date, and significant changes were found for all four seasons in the circulation approach. Seasons have been shown to be important for a variety of processes including phenological responses and human adaptation to extreme temperature environments; therefore, the consideration of season variability may be appropriate for future climatological research.

How does harvest size vary with hunting season length?

Manipulating hunting season length is often used as a population management tool but the effects of these changes on total harvest have rarely been studied. We modelled relative changes in national annual bag size as a function of relative change in hunting season length in 63 cases involving 28 species in Denmark (1957–2007). The duration of the hunting season, initially lasting 30–365 days, was modified to 39–204% of the former length. The undifferentiated effect of season length change on bag size change (all 63 cases) was not statistically significant (b = 0.16, 95%CI: ‐0.04–0.36), with a 10% (95%CI: ‐3–22%) predicted decrease in bag size upon a 50% reduction of season length. However, the functional relationship between the relative change in bag size and the change in season length differed between sedentary and non‐sedentary species and interacted with the motivation behind changing season length (population management/ethical/other). In non‐sedentary species, changes in bag size correlated positively with changes in season length (overall response: b = 0.54, 95%CI: 0.14–0.95): reducing the hunting season to 50% of its initial length would on average result in a 31% reduction (95% CI: 9–48%) of total bag size. This overall effect interacted with the motivation for season length changes, being strongest for ‘other reasons’ (mainly harmonization of hunting periods for related species) but was absent when seasons were changed for reasons of ‘population management’. In sedentary species, changes in season length had no effect on bag size. Our results suggest that manipulating hunting seasons of duration ≥ 1 month by less than 50% is generally inefficient as a means of predictably changing harvest rates. This may be because recreational hunters either invest a fixed effort or aim for a specific yield within a given season, neither strategy being affected by changes in hunting seasons.

COMPETITIVE BALANCE MEASURES IN SPORTS LEAGUES: THE EFFECTS OF VARIATION IN SEASON LENGTH

Appropriate measurement of competitive balance is central to the economic analysis of professional sports leagues. We examine the distributional properties of the ratio of standard deviations (RSD) of points percentages, the most widely used measure of competitive balance in the sports economics literature, in comparison with other standard‐deviation‐based measures. Simulation methods are used to evaluate the effects of changes in season length on the distributions of competitive balance measures for different distributions of the strengths of teams in a league. The popular RSD measure performs as expected only in cases of perfect balance; if there is imbalance in team strengths, its distribution is sensitive to changes in season length. It is therefore not recommended for comparisons of competitive balance for different sports leagues with different numbers of teams and/or games played. (JEL L83, D63, C63)

Global wildland fire season severity in the 21st century

We used Cumulative Severity Rating (CSR), a weather-based fire danger metric, to examine the potential influence of climate change on global fire season severity. The potential influence of climate change on fire season length was also addressed. We used three General Circulation Models (GCMs) and three emission scenarios to calculate the CSR and fire season length for mid-century (2041–2050) and late century (2091–2100) relative to the 1971–2000 baseline. Our results suggest significant increases in the CSR for all models and scenarios. Increases were greatest (more than three times greater than the baseline CSR) for the Northern Hemisphere at the end of the century. Fire season length changes were also most pronounced at the end of the century and for northern high latitudes where fire season lengths will increase by more than 20days per year. The implications from this study are that fire seasons will be more severe in future and that conventional fire management approaches may no longer be effective.

Reproduction in Male Crotalus adamanteus Beauvois (Eastern Diamond-Backed Rattlesnake): Relationship of Plasma Testosterone to Testis and Kidney Dimensions and the Mating Season

The reproductive ecology of male Crotalus adamanteus Beauvois (Eastern Diamond-backed Rattlesnake) from southwestern Georgia (Joseph W. Jones Ecological Research Center, Baker County) was studied from 14 August 2003 to 14 August 2006. Few studies provide information on reproduction of free-living Eastern Diamondbacked Rattlesnakes, and no information is available on the seasonal relationship of plasma sex steroids of males to changes in the reproductive organs (e.g., mass of the testis and kidney) and the mating season. Here, the main goals were to determine whether: (i) males show variation in concentrations of plasma testosterone (T) during the active season (late March through November), (ii) males have elevated (peak) concentrations of plasma T during the single mating season, which has been documented to occur from late summer through early fall in nearby populations, and (iii) there are seasonal changes in length, width, and mass of the testis and kidney during the active season, particularly during the breeding period. There was a significant difference in mean concentrations of plasma T among seasons, with levels in summer significantly greater than those of spring, and levels in spring and fall were not significantly different. Testis mass and width, but not length, varied significantly across seasons. Testis mass paralleled elevated levels of plasma T, with peak mass occurring in the summer. Similarly, testis width was significantly greater in summer than in fall, but there was no significant difference between summer and spring, nor between spring and fall. We found no significant seasonal changes in any of the kidney measurements. Bisexual pairings were coincident or followed the occurrence of elevated levels of plasma T and changes in testis size; however, despite frequent observations, copulations were not observed. Nonetheless, our results support a mating season of late summer/early fall for the present population of Eastern Diamond-backed Rattlesnakes.

Assessing impact of climate change on season length in Karnataka for IPCC SRES scenarios

Changes in seasons and season length are an indicator, as well as an effect, of climate change. Seasonal change profoundly affects the balance of life in ecosystems and impacts essential human activities such as agriculture and irrigation. This study investigates the uncertainty of season length in Karnataka state, India, due to the choice of scenarios, season type and number of seasons. Based on the type of season, the monthly sequences of variables (predictors) were selected from datasets of NCEP and Canadian General Circulation Model (CGCM3). Seasonal stratifications were carried out on the selected predictors using K-means clustering technique. The results of cluster analysis revealed increase in average, wet season length in A2, A1B and B1 scenarios towards the end of 21st century. The increase in season length was higher for A2 scenario whereas it was the least for B1 scenario. COMMIT scenario did not show any change in season length. However, no change in average warm and cold season length was observed across the four scenarios considered. The number of seasons was increased from 2 to 5. The results of the analysis revealed that no distinct cluster could be obtained when the number of seasons was increased beyond three.