March Precipitation Research Articles

Linking atmospheric circulation to daily precipitation patterns over the territory of Bulgaria

An eight states non-homogeneous hidden Markov model is developed for linking daily precipitation amounts data at a network of 32 stations broadly covering the territory of Bulgaria to large-scale atmospheric patterns. At each site a 40-year record 1960–2000 of daily October–March precipitation amounts is modeled. The atmospheric data consists of daily sea-level pressure, geopotential height at 500 and 850 hPa, air temperature at 850 hPa and relative humidity at 700 and 850 hPa on a 2.5 × 2.5 grid based on NCEP-NCAR reanalysis data set covering the Europe-Atlantic sector 30W–60E, 20N–70N for the same period. The first 30 years data are used for model fitting purposes while the remaining 10 years are used for model evaluation. Detailed model validation is carried out on various aspects. The proposed model reproduces well the rainfall statistics for the observed and reserved data whereas the identified states are found to be physically interpretable in terms of regional climatology.

Reproductive timing and investment in relation to spring warming and advancing agricultural schedules

Advances in mowing schedules have led to early and rapid declines in the seasonal food availability for, and survival rates of, chicks of grassland-breeding waders. Concurrently, increased levels of soil fertilization may have improved food abundance for adults. These developments are assumed to have resulted in an advancement of laying during 1930–1976 in several meadowbird species, including Black-tailed Godwits. Despite an apparent selective advantage of early breeding, after 1976 Godwits stopped advancing their laying dates. We have analyzed the timing of breeding and reproductive investment in Dutch Black-tailed Godwits relative to recent changes in agricultural practices and climate during 1976–2007. Early and late spring temperatures and precipitation in March were used as indicators for the timing of fertilizer application and mowing, and also as qualitative measures of relative food availability for adults and chicks. When precipitation was higher in March, Black-tailed Godwits laid earlier. Following warmer winters, the earliest females laid larger eggs, which hatched heavier chicks with a higher survival probability. We suggest that the positive effect of an increasing March precipitation on invertebrate abundance may be constrained by the current policy of rigid control of the water table. This policy prevents Godwits from further advancing laying dates, which would increase their chick’s survival prospects under increasingly early mowing schedules. Policy-makers should, next to delaying mowing schedules, also consider reduced draining in early spring as a tool to help stop the population decline of the Black-tailed Godwit.

Modelling past and future wine production in the Portuguese Douro Valley

Climate is a major factor driving wine productivity in the Douro Valley region of Portu- gal because vineyards are generally grown under marginal conditions for agricultural production. Using monthly means of climate variables (daily maximum, minimum and mean temperature, diurnal thermal amplitude and daily precipitation) and the normalised difference vegetation index, we analysed the vegetative cycle of vineyards and the vulnerability of Douro wine production to climate variability and change. A good wine production year reflects high photosynthetic activity during spring followed by reduced greenness during summer. Lower precipitation in March has a positive effect during the growing stage, and higher temperatures during late spring are beneficial for pro- duction. Two linear regression models were developed with the aim of forecasting Douro wine pro- duction at the early (March) and mid-season (July) stages of the vine vegetative cycle. Both models performed well in terms of robustness and reliability. The early season model has the advantage of providing a reliable production scenario immediately after the dormancy stage. All predictors of the mid-season model are meteorological parameters; combined with the very high value (90%) of explained variance, this suggests its usefulness to assess the crucial role of climate in wine produc- tion. Limitations result from the linear nature of the model, and effects due to the increase in CO2 were disregarded. Nevertheless, our results indicate an increase in production from 1956-1985 to 1986-2006 due to changes in the winter precipitation regime. Moreover, 2071-2100 climate scenarios (A2 and B2) are expected to favour an increase in wine production because of the combined effects of tem perature and precipitation in late spring and early summer.

Regional Differences in South American Monsoon Precipitation Inferred from the Growth and Isotopic Composition of Tropical Trees*

Abstract The authors present results on the relationship between tree-ring proxies and regional precipitation for several sites in tropical South America. The responsiveness of oxygen isotopes (δ18O) and seasonal growth as precipitation proxies was first validated by high-resolution sampling of a Tachigali myrmecophila from Manaus, Brazil (3.1°S, 60.0°W). Monthly growth of Tachigali spp. was significantly correlated with monthly precipitation. Intra-annual measurements of cellulose δ18O in Tachigali spp. were also significantly correlated with monthly precipitation at a lag of approximately one month. The annual ring widths of two tropical tree taxa, Cedrela odorata growing in the Amazon (12.6°S, 69.2°W) and Polylepis tarapacana growing in the Altiplano (22.0°S, 66.0°W), were validated using bomb-derived radiocarbon 14C. Estimated dates were within two to three years of bomb-inferred 14C dates, indicating that these species exhibit annual rings but uncertainties in our chronologies remain. A multiproxy record spanning 180 years from Cedrela spp. showed a significant negative relationship between cellulose δ18O and January precipitation. A 150-yr record obtained from Polylepis spp. also showed a significant negative relationship between δ18O and March precipitation, whereas annual ring width showed a significant positive correlation with December precipitation. These proxies were combined in a multivariate framework to reconstruct past precipitation, revealing a significant increase in monsoon precipitation at the Amazon site since 1890 and a significant decrease in monsoon precipitation at the Altiplano since 1880. Proxy time series also showed spatial and temporal coherence with precipitation variability due to El Niño forcing, suggesting that oxygen isotopes and ring widths in tropical trees may be important diagnostics for identifying regional differences in the response of the tropical hydrologic cycle to anthropogenic warming.

Climatic and morphometric controls on the altitudinal range of glaciers, British Columbia, Canada

To examine the relation between climate and glacier extent, we compared gridded, monthly temperature and precipitation data to the altitudinal range of glaciers in British Columbia, Canada. We related glacier relief to ablation season temperature (June—August), accumulation season precipitation (September— March), and morphometric variables that included slope, glacier order, and a shape index for 523 alpine glaciers that ranged from 5 to 15 km2 in surface area. A 1°C increase in mean June—August temperature equates to a 109 to 182 m decrease in glacier relief, and a 1 mm increase in mean monthly September— March precipitation equates to a 0.78 to 2.20 m increase in glacier relief. The most important morphometric controls on this glacier—climate relation include average surface slope, glacier order (analogous to stream order), and the ratio of upper accumulation area to lower ablation area width, all of which are positively related to glacier relief. We note strong relations between glacier relief and climate in all mountain regions of British Columbia, with glaciers of the interior ranges being most sensitive to spatial climatic variability. We show how our approach can be used to estimate past climatic conditions based on historical ice extents, such as at the ‘Little Ice Age’ maximum, and to predict potential future equilibrium glacier extents in a changed climate regime, such as those predicted by general and regional circulation models.

On the Relationships between the Madden–Julian Oscillation and Precipitation Variability in Southern Iran and the Arabian Peninsula: Atmospheric Circulation Analysis

Abstract The influence of the Madden–Julian oscillation (MJO) on daily, monthly, and seasonal precipitation was investigated for southern Iran and the Arabian Peninsula using November–April data for the period of 1979–2005. The positive MJO phase is considered to be the periods for which the enhanced convection center was placed over the south Indonesian–north Australian region. On the other hand, the convection center shifts over the western Indian Ocean tropics and most of the study area as the negative MJO phase prevails. Seasonal precipitation and the frequency of wet events were significantly increased during the negative phase. The ratios of the precipitation amount during the negative phase to the corresponding values during the positive phase were about 1.75–2.75 and 2.75–4.00 for the southwestern and southeastern parts of Iran, respectively. This ratio reached to about 3.00 for Riyadh, 4.20 and 5.50 for Masqat and Doha, 2.10 for Kuwait, and 1.20 for Bahrain. The results of the seasonal and monthly analysis were generally found to be consistent, although because of the smaller sample size the outcomes of the monthly investigations were less statistically significant. While the negative MJO phase does not have a consistent effect on March precipitation over some parts of southern Iran, it has consistently enhanced precipitation over the eastern and southern coasts of the peninsula in Oman, Yemen, and Saudi Arabia. During the negative MJO phase, while enhanced low-level southerly winds transfer a substantial amount of moisture to the study area, upward motion increases in the middle layers of the atmosphere. Synchronized with the prevalence of these rain-bearing southerly winds, the existence of a strong horizontal wind speed gradient at the exit region of the North Africa–Arabian jet enhances precipitation. The jet exit, which was mostly located over Egypt in November, moved westward into the study area in Iran and Saudi Arabia during the rainy period of January–March. The direction of near-surface wind anomalies changed from mostly southeasterly in November to southwesterly in March and April, influencing precipitation pattern during various months of the rainy season. In contrast to the negative phase, an enhanced low-level dry northerly wind and suppressed horizontal wind speed gradient at the jet exits are the main characteristics of atmospheric circulation over the study area during the positive MJO phase. Furthermore, an increased downward air motion at the middle levels of the atmosphere and a significant shortage in precipitation are the other climatic components of the southwest Asian region during such a period.

The Value of ENSO Forecast Information to Dual-Purpose Winter Wheat Production in the U.S. Southern High Plains

Abstract The value of El Niño–Southern Oscillation (ENSO) forecast information to southern high plains winter wheat and cattle-grazing production systems was estimated here by simulation. Although previous work has calculated average forecast value, the approach here was to estimate probabilities of the value of single forecasts from value distributions associated with categorical ENSO forecast conditions. A simple ENSO-phase forecast system’s value was compared with that of an ideal forecast method that exactly predicted the tercile category of regional November–March precipitation. Simulations were conducted for four price scenarios with wheat prices that randomly varied about a historical ($3.22 per bushel) and elevated ($7.00 per bushel) mean and with returns on live weight gain that are consistent with the grain producer leasing pasturage or owning cattle. In the simulations at $3.22 per bushel, the best practices for specific forecast conditions varied with cattle-ownership conditions. However, the ENSO-phase system’s value distributions were comparable to that of the perfect forecast system; thus more-accurate regional precipitation forecasts may not lead to more forecast value at the farm level. In the simulations at $7.00 per bushel, even perfect categorical forecasts produced only minor profit effects, a result that is attributed here to an increased profit margin rather than to increased wheat value. Under both wheat-price conditions, however, the best no-forecast baseline practices are also shown to have value relative to an arbitrarily chosen management practice. Thus, following practices optimized to climatic conditions and current price and cost conditions might increase profits when no forecast information is available.

Structure and Detectability of Trends in Hydrological Measures over the Western United States

Abstract This study examines the geographic structure of observed trends in key hydrologically relevant variables across the western United States at ⅛° spatial resolution during the period 1950–99. Geographical regions, latitude bands, and elevation classes where these trends are statistically significantly different from trends associated with natural climate variations are identified. Variables analyzed include late-winter and spring temperature, winter-total snowy days as a fraction of winter-total wet days, 1 April snow water equivalent (SWE) as a fraction of October–March (ONDJFM) precipitation total [precip(ONDJFM)], and seasonal [JFM] accumulated runoff as a fraction of water-year accumulated runoff. Observed changes were compared to natural internal climate variability simulated by an 850-yr control run of the finite volume version of the Community Climate System Model, version 3 (CCSM3-FV), statistically downscaled to a ⅛° grid using the method of constructed analogs. Both observed and downscaled model temperature and precipitation data were then used to drive the Variable Infiltration Capacity (VIC) hydrological model to obtain the hydrological variables analyzed in this study. Large trends (magnitudes found less than 5% of the time in the long control run) are common in the observations and occupy a substantial part (37%–42%) of the mountainous western United States. These trends are strongly related to the large-scale warming that appears over 89% of the domain. The strongest changes in the hydrologic variables, unlikely to be associated with natural variability alone, have occurred at medium elevations [750–2500 m for JFM runoff fractions and 500–3000 m for SWE/Precip(ONDJFM)] where warming has pushed temperatures from slightly below to slightly above freezing. Further analysis using the data on selected catchments indicates that hydroclimatic variables must have changed significantly (at 95% confidence level) over at least 45% of the total catchment area to achieve a detectable trend in measures accumulated to the catchment scale.

Influence of temperatures and precipitation on radial increment of Orlické hory Mts. spruce stands at altitudes over 800 m a.s.l.

Research on the influence of temperatures and precipitation on radial increment was carried out in spruce stands over ninety years old in the surroundings of Anenský vrch in the Orlické hory Mts. at altitudes over 800 m above sea level. To model diameter increment in dependence on climatic conditions, the standard tree-ring and correlation analysis together with the analysis of negative pointer years were used. The diameter increment has a statistically significant correlation with temperatures in July of each year in question. The growth of spruce is also affected to a statistically significant degree by precipitation in July of the previous year and by precipitation in February and March of the year in question. The standard tree-ring chronology shows an obvious decrease in radial increments starting at the beginning of the 1970s and ending at the end of the 1980s. The lowest increments were recorded for 1974, 1980, 1984 and 1986. These years with low increments were also confirmed by the analysis of negative pointer years. In the following period there is an increase in increments, with slight decreases in 1996 and 2000, which, however, according to the analysis of negative pointer years do not demonstrate any significant reduction of increments. Another decrease was recorded starting in 2003 and this lasted until the studied period, i.e. 2007. The current condition of spruce stands is certainly the result of more stressors but it appears that with the current air pollution load the climatic conditions are the factor determining the resulting effect of the synergic influence of the stressors on the stands.

Synchronicity and Geographic Variation in Oregon White Oak Acorn Production in the Pacific Northwest

We explored geographic patterns and synchrony of Oregon white oak (Quercus garryana) acorn production over 8 years from Vancouver Island, British Columbia to Medford, Oregon. We divided our data into geographic areas: Puget-Willamette Trough, Columbia Gorge-East Cascades (Eastside) xeric, Eastside mesic, Cascade Mountain foothills, Roseburg, and Medford to compare annual acorn production among areas. We observed high within-area synchrony, but synchrony across areas was only apparent in 2004 and 2006 (high production), and 2005 (low production). Correlogram analysis indicated significant acorn crop correlation throughout the Puget-Willamette Trough, but synchrony was higher over greater distances among stands than among trees. Relationships between acorn production and mean monthly temperature or precipitation were examined with correlation analyses for each month between floral initiation and acorn maturation over 8 years of observations. Acorn production in the Puget-Willamette Trough was negatively correlated with spring precipitation, possibly due to an effect on floral processes, and winter temperature, which might relate to bud chilling requirements. In Eastside uplands, June precipitation positively correlated with current acorn production, but negatively correlated with the following year's production suggesting a climatically mediated depression by one year's production on that in the following year. Eastside production negatively correlated with precipitation in March suggesting precipitation interferes with floral processes at that time. We developed predictive linear regression models for the two analysis areas with largest sample sizes. Oregon white oak masting is similar to that in other white oaks in terms of periodicity and the effects of spring weather, but is also influenced by other weather related factors following floral induction.

Dendrochonological Potential of Japanese Barberry (Berberis thunbergii): A Case Study in the Black Rock Forest, New York

The deciduous forests of northeastern United States are currently experiencing an invasion of the exotic plant species Japanese barberry (Berberis thunbergii). This recent and rapid invasion leads to rising concern about its potential threats to native species as well as natural ecosystems, demanding a better understanding of its invasion mechanisms and potential responses to climate change. Unfortunately, few studies have been conducted to understand the influence of climate on the growth of B. thunbergii, largely because of the absence of long-term growth records. In this study we demonstrate growth rings of B. thunbergii are annually resolved and crossdatable. The first ring-width chronology of B. thunbergii was therefore developed using samples collected from the Black Rock Forest (BRF), New York. Climate-growth relationship analysis indicates the growth of B. thunbergii in the BRF is positively correlated with precipitation in prior October, current February and May–August, but is negatively correlated with current March precipitation. The growth of B. thunbergii is also negatively correlated with temperatures in prior winter (November–January) and current summer (June–July), but is positively correlated with current spring temperature (March–May). These dendrochronological results on B. thunbergii, together with further physiological studies, will improve our understanding on how the growth of this invasive species is affected by local climate dynamics, as well as the long-term invasion potential that is tied to its responses to climate change.

Long‐Term Dynamics of Fecal Corticosterone in Male Great Gerbils (Rhombomys opimus Licht.): Effects of Environment and Social Demography

We examined the relationship among seasonal characteristics of climate, food, and population demography (social structure) and fecal corticosterone (CORT) concentrations over 6 yr in adult males of an arid-adapted species, the great gerbil (Rhombomys opimus Licht., Gerbillidae, Rodentia), as a measure of chronic stress in high, low, and recovering population densities. Results showed yearly differences in the seasonal means of CORT, with the highest concentrations in the year of the highest population density. Analysis of year-specific relationships revealed a positive correlation between mean CORT and total precipitation in January and February and a negative correlation with precipitation in March. In the beginning of spring, when gerbils were in maximum reproductive effort, CORT correlated positively with the saturation of burrow systems and with the number of adult females with an adult male. A linear stepwise regression of CORT in individual males in spring seasons of all 6 yr combined after removal of year effects revealed that CORT depended positively on the number of females associated with a single male but negatively on the abundance of annual herbs. Disappearance of adult males was not related to CORT in most cases. We found no correlation between overall mortality from season to season and mean CORT in either spring (March-May) or fall. In fact, we found a highly negative correlation between mean CORT and the proportion of disappeared males at the beginning of spring. Only at the high population density when cases of probable catastrophic mortality of all adults in the group were excluded was CORT of individual males related positively to their disappearance during the summer drought. Our results suggest that desert rodents with irregular population fluctuations are more sensitive to suppression by external factors than by density-dependent mortality mediated by stress. The favorable feeding and climatic conditions may have compensated for density-dependent increases of CORT and the negative effects it might have had on survival.

A Weather-Type Approach to Analyzing Winter Precipitation in France: Twentieth-Century Trends and the Role of Anthropogenic Forcing

Abstract The relationship between large-scale atmospheric circulation and November–March precipitation over France during the twentieth century is investigated. A long daily MSLP dataset is used to derive daily weather types that are discriminant for precipitation. A linear regression model is then used to relate the November–March-accumulated precipitation amount and the occurrence frequency of the weather types. This simple model shows that an important part of the interannual variability of precipitation is directly linked to large-scale circulation changes. Trends in observed precipitation and precipitation series reconstructed by regression are computed and compared. Spatially coherent trends in November–March precipitation during the second half of the twentieth century are observed, with an increase in the north and a decrease in the south. The spatial pattern of the trends in reconstructed precipitation is very similar to that observed, even if an underestimation of the positive trends in the north is seen, indicating that other mechanisms play a role. A detection study then leads to a better understanding of the respective roles of anthropogenic forcing (greenhouse gases and sulfate aerosol) and sea surface temperature in the evolution of the weather-type occurrence. Finally, it is shown that intratype dynamical variability has also played a role in precipitation changes in northern France, whereas no impact of temperature changes is seen.

A Two-Tier Statistical Forecast Method for Agricultural and Resource Management Simulations

Abstract Simple phase schemes to predict seasonal climate based on leading ENSO indicators can be used to estimate the value of forecast information in agriculture and watershed management, but may be limited in predictive skill. Here, a simple two-tier statistical method is used to hindcast seasonal precipitation over the continental United States, and the resulting skill is compared with that of ENSO phase systems based on Niño-3 sea surface temperature anomaly (SSTA) and Southern Oscillation index (SOI) persistence. The two-tier approach first predicts Niño-3 winter season SSTA, and then converts those predictions to categorical precipitation hindcasts via a simple phase translation process. The hindcasting problem used to make these comparisons is relevant to winter wheat production over the central United States. Thus, given the state of seasonal SOI and Niño-3 indicators defined before August, the goal is to predict the tercile category of the following November–March precipitation. Generally, it was found that the methods based on either predicted or persisted winter Niño-3 conditions were skillful over areas where ENSO affects U.S. winter precipitation—that is, the Southeast and the Gulf Coast, Texas, the southern and central plains, the Southwest, Northwest, and the Ohio River valley—and that the two-tier approach based on predicted Niño-3 conditions was more likely to provide the best skill. Skill based on SOI persistence was generally lower over many of those regions and was insignificant over broad parts of the central and southwest United States, but did lead the other methods over the Ohio River valley and the northwest. A more restrictive test of leading hindcast skill showed that the skill advantages of the two-tier approach over the central and western United States were not substantial, and mainly highlighted SOI persistence’s lack of skill over the central United States and leading skill over the Ohio River valley. However, two-tier hindcasts based on neural-network-predicted Niño-3 SSTA were clearly more skillful than both ENSO phase methods over areas of the Southeast. It is suggested that the relative skill advantage of the two-tier approach may be due in part to the use of arbitrary thresholds in ENSO phase systems.

Forecasting the impact of the Gypsy moth on lowland hardwood forests by analyzing the cyclical pattern of population and climate data series

This paper presents the analytical results of cyclical behavior of Gypsy moth population dynamics monitored from 1970 in the continental part of Croatia. The analysis of the gathered Gypsy moth population series, in addition to temperature and precipitation data measured at the Jastrebarsko meteorological station, was provided with the aid of Fast Fourier Transform. Strong Gypsy moth outbreaks occur regularly with a significant periodicity of 10.6 years. A peak in the Gypsy moth population density can be expected 5.2 years after the onset of the latency period, i.e., upon the ending of the previous gradation. In the climate data, significant periodicities of 2.1–2.9 were found in yearly temperature and precipitation, in monthly temperature (February, April, October, November, December) and precipitation series (May, September). Gypsy moth outbreaks of 10.6 years are synchronized with temperature and precipitation as harmonics, i.e., as an integer multiple of the short periods of climate data series. From the beginning of the latency phase to maximal increase of population density (5.2 years) two periodic increases of temperature usually occur. It was confirmed by use of logistic regression that the strong increase of population density is related to a significantly higher temperature in December. Strong collapse of outbreaks is related to a significantly higher precipitation in March. These events occur simultaneously during the Gypsy moth population cycle and moderate its population density. Knowledge of the systematic cyclical behavior of the Gypsy moth series and climatic data can be used in the short term to forecast outbreaks with the aim of reducing forest damage in future.

Boreal forest provenance tests used to predict optimal growth and response to climate change. 1. Jack pine

Height, diameter, and survival data were obtained from 16 rangewide jack pine provenance trials in eastern Canada and the United States. Climate data for each seed source and test location were used to relate height growth to 72 climate variables. Population response functions based on August minimum and January maximum temperatures were developed to predict climate values maximizing height growth for individual seed sources. Site transfer functions based on March precipitation and December minimum temperature were developed to predict climate values maximizing height growth for test locations. Contour lines representing optimal performance were fitted to current (1971–2000) and future (2041–2070) climate grids. Optimal growth is currently achieved between 46°N and 47°N latitude for most seed sources. Future temperature increases are expected to cause a northward shift of the optimal habitat by approximately 2°. Northern sources are growing at temperatures below optimum and would benefit from warmer environments provided other environmental factors do not become limiting. Central sources are growing at close to optimum and will be negatively affected by increased temperatures in the future. Southern sources performed better in cooler environments, and warmer temperatures may cause significant height growth loss and the potential extirpation of these populations.

Comparing Juniperus virginiana tree-ring chronologies from forest edge vs. forest interior positions in the Cedars Natural Area Preserve in Virginia, USA

We created two eastern red cedar master chronologies, one from trees growing along the edge of grassy openings and another from trees growing within the intact forest canopy. Correlation coefficients were calculated between ring width indices from two time periods (1895–1949 and 1950–2001) of the residual chronology and temperature, precipitation, and Palmer Drought Severity Indices (a standardized measure of dryness). The two time periods represented younger and older eastern red cedar. The younger, interior eastern red cedar had significant, positive correlations between ring width index (RWI) and June and November precipitation, March temperature, and Palmer Drought Severity Index (PDSI) from May through December. There were significant, negative correlations between RWI and May, June, and December temperature and May through July PDSI from the previous year. For the older, interior eastern red cedar significant, positive correlations existed between RWI and precipitation from the previous June, October, and December, and PDSI from July. Significant, negative correlations existed between RWI and January precipitation and May temperature. For the edge eastern red cedar within the earlier time segment (1895–1949) there was only one significant dendroclimatic correlation and this was a negative correlation with December temperature. For the edge eastern red cedar within the later time segment (1950–2001) there were significant, positive correlations between RWI and precipitation from June, September, October, and December of the previous year, March precipitation from the current growing season, and PDSI from July. There were significant, negative correlations between RWI and precipitation from January and November, temperature from the previous June, temperature from May and December, and PDSI from June of the previous year. Thus, eastern red cedar from the interior had more significant correlations to climate than trees growing along the edge. This result does not match other studies that have found edge trees to be more responsive to climate than interior trees. Perhaps this difference can be explained by some of the variations in the significant dendroclimatic correlations between the earlier and later time periods. The differences between the two time periods (within a single site) imply that the environmental conditions of trees changed over time. These differences may be a result of tree encroachment into the forest openings which creates a constantly changing environment for the eastern red cedar and results in some of the high variability of dendroclimatic relationships identified in this study. These results imply that trees growing in communities without stable edges, i.e. where the environment around the trees is in a constant state of flux, would be unsuitable for climatic reconstruction because they do not conform to the uniformitarian principle.

Statistical–Dynamical Seasonal Forecasts of Central-Southwest Asian Winter Precipitation

Abstract Interannual precipitation variability in central-southwest (CSW) Asia has been associated with East Asian jet stream variability and western Pacific tropical convection. However, atmospheric general circulation models (AGCMs) forced by observed sea surface temperature (SST) poorly simulate the region’s interannual precipitation variability. The statistical–dynamical approach uses statistical methods to correct systematic deficiencies in the response of AGCMs to SST forcing. Statistical correction methods linking model-simulated Indo–west Pacific precipitation and observed CSW Asia precipitation result in modest, but statistically significant, cross-validated simulation skill in the northeast part of the domain for the period from 1951 to 1998. The statistical–dynamical method is also applied to recent (winter 1998/99 to 2002/03) multimodel, two-tier December–March precipitation forecasts initiated in October. This period includes 4 yr (winter of 1998/99 to 2001/02) of severe drought. Tercile probability forecasts are produced using ensemble-mean forecasts and forecast error estimates. The statistical–dynamical forecasts show enhanced probability of below-normal precipitation for the four drought years and capture the return to normal conditions in part of the region during the winter of 2002/03. May Kabul be without gold, but not without snow. —Traditional Afghan proverb

Inter-annual variability and interaction of remote-sensed vegetation index and atmospheric precipitation in the Aral Sea region

The remotely sensed Normalized Difference Vegetation Index (AVHRR NDVI) and precipitation data were analysed in the Aral Sea region in Central Asia during two recent decades. Both variables exhibited pronounced seasonal variation, with maximum precipitation in March and maximum NDVI in May–June. The regions of synchronous seasonal and inter-annual variability between the vegetation index and precipitation were distinguished using the Empirical Orthogonal Functions (EOF) method and time-lagged correlations between EOF modes. At a seasonal scale, precipitation and the vegetation index were correlated with a time lag from 1 to 6 months in different regions with peak plant growth following precipitation maxima.

Landscape, soil and meteorological influences on canopy dynamics of northern flooding Pampa grasslands, Argentina

AbstractQuestion: How do meteorological variations at seasonal, interannual scales differentially affect the canopy dynamics of four contrasting landscape units within a region?Location: Flooding Pampa, Buenos Aires, Argentina. 5000 km2. Central point: 35°15′S, 57°45′W.Methods: We used a 19‐year series of the normalized difference vegetation index (NDVI) derived from NOAA‐AVHRR PAL (Pathfinder AVHRR Land) images and meteorological data provided by a nearby weather station. The NDVI was used as surrogate of canopy photosynthetic status. The relationship between annually integrated NDVI and meteorological conditions was explored by stepwise multiple regressions for each defined unit. PC A was performed to compare units and growing seasons on a multivariate basis.Results: Mean seasonal NDVI curve was similarly shaped among landscapes. However, the absolute values differed widely. There was high interannual variation so that the mean seasonal pattern was seldom observed in any particular year. Annually integrated NDVI of all landscapes was negatively associated with summer temperature and positively with previous year precipitation. It was also directly related with current year winter precipitation in two landscapes and with summer precipitation in the others. NDVI response to September and March precipitation accounted for some of the differences in interannual variation among landscapes.Conclusions: Our results revealed a strong intra‐regional variation of canopy dynamics, closely linked to landscape (vegetation‐soil) and water availability (mainly in summer and during the previous year). These links may be used to predict forage production rates for livestock.