Douglas W. Gamble

Climate Change, Drought, and Jamaican Agriculture: Local Knowledge and the Climate Record

The purpose of this study is to reach a basic understanding of drought and climate change in southwestern Jamaica through an integration of local knowledge and perception of drought and its physical characteristics manifested in remotely sensed precipitation and vegetation data. Local knowledge and perception are investigated through a survey of sixty farmers in St. Elizabeth Parish and physical characteristics of drought are examined through statistical analysis of satellite precipitation and vegetation vigor time series. The survey indicates that most farmers are concerned about an increase in drought occurrence. Satellite estimates of rainfall and vegetation vigor for St. Elizabeth Parish support this perception and suggest that severe drought events are becoming more frequent. The satellite precipitation time series also suggest that the early growing season is becoming drier as compared to the primary growing season, especially since 1991. This recent divergence in growing season moisture conditions might add to farmers’ observations that drought is becoming more prevalent. Consequently, Jamaican farmers perceptions of drought are not driven by magnitude and frequency of dry months alone but rather by the difference between growing seasons. Any development of drought adaption and mitigation plans for this area must not focus solely on drought; it must also compare moisture conditions between months and seasons to be effective.

A SYNOPTIC CLIMATOLOGY OF EXTREME UNSEASONABLE FLOODS IN THE SOUTHEASTERN UNITED STATES, 1950–1990

Unseasonable floods are floods that occur in the season of lowest flood frequency, or dry season. Such floods pose a unique problem to flood planners and forecasters, yet little research has invest...

Tropical Cyclone Signals within Tree-Ring Chronologies from Weeks Bay National Estuary and Research Reserve, Alabama

Abstract This study investigates the relationship between tropical cyclones and tree-ring chronologies within a bottomland forest in coastal Alabama. Tree cores were collected from 36 slash pines in the Swift Track area of the Weeks Bay National Estuary and Research Reserve, Fairhope, Alabama. Tree cores were processed, measured to the nearest 0.01 mm, and cross-dated using standard procedures. A standardized ring index series was computed from the tree-ring measurement for each year from 1890 to 2000. The index series represents a single chronology of the entire forest stand, which we refer to as the stand-scale. An initial comparison of index series values to years of known tropical storm and hurricane strikes within the Weeks Bay area reveals no clear tropical cyclone signal. Statistical tests of the index values for 2–7 y periods before and after tropical storms and hurricanes indicate no statistically significant difference in tree-rings before and after the storms. In contrast, standardized index values computed for each individual tree-ring series (individual tree-scale) display more rapid growth (release) in years following direct hits by tropical cyclones. Individual tree-ring data also indicate slowed growth (suppression) during years when tropical cyclones are infrequent. These results indicate that researchers must be aware of scale of analysis when researching tree-ring chronologies in Gulf Coast forests. For this study, a combination of the two scales of analysis results in a recognizable tree-ring record of suppression and then release generated by tropical cyclones.

The Relationship Between Drainage Basin Area and Annual Peak-Flood Seasonality in the Southeastern United States

This study examines relationships between drainage basin area and flood seasonality in the southeastern United States. To assess this relationship, a flood seasonality analysis of annual peak flood series for 84 individual drainage basins is completed, identifying five distinct annual peak-flood seasonality regions: the Tennessee, the Gulf Coast, Peninsular Florida, the Carolinas, and the Georgia Coastal Plain. These results confirm previous research except for the Carolina region, which possesses no dominant season in annual peak-flood frequency. Further statistical analysis indicates that the Georgia Coastal Plain is the only region of the five with a statistically significant relationship between drainage basin area and annual peak-flood seasonality. The statistical relationships for this region are interpreted as spring annual peak floods occurring more frequently on larger drainage basins because of high soil moisture and frequent extratropical-cyclone passage. Weak, significant statistical relationships exist between drainage basin area and annual peak-flood seasonality when all streams are placed in a single data set representing the entire southeastern United States. These results suggest the need for a wide range in drainage-basin area to identify a relationship between drainage-basin area and annual peak-flood seasonality.

The impact of Hurricane Frances (2004) on the invasive Australian pine (Casuarina equisetifolia L.) on San Salvador Island, The Bahamas

Abstract On September 2, 2004 Hurricane Frances (Category 3) passed directly over San Salvador Island, The Bahamas. This event offered the opportunity to gather baseline data regarding the impact of hurricanes on populations of the invasive Australian pine (Casuarina equisettifolia L.) in the Bahamas. Results of vegetation surveys within both forest stands and beach environments suggest that the overall impact of this hurricane was minimal. Less than 13% of forest individuals and 17% of beach individuals surveyed were damaged, and the majority of damage was restricted to just one location for both the forest and beach study sites. The most common damage type within the forest sites was “snapped” trees (8%) and this primarily occurred within trees ranging in size from 7–12 cm in diameter. Browning of the entire foliage was the most common damage type within the beach sites (9.3%) but this damage type only occurred within tree sizes less than or equal to 90 cm in height. Thus it appears that Hurricane Frances had a negligible effect on Australian pine populations as a whole on San Salvador Island and that this disturbance event will probably not limit future population expansion. It is suggested that more powerful or more frequent hurricanes would be needed to significantly affect Australian pine populations on San Salvador Island. Similar patterns in damage should be expected with comparable hurricane events on other islands in the Bahamas and for other tropical beaches in which this species has invaded.

THE ROLE OF SCALE IN RESEARCH ON THE HIMALAYA-GANGES-BRAHMAPUTRA INTERACTION

This paper investigates the role of scale in research on the link between the Himalaya-Ganges-Brahmaputra fluvial system and floods in Bangladesh. Fifty-two studies, ranging from one hectare to near continental scales, were reviewed for variables selected in analysis and research designs. Three overall patterns of scale dependence were identified. The first is dominated by the precision with which scales and study area are defined. Local studies tend to have temporal and spatial scales which are explicitly defined while continental scale studies are dominated by general and abstract or implicitly defined scales. The second pattern indicates that local scale studies tend to focus upon physical variables such as rainfall, runoff, and mass wasting, while research at the regional and continental scales focuses on natural resource topics such as land-use change and flood mitigation policy. The third pattern identifies the degree to which studies attempt to scale up to larger regions from local scale studies. Specifically, this final pattern identifies a scale independent model which upscales stream discharge/sediment load across all three scales. The topics examined and research results presented are clearly scale dependent. It is proposed that scale perspectives are partially responsible for shaping opposing theories in the debate over the causes of flooding in Bangladesh. In conclusion, three strategies are outlined that may assist future research to incorporate multi-scale analysis of flooding in Bangladesh.

HYDROCLIMATIC ANALYSIS OF A CARBONATE ISLAND POND THROUGH THE DEVELOPMENT OF A HYDROLOGIC LANDSCAPE UNIT MODEL

The purpose of this study is to develop a methodology that allows for an estimate of the hydroclimatic influence on an inland pond system on San Salvador, Bahamas. The methodology utilizes the Hydrologic Landscape Unit (HLU) model, a new conceptual model that offers hydrologists and water-resource managers more flexibility in representing the components of the unique and complex hydrologic systems of small carbonate islands. For this case study, a linear regression model was developed to empirically assess the HLU. This analysis separates tidal and climatic impacts on water levels of the pond and indicates that astronomical tides dominate, explaining 65% of the variance in pond water-level observations. Further, clusters of days with positive and negative outliers identified in the linear regression analysis were compared to precipitation events to determine response of water levels to climatic inputs. More than 78% of the days with positive outliers were associated with precipitation events and 83% of the days with negative outliers in Crescent Pond were explained by a lack of precipitation, signifying cumulative evaporation effects. Thus, while tidal variation is the principle forcing mechanism for Crescent Pond water-level variability, significant interaction between the atmosphere and the pond surface can be identified with this methodology at the daily to weekly time scale. Such a tool can be used by hydrologists and water-resource managers on small carbonate islands to assess the degree of freshwater input into inland water bodies and the appropriate time scale for potential freshwater harvest.

The Midsummer Dry Spell’s Impact on Vegetation in Jamaica

Abstract The annual rainfall pattern of the intra-Americas sea reveals a bimodal feature with a minimum during the midsummer known as the midsummer dry spell (MSD). A first attempt is made to examine the impact of the MSD on vegetation through a normalized difference vegetation index (NDVI) analysis in Jamaica. Tropical Rainfall Measuring Mission rainfall estimates and NDVI derived from the Terra Moderate Resolution Imaging Spectroradiometer highlight a consistent MSD feature in both rainfall and vegetative vigor. Spatial variation of this MSD NDVI response is evident throughout Jamaica, with the strongest relationship between the rainfall reduction and NDVI decline throughout the southern portions of Jamaica including the area of major domestic food production. In all years except 2005 there is a notable reduction from early-summer NDVI to midsummer NDVI in this agricultural region. However, the lagged vegetative response undergoes clear interannual variation and is affected by other forcings besides rai...

Sensitivity of Crop Water Need to 2071-95 Projected Temperature and Precipitation Changes in Jamaica

AbstractThis study uses empirical models to examine the potential impact of climate change, based on a range of 100-yr phase 5 of the Coupled Model Intercomparison Project (CMIP5) projections, on crop water need in Jamaica. As expected, crop water need increases with rising temperature and decreasing precipitation, especially in May–July. Comparing the temperature and precipitation impacts on crop water need indicates that the 25th percentile of CMIP5 temperature change (moderate warming) yields a larger crop water deficit than the 75th percentile of CMIP5 precipitation change (wet winter and dry summer), but the 25th percentile of CMIP5 precipitation change (substantial drying) dominates the 75th percentile of CMIP5 temperature change (extreme warming). Over the annual cycle, the warming contributes to larger crop water deficits from November to April, while the drying has a greater influence from May to October. All experiments decrease crop suitability, with the largest impact from March to August.

Rethinking the Region: SEDAAG and the Caribbean

This essay discusses the need to raise the profile of Caribbean studies within the Southeastern Geographer and the professional activities of the Southeastern Division of the Association of American Geographers (SEDAAG). My discussion addresses four basic questions. First, what is the geographic link between the Southeast and the Caribbean? Second, to what extent is this geographic link reflected in SEDAAG membership, publications, and activities? Third, how can the study of the Caribbean achieve a higher profile in the Southeastern Geographer and SEDAAG? Fourth, why is it necessary to incorporate the Caribbean into SEDAAG? Responses to each of these questions indicate that some of the greatest potential for growth of the Southeastern Geographer and SEDAAG comes with a critical rethinking of its traditional regional boundaries and interactions.