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Climate is affected more by maritime than by continental land use change: A multiple scale analysis

Sat, 07/30/2011 - 12:31 — ckass

Van der Molen, M. K., Dolman, A. J.,Waterloo, M. J. and Bruijnzeel, L.
A. 2006. Climate is affected more by maritime than by continental land
use change: A multiple scale analysis. Global and Planetary Change,
54, 128–149.

Abstract: 
Tropical deforestation appears to have larger impacts on local, regional and global climate when it occurs under maritime conditions rather then under continental conditions. At the local scale, we compare results from a field experiment in Puerto Rico with other long-term studies of the changes in surface fluxes after deforestation. Changes in surface fluxes are larger in maritime situations because a number of feedback mechanisms appears less relevant (e.g. the dependency of soil moisture on recycling of water and the larger reduction of net radiation in the wet season due to clouds in continental regions). Pastures may evaporate at similarly high rates as forests when soil moisture is sufficient, which has a strong reducing effect on the sensible heat flux after deforestation. At the regional scale (∼102 km2), model simulations show that the meso-scale sea breeze circulation under maritime conditions is more effective in transporting heat and moisture to the upper troposphere than convection is in the continental case. Thus islands function as triggers of convection, whereas the intensity of the sea breeze-trigger is sensitive to land use change. At the global scale, using satellite-derived latent heating rates of the upper troposphere, it is shown that 40% of the latent heating associated with deep convection takes place in the Maritime Continent (Indonesia and surroundings) and may be produced mostly by small islands. Continents contribute only 20% of the latent heating of the upper troposphere. Thus, sea breeze circulations exert significant influence on the Hadley cell circulation. These results imply that, from a climate perspective, further deforestation studies would do well to focus more on maritime conditions.

Urban Heat Islands Developing in Coastal Tropical Cities

Sat, 07/30/2011 - 12:09 — ckass

Gonza´lez, J. E., C. Luvall, D. Rickman, D. Comarazamy, A. Picon,
E. Harmsen, H. Parsiani, N. Va´squez, R. Williams, and R. W. Waide
(2005), Urban heat islands developing in coastal tropical cities, Eos
Trans. AGU, 86(42), 397, doi:10.1029/2005EO420001.

Abstract: 
Beautiful and breezy cities on small tropical islands, it turns out, may not be exempt from the same local climate change effects and urban heat island effects seen in large continental cities such as Los Angeles or Mexico City. A surprising, recent discovery indicates that this is the case for San Juan, Puerto Rico, a relatively affluent coastal tropical city of about two million inhabitants that is spreading rapidly into the once-rural areas around it. A recent climatological analysis of the surface temperature of the city has revealed that the local temperature has been increasing over the neighboring vegetated areas at a rate of 0.06°C per year for the past 30 years.This is a trend that may be comparable to climate changes induced by global warming. These results encouraged the planning and execution of an intense field campaign in February 2004, referred to as the San Juan Atlas Mission, to verify the spatial and temporal extent of this urban heat index. Results of this field campaign recently have been analyzed and are the main topic of this article. These results reveal the warming of a tropical coastal city that is significantly higher than typical temperatures in vegetated areas.This may be the first set of high-resolution thermal images taken in a tropical coastal city. Figure 1 shows that the daytime surface temperatures of a portion of San Juan at fi ve-meter resolution are as high as 60°C,and that differences between urbanized and limited vegetation areas are in excess of 30°C.

POTENTIAL CAUSES FOR AMPHIBIAN DECLINES IN PUERTO RICO

Fri, 07/29/2011 - 11:45 — ckass

P. A. Burrowes, R. L. Joglar and D. E. Green, Potential causes for
amphibian declines in Puerto Rico, Herpetologica, 2004, 60, 141–154.

Abstract: 
We monitored 11 populations of eight species of Eleutherodactylus in Puerto Rico from 1989 through 2001. We determined relative abundance of active frogs along transects established in the Caribbean National Forest (El Yunque), Carite Forest, San Lorenzo, and in the vicinity of San Juan. Three species (Eleutherodactylus karlschmidti, E. jasperi, and E. eneidae) are presumed to be extinct and eight populations of six different species of endemic Eleutherodactylus are significantly declining at elevations above 400 m. Of the many suspected causes of amphibian declines around the world, we focused on climate change and disease. Temperature and precipitation data from 1970–2000 were analyzed to determine the general pattern of oscillations and deviations that could be correlated with amphibian declines. We examined a total of 106 tissues taken from museum specimens collected from 1961–1978 and from live frogs in 2000. We found chytrid fungi in two species collected at El Yunque as early as 1976, this is the first report of chytrid fungus in the Caribbean. Analysis of weather data indicates a significant warming trend and an association between years with extended periods of drought and the decline of amphibians in Puerto Rico. The 1970’s and 1990’s, which represent the periods of amphibian extirpations and declines, were significantly drier than average. We suggest a possible synergistic interaction between drought and the pathological effect of the chytrid fungus on amphibian populations.

V FRIEND World Conference, Havana, Cuba, 2006 Hydrological Impacts of Climate Variability and Change Selected presentations on Latin America and the Caribbean

Fri, 07/29/2011 - 11:37 — ckass
Abstract: 
The science of water is an endless world for scientific research and creativity, in the water all the needs converge, the feelings and human traditions, water is the origin of life and its sustain, water is food supply, and it is also a base of the culture, traditions and religions; and, unfortunately, the cause of diverse conflicts among people and countries. Water is a renewable, but finite resource, endangered in many places by its non-rational use, in such a proportion, that the unmeasured disposal of pollutants in the water bodies or its exploitation over its natural capacity of renewal, might also put at risk its condition of renewable resource. Water is under the threat of climatic change that will affect its spatial and temporal distribution in a negative way in every place. The environmental situation of Latin America and the Caribbean is fragile, and particularly in relation to water many threats exist that justify the need of urgent actions. The intensive deforestation in the tropical forest and woods from temperate and cold regions; the modification or destruction of coastal ecosystems, the high degree of erosion due to inadecuated agriculture practices and incorrect use of the soil; the indiscriminated use of chemical and synthetic products in agriculture and urban industries; integrated to global environmental problems, among them, climate change and the ozone layer depletion, are being felt in different degrees in various parts of the continent. An evaluation of the Forum of Ministries of Environment in Latin America and the Caribbean, carried out in Bridgetown, Barbados, in 2000, recognized the continuation of the environmental deterioration in the region and in analizing the problem of water, the following were indicated among the main problems:

Impact of experimental drought on greenhouse gas emissions and nutrient availability in a humid tropical forest

Thu, 07/28/2011 - 15:53 — ckass
Abstract: 
We excluded throughfall from humid tropical forests in Puerto Rico for a period of three months to determine how drought affects greenhouse gas emissions from tropical forest soils. We established five 1.24 m2 throughfall exclusion and five control plots of equal size in three sites located on ridges, slopes, and an upland valley dominated by palms (total of 30 plots). We measured weekly changes in carbon dioxide (CO2) and bi-weekly changes in nitrous oxide (N2O) and methane (CH4) in response to manipulation. We additionally measured the effects of throughfall exclusion on soil temperature and moisture, nutrient availability, and pH. Rainout shelters significantly reduced throughfall by 22 to 32 % and decreased soil moisture by 16 to 36% (top 10 cm). Rates of CO2 emissions decreased significantly in the ridge and slope sites (30%, 28%, respectively), but not the palm during the experimental drought. In contrast, the palm site became a significantly stronger sink for CH4 in response to drying (480% decline relative to controls), while CH4 fluxes in the ridge and slope sites did not respond to drought. Both the palm and ridge site became a sink for N2O in response to drought and the slope site followed a similar trend. Soil pH and available P decreased significantly in response to soil drying; however, available N was not affected. Variability in the response of greenhouse gas emissions to drought among the three sites highlights the complexity of biogeochemical cycling in tropical forested ecosystems, as well as the need for research that incorporates the high degree of spatial heterogeneity in experimental designs. Our results show that humid tropical forests are sensitive to climate change and that short-term declines in rainfall could result in a negative feedback to climate change via lowered greenhouse gas emissions and increased greenhouse gas consumption by soils.

Spatial and seasonal dynamics of surface soil carbon in the Luquillo Experimental Forest, Puerto Rico

Thu, 07/28/2011 - 15:48 — ckass

Wang, Hongqing; Cornell, Joseph D.; Hall, Charles A.S.; Marley, David P. 2002. Spatial and seasonal dynamics of surface soil carbon in the Luquillo Experimental Forest, Puerto Rico.. Ecological Modelling 147 105-122.

Abstract: 
We developed a spatially-explicit version of the CENTURY soil model to characterize the storage and flux of soil organic carbon (SOC, 0–30 cm depth) in the Luquillo Experimental Forest (LEF), Puerto Rico as a function of climate, vegetation, and soils. The model was driven by monthly estimates of average air temperature, precipitation, and potential evapotranspiration (PET), which in turn were simulated as a function of elevation, slope, and aspect using a spatially-explicit and validated model (TOPOCLIM) of solar insolation/microclimate in mountainous areas. We simulated forest gross primary productivity (GPP) and distribution of above- and below-ground biomass production using a forest productivity model (TOPOPROD). Output from TOPOCLIM and TOPOPROD models was used to run the CENTURY soil model for 1200 months under current climate conditions and in response to potential global warming. We validated our version of CENTURY soil model using 69 soil samples taken throughout the LEF. Simulated SOC storage agrees reasonably well with the observed storage (R2=0.71). The simulated SOC storage in the top 30 cm within the LEF is highly variable, ranging from approximately 20–230 Mg/ha. The rates of decomposition were especially sensitive to changes in elevation. Carbon release rates due to decomposition were close to carbon assimilation rates and ranged from 0.6–0.96 Mg/ha per year at high elevations to 1.2–1.68 Mg/ha per year at lower elevations. Our simulations indicated that differences in elevation affect decomposition and SOC content primarily by changing microclimate. Finally, we found that a projected warming of 2.0 °C is likely to result in losses of SOC in the lower and higher elevation, but increased storage in the middle elevations in the LEF.

Cloud water in windward and leeward mountain forests: The stable isotope signature of orographic cloud water

Thu, 07/28/2011 - 15:09 — ckass

Scholl, M. A., T. W. Giambelluca, S. B. Gingerich, M. A. Nullet, and L. L. Loope (2007), Cloud water in windward
and leeward mountain forests: The stable isotope signature of orographic cloud water, Water Resour. Res., 43, W12411,
doi:10.1029/2007WR006011.

Abstract: 
Cloud water can be a significant hydrologic input to mountain forests. Because it is a precipitation source that is vulnerable to climate change, it is important to quantify amounts of cloud water input at watershed and regional scales. During this study, cloud water and rain samples were collected monthly for 2 years at sites on windward and leeward East Maui. The difference in isotopic composition between volume-weighted average cloud water and rain samples was 1.4% d18O and 12% d2H for the windward site and 2.8% d18O and 25% d2H for the leeward site, with the cloud water samples enriched in 18O and 2H relative to the rain samples. A summary of previous literature shows that fog and/or cloud water is enriched in 18O and 2H compared to rain at many locations around the world; this study documents cloud water and rain isotopic composition resulting from weather patterns common to montane environments in the trade wind latitudes. An end-member isotopic composition for cloud water was identified for each site and was used in an isotopic mixing model to estimate the proportion of precipitation input from orographic clouds. Orographic cloud water input was 37% of the total precipitation at the windward site and 46% at the leeward site. This represents an estimate of water input to the forest that could be altered by changes in cloud base altitude resulting from global climate change or deforestation.

Why tropical forest lizards are vulnerable to climate warming

Wed, 07/27/2011 - 13:58 — ckass

Huey, R.B. et al. (2009) Why tropical forest lizards are vulnerable to
climate warming. Proc. R. Soc. Lond., B, Biol. Sci. 276, 1939–1948

Abstract: 
Biological impacts of climate warming are predicted to increase with latitude, paralleling increases in warming. However, the magnitude of impacts depends not only on the degree of warming but also on the number of species at risk, their physiological sensitivity to warming and their options for behavioural and physiological compensation. Lizards are useful for evaluating risks of warming because their thermal biology is well studied.We conducted macrophysiological analyses of diurnal lizards from diverse latitudes plus focal species analyses of Puerto Rican Anolis and Sphaerodactyus. Although tropical lowland lizards live in environments that are warm all year, macrophysiological analyses indicate that some tropical lineages (thermoconformers that live in forests) are active at low body temperature and are intolerant of warm temperatures. Focal species analyses show that some tropical forest lizards were already experiencing stressful body temperatures in summer when studied several decades ago. Simulations suggest that warming will not only further depress their physiological performance in summer, but will also enable warm-adapted, open-habitat competitors and predators to invade forests. Forest lizards are key components of tropical ecosystems, but appear vulnerable to the cascading physiological and ecological effects of climate warming, even though rates of tropical warming may be relatively low.

Hurricane-induced nitrous oxide fluxes from a wet tropical forest

Wed, 07/27/2011 - 12:58 — ckass

Erickson HE, Ayala G (2004) Hurricane-induced nitrous oxide
fluxes from a wet tropical forest. Global Change Biology, 10,
1155–1162.

Abstract: 
Hurricane activity is predicted to increase over the mid-Atlantic as global temperatures rise. Nitrous oxide (N2O), a greenhouse gas with a substantial source from tropical soils, may increase after hurricanes yet this effect has been insufficiently documented. On September 21, 1998, Hurricane Georges crossed Puerto Rico causing extensive defoliation. We used a before–after design to assess the effect of Georges on N2O emissions, and factors likely influencing N2O fluxes including soil inorganic nitrogen pools and soil water content in a humid tropical forest at El Verde, Puerto Rico. Emissions of N2O up to 7 months post-Georges ranged from 5.92 to 4.26 ng cm2 h1 and averaged five times greater than fluxes previously measured at the site. N2O emissions 27 months after the hurricane remained over two times greater than previously measured fluxes. Soil ammonium pools decreased after Georges and remained low. The first year after the hurricane, nitrate pools increased, but not significantly when compared against a single measurement made before the hurricane. Soil moisture and temperature did not differ significantly in the two sampling periods. These results suggest that hurricanes increase N2O fluxes in these forests by altering soil N transformations and the relative availabilities of inorganic nitrogen.

Low Atlantic hurricane activity in the 1970s and 1980s compared to the past 270 years

Sat, 07/23/2011 - 20:30 — ckass

Nyberg, J., B. A. Malmgren, A. Winter, M. R.
Jury, K. H. Kilbourne, and T. M. Quinn
(2007), Low Atlantic hurricane activity in the
1970s and 1980s compared to the past 270
years, Nature, 447, 698–701.

Abstract: 
Hurricane activity in the North Atlantic Ocean has increased significantly since 1995 (refs 1, 2). This trend has been attributed to both anthropogenically induced climate change3 and natural variability1, but the primary cause remains uncertain. Changes in the frequency and intensity of hurricanes in the past can provide insights into the factors that influence hurricane activity, but reliable observations of hurricane activity in the North Atlantic only cover the past few decades2. Here we construct a record of the frequency of major Atlantic hurricanes over the past 270 years using proxy records of vertical wind shear and sea surface temperature (the main controls on the formation of major hurricanes in this region1,3–5) from corals and a marine sediment core. The record indicates that the average frequency of major hurricanes decreased gradually from the 1760s until the early 1990s, reaching anomalously low values during the 1970s and 1980s. Furthermore, the phase of enhanced hurricane activity since 1995 is not unusual compared to other periods of high hurricane activity in the record and thus appears to represent a recovery to normal hurricane activity, rather than a direct response to increasing sea surface temperature. Comparison of the record with a reconstruction of vertical wind shear indicates that variability in this parameter primarily controlled the frequency of major hurricanes in the Atlantic over the past 270 years, suggesting that changes in the magnitude of vertical wind shear will have a significant influence on future hurricane activity.
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