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

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,

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.

Organic carbon, total nitrogen, and water-soluble ions in clouds from a tropical montane cloud forest in Puerto Rico

G.J. Reyes-Rodriguez, A. Gioda, O.L. Mayol-Bracero and J. Collett, Organic carbon, total nitrogen, and water-soluble ions in clouds from a tropical montane cloud forest in Puerto Rico, Atmospheric Environment 43 (2009), pp. 4171–4177. Abstract | Article | PDF (530 K) | View Record in Scopus | Cited By in Scopus (3)

samples collected in a mountaintop site in Puerto Rico. Cloudwater samples showed average concentrations of 1.09 mg L1 of total organic carbon (TOC), of 0.85 mg L1 for dissolved organic carbon (DOC) and of and 1.25 mg L1 for total nitrogen (TN). Concentrations of organic nitrogen (ON) changed with the origin of the air mass. Changes in their concentrationswere observed during periods under the influence of African dust (AD). The ON/TN ratios were 0.26 for the clean and 0.35 for the AD periods. Average concentrations of all these species were similar to those found in remote environments with no anthropogenic contribution. In the AD period, for cloud water the concentrations of TOC were 4 times higher and TN were 3 times higher than during periods of clean air masses associated with the trade winds. These results suggest that a significant fraction of TOC and TN in cloud and rainwater is associated to airborne particulate matter present in dust. Functional groups were identified using proton nuclear magnetic resonance (1H NMR) spectroscopy. This characterization led to the conclusion that water-soluble organic compounds in these samples are mainly aliphatic oxygenated compounds, with a small amount of aromatics. The ion chromatography results showed that the ionic specieswere predominantly of marine origin, for air masses with and without African dust influence, with cloud water concentrations of NO3  and NH4 þ much lower than from polluted areas in the US. An increase of such species as SO42, Cl, Mg2þ, Kþ and Ca2þ was seen when air masses originated from northwest Africa. The changes in the chemical composition and physical properties of clouds associated with these different types of aerosol particles could affect on cloud formation and processes.

Clouds and aerosols in Puerto Rico – a new evaluation

Allan, J.D., et al., 2007. Clouds and aerosols in Puerto Rico — a new evaluation. Atmos.
Chem. Phys. Discuss. 7, 12573–12616.

The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to better understand warm cloud formation in a tropical 5 marine environment, a period of intensive measurements using some of the latest developments in online instrumentation took place in December 2004 in Puerto Rico. Simultaneous online measurements of aerosol size distributions, composition, hygroscopicity and optical properties were made near the lighthouse of Cape San Juan in the north-eastern corner of the island and at the top of East Peak mountain (1040m 10 a.s.l.), the two sites separated by 17 km. Additional measurements of the cloud droplet residual and interstitial aerosol properties were made at the mountain site, accompanied by measurements of cloud droplet size distributions, liquid water content and the chemical composition of cloud and rain water samples. Both aerosol composition and cloud properties were found to be sensitive to wind 15 sector. Air from the east-northeast (ENE) was mostly free of anthropogenic influences, the submircron fraction being mainly composed of non-sea salt sulphate, while that from the east-southeast (ESE) was found to be moderately influenced by populated islands upwind, adding smaller (<100 nm), externally mixed, carbonaceous particles to the aerosol that increased the number concentrations by over a factor of 3. This 20 change in composition was also accompanied with a reduction in the measured hygroscopicity and fractional cloud activation potential of the aerosol. At the mountain site, the average cloud droplet concentrations increased from 193 to 519 cm−3, median volume diameter decreased from 20 to 14 μm and the liquid water content increased from 0.24 to 0.31 gm−3 when the winds shifted from the ENE to ESE. Larger numbers 25 of interstitial particles were recorded, most notably at sizes greater than 100 nm, which were absent during clean conditions. The average size of the residual particles and concentrations of cloudwater nitrate, sulphate and insoluble material increased during polluted conditions.

Why tropical forest lizards are vulnerable to climate warming

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

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.


Boose, E.R., Serrano, M.I. & Foster, D.R. (2004) Landscape
and regional impacts of hurricanes in Puerto Rico. Ecological
Monographs, 74, 335–352.

Puerto Rico is subject to frequent and severe impacts from hurricanes, whose long-term ecological role must be assessed on a scale of centuries. In this study we applied a method for reconstructing hurricane disturbance regimes developed in an earlier study of hurricanes in New England. Patterns of actual wind damage from historical records were analyzed for 85 hurricanes since European settlement in 1508. A simple meteorological model (HURRECON) was used to reconstruct the impacts of 43 hurricanes since 1851. Long-term effects of topography on a landscape scale in the Luquillo Experimental Forest (LEF) were simulated with a simple topographic exposure model (EXPOS). Average return intervals across Puerto Rico for F0 damage (loss of leaves and branches) and F1 damage (scattered blowdowns, small gaps) on the Fujita scale were 4 and 6 years, respectively. At higher damage levels, a gradient was created by the direction of the storm tracks and the weakening of hurricanes over the interior mountains. Average return intervals for F2 damage (extensive blowdowns) and F3 damage (forests leveled) ranged from 15 to 33 years and 50 to 150 years, respectively, from east to west. In the LEF, the combination of steep topography and constrained peak wind directions created a complex mosaic of topographic exposure and protection, with average return intervals for F3 damage ranging from 50 years to .150 years. Actual forest damage was strongly dependent on land-use history and the effects of recent hurricanes. Annual and decadal timing of hurricanes varied widely. There was no clear centennial-scale trend in the number of major hurricanes over the historical period.

Erosional and climatic effects on long-term chemical weathering rates in granitic landscapes spanning diverse climate regimes

C. Riebe, J.W. Kirchner, R. Finkel, Erosional and climatic
effects on long-term chemical weathering rates in granitic C. Riebe, J.W. Kirchner, R. Finkel, Erosional and climatic
effects on long-term chemical weathering rates in granitic

We used cosmogenic nuclide and geochemical mass balance methods to measure long-term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes. Our 42 study sites encompass widely varying climatic and erosional regimes, with mean annual temperatures ranging from 2 to 25 jC, average precipitation ranging from 22 to 420 cmyear 1, and denudation rates ranging from 23 to 755 tkm 2year 1. Long-term chemical weathering rates range from 0 to 173 tkm 2 year 1, in several cases exceeding the highest granitic weathering rates on record from previous work. Chemical weathering rates are highest at the sites with rapid denudation rates, consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock. A simple empirical relationship based on temperature, precipitation and long-term denudation rates explains 89–95% of the variation in long-term weathering rates across our network of sites. Our analysis shows that, for a given precipitation and temperature, chemical weathering rates increase proportionally with freshmaterial supply rates. We refer to this as ‘‘supply-limited’’ weathering, in which fresh material is chemically depleted to roughly the same degree, regardless of its rate of supply from breakdown of rock. The temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter-comparisons of catchment mass-balance data from the field. Our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought, at least in actively eroding, unglaciated terrain similar to our study sites. To the extent that chemical weathering rates are supply-limited in mountainous landscapes, factors that regulate rates of mineral supply from erosion, such as tectonic uplift, may lead to significant fluctuations in global climate over the long term.

The Hurricane-Flood-Landslide Continuum

Negri, A; Burkardt, N.; Golden, J.H.; Halverson, J.B.; Huffman, G.J.; Larsen, M.C.; Mcginley,
J.A.; Updike, R.G.; Verdin, J.P; Wieczorek, J.F. The Hurricane-Flood-Landslide Continuum,
Bulletin of American Meteorological Society 2004 (doi:10.1175/BAMS-86-9-1241).

The global losses of life and property from the floods, landslides, and debris flows caused by tropical storms are staggering. One key to reducing these losses, both in the United States and internationally, is to improve forecasts of pending events in a time frame of several hours to days before the event. In some instances, the loss of life and property is the direct result of high winds and heavy rains. However, 82% of tropical cyclone deaths are due to fl ooding (Fig. 1), most of which occur well inland. For example, in 1998, Hurricane Mitch deluged parts of Guatemala, Honduras, El Salvador, and Nicaragua with rain, triggering intense fl oods and thousands of landslides that killed 11,000 people. In northwestern Nicaragua, at least 2000 people from a single village were buried alive by a massive lahar (debris fl ow). Although the National Oceanic and Atmospheric Administration (NOAA) released warnings for dangerously heavy rain fall during Mitch, much of this information either never reached local munici pal offi cials in Central America, was misunderstood, or was not acted upon. In addition, the countries impacted most by the storm have only modest national weather ser vices. We believe that if people had been better informed and prepared, substantially fewer would have died.

Forecasting hurricane-related disasters

The punch from hurricane-strength winds is quick. In the Caribbean, the storms whip across the islands tearing out trees and shattering buildings. Monitoring hurricanes is a centuries-long tradition. But with all hurricanes, and even with less formidable rain storms, comes the threat of landslides and flooding to the hills and valleys on the islands' mountainous terrain. To help emergency personnel evacuate regions at high risk to these secondary rain-induced hazards, a consolidation of technology is needed, says Randall Updike of the U.S. Geological Survey in Denver. He is working with colleagues at the USGS, along with scientists from the National Oceanic and Atmospheric Association (NOAA) and NASA, to establish a united front on forecasting landfall disasters from hurricanes in the Caribbean. UNESCO (United Nations Educational, Scientific and Cultural Organization) and The World Meteorological Organization also support the proposed idea, Updike added. Currently these organizations operate independently of each other. Updike presented his proposal of bringing the groups together at the annual meeting of the American Association for the Advancement of Science in Denver on Feb. 15.

Hydrometeorology of tropical montane cloud forests: emerging patterns

Bruijnzeel LA, Mulligan M, Scatena FN. 2010. Hydrometeorology of
tropical montane cloud forests: emerging patterns. Hydrological
Processes. DOI: 10.1002/hyp.7974.

altitudinal limits between which TMCF generally occur (800–3500 m.a.s.l. depending on mountain size and distance to coast) their current areal extent is estimated at ¾215 000 km2 or 6Ð6% of all montane tropical forests. Alternatively, on the basis of remotely sensed frequencies of cloud occurrence, fog-affected forest may occupy as much as 2Ð21 Mkm2. Four hydrologically distinct montane forest types may be distinguished, viz. lower montane rain forest below the cloud belt (LMRF), tall lower montane cloud forest (LMCF), upper montane cloud forest (UMCF) of intermediate stature and a group that combines stunted sub-alpine cloud forest (SACF) and ‘elfin’ cloud forest (ECF). Average throughfall to precipitation ratios increase from 0Ð72 š 0Ð07 in LMRF (n D 15) to 0Ð81 š 0Ð11 in LMCF (n D 23), to 1Ð0 š 0Ð27 (n D 18) and 1Ð04 š 0Ð25 (n D 8) in UMCF and SACF–ECF, respectively. Average stemflow fractions increase from LMRF to UMCF and ECF, whereas leaf area index (LAI) and annual evapotranspiration (ET) decrease along the same sequence. Although the data sets for UMCF (n D 3) and ECF (n D 2) are very limited, the ET from UMCF (783 š 112 mm) and ECF (547 š 25 mm) is distinctly lower than that from LMCF (1188 š 239 mm, n D 9) and LMRF (1280 š 72 mm; n D 7). Field-measured annual ‘cloud-water’ interception (CWI) totals determined with the wet-canopy water budget method (WCWB) vary widely between locations and range between 22 and 1990 mm (n D 15). Field measured values also tend to be much larger than modelled amounts of fog interception, particularly at exposed sites. This is thought to reflect a combination of potential model limitations, a mismatch between the scale at which the model was applied (1 ð 1 km) and the scale of the measurements (small plots), as well as the inclusion of near-horizontal wind-driven precipitation in the WCWB-based estimate of CWI. Regional maps of modelled amounts of fog interception across the tropics are presented, showing major spatial variability. Modelled contributions by CWI make up less than 5% of total precipitation in wet areas to more than 75% in low-rainfall areas. Catchment water yields typically increase from LMRF to UMCF and SACF–ECF reflecting concurrent increases in incident precipitation and decreases in evaporative losses. The conversion of LMCF (or LMRF) to pasture likely results in substantial increases in water yield. Changes in water yield after UMCF conversion are probably modest due to trade-offs between concurrent changes in ET and CWI. General circulation model (GCM)-projected rates of climatic drying under SRES greenhouse gas scenarios to the year 2050 are considered to have a profound effect on TMCF hydrological functioning and ecology, although different GCMs produce different and sometimes opposing results. Whilst there have been substantial increases in our understanding of the hydrological processes operating in TMCF, additional research is needed to improve the quantification of occult precipitation inputs (CWI and wind-driven precipitation), and to better understand the hydrological impacts of climate- and land-use change. Copyright  2010 John Wiley & Sons, Ltd.

Characteristics of fog and fogwater fluxes in a Puerto Rican elfin cloud forest

Eugster, Werner ; Burkard, Reto; Holwerda, Friso; Scatena, Frederick N.; Bruijnzeel, L.A.(Sampurno) 2006. Characteristics of fog and fogwater fluxes in a Puerto Rican elfin cloud forest.. Agricultural and Forest Meteorology 139 :288-306.

The Luquillo Mountains of northeastern Puerto Rico harbours important fractions of tropical montane cloud forests. Although it is well known that the frequent occurrence of dense fog is a common climatic characteristic of cloud forests around the world, it is poorly understood how fog processes shape and influence these ecosystems. Our study focuses on the physical characteristics of fog and quantifies the fogwater input to elfin cloud forest using direct eddy covariance net flux measurements during a 43-day period in 2002.We used an ultrasonic anemometer–thermometer in combination with a size-resolving cloud droplet spectrometer capable of providing number counts in 40 droplet size classes at a rate of 12.5 times per second. Fog occurred during 85% of the time, and dense fog with a visibility <200 m persisted during 74% of the period. Fog droplet size depended linearly on liquid water content(r2 ¼ 0:89) with a volume-weighted mean diameter of 13.8 mm. Due to the high frequency of occurrence of fog the total fogwater deposition measured with the eddy covariance method and corrected for condensation and advection effects in the persistent upslope air flow, averaged 4.36 mm day1, rainfall during the same period was 28 mm day1. Thus, our estimates of the contribution of fogwater to the hydrological budget of elfin cloud forests is considerable and higher than in any other location for which comparable data exist but still not a very large component in the hydrological budget. For estimating fogwater fluxes for locations without detailed information about fog droplet distributions we provide simple empirical relationships using visibility data.
Syndicate content