precipitation

Mapping the Climate of Puerto Rico, Vieques and Culebra

DALY C.,HELMER E. H.,QUIÑONES M. Mapping the Climate of Puerto Rico, Vieques and Culebra. International Journal of Climatology. Int. J. Climatol. 23: 1359-1381 (2003).

Abstract: 
Spatially explicit climate data contribute to watershed resource management, mapping vegetation type with satellite imagery, mapping present and hypothetical future ecological zones, and predicting species distributions. The regression based Parameter-elevation Regressions on Independent Slopes Model (PRISM) uses spatial data sets, a knowledge base and expert interaction to generate GIS-compatible grids of climate variables. This study applied PRISM to generate maps of mean monthly and annual precipitation and minimum and maximum temperature for the Caribbean islands of Puerto Rico, Vieques and Culebra over the 1963-1995 averaging period. PRISM was run under alternative parameterizations that simulated simpler interpolation methods as well as the full PRISM model. For temperature, the standard PRISM parameterization was compared to a hypsometric method, in which the temperature/elevation slope was assumed to be -6.5°C/km (HYPS). For precipitation, the standard PRISM parameterization was compared to an inverse-distance weighting interpolation (IDW). Spatial temperature patterns were linked closely to elevation, topographic position, and coastal proximity. Both PRISM and HYPS performed well for July maximum temperature, but HYPS performed relatively poorly for January minimum temperature, due primarily to lack of a spatially varying temperature/elevation slope, vertical atmospheric layer definition, and coastal proximity guidance. Mean monthly precipitation varied significantly throughout the year, reflecting seasonally differing moisture trajectories. Spatial precipitation patterns were associated most strongly with elevation, upslope exposure to predominant moisture-bearing winds, and proximity to the ocean. IDW performed poorly compared to PRISM, due largely to the lack of elevation and moisture availability information. Overall, the full PRISM approach resulted in greatly improved performance over simpler methods for precipitation and January minimum temperature, but only a small improvement for July maximum temperature. Comparisons of PRISM mean annual temperature and precipitation maps to previously-published, hand-drawn maps showed similar overall patterns and magnitudes, but the PRISM maps provided much more spatial detail.

PUERTO RICO AND VIRGIN ISLANDS PRECIPITATION FREQUENCY STUDY

Abstract: 
The Hydrometeorological Design Studies Center (HDSC), Hydrology Laboratory, Office of Hydrologic Development, U.S. National Weather Service is updating its precipitation frequency analysis for Puerto Rico and the Virgin Islands. Current precipitation frequency studies for the area are contained in Technical Paper No. 42 "Generalized estimates of probable maximum precipitation and rainfall-frequency data for Puerto Rico and Virgin Islands" (U.S. Weather Bureau 1961) and Technical Paper No. 53 "Two- to ten-day rainfall for return periods of 2 to 100 years in Puerto Rico and Virgin Islands" (Miller 1965). The current study includes collecting data and performing quality control, compiling and formatting datasets for analyses, selecting applicable frequency distributions and fitting techniques, analyzing data, mapping and preparing reports and other documentation. The study will determine annual and seasonal precipitation frequencies for durations from 5 minutes to 60 days, for return periods from 2 to 1000 years. The study will review and process all available rainfall data for the Puerto Rico and Virgin Island study area and use accepted statistical methods. The study results will be published as a Volume of NOAA Atlas 14. They will also be made available on the internet using web pages with the additional ability to download digital files.

a census of cumulus-cloud height versus precipitation in the vicinity of puerto rico during the winter and spring of 1953-1954

Byers, H. R., and R. K. Hall, 1955: A census of cumulus-
cloud height versus precipitation in the vicinity
of Puerto Rico during the winter and spring of
1953–1954. J. Meteor., 12, 176–178.

Abstract: 
The analysis of fifteen cloud-census flights confirms the common existence of warm precipitation from trade-wind cumuli. A probability that over-water clouds of certain vertical developments will contain precipitation is presented. Since the examined over-water clouds with tops higher than 11,500 feet always contained precipitation and yet were well below the freezing level, the futility of initiating rain by seeding clouds with freezing reagents becomes obvious.

MAPPING THE CLIMATE OF PUERTO RICO, VIEQUES AND CULEBRA

CHRISTOPHER DALY, E.H. HELMER, AND MAYA QUIÑONES 2003. Mapping the Climate of Puerto Rico, Vieques and Culebra.. Int. J. Climatol. 23 :1359-1381 .

Abstract: 
Spatially explicit climate data contribute to watershed resource management, mapping vegetation type with satellite imagery, mapping present and hypothetical future ecological zones, and predicting species distributions. The regression based Parameter-elevation Regressions on Independent Slopes Model (PRISM) uses spatial data sets, a knowledge base and expert interaction to generate GIS-compatible grids of climate variables. This study applied PRISM to generate maps of mean monthly and annual precipitation and minimum and maximum temperature for the Caribbean islands of Puerto Rico, Vieques and Culebra over the 1963-1995 averaging period. PRISM was run under alternative parameterizations that simulated simpler interpolation methods as well as the full PRISM model. For temperature, the standard PRISM parameterization was compared to a hypsometric method, in which the temperature/elevation slope was assumed to be -6.5°C/km (HYPS). For precipitation, the standard PRISM parameterization was compared to an inverse-distance weighting interpolation (IDW). Spatial temperature patterns were linked closely to elevation, topographic position, and coastal proximity. Both PRISM and HYPS performed well for July maximum temperature, but HYPS performed relatively poorly for January minimum temperature, due primarily to lack of a spatially varying temperature/elevation slope, vertical atmospheric layer definition, and coastal proximity guidance. Mean monthly precipitation varied significantly throughout the year, reflecting seasonally differing moisture trajectories. Spatial precipitation patterns were associated most strongly with elevation, upslope exposure to predominant moisture-bearing winds, and proximity to the ocean. IDW performed poorly compared to PRISM, due largely to the lack of elevation and moisture availability information. Overall, the full PRISM approach resulted in greatly improved performance over simpler methods for precipitation and January minimum temperature, but only a small improvement for July maximum temperature. Comparisons of PRISM mean annual temperature and precipitation maps to previously-published, hand-drawn maps showed similar overall patterns and magnitudes, but the PRISM maps provided much more spatial detail

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,
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.

The stable isotope amount effect: New insights from NEXRAD echo tops, Luquillo Mountains, Puerto Rico

Scholl MA, Shanley JB, Zegarra JP, Coplen TB. 2009. The stable isotope
amount effect: new insights from NEXRAD echo tops, Luquillo
Mountains, Puerto Rico. Water Resources Research 45: W12407, DOI:
10.1029/2008WR007515.

Abstract: 
The stable isotope amount effect has often been invoked to explain patterns of isotopic composition of rainfall in the tropics. This paper describes a new approach, correlating the isotopic composition of precipitation with cloud height and atmospheric temperature using NEXRAD radar echo tops, which are a measure of the maximum altitude of rainfall within the clouds. The seasonal differences in echo top altitudes and their corresponding temperatures are correlated with the isotopic composition of rainfall. These results offer another factor to consider in interpretation of the seasonal variation in isotopic composition of tropical rainfall, which has previously been linked to amount or rainout effects and not to temperature effects. Rain and cloud water isotope collectors in the Luquillo Mountains in northeastern Puerto Rico were sampled monthly for three years and precipitation was analyzed for δ18O and δ2H. Precipitation enriched in 18O and 2H occurred during the winter dry season (approximately December-May) and was associated with a weather pattern of trade-wind showers and frontal systems. During the summer rainy season (approximately June-November), precipitation was depleted in 18O and 2H and originated in low pressure systems and convection associated with waves embedded in the prevailing easterly airflow. Rain substantially depleted in 18O and 2H compared to the aforementioned weather patterns occurred during large low pressure systems. Weather analysis showed that 29 % of rain input to the Luquillo Mountains was trade-wind orographic rainfall, and 30 % of rainfall could be attributed to easterly waves and low pressure systems. Isotopic signatures associated with these major climate patterns can be used to determine their influence on streamflow and groundwater recharge and to monitor possible effects of climate change on regional water resources.

Precipitation distribution and raingage networks in the luquillo mountains

HOLBEN, B. N., J. A. COLON, M. CANALS, F. SANTOS, AND
R. G. CLEMENTS. 1979. Precipitation distribution
and raingage networks in the Luquillo Mountains, p.
57-66. Zn River basin energy and environmental
planning. Univ. Puerto Rico, CEER-T-40.

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

Abstract: 
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.
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