Annual Precipitation Estimates Research Articles

Palaeoenvironmental reconstructions using the modern analogue technique: the effects of sample size and decision rules

Palaeoenvironmental information is often extracted from pollen records using the modem analogue technique (MAT). It is largely unknown how sensitive the MAT is to subsampling-induced variation in pollen assemblages, or to the decision rules used to reconstruct climate and vegetation. We examine these issues in a Monte Carlo framework in which simulated pollen assemblages at eight count sizes were created from four fossil pollen assemblages. Simulated and fossil assemblages are compared with modern data sets at squared chord distance cut-off values between 0.05 and 0.55 to: (1) quantify count-size-induced variation in pollen assemblages, and (2) determine how count-size-induced variation affects analogue selection and climate reconstruction. The effects of sample size and decision rules on vegetation reconstructions are examined using two analogue selection schemes and two levels of minimum required analogues. The results show that decision rules have as much impact on reconstruction precision and accuracy as do large differences in count size. At counts of 150 grains, the best-performing cut-off values yield annual precipitation estimates within 75 mm of those produced by the reference fossil assemblages, and January and July temperature estimates within 0.75C. Counts as low as 150 grains yield vegetation reconstruction accuracies of?90% using the best-case reconstruction rules; the worst-case reconstruction rules may not achieve this accuracy at 1000 grain counts. Although larger count sizes do lead to greater reconstruction precision and accuracy, the results indicate that analyses of the kind presented here can inform count-size decisions and allow significant re-allocation of analytical effort.

Chloride Mass Balance: Cautions in Predicting Increased Recharge Rates

The chloride-mass-balance (CMB) method has been used extensively to estimate recharge in arid and semi-arid environments. Required data include estimates of annual precipitation, total chloride input (from dry fallout and precipitation), and pore-water chloride concentrations. Typically, CMB has been used to estimate ancient recharge but recharge from recent land-use change has also been documented. Recharge rates below a few mm/yr are reliably detected with CMB; however, estimates above a few mm/yr appear to be less reliable. We tested the CMB method against 26 years of drainage from a 7.6 m deep lysimeter at a simulated waste-burial ground, located on the Department of Energy’s Hanford Site in southeastern Washington State, USA where land-use change has increased recharge rates. Measured drainage from the lysimeter for the past 26 years averaged 62 mm/yr. Precipitation averaged 190 mm/yr with an estimated chloride input of 0.225 mg/L. Initial pore-water chloride concentration was 88 mg/L and decreased to about 6 mg/L after 26 years, while the drainage water decreased to less than 1 mg/L. A recharge estimate made using chloride concentrations in drain water was within 20% of the measured drainage rate. In contrast, recharge estimates using 1:1 (water: soil) extracts were lower than actual bymore » factors ranging from 2 to 8 or more. The results suggest that when recharge is above a few mm/yr, soil water extracts can lead to unreliable estimates of recharge. For conditions of elevated recharge, direct sampling of pore water is the preferred method, because chloride concentrations are often 20 to 50 times higher in directly-sampled pore water than in pore-water extracts.« less

Eocene dry climate and woodland vegetation in tropical Africa reconstructed from fossil leaves from northern Tanzania

Eocene vegetation and climate data from tropical latitudes are sparse despite special interest in the Eocene as the warmest epoch of the Cenozoic and an often-cited analogue for greenhouse Earth conditions. Tropical Africa is noteworthy for its shortage of Eocene fossils, which could serve as proxies for climate and reveal community structural evolution during the continent's geographic isolation. In this paper, we report paleobotanical remains from a middle Eocene crater lake at 12°S paleolatitude in north central Tanzania, which provide a plant community reconstruction indicating wooded, rather than forest, vegetation and precipitation estimates near modern (660 mm/year). The plant community was dominated by caesalpinioid legumes and was physiognomically comparable to modern miombo woodland. Paleoprecipitation estimates, the first for the Paleogene of Africa, are calculated from fossil leaf morphology using regression equations derived from modern low-latitude leaves and climate. Mean annual precipitation estimates are 643±32 and 776±39 mm/year, and wet months precipitation estimates (all months averaging≥50 mm) are 630±38 and 661±38 mm. A slightly larger proportion of annual precipitation occurred in the dry months compared with today, which may indicate greater equability of precipitation in the Eocene.

Eocene dry climate and woodland vegetation in tropical Africa reconstructed from fossil leaves from northern Tanzania

Eocene vegetation and climate data from tropical latitudes are sparse despite special interest in the Eocene as the warmest epoch of the Cenozoic and an often-cited analogue for greenhouse Earth conditions. Tropical Africa is noteworthy for its shortage of Eocene fossils, which could serve as proxies for climate and reveal community structural evolution during the continent's geographic isolation. In this paper, we report paleobotanical remains from a middle Eocene crater lake at 12°S paleolatitude in north central Tanzania, which provide a plant community reconstruction indicating wooded, rather than forest, vegetation and precipitation estimates near modern (660 mm/year). The plant community was dominated by caesalpinioid legumes and was physiognomically comparable to modern miombo woodland. Paleoprecipitation estimates, the first for the Paleogene of Africa, are calculated from fossil leaf morphology using regression equations derived from modern low-latitude leaves and climate. Mean annual precipitation estimates are 643±32 and 776±39 mm/year, and wet months precipitation estimates (all months averaging≥50 mm) are 630±38 and 661±38 mm. A slightly larger proportion of annual precipitation occurred in the dry months compared with today, which may indicate greater equability of precipitation in the Eocene.

Orographic Precipitation Modeling with Multiple Linear Regression

A multiple linear regression (MLR) model, in conjunction with Geographic Information Systems technology, was used to derive the relationship between annual precipitation and elevation, longitude, and latitude. The island of Crete, in Greece, was used as the case study. A multiscale precipitation analysis was performed on areas ranging from large areas (the whole island and the northern, southern, and eastern parts of the island), to medium areas (watersheds), to small areas (sub-basins). While the MLR annual precipitation estimates (which used elevation, latitude, and longitude information) were found to be more reasonable than estimates obtained using elevation only when applied to the whole island, the difference between the MLR estimates and the elevation-only estimates was smaller when applied to individual watersheds. The MLR provides realistic estimates for mean areal precipitation for the island of Crete: 700±100, 950±150, and 1,300±200 mm for dry, average, and wet years, respectively. Elevation-ra...

A multiple linear regression GIS module using spatial variables to model orographic rainfall

This paper aims to document the development of a new GIS-based spatial interpolation module that adopts a multiple linear regression technique. The functionality of the GIS module is illustrated through a test case represented by the island of Crete, Greece, where the models generated were applied to locations where estimates of annual precipitation were required. The response variable is ‘precipitation’ and the predictor variables are ‘elevation’, ‘longitude’ and ‘latitude’, or any combination of these. The module is capable of performing a sequence of tasks which will eventually lead to an estimation of mean areal precipitation and the total volume of precipitation. In addition, it can generate up to nine predictor variables and their parameters, and can estimate areal rainfall for a user-specified three-dimensional extent. The developed module performed satisfactorily. Precipitation estimates at ungauged locations were obtained using the multiple linear regression method in addition to some conventional spatial interpolation techniques (i.e. IDW, Spline, Kriging, etc.). The multiple linear regression models provided better estimates than the other spatial interpolation techniques.

Assessment of the impact of meteorological network density on the estimation of basin precipitation and runoff: a case study

AbstractIn recent years in North America, a number of government agencies and industries have begun to reinvest in meteorological networks. This investment must be based on sound scientific advice. Increased meteorological station network density can be beneficial for a number of purposes, including flood forecasting. This study aimed at investigating the impact of network density at two temporal scales, i.e. for the estimation of total annual precipitation and for the estimation of daily precipitation during specific rain events. This was done using kriging as a means to estimate the spatial distribution and variance of rainfall. Kriged precipitation from two network scenarios (sparse and dense) were used as input into the HSAMI hydrological model and simulations were compared on five drainage basins in the Mauricie area (Québec, Canada).A comparison of the distribution of total annual precipitation interpolated from the two network scenarios showed that adding stations changed the distribution and magnitude of rainfall in the study area. High precipitation cells were better defined with the denser network, and decreases in the relative spatial variance were observed. Similarly, kriged daily precipitation provided a more defined spatial distribution of rainfall during important rain events of 1999, and variance was also reduced when the denser network was used.Finally, simulations performed with the HSAMI model were generally improved when the precipitation inputs were estimated using a denser station network for most drainage basins studied, as expressed by increased Nash coefficients and a decreased root‐mean‐square error. Peak flows during important summer flood events were generally better simulated when a denser network was used to calculate the mean daily precipitation used as input. Total cumulated volume estimations during the rain events were also generally improved with a denser network.This study showed that the estimation of variance remains an important tool for rain gauge network design. Moreover, network density was shown to have an important impact on the quality of flow simulations, even when a lumped model is used. Copyright © 2003 John Wiley & Sons, Ltd.

Precipitation recycling

The water cycle regulates and reflects natural variability in climate at the regional and global scales. Large‐scale human activities that involve changes in land cover, such as tropical deforestation, are likely to modify climate through changes in the water cycle. In order to understand, and hopefully be able to predict, the extent of these potential global and regional changes, we need first to understand how the water cycle works. In the past, most of the research in hydrology focused on the land branch of the water cycle, with little attention given to the atmospheric branch. The study of precipitation recycling, which is defined as the contribution of local evaporation to local precipitation, aims at understanding hydrologic processes in the atmospheric branch of the water cycle. Simply stated, any study on precipitation recycling is about how the atmospheric branch of the water cycle works, namely, what happens to water vapor molecules after they evaporate from the surface, and where will they precipitate? Estimation of precipitation recycling over any large basin, such as the Mississippi or the Amazon, is a necessary step before developing a quantitative description of the regional water cycle. This paper reviews the research on the concept of precipitation recycling and emphasizes the basic role of this process in defining the different components of the atmospheric branch in any regional water cycle. To illustrate the assumptions and limitations involved in estimation of precipitation recycling, we present and discuss a general formula for estimation of precipitation recycling. The recent estimates of annual precipitation recycling ratio from different regions are reviewed and compared. Finally, the dependence of precipitation recycling over any region on the spatial scale is discussed and illustrated by the example of the Amazon basin.

Multivariate geostatistical analysis of evapotranspiration and precipitation in mountainous terrain

This paper reports the evaluation of three geostatistical interpolation methods (ordinary kriging, cokriging and modified residual kriging) to interpolate long-term mean total annual reference evapotranspiration (AETO) and long-term mean total annual precipitation (APRE) in a mountainous region, where the stationarity hypothesis probably do not hold for the whole region, but do hold locally. AETO and APRE estimates and estimation errors were evaluated at validation stations. Estimates and computed estimation error variances (used as indicators of estimation uncertainty) were also obtained at 1913 5 km grid points. In general, estimates at validation stations were in good agreement with observed values for all interpolation methods, although modified residual kriging estimates of APRE were slightly worse than those obtained by the other two methods. Based on mean absolute error (MAE) and mean squared error (MSE) at validation stations, no method ranked clearly above other for interpolation of AETO. At grid points, AETO estimation uncertainty was improved by cokriging by about 11.5% and 8.4% compared with ordinary kriging and modified residual kriging, respectively. Likewise, cokriging was superior for interpolation of APRE in terms of MAE and MSE obtained at validation stations. At grid points, cokriging reduced estimation uncertainty by 18.7% and 24.3% compared with ordinary kriging and modified residual kriging, respectively, whereas modified residual kriging in general did not improve ordinary kriging results. Computed estimation error variance values indicated that modified residual kriging would reduce estimation uncertainty in areas where very few weather stations are available for interpolation.

Vegetation zones in NW Africa during the brunhes chron reconstructed from marine palynological data

Six East Atlantic sites between 9° and 35°N allow the reconstruction of the latitudinal position and extension of the NW African vegetation zones. During the last 0.7 Ma, the response of the vegetation to alternating glacial (dry) and interglacial (humid) climatic conditions has been recorded. The vegetation response to a climatic amelioration starts with the northward expansion of the tropical rain forest, followed by the northward shift of the Saharan-Sahelian boundary, and ends with the southward shift of the Saharan-Mediterranean transitional steppes and the expansion of the Mediterranean oak forests. Most sensitive is the reaction of the Saharan-Sahelian boundary to climatic change. Large shifts of the Saharan-Sahelian boundary seem to occur faster than small ones. Annual precipitation estimates for the latitude of Dakar (15°N) range from 100 to 1000 mm. At 24°N, yearly precipitation probably ranged from 0 to 150 mm. Smallest extent of the Guinean tropical rain forest probably occurred during the arid conditions of Isotope Stages 2 and 6 reducing the carbon fixation of these forests to a minimum. Large extent of the Guinean tropical rain forest occurred during most of the odd isotope stages (more humid interglacials).

A comparison of geostatistical procedures for spatial analysis of precipitation in mountainous terrain

Spatially distributed measurements or estimates of precipitation over a region are required for modelling of hydrologic processes and soil moisture for agricultural and natural resource management. Simple interpolation methods fail to consider the effects of topography on precipitation and may be in considerable error in mountainous regions. The performance of three geostatistical methods for making mean annual precipitation estimates on a regular grid of points in mountainous terrain was evaluated. The methods were: (1) kriging; (2) kriging elevation-detrended data; and (3) cokriging with elevation as an auxiliary variable. The study area was the Willamette River basin, a 2.9 million hectare region spanning the area between the Coast Range and the Cascade Range in western Oregon. Compared with kriging, detrended kriging and cokriging both exhibited better precision (as indicated by estimation coefficients of variation of 16 and 17% vs. 21%; and average absolute errors of 19 and 20 cm vs. 26 cm) and accuracy (as indicated by average errors of −1.4 and −2.0 cm vs. −5.2 cm) in the estimation of mean annual precipitation. Contour diagrams for kriging and detrended kriging exhibited smooth zonation following general elevation trends, while cokriging showed a patchier pattern more closely corresponding to local topographic features. Detrended kriging and cokriging offer improved spatially distributed precipitation estimates in mountainous terrain on the scale of a few million hectares. Application of these methods for a larger region, the Columbia River drainage in the USA (57 million hectares), was unsuccessful due to the lack of a consistent precipitation-elevation relationship at this scale. Precipitation estimation incorporating the effects of topography at larger scales will require either piecewise estimation using the methods described here or development of a physically based orographic model.

Effect of Length of Record on Estimates of Annual Precipitation in Nevada

In a previous study, it was noted that the addition of six years of data to the Nevada Test Site daily precipitation data base resulted in significant changes in the calculated values of annual average precipitation. The goal of the investigation described here was to examine the effect of the period of record available for analysis on estimates of annual precipitation and to discuss the effect of changing estimates of annual precipitation on estimates of regional groundwater recharge.

Reconnaissance estimates of natural recharge to desert basins in Nevada, U.S.A., by using chloride-balance calculations

A chloride-balance method for estimating average natural recharge to groundwater basins in the Basin and Range Province of the western United States may be a useful alternative or complement to current techniques. The chloride-balance method, as presented in this paper, equates chloride in recharge water and runoff to chloride deposited in mountainous recharge-source areas by precipitation and dry fallout. Given estimates of annual precipitation on these source areas and chloride concentrations of bulk precipitation and recharge water, the rate of recharge can be estimated providing that: (1) no other major sources of chloride exist; (2) direct runoff to discharge areas in the basin is small or can otherwise be taken in account in the balance; and (3) the recharge sources for the basin are correctly delineated. The estimates are sensitive to the estimated rate of input of chloride from the atmosphere; this is the greatest data need for future applications of the method. Preliminary applications of the method to sixteen basins in Nevada, including Las Vegas Valley, indicate that the method can be a useful tool for hydrologists and resource managers. Correlation coefficients between recharge efficiencies for the basins — estimated on the basis of recharge estimates that use the chloride-balance method and two other currently used techniques — range from 0.54 to 0.95, depending on assumptions about where the method may be applied.

Pure culture response of ectomycorrhizal fungi to imposed water stress

The ability of ectomycorrhizal fungal isolates to tolerate imposed water stress in pure culture was examined in 55 isolates of 18 species. Water potential treatments, adjusted with polyethylene glycol, were applied to Petri dish units. These units allowed colony diameter measurements of fungi grown on liquid media. Delayed growth initiation and inhibition of growth rate occurred with increasing water stress. For 87% of the isolates, growth rate was inhibited by the initial water potential treatment applied, leaving only seven isolates where growth increased with initial water potential treatments. No growth was evident under the imposed stress treatments for isolates of Laccaria bicolor, Laccaria laccata, and Lactarius controversus; growth occurred only in the control. Drought tolerant species, demonstrated by an ability to grow at a water potential of −3 MPa, included Boletus edulis, Cenococcum geophilum, Rhizopogon vinicolor, and five out of eight Suillus species. Species intolerant of −1 MPa included Hebeloma crustuliniforme, Laccaria bicolor, Laccaria laccata, and Suillus caerulescens. Fungal drought tolerance was poorly correlated with estimates of annual precipitation for collection locations. Estimates of drought tolerance seems to depend more on fungal classification than on annual precipitation at the site of collection. Reisolation of Laccaria bicolor increased growth rate and water stress tolerance when compared with the same fungus prior to reisolation.

A dendroclimatic reconstruction of annual precipitation amounts in Iowa since 1680

Tree ring widths from white oak (Quercus alba) in central Iowa were found to be accurate indicators of total precipitation for a period beginning near the end of the prior growing season and extending until the end of the growing season in the year of ring formation. Regression‐based estimates of annual (August–July) precipitation for Iowa were obtained for the 300‐year period of tree ring record (1680–1979). The correlation coefficient between actual and estimated precipitation values was +0.74 for the 60‐year period of data used to calculate the regression coefficients and +0.72 for the preceding 46 years of independent data. These results show that tree rings are reliable indicators of wet and dry periods in Iowa, thereby providing a 300‐year record of precipitation variations for use by scientists and planners.

Relationship between precipitation, evaporation, and runoff in tropical‐equatorial regions

Bouchet's theory on actual and potential evaporation can be used as a basis to develop semi‐empirical relationships between precipitation, actual evaporation, and radiation. These relationships are curvilinear, and the derived precipitation‐runoff relationships are also curvilinear. Since the variation of annual radiation from one year to another in tropical‐equatorial regions is not very significant, the average value of annual radiation can be approximated using direct measurements or indirect estimates from data taken over a period of from two to five years. This value can be used with the semi‐empirical relationship developed in the paper to obtain fair estimates of the annual variation of actual evaporation and runoff from data on annual precipitation and good estimates of the long‐term averages of these hydrologie characteristics. Bouchet's theory can be used to analyze evaporation and runoff for periods of less than one year and for estimating lake and reservoir evaporation. However, in this case, the assessment of the effect of heat and moisture storage requires further investigation.