Rainfall Classes Research Articles

Estudo da precipitação mensal durante a estação chuvosa em Diamantina, Minas Gerais

O objetivo deste trabalho foi estudar o comportamento da precipitação pluvial no período da estação chuvosa na região de Diamantina, MG. Dados de precipitação pluviométrica mensal, da série histórica de 1977 a 2006, foram utilizados e averiguada a probabilidade para várias classes de precipitação, através da função de frequência acumulada, usando-se a metodologia da distribuição Weibull com averiguação de aderência pelo teste Kolmogorov-Smirnov com nível de significância de 5%; de classes definidas em função de percentis predeterminados. Os resultados mostram que a estação chuvosa, compreendida entre outubro e março, representa 88% do total precipitado anual. Os meses de janeiro e dezembro apontam as maiores probabilidades de ocorrência de precipitação com 220,1 mm e 167,8 mm, respectivamente, a nível de 25% de probabilidade de ocorrência. O modelo de distribuição Weibull apresentou bom ajuste da série climatológica para estudos probabilísticos mostrando os parâmetros dentro dos limites estatísticos preestabelecidos.

Modeling and evaluation of compliance to water quality regulations in bathing areas on the Daoulas catchment and estuary (France)

The microbiological quality of waters in estuaries determines their acceptability for recreational uses. Microbiological contamination often results from urban wastewater discharges or non-point source pollution (manure spreading), and can cause bathing zones to be closed. European regulations (EC/7/2006) have proposed standards (500 E. coli/100 ml) for the acceptability areas for bathing. In this study, two models were associated to simulate contamination: SWAT on a catchment and MARS 2D in the downstream estuary. After river flow calibration and validation, two scenarios were simulated in SWAT, and E. coli fluxes obtained at the main outlet of the catchment were then introduced into MARS 2D to follow E. coli concentrations in the estuary. An annual evaluation of compliance to bathing area water quality standards was then calculated, linked with daily rainfall classes. Water quality in the estuary was below the standard on 13 days, including 5 days with rainfall superior to 10 mm, due to faecal contamination from soil leaching by rain, and 5 days with rainfall ranging from 0.1 to 5 mm/day, due to the high frequency of this level of rainfall. To conclude, this study allowed us to demonstrate the efficiency of models to gain a better understanding on water quality degradation factors.

Heavy daily-rainfall characteristics over the Gauteng Province

Daily rainfall over the Gauteng Province, South Africa, was analysed for the summer months of October to March using 32-yr (1977 to 2009) daily rainfall data from about 70 South African Weather Service stations. The monthly and seasonal variation of heavy rainfall occurrences was also analysed. Three 24-h heavy rainfall classes are defined considering the area-average rainfall. A significant rainfall event is defined when the average rainfall exceeds 10 mm, a heavy rainfall event when the average rainfall exceeds 15 mm and a very heavy rainfall event when the average rainfall exceeds 25 mm. January months have the highest monthly average rainfall as well as the highest number of heavy and very heavy rainfall days. The month with the second-highest number of heavy and very heavy rainfall days is February followed by March and October. December has the second-highest monthly average rainfall and the most days with rain. However, it is also the month with the lowest number of heavy and very heavy rainfall days. The highest 24-h rainfall recorded at a single station during the 32-yr period was 300 mm in December 2006. However, rainfall exceeding 115 mm at a single rainfall station in the Gauteng Province is very rare and does not occur every year. January months receive these events more than any other month but this only transpires in approximately a third of years. The central and north-western parts of the Province experience the most events where the rainfall at a single station surpasses 75 and 115 mm. With regard to seasonal rainfall, the 1995/96 summer rainfall season had the highest seasonal rainfall during this 32-yr period followed by the 1999/2000 season. The 1995/96 season had above normal rainfall in both early and late summer but the 1999/2000 season was dry in early summer and very wet in late summer. Significantly high seasonal rainfall is associated with above-normal rainfall in late summer.

Investigating the impacts of adjoining wet days on the distribution of daily rainfall amounts in Peninsular Malaysia

The amount of daily rainfall for a solitary wet day (Class 0) is normally less than the rainfall for a wet day that is enclosed by wet days on either side (Class 2). The same characteristics hold true for the case of the first or last day of wet spells (Class 1) where the rainfall here is found to be smaller than the Class 2 rainfall. In many cases, there exist large differences between these rainfall classes. However, this is not the case for the Malaysian rainfall data. The daily rainfall data from 50 rain gauge stations which represent four regions in Peninsular Malaysia are classified according to the number of adjoining wet days (0, 1 and 2). For some stations, the mean rainfall for Class 0 is found to be higher than the other two classes during part of the year. There are also a few cases where there is only a slight difference between these three classes. To examine the impact of adjoining wet days on the distribution of rainfall amounts, models for rainfall amounts are tested with all rainfall classes grouped together, with solitary wet days fitted separately from other wet days, and finally with all rainfall classes separately. The results show that the models which treat the rainfall classes separately are a better fit for stations in the East and a few stations in the Southwest regions. The Akaike Information Criterion (AIC) values are significantly reduced as the rainfall data are split into rainfall classes. However, for the West and Northwest regions, the models which group all the data together are preferred. These differences may be influenced by factors such as geographical location, topography and monsoon changes.

Quantitative evaluation of climatic variability and risks for wheat yield in India

This study comprises (1) an analysis of recent climate trends at two sites in north-west India (Ludhiana in Punjab and Delhi) and (2) an impact and risk assessment for wheat yields associated with climatic variability. North-west Indian agriculture is dominated by rice-wheat rotation in which the wheat season (‘rabi’, November to March) is characterized by predominantly dry conditions—superimposed by very high inter-annual variability of rainfall (17 to 260 mm in Ludhiana and <1 to 155 mm in Delhi). While rainfall remained without discernable trend over the last three decades, minimum and average temperatures showed increasing trends of 0.06 and 0.03°C year − 1, respectively, at Ludhiana. The site in (metropolitan) Delhi was apparently influenced by city-effects, which was noticeable from the decrease in solar radiation of 0.09 MJ m − 2 day − 1 year − 1. The CERES-wheat model was used to calculate yields of rainfed wheat that were at both locations highly correlated with seasonal rainfall. An assessment framework was developed to quantify yield impacts due to rainfall variability in three steps: (1) data from different years were aggregated into four classes, i.e., years with scarce, low, moderate, and high rainfall, (2) yield records of each rainfall class were ranked according to yield to facilitate (3) a comparison of yields with identical rank, i.e. among the best yield of each class, the second-best, etc. The class with moderate rainfall was taken as baseline yield to compute yield impacts of other rainfall scenarios. Years with scarce rainfall resulted in only 34% (Ludhiana) and 35% (Delhi) of the baseline yield. The yields in years with low rainfall accounted for 61% (Delhi) and 49% (Ludhiana) of the baseline yields. In Ludhiana, high rainfall years resulted in 200% yield as compared to the baseline yield, whereas they reached only 105% in Delhi. Low-intensity (1× and 3×) irrigation decreased the relative yield losses, but entailed a higher vulnerability in terms of absolute yield losses. Only high-intensity (4×) irrigation buffered wheat yields against adverse rainfall years. Early sowing was beneficial for wheat yields under all rainfall scenarios. The framework could be a valuable decision-support tool at the farm level where seasonal rainfall variability is high.

Spatial and temporal daily rainfall regime in Catalonia (NE Spain) derived from four precipitation indices, years 1950–2000

AbstractAnnual rainfall amount, P, number of rainy days per year, N, average daily intensity in a year, I, and relevance, R, of the contribution of a rainfall class interval to the annual amount are used as pluviometric indices to deeply analyse the description of the complex behaviour of the daily rainfall regime of Catalonia (NE Spain). For this analysis, daily amounts of rainfall from 75 rain gauges for the period 1950–2000 have been considered. Indices N and I are analysed by distinguishing five percentiles (25th, 50th, 75th, 90th and 95th) of the daily rainfall amounts. Index R is evaluated taking into account &lt;25%, 25–50%, 50–75%, 75–90%, ≥90% and ≥95% class intervals. All these indices are described by their mean annual values, standard deviations and consecutive temporal irregularities. Besides the complex orography of the country, effects of the influence of the Mediterranean regime and remoteness of the Iberian Peninsula to the Atlantic coast are detected in the diversity of spatial patterns of the indices. The influence of the Atlantic regime is also found at some places in the Pyrenees, especially those that faced north. All these features are described through a Principal Component Analysis (PCA), which is applied to average annual values of the pluviometric indices, and the subsequent clustering process. Additionally, time trends of the annual indices are analysed for a selected set of 39 rain gauges with an optimum recording continuity. Trends are derived from linear regression, and local statistical significances at the 95% confidence level are established using the Mann–Kendall test. Field significant trends are investigated by means of Monte Carlo simulations. It is worthy of mention that field significant trends have been detected in the number of rainy days for percentiles up to the 75th, all local trends being negative. Field significant trends are also detected in daily intensity, whatever the threshold level, with positive and negative local trends. The relevance index R depicts field significant trends for the first three class intervals, with a predominance of positive local trends in the first two, thus indicating an increasing contribution of light and moderate daily episodes to the annual amounts. Copyright © 2006 Royal Meteorological Society

Structure of biological soil crust communities inCallitris glaucophyllawoodlands of New South Wales, Australia

Abstract:Question:What is the nature of the relationships between cover, diversity and abundance of biological soil crusts, cover and diversity of vascular plants, and annual rainfall, soil texture and forestry practices inCallitris glaucophyllawoodlands? Location: Arid and semi‐aridCallitris glaucophylla‐domi‐nated woodlands of eastern Australia.Methods:We documented soil crust‐forming mosses, lichens and liverworts at 83 woodland sites along a gradient of declining rainfall. Linear and non‐linear regression were used to examine relationships between soil crust species and attributes of vascular plant communities, and a similarity matrix (species abundance X sites) was subjected to Non‐metric Multi‐Dimensional Scaling (MDS), and Analysis of Similarities (ANOSIM) to show the degree of association between groups of taxa, and soil texture, rainfall classes and forestry practices.Results: We collected 86 taxa. Mosses were dominated by the familyPottiaceae, and lichens were dominated by squamulose forms. Average annual rainfall was highly correlated with soil crust community composition, and loamy soils supported a greater cover and diversity of taxa compared with sandy soils. Increases in tree cover were associated with significant, though weak, increases in abundance, but not diversity, of crusts. Crusts tended to be more diverse in areas that (1) had a sparse cover of ground‐storey plants; (2) were relatively stable ‐ as indicated by the proportion of perennial and/or native plants; (3) had more stable soil surfaces; and (4) were unlogged. Litter cover, overstorey thinning, and livestock grazing had no appreciable effect on crust diversity or cover.Conclusions:Callitris glaucophyllawoodlands provide substantial habitat for soil crust organisms, and the dense tree cover and closed canopies ofCallitrisdo not appear to have a major influence on the structure of biological crust communities. Unlike other woodland systems, relatively few patches would be required to reserve a high diversity of crust species.

Structure of biological soil crust communities in Callitris glaucophylla woodlands of New South Wales, Australia

Question: What is the nature of the relationships between cover, diversity and abundance of biological soil crusts, cover and diversity of vascular plants, and annual rainfall, soil texture and forestry practices in Callitris glaucophylla woodlands? Location: Arid and semi-arid Callitris glaucophylla-dominated woodlands of eastern Australia. Methods: We documented soil crust-forming mosses, lichens and liverworts at 83 woodland sites along a gradient of declining rainfall. Linear and non-linear regression were used to examine relationships between soil crust species and attributes of vascular plant communities, and a similarity matrix (species abundance ∞ sites) was subjected to Non-metric Multi-Dimensional Scaling (MDS), and Analysis of Similarities (ANOSIM) to show the degree of association between groups of taxa, and soil texture, rainfall classes and forestry practices. Results: We collected 86 taxa. Mosses were dominated by the family Pottiaceae, and lichens were dominated by squamulose forms. Average annual rainfall was highly correlated with soil crust community composition, and loamy soils supported a greater cover and diversity of taxa compared with sandy soils. Increases in tree cover were associated with significant, though weak, increases in abundance, but not diversity, of crusts. Crusts tended to be more diverse in areas that (1) had a sparse cover of ground-storey plants; (2) were relatively stable – as indicated by the proportion of perennial and/or native plants; (3) had more stable soil surfaces; and (4) were unlogged. Litter cover, overstorey thinning, and livestock grazing had no appreciable effect on crust diversity or cover. Conclusions: Callitris glaucophylla woodlands provide substantial habitat for soil crust organisms, and the dense tree cover and closed canopies of Callitris do not appear to have a major influence on the structure of biological crust communities. Unlike other woodland systems, relatively few patches would be required to reserve a high diversity of crust species.

Climatology and Trends in Summer Precipitation Characteristics in Mongolia for the Period 1960-98

Changes in rainfall characteristics over Mongolia and adjacent regions during summer were examined for the period 1960 to 1998, using daily and monthly precipitation data for Mongolia, China and the former USSR. Climatologically, mean summer (June to August) total precipitation was greater in northern Mongolia, and tended to decrease toward the south and southwest. Summer total precipitation contributed more than 60% of annual precipitation in Mongolia. ‘Wet days’ is defined as a day exceeding precipitation more than 0.1 mm. The number of wet days was approximately 40 days in northern Mongolia, while the number of wet days was less than 20 days in the south.Between 1960 and 1998, trends in summer total precipitation, the number of wet days in summer, and summer mean precipitation intensity were examined. The daily precipitation data were sorted into ascending order, and grouped into 10 classes which have an interval width equal to 10% of total number of wet days. Summer total precipitation increased in eastern and western Mongolia. Trends in heaviest precipitation class were also evaluated. The amounts of precipitation in the heaviest rainfall class, also increased in eastern and southern Mongolia and the Altai Mountains. The number of wet days increased over almost all of Mongolia. The frequency of relatively heavy rainfall events increased in eastern and southern areas, whereas during the same period weaker rainfall events became dominant in the northern part of central Mongolia.

Using High-Resolution Soil Moisture Data to Assess Soil Water Dynamics in the Vadose Zone

Vadose Zone J. 3:926–935 (August 2004) Tables 3 and 4 include errors in the footnotes. Both footnotes misidentify the purpose of the letters following the values in the tables: Table 3, p. 931 ¶Values followed by the same lowercase letter within a row indicate significant differences between tillage treatments within a rainfall class (p = 0.05). Table 4, p. 932 ¶Values followed by the same lowercase letter within a row indicate significant differences for comparisons among row positions within a tillage treatment and rainfall class (p = 0.05). #Values followed by the same uppercase letter within a column indicate significant differences for comparisons between tillage treatments within season, rainfall class, and row position (p = 0.05). The letters actually denote values that are not significantly different. The footnotes should read: Table 3, p. 931 ¶Values followed by the same lowercase letter within a row are not significantly different between tillage treatments within a rainfall class (p = 0.05). Table 4, p. 932 ¶Values followed by the same lowercase letter within a row are not significantly different for comparisons among row positions within a tillage treatment and rainfall class (p = 0.05). #Values followed by the same uppercase letter within a column are not significantly different for comparisons between tillage treatments within season, rainfall class, and row position (p = 0.05).

Using High‐Resolution Soil Moisture Data to Assess Soil Water Dynamics in the Vadose Zone

Vadose Zone J. 3:926–935 (August 2004) Tables 3 and 4 include errors in the footnotes. Both footnotes misidentify the purpose of the letters following the values in the tables: Table 3, p. 931 ¶Values followed by the same lowercase letter within a row indicate significant differences between tillage treatments within a rainfall class (p = 0.05). Table 4, p. 932 ¶Values followed by the same lowercase letter within a row indicate significant differences for comparisons among row positions within a tillage treatment and rainfall class (p = 0.05). #Values followed by the same uppercase letter within a column indicate significant differences for comparisons between tillage treatments within season, rainfall class, and row position (p = 0.05). The letters actually denote values that are not significantly different. The footnotes should read: Table 3, p. 931 ¶Values followed by the same lowercase letter within a row are not significantly different between tillage treatments within a rainfall class (p = 0.05). Table 4, p. 932 ¶Values followed by the same lowercase letter within a row are not significantly different for comparisons among row positions within a tillage treatment and rainfall class (p = 0.05). #Values followed by the same uppercase letter within a column are not significantly different for comparisons between tillage treatments within season, rainfall class, and row position (p = 0.05).

The association of rainfall and other weather variables with road traffic volume in Melbourne, Australia

An investigation into the effect of weather variables on traffic flow at a site in Melbourne, Australia, for the period 1989–1996 was performed. Rainfall was the strongest correlated weather parameter and it had the greatest impact in winter and spring, when traffic volume is reduced on wet days. There are statistically significant decreases of 1.35 and 2.11% in traffic volume on wet days in winter and spring. The reduction increases to 2–3% over the 2–10 mm range, the largest being 3.43% for the 2–5 mm class in spring. For the first time, our study considers separately daytime and nighttime periods. We found a reduction of 1.86% in winter and 2.16% in spring during daytime rainfall. The reduction at nighttime is significant over all seasons, ranging from 0.87% in winter to 2.91% in spring. We have explored an application where the traffic volume was used to normalise the road accident count and found the rain effect to increase by 2.4, 1.9 and 5.2% relative to the daily, daytime and nighttime dry mean accident count. Generally, the normalised count is greater than the raw count, with a larger increase for the higher rainfall classes.

Transport of labile carbon in runoff as affected by land use and rainfall characteristics

The mobilization of organic carbon (C) by water erosion could impact the terrestrial C budget, but the magnitude and direction of that impact remain uncertain due to a lack of data regarding the fates and quality of eroded C. A study was conducted to monitor total organic C and mineralizable C (MinC) in eroded materials from watersheds under no till (NT), chisel till (CT), disk till low input (DT-LI), pasture and forest. The DT-LI treatment relies on manure application and legume cover crops to partly supply the N needed when corn is grown, and on cultivation to reduce the use of herbicides. Each watershed was instrumented with a flume and a Coshocton wheel sampler for runoff measurement. Carbon dioxide (CO 2) evolved during incubation (115 days) of runoff samples was fitted to a first-order decomposition model to derive MinC. Annual soil (6.2 Mg ha −1) and organic C (113.8 kg C ha −1) losses were twice as much in the DT-LI than in the other watersheds (<2.7 Mg soil ha −1, <60 kg C ha −1). More than management practices, rainfall class (based on intensity and energy) was a better controller of sediment C concentration and biodegradability. Sediment collected during the low-intensity (fall/winter) storms contained more organic C (37 g C kg −1) and MinC (30–40% of sediment C) than materials displaced during the high-intensity summer storms (22.1 g C kg −1 and 13%, respectively). These results suggest a more selective detachment and sorting of labile C fractions during low-intensity storms. However, despite the control of low-intensity storm on sediment C concentration and quality, increased soil loss with high-energy rainfall suggests that a few infrequent but high-energy storms could determine the overall impact of erosional events on terrestrial C cycling.

Verification of rainfall forecasts for the Vaal Dam catchment for the summer rainfall seasons of 1994 to 1998

Rainfall forecasts compiled by the South African Weather Service (SAWS) are used daily by agriculture, industry, sportsmen and the general public. Because of the importance of the rainfall forecast, it is of considerable interest to know how reliable these forecasts are. The SAWS evaluates the rainfall forecasts issued by the Central Forecasting Office (CFO) on a daily basis. A hit score is determined in each of 19 rainfall districts throughout South Africa. This renders a result of approximately 60% correct forecasts for all 19 districts. This paper investigates the accuracy of the predicted rainfall percentages or rainfall classes. The 24h rainfall forecasts are verified for the summer months (October to March) of 1994 to 1998 for the Vaal Dam catchment. The rainfall distribution classes were chosen to represent no-rain, isolated rain, scattered rain and widespread rain. Results indicate that the percentage of correct forecasts is less than the values obtained by using the SAWS's hit score method. The predicted widespread rain class is less than 25% correct. The tendency exists to forecast scattered rain whenever any rain event is predicted. A rain event is seldom missed (3%), but some rain is often forecast (45%) for days, which then remain dry days. A more comprehensive rainfall forecast evaluation system is recommended. Keywords: Rainfall forecasts, Verification, Rainfall distribution classes, Vaal Dam catchment (WaterSA: 2003 29(2): 195-200)

Optimal allocation of water from a single purpose reservoir to an irrigation project with pre-determined multiple cropping patterns

A model for optimal allocation of water from a single-purpose reservoir to an irrigation project with pre-determined multiple cropping patterns was developed. The model consisted of two modules: (I) the intra-seasonal allocation model (non-linear programming) which is used for allocation of water among different crops for a definite combination of state variables (inflow class, rainfall class, reservoir storage classes at the beginning and at the end of the season) for the non-dormant season to maximize total farm income; and (II) the seasonal allocation model (stochastic-dynamic programming) which is used for the convergent operating policy over seasons for optimal expected farm income over a year. The model was applied to Ardak reservoir dam (I.R. Iran) in an arid region. Low river inflow in the dormant season at the study area could not admit the reservoir class changes for specific combinations of state variables, and therefore resulted in a non-usable result. Imposing a fictitious positive relative net benefit for all possible combinations of reservoir class changes eliminated this problem. It was also shown that rainfall did not play a marked role in the study area, which is an arid region, and its stochastic nature can be removed from the model.

The role of rainfall in the landslide hazard: the case of the Avigliano urban area (Southern Apennines, Italy)

Mass movements varying in type and size, some of which are periodically reactivated, affect the urban area of Avigliano. The disturbed and remoulded masses consist of sandy–silty or silty–clayey plastic material interbedded with stone fragments and conglomerate blocks. Five landslides that were markedly liable to rainfall-associated instability phenomena were selected. The relationships between landslides and rainfall were investigated using a hydrological and statistical model based on long-term series of daily rainfall data. The model was used to determine the return period of cumulative daily rainfall over 1–180 days. The resulting hydrological and statistical findings are discussed with the aim of identifying the rainfall duration most critical to landslides. The concept of a precipitation threshold was generalized by defining some probability classes of cumulative rainfall. These classes indicate the thresholds beyond which reactivation is likely to occur. The probability classes are defined according to the return period of the cumulative rainfall concomitant with landslide reactivation.

The effect of land-use on the vegetation communities along a topo-moisture gradient in the mid-Fish River valley, South Africa

The objectives of this study were to identify the major physical environmental variables affecting plant community distribution, and to determine whether a shift occurred in plant community position along an environmental gradient of different land-use practises. To achieve these objectives the study area was stratified into a number of topographical-moisture classes and the vegetation was sampled randomly within each class along the gradient. The data were analysed using canonical correspondence analysis and various statistical tests in order to determine whether the plant communities occurred at different positions along the environmental gradient under different management regimes. The study showed that rainfall and elevation are the major environmental variables within the mid-Fish River valley. The results also revealed that a change in management regime caused a shift in plant community position along the environmental gradients. This shift was towards communities occupying higher rainfall and elevation classes with increasing grazing pressure.

Identification of priority regions for animal conservation in afforestable montane grasslands of the northern Eastern Cape Province, South Africa

Large-scale afforestation with pines is taking place in montane grasslands of South Africa. Many species dependent on the grass sward will be eliminated from the planted areas. Land should be maintained as conservation areas to ensure the long-term survival of the wildlife within the afforestable region. Ten land types, defined by combinations of classes of geology, altitude and rainfall, were sampled in the afforestable part of the Maclear district, Eastern Cape Province. Areas of five land types are required in a network of conservation areas to protect all the montane-endemic grasshopper, butterfly and bird species recorded. The addition of a sixth land type to this set of five would protect 93·8% of all the taxa considered. Regions within which conservation areas should be situated are indicated at the district scale.

Stochastic models for daily rainfall in the Western Pacific

Abstract Several stochastic models of rainfall occurrence and daily rainfall amount have been applied to data sets, of 18–20 years duration, for 22 islands in the Western Pacific. The models for rainfall occurrence were first- and second-order Markov chains, the truncated negative binomial distribution, and the truncated geometric distribution; each was applied with parameters determined independently for each month, and with parameters assumed to vary smoothly through the year according to a Fourier series. The models tested for daily rainfall amounts were the Weibull distribution, a mixed exponential distribution, the two-parameter gamma distribution, a skewed normal distribution, the kappa distribution, and the Srikanthan-McMahon model. The rainfall data were classified according to the number of adjoining wet days, and the models tested with all data grouped together, solitary wet days fitted separately from other wet days, and each class of data fitted separately. The results of these tests showed that this classification improves model fitting, in spite of the additional number of parameters required. For several months of the year, there are significant differences between the distributions of rainfall amounts for the three classes. However, for 18 of the 22 stations, the Srikanthan-McMahon model outperformed all others, and successfully simulated the differences between the rainfall classes.

Modeling nitrous oxide emissions from agriculture: A Florida case study

The DNDC (Denitrification-Decomposition) model is shown to simulate emissions of nitrous oxide (N 2O), changes in soil nitrate, and nitrogen mineralization rates consistent with field measurements at three agricultural sites in Florida. As a case study of the potential policy relevance of a process-oriented biogeochemical model, we estimated N 2O emissions to the atmosphere from all agricultural lands in Florida, a state with significant agriculture on both organic and mineral soils. Nine landscape classes (3 soil classes × 3 annual rainfall classes) were coupled with county-based data on crops (5 major crops + pasture + fallow), fertilization, irrigation, and representative areas, to generate 86 model scenarios. Annual simulations were run for each case, and county and state emissions were tabulated. Total N 2O emissions from Florida's agricultural lands were estimated to be 0.024 Tg N 2ON y −1. Emissions were unevenly distributed with approximately 50 percent of the N 2O being emitted from soils in six (of 68) Florida counties. Organic soils, while occupying only 9% of the total agricultural land area and receiving no nitrogen fertilizer additions, accounted for 38% of the state's total N 2O flux. Sensitivity studies suggest that the most effective means for mitigating N 2O emissions would involve a combination of measures including reductions in drainage of organic soils, injection of fertilizers to soil depths of 10 cm or greater, and increased attention to precision irrigation. Biogeochemical modeling will be critical to developing an integrated framework for assessing policies for reducing N 2O emissions from agricultural systems.