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Tools for accurately predicting environmental risks, such as the location and spatial extent of potential inundation, are not widely available. A dependence on calibration and a lack of available flood data have prevented the widespread application of existing hydrodynamic methods for predicting the extent of inundation. We use the height above the nearest drainage (HAND) terrain model to develop a simple static approach for mapping the potential extent of inundation that does not depend on flood observations and extends beyond methods for mapping low-lying areas. While relying on the contour concept, the method utilizes drainage-normalized topography and flowpaths to delineate the relative vertical distances (drop) to the nearest river. The HAND-delineated relative drop is an effective distributed predictor of flood potential, which is directly related to the river stage height. We validated the new HAND contour approach using a flood event in Southern Brazil for which high-resolution maps were available. The results indicated that the flood hazard-mapping method accurately predicted the inundation extent of the channel carrying the flood wave and the channels influenced by flooding. For channels positioned outside of the flood-wave area, the method overestimated the actual flood extent. As an original static assessment of floodwaters across the landscape, the HAND contour method could be used to map flood hazards in areas with poor information and could promote the development of new methods for predicting hydrological hazards. Copyright © 2015 John Wiley & Sons, Ltd.

The contribution of coherent structures (CSs) to daytime buoyancy heat flux was calculated for three forest sites in the Amazon region and a wetland site. Ejections and sweeps had similar contributions to fluxes at all sites, and when decomposing this contribution in scales, the resulting spectra were narrower for the forests. When accounting for times scales from 10 to 200s, CSs contributed to approximately 80% of fluxes for Caxiuana forest site, with lower values for other locations. Among the forest, the contribution for the Jaru site was the lowest (≈66%) due to peak of contribution being close to 200s.

This work analysed heavy rainfall events and their predictability on Rio de Janeiro, Brazil, using rain gauge data from 2000 to 2010, atmospheric model outputs, and an artificial neural network based on adaptive resonance theory. The latter was applied on top of atmospheric simulations for 2009 and 2010, and we were able to predict 55% of the heavy rainfall events using a combination of relative humidity at 900 hPa and meridional winds at 10 m for a domain covering central and southern Brazil, which represents a relative gain of 67% on predictability when compared to the model predicted rainfall. Copyright © 2012 Royal Meteorological Society

The climatic effects of concurrent land-cover changes in Amazonia and Northeast Brazil (NEB) were evaluated by simulations using the Center for Weather Forecasting and Climate Studies Atmospheric General Circulation Model (CPTEC-AGCM). Three experiments were performed: Amazon savannization, NEB desertification and both land-cover changes occurring concurrently. We found that land-cover change from adjacent areas do affect both Amazon and NEB regions and that the negative precipitation anomaly in NEB due to concurrent land-cover changes in Amazon and NEB is weaker than the linear addition of the anomalies considering the land-cover changes separately (synergistic behaviour). A simple mechanism was proposed to explain this behaviour. Copyright © 2011 Royal Meteorological Society

Summary • We used a climate–vegetation–natural fire (CVNF) conceptual model to evaluate the sensitivity and vulnerability of forest, savanna, and the forest–savanna transition to environmental changes in tropical South America. • Initially, under current environmental conditions, CVNF model results suggested that, in the absence of fires, tropical forests would extend c. 200 km into the presently observed savanna domain. • Environmental changes were then imposed upon the model in temperature, precipitation and lightning strikes. These changes ranged from 2 to 6� C warming, +10 to )20% precipitation change and 0 to 15% increase in lightning frequency, which, in aggregate form, represent expected future climatic changes in response to global warming and deforestation. • The most critical vegetation changes are projected to take place over the easternmost portions of the basin, with a widening of the forest–savanna transition. The transition width would increase from 150 to c. 300 km, with tree cover losses ranging from 20 to 85%. This means that c. 6% of the areas currently covered by forests could potentially turn into grass-dominated savanna landscapes. The mechanism driving tree cover reduction consists of the combination of less favorable climate conditions for trees and more fire activity. In addition, this sensitivity analysis predicts that the current dry shrubland vegetation of northeast Brazil could potentially turn into a bare soil landscape.

Aim This study aims to improve the formulation and results of the Brazilian Center for Weather Forecasting and Climate Studies Potential Vegetation Model (CPTECPVM) by developing a new parameterization for the long-term occurrence of fire in regions of potential savannas in the tropics. Compared with the relatively slow processes of carbon uptake and growth in vegetation, fast mortality and biomass consumption by fires may favour grasses and reduce tree coverage. Location The tropics. Methods For finding large-scale relationships between fires and other environmental factors, we made two main simplifying assumptions. First, lightning is the most important source of ignition for natural fires. Second, over continental areas in the tropics, lightning is mainly related to the zonal flux of moisture transport. Results The parameterization of fire occurrence was built based on a simple empirical relationship, combining information on mean and intra-annual variance of the zonal wind. Main conclusions The implementation of this new relationship improved the formulation and the results of the CPTEC-PVM. As a result of this new parameter, the accuracy of the model in allocating the correct vegetation (seasonal forests) instead of savannas for large regions in India and Southeast Asia is now substantially higher than in previous studies.

We investigated the spatial and temporal variabilities of Climate Prediction Center merged analysis of precipitation (CMAP) in tropical South America from 1979 to 1998. First, we validated CMAP using other hydrometeorological data. In comparison with the high-density precipitation data of the Global Historical Climatology Network (GHCN) Ver. 2, CMAP reproduces the spatial pattern well, although it underestimates (overestimates) heavy (light) precipitation. CMAP also reproduces the interannual variability well, compared with the discharge data of the River Amazon. Next, we applied the rotated empirical orthogonal function (REOF) to CMAP after subtracting the annual cycle. Simultaneous and lag correlations were calculated among the scores of REOFs 1 to 4, the southern oscillation index, and the dipole index of the Atlantic. REOF 1 (15%) represents the north–south pattern that exhibits the maximum precipitation in the summer hemisphere. REOF 2 (12%) indicates the gradual decrease of precipitation in the northern part of tropical South America, reflecting the effect of the Atlantic. REOF 3 (11%) exhibits an east–west pattern related to El Nino. In REOF 4 (7%), the centre of the factor loading is located in Colombia, and the score jumps abruptly around 1985–86. The Lepage test detected the abrupt increase of CMAP in 1985–86 around Colombia. Since such a jump is not found in GHCN Ver. 2, the discontinuous changes of CMAP and REOF 4 around 1985–86 are artificial and peculiar to CMAP. In this region, CMAP should be applied with caution when evaluating recent trends and the interannual variability. The importance of the abrupt increase of precipitation around Colombia is also addressed. Copyright © 2002 Royal Meteorological Society.

SUMMARY The recent high deforestation rates in Amazonia have raised the question of how climate, mainly the precipitation patterns, might be affected as pasture land replaces the primary forest. This work initially shows how the dry season soil moisture and water stress in typical Amazonian pasture modifies the energy partitioning at the surface. Low-level moisture convergence is a primary mechanism to trigger convective cloud formation and precipitation. The relationship between moisture convergence and local surface evaporation in generating precipitation in Amazonia is studied utilizing a one-dimensional 'single column' model (SIB-1D). SiB-1D couples a surface-vegetation model (SIB) to a physical parametrization of deep convection (Kuo scheme), radiation, turbulent diffusion and large-scale precipitation. Model simulations for short periods (2 days).show its ability to calculate the Amazonian surface energy-balance components and boundary-layer dynamics when compared with field observations from the Rondbnia Boundary-Layer Experiment and the Anglo-Brazilian Amazonian' Climate Observation Study. The model was further used to test the sensitivity of the deep convection scheme to a range of typical low-level moisture convergence situations in a second experiment, and a third test investigated the local convective precipitation generated over forest and grass vegetation as a function of available soil moisture. Results showed that the rainfall over forest vegetation appeared to be almost insensitive to soil water stress whereas reduced precipitation was generated over pasture. When available soil water fell below a threshold of 60% the calculated precipitation over the pasture sites rapidly declined. Although these results are confined by the short integration period and the initial atmospheric profiles, they help to strengthen the notion that deforestation reduces evaporation and convective precipitation, especially during the dry season: a result already indicated by some previous general-circulation model experiments.

A normalized difference vegetation index (NDVI) derived from satellite data is used to study drought evolution in the South American continent. National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) Global Area Coverage (GAC) data are used to produce NDVI maps for the South American continent during the period from 1 August 1981 to 30 June 1987. A 15-day maximum-value composite procedure is used to partially eliminate cloud contamination and atmospheric attenuation. Vegetation response to drought is studied by inspection of the temporal and spatial evolutions of monthly drought area maps, which are delineated by NDVI values lower than 0.22. Drought area evolution patterns over the continent during the period of 1981–1987 for the months of May and September are discussed. The results show a well-defined regional dependence of the drought area variability. Drought dynamics analyses are performed for the dry year of 1982–1983 and for the wet year of 1984–1985. This information is used to discuss the relationship of the drought pattern with the El Nino-Southern Oscillation (ENSO). Emphasis is given to the north-eastern region of Brazil, for which the relative drought area coverage was computed to demonstrate its high interannual drought variability. An intensification of this behaviour during the 1982–1983 ENSO event was identified in this area. The results indicate the potential use of satellite NDVI imagery to monitor drought occurrences as well as to study climatic variability on regional and continental scales.

Measurements from the first comparative study of climate over Amazonian tropical forest and an embedded deforested clearing are presented. Observations comprise a continuous 60-day run of data from mid-October to mid-December 1990, covering the end of the dry season and the beginning of the wet season. Mean hourly observations are calculated for the whole period; and for two 10-day periods, one in the dry season and one at the start of the wet season. Much greater variation in weather variables was observed at the clearing compared with over the forest. While the mean values of temperature and specific humidity deficit differed by less than 1°C and 1 g kg-' respectively, their daily ranges at the clearing were twice those at the forest. Mean daily albedo of the forest was 13.1 per cent, agreeing well with other tropical forest measurements, and of the clearing was 16.3 per cent, somewhat lower than the values currently being used in GCMs. The surface energy balance was investigated and mean available energy calculated for each site. The significant difference in the daily pattern of net radiation between the sites was found to be at least as much due to differences in the longwave radiation balance as to differences in albedo. The diurnal pattern of net radiation therefore changed between dry and wet periods as the higher plant water stress experienced by clearing vegetation altered the daily temperature cycle.

This paper presents the first comprehensive micrometeorological measurements to be recorded over post-deforestation Amazonian ranchland. the ranch was managed for the production of beef cattle and had been created by felling and burning the original rainforest 12 years previously. the measurements allow derivation of the aerodynamic roughness, and a description of the response of the energy balance and surface conductance to the progressing dry season. Zero-plane displacement and roughness length were derived from wind-speed profiles as O.17 ± 0.03 m and 0.026 ± 0.003m respectively, while measurement of energy partition was achieved, with excellent agreement, between three independent measurement systems. During the 1990 dry season, average evaporation diminished from 3.8 to 2.1 mm d-1 as the Bowen ratio increased from 0.43 to 0.67. Values of surface conductance were derived and these compare well with expected trends.

Measurements of energy partition for Amazonian forest made with novel eddy correlation equipment are presented for eight dry days in September 1983. These are interpreted to provide estimates of the aerodynamic and surface resistance for this vegetation type. Daily total evaporation for a transpiring canopy accounts for 70% of the available radiant energy, and is two thirds of conventional estimates of potential evaporation. The results are used to provide an initial calibration of a simple, physically based model of daily evaporation for Amazonian rain forest.