The implications of general circulation model estimates of rainfall for future erosion: a case study from Brazil

doi:10.1016/S0341-8162(99)00025-9

CATENA

Volume 37, Issues 3–4, October 1999, Pages 329-354

https://doi.org/10.1016/S0341-8162(99)00025-9 Get rights and content

Abstract

One consequence of global change will be shifts in the probability of occurrence of soil erosion by water. This could have serious consequences for those areas of the world which are present-day `hotspots' for erosion. By means of a case study, this paper suggests an approach to quantifying the change in risk of serious erosion for sites in such areas. The case study focuses on future erosion under intensive soya bean cultivation in the Mato Grosso area of Brazil. On the area's highly erodible latosols, current erosion problems are severe. Scenarios of change future climate change are taken from general circulation models (GCMs) and used to perturb current-climate weather data. These are input to an erosion model (water erosion prediction project (WEPP)-CO2), together with local knowledge regarding current and probable future land use, in order to estimate future changes in erosion rates. WEPP-simulated average annual sediment yield increases in one of the scenarios and decreases in the other two, reflecting the range of uncertainty in predictions of future rainfall. Using the `best-guess' climate scenario from the UK Meteorological Office's HADCM2 GCM, the increase in mean annual sediment yield is 27%. Increases are disproportionately greater in wetter years. Average rates for individual months increase by over 100%. Erosion increases most on those parts of the hillslope profile which are currently hardest-hit by erosion. At present, an annual sediment yield of 5 t ha⁻¹ is currently exceeded in about 1 year in 2. The HADCM2 simulations suggest that an equal or greater rate will occur in about 70% of years by around 2050. A rate of at least 10 t ha⁻¹ yr⁻¹ is currently exceeded in about 1 year in 5. The HADCM2 simulations suggest that this will rise, to about 1 year in 4.

Introduction

A central aim of the GCTE Soil Erosion Network is to develop an improved predictive capability for soil erosion under global change, in part by refining and adapting current soil erosion models for use in global change studies (Valentin, 1998). An essential component of this strategy, the GCTE evaluation of erosion models, is now well under way (Boardman and Favis-Mortlock, 1998; other papers, this volume).

Favis-Mortlock et al. (1996)presented an `experimental design' for this evaluation (Table 1). Both field-scale and catchment-scale model evaluations have now completed the second stage of this design: the third and fourth stages still remain. In addition, there are likely to be advantages in thinking ahead to the eventual use of erosion models for global change studies. For example, if we are able to identify—and ideally rank by severity of impact—those areas of the world in which global change is likely to produce erosion problems, then the potentially worst-hit of such areas could be included in these future stages of GCTE activity. This paper outlines the first steps toward a possible approach.

Section snippets

The role of land use and climate

At any location, two conditions must be met if there is to be a future water erosion problem (Table 2). There must be sufficient future rainfall; and this rainfall must occur at time(s) when the soil's surface is insufficiently protected, for example as a result of cultivation.

Note though that there may or may not be a present-day erosion problem at such locations. This is because future global change (i.e., climate change, land use change, or both) may work to exacerbate or ameliorate a

General characteristics of the area

Sorriso is a rural municipality which was founded in 1986 and covers an area of 10 048 km²; it is situated in Mato Grosso State (12°S, 56°W), in the Centre West Region of Brazil (Fig. 2), some 400 km north of Cuiabá, the state capital. Sorriso lies on the Central Plateau, which has a mean altitude of 350 m with areas ranging between 500 m and 3000 m. Mean annual rainfall is around 1550 mm, with rains concentrated between November and April, and small values especially for the winter months

Uncertainties

As with any study of erosion under future global change, there are a large number of uncertainties involved. These are summarised in Table 11. They fall into two categories: those due to model shortcomings, and those resulting from the assumptions made regarding future conditions.

Conclusions

This case study outlines an approach to quantifying the change in future erosion rates as well as shifts in the risk of erosion. While fraught with uncertainties, it appears that, by bringing together data from GCM estimates of future climate and local knowledge regarding current and probable future land usage practices, tentative estimates may be made of the effects of global change upon soil erosion in those places where an erosion problem currently exists.

Authors' note

Results in this second draft of the paper differ from those presented at the GCTE Soil Erosion Network Meeting `Global Change: Modelling Soil erosion by Water at the Catchment Scale' in Utrecht, April 1997. This is due to errors in the output of SCENGEN 1.0 (Mike Hulme, personal communication, 1998) which was used to derive the future climate scenario in the presented version of the paper.

Acknowledgements

We are most grateful to the late Arlin D. Nicks (USDA) for supplying weather data, as well for advice regarding CLIGEN. Our thanks also to Flavio G. Almeida (GEODINAMICO/Department of Geography—UFF) and Anderson S. Lamin (LAGESOLOS/Department of Geography—UFRJ) for supplying data for the Sorriso site; Antonio S. Silva and Rosangela G. Botelho LAGESOLOS/Department of Geography—UFRJ) for Fig. 2; Ruth Butterfield (ECU) for information on soya beans; Mike Hulme (Climatic Research Unit) for SCENGEN;

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The implications of general circulation model estimates of rainfall for future erosion: a case study from Brazil

Abstract

Introduction

Section snippets

The role of land use and climate

General characteristics of the area

Uncertainties

Conclusions

Authors' note

Acknowledgements

Agricultural and Forest Meteorology

Agricultural and Forest Meteorology

Catena

Agricultural Systems

Agricultural Systems

Agricultural Systems

Contrasting crop species responses to CO2 and temperature: rice, soybean and citrus

Vegetation

Climate change and soil erosion in Britain

Geographical Journal

Climate change and soil erosion on agricultural land in England and Wales

Land Degradation and Rehabilitation

Changing contributions of suspended sediment sources in small basins resulting from European settlement on the Canadian prairies

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Journal of Soil and Water Conservation

Modelling long-term anthropogenic erosion of a loess cover: South Downs, UK

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Contrasting crop species responses to CO₂ and temperature: rice, soybean and citrus