0 Soil erosion assessment in the dryland areas of Bolivia using the RUSLE 3D model MSc thesis by Annemieke de Kort September 2013 Soil Physics and Land Management Group 1 2 Soil erosion assessment in the dryland areas of Bolivia using the RUSLE 3D model Master thesis Soil Physics and Land Management Group submitted in partial fulfillment of the degree of Master of Science in International Land and Water Management at Wageningen University, the Netherlands Study program: MSc International Land and Water Management Student registration number: 710610468100 LDD 80336 Supervisors: Dr.ir. A. Kessler Wageningen University, The Netherlands C.K. Ovando Crespo MSc CISTEL, Cochabamba, Bolivia R.J. Vargas Rojas MSc FAO, Rome, Italy Examinator: Prof. Coen Ritsema Wageningen University, The Netherlands Date: 17/09/2013 Soil Physics and Land Management Group, Wageningen University 3 4 Abstract RUSLE 3D, a modification of the USLE model, was used in this thesis research to calculate soil loss in the dryland areas of Bolivia. Calculation results showed that annual soil loss amounts were less than five ton ha-1 in more than 50 per cent of the study area. This is not in accordance with literature where it is often mentioned that soil losses in Bolivia are severe. However, since the USLE model was originally developed for small scale use it might not be the best suitable model in this research and the reliability of the used data, used methods and the end result were therefore assessed. The reliability assessment showed that data were not always complete, did not always have the correct spatial resolution or map scale, or were outdated. Moreover, calculation methods sometimes overestimated or underestimated calculation results. Nevertheless, soil loss amounts in 99,1 per cent of the study area fell within the range of soil loss amounts obtained from other researches. However, RUSLE 3D calculation might provide a fake reality whereby the end result looks correct while that is in fact caused by compensation of an overestimated parameter with an underestimated parameter and vice versa and not because the calculation of each separate parameter gave correct results. In general, it can be said that the reliability of the used data and used methods is too low and too many uncertainties exist for a reliable calculation of soil loss amounts in the dryland areas of Bolivia using the RUSLE 3D model. Keywords: Bolivia, dryland area, soil erosion, RUSLE 3D 5 6 Table of contents Abstract ....................................................................................................................................... 5 1 Introduction ............................................................................................................................ 9 1.1 General introduction .................................................................................................................9 1.2 Soil degradation in the dryland areas of Bolivia .................................................................... 10 1.3 Problem definition ................................................................................................................. 12 1.4 Research objective and research questions .......................................................................... 13 1.5 Context of the research ......................................................................................................... 14 2 Materials and methods ........................................................................................................... 15 2.1 Study area description ........................................................................................................... 15 2.2 The RUSLE 3D model .............................................................................................................. 21 2.2.1 Concept of the RUSLE 3D model ................................................................................ 21 2.2.2 Rainfall-runoff erosivity (R) ....................................................................................... 22 2.2.3 Slope length and slope steepness (LS) ....................................................................... 23 2.2.4 Soil erodibility (K) ...................................................................................................... 25 2.2.5 Cover and management (C) ...................................................................................... 26 2.2.6 Conservation practices (P) ......................................................................................... 27 3 Results ................................................................................................................................... 28 3.1 Rainfall-runoff erosivity (R) .................................................................................................... 28 3.2 Slope length and slope steepness (LS) ................................................................................... 28 3.3 Soil erodibility (K) ................................................................................................................... 29 3.4 Cover and management (C) ................................................................................................... 30 3.5 Conservation practices (P) ..................................................................................................... 31 3.6 Annual soil loss by water in the dryland areas of Bolivia....................................................... 31 4 Discussion .............................................................................................................................. 33 4.1 Data availability and reliability ............................................................................................... 33 4.2 Method reliability .................................................................................................................. 39 4.3 Model reliability ..................................................................................................................... 46 5 Conclusion and recommendations .......................................................................................... 49 References .................................................................................................................................. 51 Appendix A: Overview of C factor vegetation classes .............................................................. 59 Appendix B: Soil loss classes according to Morgan (2005) ....................................................... 61 7 8 Introduction 1 Introduction Land degradation is a common problem in the world. If not tackled properly, it can lead to food insecurity, decreases in livelihood situations and poverty. Suitable measures need to be taken to decrease land degradation, but for that one needs to know where and how much land degradation takes place. Soil degradation, one of the major forms of land degradation, can be calculated with the help of models. In this thesis research, the RUSLE 3D model is used to calculate the amount of soil loss by water in the dryland areas of Bolivia, areas that are susceptible to soil degradation due to their natural landscape form and location. In Chapter 1, a general introduction about land and soil degradation is given (1.1), followed by a more detailed description of soil degradation in Bolivia (1.2). Then, successively, the problem definition in the framework of this research (1.3) and the research objective and research questions (1.4) will be defined. Finally, the context in which this research takes place will be explained (1.5). 1.1 General introduction In 2005, the FAO defined land degradation as “the reduction in the capacity of the land to perform ecosystem functions and services (including those of agro-ecosystems and urban systems) that support society and development” (Nachtergaele and Licona-Manzur, 2008). In this era of high population growth and climate change, land degradation has become an increasing stress factor in the environment and in human life. Population growth increases pressure on land. On the one hand more food and fodder needs to be produced for the increasing population and its livestock, while on the other hand more land is needed to expand urban areas and infrastructure. To fulfil these needs, deforestation and expansion to marginal lands get more common nowadays, since land in more suitable areas is already in production. Marginal lands are often situated in dryland areas, areas that are defined by UNESCO as semi-arid and sub-humid areas with an average annual P/ETP ratio between 0,20 and 0,75 (Dietz and Veldhuizen, 2004). Main agricultural production in dryland areas exists of pastoralism and rain fed subsistence crop production. Risk of crop failures is high because precipitation is unreliable and droughts, and occasionally flooding, are common in these areas. However, despite the risk factors, a large part of the world population lives in dryland areas. In Africa, Asia and South America, respectively 40, 39 and 30 per cent of the population lives in dryland areas (UNEP 1997, in Dietz and Veldhuizen, 2004, p.106). Many dryland areas have poor, unfertile soils and sparse vegetation covers that make them vulnerable to land degradation. Natural land degradation can be accelerated by climate change and anthropogenic factors such as unsustainable land use management. Unsustainable land use management practices such as overgrazing and deforestation can lead to bare soils that are vulnerable